Created: 2026/11/03 05:05

EWCE 471 — Exam-Ready Question & Answer Guide (2019–2025)

How to Use This Guide

The "< 1 Minute per Mark" Rule: In a 3-hour exam of 180 marks (6 question sets $\times$ 30 marks), 1 mark gives you 1 minute total (~15 sec to think + ~45 sec to write). At a normal handwriting speed of 20–25 words/min, 1 mark = 15 to 18 words (about 1 short bullet point).
Zero Fluff & Plain Language: Skip long introductions and heavy academic jargon. Use bullet points, comparison tables, and quick 30-second labeled sketches.
Scaling Answers to Marks: Some questions appeared for 4–5 marks in one year and 10–12 marks in another. Each answer below gives the core definition first, followed by bulleted points—write 1 bullet point per 1–1.5 marks allocated in your exam paper.
Math & Design Questions: Marked with [Math] or [Design Math]. Rather than solving every past-year number variation, these give the exact step-by-step recipe, formulas, and graph/nomogram look-up procedure to follow in the exam.

Section A Lecture Materials (EWCE 471/SA/)
Section B Lecture Materials (EWCE 471/SB/)
Unmapped / Earlier-Syllabus Past Exam Questions (SA / Lec 02 & SA / Lec 15-16)

1. Section A Lecture Materials (`EWCE 471/SA/`)

SA / Lec 01 — Introduction to Coastal Engineering & Bangladesh Coast

Q1.1: Define Coastal Engineering and explain why it is different from other ocean-related studies.

Appeared in: 2019 (Q1a, 5m), 2023 (Q1a, 10m part) (Rank #19)
Time & Length Budget: 4–5 mins (~70–85 words)
Reference: SA/Lec 01/EWC471_lecture 1.pdf, SB/Topic 01/EWCE 471_LEC-01 & 02_Introduction to Coastal Engineering, Coast and Coastal Features.pdf

Answer:

Definition: Coastal Engineering is a branch of civil engineering that plans, designs, constructs, and manages works at or near the shoreline—where water, land, and air meet.
Why It Differs from Other Ocean Studies:
1. Shallow-Water Focus vs. Deep Ocean: Unlike oceanography or offshore engineering (which study deep seas), it focuses on the nearshore and surf zone where the seabed strongly alters waves.
2. Moving Boundary: The shoreline constantly shifts due to erosion and sediment deposition (littoral transport).
3. Action vs. Pure Observation: While marine scientists observe natural ocean processes, coastal engineers build solutions (seawalls, breakwaters, harbors, dredging, beach nourishment) to protect land and infrastructure.
4. Combined Forces: Must design for breaking waves, astronomical tides, storm surges, and river inflows acting together.

Q1.2: What are the basic information needed for oceanology, and what are their applications?

Appeared in: 2019 (Q3b, 5m) (Rank #31)
Time & Length Budget: 4–5 mins (~75 words)
Reference: SA/Lec 01/EWC471_lecture 1.pdf

Answer:

Basic Information Needed:
1. Bathymetry & Topography: Seabed depth contours and shoreline elevations.
2. Wave Climate: Wave height ( $H$ ), period ( $T$ ), and direction.
3. Tides & Water Levels: Spring/neap tidal ranges and storm surge heights.
4. Currents & Winds: Nearshore, tidal, and wind-driven flow speeds.
5. Sediment & Water Properties: Grain size ( $D_{50}$ ), suspended load, salinity, and temperature.
Engineering Applications:
- Harbor & Channel Design: Safe ship navigation, entrance orientation, and dredging depth.
- Shore Protection: Sizing seawalls, revetments, groins, and breakwaters against wave forces.
- Disaster Management: Forecasting cyclone storm surges, coastal flooding, and salinity intrusion.

Q1.3: Give a physical description of the coastal zone of Bangladesh and explain how it is managed against cyclones and storm surges.

Appeared in: 2021 (Q3a, 10m), 2022 (Q1a, 7m) (Rank #26)
Time & Length Budget: 7–9 mins (~120–150 words)
Reference: SA/Lec 01/EWC471_lecture 1.pdf

Answer:

Overview of Bangladesh Coast:
- Covers 19 districts (147 upazilas), 47,201 km² (32% of total land area), and a 710 km long coastline.
- Divided by hazard exposure into Exposed Coast (48 upazilas directly facing the sea/estuary) and Interior Coast (99 upazilas behind).
Three Geomorphological Regions:
1. Western Region (Ganges Tidal Plain): Semi-active delta covered by the Sundarbans mangrove forest; flat land crisscrossed by tidal rivers (Swatch of No Ground canyon lies offshore).
2. Central Region (Meghna Estuary): Most active and dynamic zone; receives massive water and sediment from the Ganges-Brahmaputra-Meghna (GBM) system, causing rapid island (char) erosion and accretion; funnel shape amplifies storm surges.
3. Eastern Region (Chittagong–Cox's Bazar Coast): Narrow, stable strip backed by folded hills; features the unbroken sandy beach from Cox's Bazar to Teknaf and the Karnafuli/Matamuhuri rivers.
Management Against Cyclones & Storm Surges:
- Cyclone Preparedness Programme (CPP): Jointly run by the Government and Bangladesh Red Crescent Society using 70,000+ trained community volunteers for early warning (flag/megaphone signals), evacuation, and rescue.
- Structural Measures: Multi-purpose cyclone shelters, coastal polders (139 polders) with earthen embankments and drainage sluices, and coastal greenbelt (mangrove afforestation) to reduce wave and surge energy.

SA / Lec 03 — Wave Classification, Basic Wave Parameters & Transformation Overview

Q3.1: Define and differentiate between Swell, Seiche, and Tsunami with respect to wave generation and water level variation.

Appeared in: 2019 (Q1c, 5m), 2023 (Q5b-i, 4m) (Rank #27)
Time & Length Budget: 4 mins (~70–80 words)
Reference: SA/Lec 03/EWC471_lecture 3.pdf

Answer:

Feature	Swell	Seiche	Tsunami
Definition	Smooth, regular wind waves that have traveled out of their storm generation area.	Long-period standing wave oscillating back and forth in an enclosed or semi-enclosed basin (harbor, bay, lake).	Very long-wavelength shallow-water wave triggered by sudden seafloor displacement.
Generation Cause	Distant wind storms (`wind-generated`).	Atmospheric pressure jumps, strong wind shifts, or long-period ocean waves matching the basin's natural period.	Underwater earthquakes, volcanic eruptions, or submarine landslides.
Period ( $T$ )	`8 – 20 sec`	`Few minutes to several hours`	`5 – 60 minutes` (`L = 100+ km`)
Water Level Variation	Regular sinusoidal surface ripples; short crest-to-trough oscillation (`1–5 m`).	Water tilts up at one end of the harbor/bay while dropping at the other, with zero vertical change at nodes.	Barely noticeable in deep ocean (`< 1 m`), but piles up into a massive wall of water (`10–30+ m` surge) in shallow coastal water.

Q3.2: Differentiate between pure oscillatory waves and finite-amplitude waves.

Appeared in: 2022 (Q2b, 7m part), 2023 (Q5b-ii, 4m), 2024 (Q1a, 6m part) (Rank #10)
Time & Length Budget: 3.5 mins (~65 words)
Reference: SA/Lec 03/EWC471_lecture 3.pdf, SA/Lec 07-08/EWC471_lecture 7 and 8.pdf

Answer:

Feature	Pure Oscillatory (Small-Amplitude / Airy) Waves	Finite-Amplitude (Nonlinear) Waves
Wave Height Assumption	Infinitesimally small ( $H ≪ L$ and $H ≪ d$ ).	Large wave height relative to wavelength or depth.
Surface Profile	Symmetric sine/cosine curve; crest height = trough depth ( $H / 2$ ).	Peaked, steep crests and flat, shallow troughs.
Particle Orbits	Closed circles/ellipses; particles return to their exact starting point after each period ( $T$ ).	Open orbits; particles move slightly forward each wave cycle (mass transport / Stokes drift).
Wave Speed ( $C$ )	Depends only on period $T$ and depth $d$ .	Depends on wave height $H$ as well as $T$ and $d$ .

Q3.3: Define basic wave parameters: Wave Height ( $H$ ), Wave Number ( $k$ ), Relative Depth ( $d / L$ ), Wave Steepness ( $H / L$ ), and Sinusoidal Wave Profile.

Appeared in: 2019 (Q3d-iii, 2.5m; Q4c, 10m), 2023 (Q7b-iii, 2m) (Rank #15)
Time & Length Budget: 2–6 mins (~40–100 words depending on marks)
Reference: SA/Lec 03/EWC471_lecture 3.pdf

Answer:

       Crest (+)         <------- Wavelength (L) ------->
         _.-._                                    _.-._
       .'  |  '.                                .'     '.
------/----+----\------------------------------/---------\---- Still Water Level (SWL, z = 0)
     /     | H   '.          Trough (-)      .'
           v       '-._                  _.-'
                       '----------------'                      Water Depth = d
============================================================== Sea Bottom (z = -d)

Wave Height ( $H$ ): Vertical distance between a wave crest and the adjacent wave trough ( $H = 2 a$ , where $a$ is amplitude).
Wavelength ( $L$ ) & Period ( $T$ ): $L$ is the horizontal distance between two successive crests; $T$ is the time for two successive crests to pass a fixed point. Wave speed (celerity) is $C = L / T$ .
Wave Number ( $k$ ): Spatial frequency showing how many radians of wave cycle fit into a unit distance: $k = \frac{2 π}{L}$
Relative Depth ( $d / L$ ): Ratio of water depth ( $d$ ) to wavelength ( $L$ ). It classifies waves into deep water ( $d / L > 0.5$ ), transitional ( $0.05 < d / L < 0.5$ ), and shallow water ( $d / L < 0.05$ ).
Wave Steepness ( $H / L$ ): Ratio of wave height ( $H$ ) to wavelength ( $L$ ). Measures wave stability; a wave breaks in deep water when steepness exceeds $\frac{H}{L} \approx \frac{1}{7} \approx 0.142$ .
Sinusoidal Wave Profile ( $η$ ): Instantaneous vertical displacement of the water surface from Still Water Level (SWL): $η (x, t) = a \cos (k x - σ t) = \frac{H}{2} \cos (\frac{2 π x}{L} - \frac{2 π t}{T})$

Q3.4: Differentiate between deep-water, transitional, and shallow-water waves and sketch water particle displacement / velocity profiles.

Appeared in: 2019 (Q2d, 5m; Q2e, 5m), 2023 (Q6c, 10m), 2024 (Q3a, 8m), 2025 (Q2a, 10m) (Rank #5)
Time & Length Budget: 6–8 mins (~110–130 words + sketch)
Reference: SA/Lec 03/EWC471_lecture 3.pdf, SA/Lec 05-06/Corrected EWC471_lecture 5 and 6 .pdf

Answer:

DEEP WATER (d/L > 0.5)          TRANSITIONAL (0.05 < d/L < 0.5)   SHALLOW WATER (d/L < 0.05)
~~~~~~~~~~~~~~~~~~~~~~          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~   ~~~~~~~~~~~~~~~~~~~~~~~~~~
      (  O  )                            (  O  )                        <--- O --->
       ( o )                              ( o )                         <--- o --->
        (.)                                (_)                          <--- . --->
                      =======                             ==================================
                      Seabed                              Seabed (Back-and-forth motion)
===================
Seabed (No motion)

Criterion	Deep-Water Wave	Transitional (Intermediate) Wave	Shallow-Water Wave
Relative Depth ( $d / L$ )	$\frac{d}{L} > \frac{1}{2}$ (`0.5`)	$\frac{1}{20} < \frac{d}{L} < \frac{1}{2}$ (`0.05` to `0.5`)	$\frac{d}{L} < \frac{1}{20}$ (`0.05`)
Hyperbolic Approximation	$\tanh (k d) \approx 1$	Exact $\tanh (k d)$ required	$\tanh (k d) \approx k d$
Wave Celerity ( $C$ )	$C_{0} = \frac{g T}{2 π} \approx 1.56 T$ (depends only on $T$ )	$C = \frac{g T}{2 π} \tanh (\frac{2 π d}{L})$ (depends on $T$ and $d$ )	$C = \sqrt{g d}$ (depends only on depth $d$ )
Wavelength ( $L$ )	$L_{0} = \frac{g T^{2}}{2 π} \approx 1.56 T^{2}$	$L = L_{0} \tanh (\frac{2 π d}{L})$	$L = T \sqrt{g d}$
Water Particle Orbits	Circles that shrink exponentially with depth and vanish at $z = - L / 2$ .	Ellipses that flatten with depth into horizontal back-and-forth motion at the seabed.	Flat ellipses; horizontal velocity is nearly uniform from surface to seabed.

Velocity Direction along Wave Profile:
- Under Crest ( $θ = 0$ ): Maximum horizontal forward velocity ( $+ u_{\max}$ ), zero vertical velocity ( $w = 0$ ).
- Under Trough ( $θ = π$ ): Maximum horizontal backward velocity ( $- u_{\max}$ ), zero vertical velocity ( $w = 0$ ).
- At Upward Zero-Crossing ( $θ = π / 2$ ): Maximum upward vertical velocity ( $+ w_{\max}$ ), zero horizontal velocity ( $u = 0$ ).

Q3.5 & Q3.6: Overview of Wave Transformation & Wave Breaking

Note: Detailed answers for Wave Shoaling, Refraction, and Diffraction (2019 Q1e, 2024 Q2a-i,ii, 2025 Q2c) are provided in Q9.1 (SA / Lec 09-10). Detailed answers for Wave Breaking and the 4 Breaker Types (2019 Q3d-i, 2022 Q3b, 2023 Q7a, Q7b-i,ii, 2024 Q2a-iii,iv, Q3d) are provided in Q11.1 (SA / Lec 11-12).

SA / Lec 04 — Derivations & Assumptions of Small-Amplitude (Airy) Wave Theory

Q4.1: State the basic physical and mathematical assumptions made to derive Small-Amplitude (Airy / Linear) Surface Wave Theory.

Appeared in: 2019 (Q1b, 5m), 2023 (Q8c, 5m) (Rank #28)
Time & Length Budget: 4 mins (~75 words)
Reference: SA/Lec 04/EWC471_lecture 4.pdf

Answer:

Incompressible & Homogeneous Fluid: Water density $ρ$ is constant everywhere, so continuity satisfies $\frac{\partial u}{\partial x} + \frac{\partial w}{\partial z} = 0$ .
Inviscid & Irrotational Flow: Viscosity and turbulence are neglected, allowing a velocity potential ( $ϕ$ ) that satisfies the Laplace Equation ( $\nabla^{2} ϕ = \frac{\partial^{2} ϕ}{\partial x^{2}} + \frac{\partial^{2} ϕ}{\partial z^{2}} = 0$ ).
Small Wave Amplitude (Linearity): Wave height $H$ is very small compared to both wavelength $L$ and water depth $d$ ( $H ≪ L$ and $H ≪ d$ ). Thus, higher-order nonlinear terms ( $u^{2}, w^{2}$ ) are dropped, and free-surface boundary conditions are applied at $z = 0$ instead of $z = η$ .
Horizontal, Fixed, Impermeable Seabed: Water depth $d$ is constant and vertical velocity at the bottom is zero ( $w = 0$ at $z = - d$ ).
Uniform Atmospheric Pressure & No Surface Tension: Pressure at the free surface is zero gauge ( $p = 0$ at $z = η$ ), and Coriolis/capillary forces are neglected.

SA / Lec 05-06 — Wave Celerity, Wavelength, Orbital Kinematics & Wave Energy

Q5.1 `[Math]`: Method to calculate Wave Celerity ( $C$ ) and Wavelength ( $L$ ) across deep, transitional, and shallow water depths.

Appeared in: 2019 (Q2c, Q4d), 2021 (Q1b), 2022 (Q1c), 2023 (Q5c), 2024 (Q2b, Q2c), 2025 (Q2b) (Rank #1)
Reference: SA/Lec 05-06/Corrected EWC471_lecture 5 and 6 .pdf

Method to Follow:

Step 1 — Calculate Deep-Water Wavelength ( $L_{0}$ ) and Celerity ( $C_{0}$ ): Given wave period $T$ (sec) and $g = 9.81 m s {[PARSE ERROR: Undefined("RBrace")]}^{2}$ : $L_{0} = \frac{g T^{2}}{2 π} = 1.56 T^{2} m) [PARSE ERROR: Undefined("RBrace")], C_{0} = \frac{L_{0}}{T} = \frac{g T}{2 π} = 1.56 T m / s) [PARSE ERROR: Undefined("RBrace")]$
Step 2 — Check Relative Depth Ratio ( $d / L_{0}$ ):
- Case A (Deep Water, $d / L_{0} [PARSE ERROR: Undefined("Command(\"ge\")")] 0.5$ ): $L = L_{0}, C = C_{0}$
- Case B (Shallow Water, $d / L < 0.05$ ): $C = \sqrt{g d}, L = C \cdot T = T \sqrt{g d}$
- Case C (Transitional / Intermediate Water, $0.05 [PARSE ERROR: Undefined("Command(\"le\")")] d / L < 0.5$ ): Use the general dispersion relation: L=L0tanh(2πdL)
  - Option 1 (Wave Table Look-up): Compute $\frac{d}{L_{0}}$ , look up the corresponding $\frac{d}{L}$ and $\tanh (\frac{2 π d}{L})$ in the Wave Table, and find $L = \frac{d}{(d / L)}$ .
  - Option 2 (2–3 Trial Iterations on Calculator): Start with trial $L_{1} = L_{0} \tanh (\frac{2 π d}{L_{0}})$ , plug $L_{1}$ into the right-hand side to get $L_{2}$ , and repeat 3 times until $L$ converges, or use Eckart's explicit formula ( $\pm 5 %$ accuracy): $L \approx L_{0} \sqrt{\tanh (\frac{4 π^{2} d}{g T^{2}})}$ Then compute $C = \frac{L}{T}$ .

Q5.2 `[Math]`: Method to calculate water particle velocities ( $u, w$ ), accelerations ( $a_{x}, a_{z}$ ), displacements ( $ξ, ζ$ ), wave energy ( $E$ ), and wave power ( $P$ ).

Appeared in: 2019 (Q2c), 2021 (Q1b), 2022 (Q1c), 2023 (Q5c), 2024 (Q2c) (Rank #6)
Reference: SA/Lec 05-06/Corrected EWC471_lecture 5 and 6 .pdf

Method to Follow:

Step 1 — Set Coordinate & Phase Parameters:
- First find $L$ and $C$ at water depth $d$ using Q5.1.
- Compute wave number $k = \frac{2 π}{L}$ , angular frequency $σ = \frac{2 π}{T}$ , and phase angle $θ = k x - σ t = 2 π (\frac{x}{L} - \frac{t}{T})$ .
- Sign Convention for Depth ( $z$ ): $z$ is negative below SWL! For a point 3 m below SWL in 10 m depth, $z = - 3 m$ and $(d + z) = 10 - 3 = 7 m$ (distance above seabed).
- Note: If the problem asks for maximum velocity/acceleration/displacement, set $\cos θ = 1$ or $\sin θ = 1$ .
Step 2 — Calculate Local Fluid Velocities ( $u, w$ ): $u = \frac{g H T}{2 L} \frac{\cosh k (d + z)}{\cosh (k d)} \cos θ, w = \frac{g H T}{2 L} \frac{\sinh k (d + z)}{\cosh (k d)} \sin θ$
Step 3 — Calculate Local Fluid Accelerations ( $a_{x}, a_{z}$ ): $a_{x} = \frac{g π H}{L} \frac{\cosh k (d + z)}{\cosh (k d)} \sin θ, a_{z} = - \frac{g π H}{L} \frac{\sinh k (d + z)}{\cosh (k d)} \cos θ$
Step 4 — Calculate Orbital Displacements ( $ξ, ζ$ ) & Semi-Axes ( $A, B$ ): $ξ = - \frac{g H T^{2}}{4 π L} \frac{\cosh k (d + z)}{\cosh (k d)} \sin θ = - A \sin θ, ζ = \frac{g H T^{2}}{4 π L} \frac{\sinh k (d + z)}{\cosh (k d)} \cos θ = B \cos θ$ (where $A$ is the horizontal semi-axis and $B$ is the vertical semi-axis of the elliptical orbit).
Step 5 — Calculate Wave Energy ( $E, \bar{E}$ ) and Wave Power ( $P$ ):
- Specific Energy per unit surface area ( $\bar{E}$ ) (half kinetic + half potential): $\bar{E} = E_{k} + E_{p} = \frac{1}{16} ρ g H^{2} + \frac{1}{16} ρ g H^{2} = \frac{1}{8} ρ g H^{2} (J m {[PARSE ERROR: Undefined("RBrace")]}^{2})$
- Total Energy in one wavelength per unit crest width ( $E$ ): $E = \bar{E} \cdot L = \frac{1}{8} ρ g H^{2} L (J m [PARSE ERROR: Undefined("RBrace")])$
- Energy Flux / Wave Power per unit crest width ( $P$ ): $n = \frac{1}{2} [1 + \frac{2 k d}{\sinh (2 k d)}], C_{g} = n C, P = \bar{E} \cdot n \cdot C = \bar{E} C_{g} (W m [PARSE ERROR: Undefined("RBrace")])$

SA / Lec 07-08 — Group Velocity, Subsurface Pressure, Finite-Amplitude Waves & Wave Statistics

Q7.1 `[Theory & Math]`: Define group velocity ( $C_{g}$ ), state its relation with wave celerity ( $C$ ) in deep and shallow water, and explain its physical significance in wave energy conservation.

Appeared in: 2019 (Q4b, 7m), 2023 (Q5d, 6m), 2024 (Q1a, 6m part; Q3c, 5m) (Rank #9)
Time & Length Budget: 4–5 mins (~80–90 words)
Reference: SA/Lec 07-08/EWC471_lecture 7 and 8.pdf

Answer:

Definition: Group velocity ( $C_{g}$ ) is the speed at which an entire group (train) of waves—and therefore wave energy—travels forward: $C_{g} = n C = \frac{1}{2} [1 + \frac{2 k d}{\sinh (2 k d)}] C$
Relation with Phase Celerity ( $C$ ):
- In Deep Water ( $k d \to \infty$ ): $\frac{2 k d}{\sinh (2 k d)} \to 0 ⟹ n = \frac{1}{2}$ , so $C_{g} = 0.5 C_{0}$ . Individual waves travel twice as fast as the group, appearing at the back of the group and disappearing at the front.
- In Shallow Water ( $k d \to 0$ ): $\sinh (2 k d) \approx 2 k d ⟹ n = 1$ , so $C_{g} = C = \sqrt{g d}$ . The group and individual waves travel at the exact same speed (non-dispersive).
Physical Significance (Energy Conservation):
- Because wave energy travels at group velocity $C_{g}$ (not phase speed $C$ ), the rate of energy transmission (wave power per unit width) is $P = \bar{E} C_{g}$ .
- With zero energy loss between two depths ( $1$ and $2$ ), energy flux is conserved: $\bar{E_{1}} C_{g 1} = \bar{E_{2}} C_{g 2} ⟹ (\frac{1}{8} ρ g H_{1^{2}}) C_{g 1} = (\frac{1}{8} ρ g H_{2^{2}}) C_{g 2} ⟹ \frac{H_{2}}{H_{1}} = \sqrt{\frac{C_{g 1}}{C_{g 2}}}$ This directly governs wave shoaling as waves enter shallow water.

Q7.2 `[Theory & Math]`: Explain subsurface pressure under a progressive wave and outline the method to calculate surface wave height ( $H$ ) from an underwater pressure gauge.

Appeared in: 2019 (Q3d-iv, 2.5m), 2023 (Q6b, 10m), 2024 (Q3b, 12m) (Rank #16)
Time & Length Budget: 4–6 mins (~80–100 words)
Reference: SA/Lec 07-08/EWC471_lecture 7 and 8.pdf

Answer:

Subsurface Wave Pressure Equation: From the unsteady Bernoulli equation at depth $z$ (negative below SWL), total gauge pressure $p$ is the sum of hydrostatic pressure and dynamic wave pressure: $p = - ρ g z + ρ g η K_{p}$ where $η = \frac{H}{2} \cos θ$ and the Pressure Response Factor ( $K_{p}$ ) is: $K_{p} = \frac{\cosh k (d + z)}{\cosh (k d)}$
Why Wave Height Can Be Measured Underwater:
- At the surface ( $z = 0$ ), $K_{p} = 1$ . As depth increases toward the seabed ( $z = - d$ ), $K_{p} = \frac{1}{\cosh (k d)}$ decreases because dynamic pressure attenuates with depth (especially for short-period waves).
- By placing a pressure transducer near the seabed to record pressure fluctuations $Δ p$ and period $T$ , we can back-calculate the surface wave height $H$ .
Step-by-Step Calculation Method:
1. Given water depth $d$ , sensor elevation $z$ (z = -d if placed directly on the seabed), and wave period $T$ , compute $L_{0} = 1.56 T^{2}$ and find wavelength $L$ at depth $d$ (using Q5.1).
2. Calculate wave number $k = \frac{2 π}{L}$ and the Pressure Response Factor: $K_{p} = \frac{\cosh k (d + z)}{\cosh (k d)} (Note i f s e n s o r i s a t t h e b o t t o m, [PARSE ERROR: Undefined("RBrace")] z = - d ⟹ K_{p} = \frac{1}{\cosh (k d)})$
3. Find the dynamic pressure amplitude Δp (or total crest-to-trough pressure range Δptotal=pcrest-ptrough):
  - If dynamic pressure amplitude ( $Δ p$ ) under the crest is given (or $p_{\max} = - ρ g z + Δ p$ ): $η_{\max} = \frac{H}{2} = \frac{Δ p}{ρ g K_{p}} ⟹ H = \frac{2 Δ p}{ρ g K_{p}}$
  - If total pressure fluctuation ( $Δ p_{range} = p_{\max} - p_{\min}$ ) between crest and trough is given: $H = \frac{p_{\max} - p_{\min}}{ρ g K_{p}}$

Q7.3: Compare Airy (Linear), Stokes Finite-Amplitude, Cnoidal, and Solitary wave theories.

Appeared in: 2022 (Q2b, 7m part), 2023 (Q5b-ii, 4m), 2024 (Q1a, 6m part) (Rank #10)
Time & Length Budget: 4 mins (~75 words)
Reference: SA/Lec 07-08/EWC471_lecture 7 and 8.pdf

Answer:

Wave Theory	Depth / Ursell Regime ( $U_{R} = \frac{H L^{2}}{d^{3}}$ )	Wave Profile & Key Characteristics
Airy (Linear / Small-Amplitude)	All $d / L$ when amplitude is very small ( $H ≪ L, H ≪ d$ ).	Symmetric sinusoidal profile ( $η = \frac{H}{2} \cos θ$ ); closed particle orbits; zero net mass transport.
Stokes (2nd–5th Order)	Deep to intermediate water ( $\frac{d}{L} > \frac{1}{8}$ to $\frac{1}{10}$ , or $U_{R} < 26$ ).	Peaked crests and flatter troughs; open orbits causing forward mass transport (Stokes drift).
Cnoidal Wave Theory	Shallow water ( $\frac{d}{L} < \frac{1}{8}$ and $U_{R} > 26$ ).	Periodic shallow-water waves expressed by Jacobian elliptic function ( $cn$ ); sharp crests separated by long, flat troughs.
Solitary Wave Theory	Very shallow water near breaking ( $L \to \infty$ , $T \to \infty$ ).	Single isolated wave crest riding entirely above Still Water Level (SWL) with no trough; celerity $C = \sqrt{g (d + H)}$ .

Q7.4 `[Math]`: Method to calculate statistical wave parameters ( $H_{s}, T_{s}, H_{1 / 10}, T_{1 / 10}, H_{rms}$ ) from a wave train record.

Appeared in: 2022 (Q3c, 16m) (Rank #45)
Reference: SA/Lec 07-08/EWC471_lecture 7 and 8.pdf

Method to Follow:

Step 1 — Rank the Waves: Given $N$ individual waves with heights $H_{i}$ and periods $T_{i}$ , sort the waves in descending order of wave height ( $H_{1} [PARSE ERROR: Undefined("Command(\"ge\")")] H_{2} [PARSE ERROR: Undefined("Command(\"ge\")")] [PARSE ERROR: Undefined("Command(\"dots\")")] [PARSE ERROR: Undefined("Command(\"ge\")")] H_{N}$ ), keeping each wave's original period $T_{i}$ paired with its $H_{i}$ .
Step 2 — Mean Wave Height ( $\bar{H}$ ) and Root-Mean-Square Wave Height ( $H_{rms}$ ): $\bar{H} = \frac{1}{N} \sum_{i = 1}^{N} H_{i}, H_{rms} = \sqrt{\frac{1}{N} \sum_{i = 1}^{N} H_{i^{2}}}$
Step 3 — Significant Wave Height ( $H_{s} = H_{1 / 3}$ ) and Significant Period ( $T_{s} = T_{1 / 3}$ ): Take the top $M = \frac{N}{3}$ highest waves (round $M$ to the nearest integer): $H_{s} = H_{1 / 3} = \frac{1}{M} \sum_{i = 1}^{M} H_{i}, T_{s} = T_{1 / 3} = \frac{1}{M} \sum_{i = 1}^{M} T_{i}$
Step 4 — Highest One-Tenth Wave ( $H_{1 / 10}, T_{1 / 10}$ ): Take the top $K = \frac{N}{10}$ highest waves: $H_{1 / 10} = \frac{1}{K} \sum_{i = 1}^{K} H_{i}, T_{1 / 10} = \frac{1}{K} \sum_{i = 1}^{K} T_{i}$ (Alternatively, using Rayleigh distribution conversions from $H_{rms}$ : $\bar{H} = 0.886 H_{rms}$ , $H_{1 / 3} = 1.416 H_{rms}$ , $H_{1 / 10} = 1.800 H_{rms} = 1.27 H_{1 / 3}$ , $H_{1 / 100} = 2.359 H_{rms} = 1.67 H_{1 / 3}$ ).

SA / Lec 09-10 — Wave Shoaling, Refraction, Green's Law & Diffraction

Q9.1: Explain the necessity of studying wave transformation, wave shoaling, wave refraction, and why wave diffraction occurs in shallow water.

Appeared in: 2019 (Q1e, 5m), 2021 (Q2a, 10m), 2024 (Q2a-i,ii, 4m), 2025 (Q2c, 5m) (Rank #8)
Time & Length Budget: 4–7 mins (~70–120 words + sketch)
Reference: SA/Lec 09-10/EWC471_lecture 9 and 10.pdf

Answer:

Necessity of Studying Wave Transformation: Deep-water wave data cannot be used directly at the coast because shallow seabed contours alter wave height ( $H$ ), wavelength ( $L$ ), and direction ( $α$ ). Accurate nearshore wave heights and angles are essential for sizing coastal structures, locating harbors, and predicting longshore sediment transport.
Wave Shoaling ( $K_{s}$ ): As a wave enters shallower water, group velocity $C_{g}$ decreases. To conserve energy flux ( $\bar{E} C_{g} = constant$ ), energy packs into a shorter wavelength, causing wave height $H$ to first dip slightly (K_s min ≈ 0.91 at $d / L_{0} \approx 0.15$ ) and then rise sharply: $K_{s} = \frac{H}{H_{0^{'}}} = \sqrt{\frac{C_{g 0}}{C_{g}}} = \sqrt{\frac{1}{2 n \tanh (k d)}}$
Wave Refraction ( $K_{r}$ ):
- Cause: When a wave approaches depth contours at an angle, the part of the crest in shallower water slows down ( $C = \sqrt{g d}$ ) while the part in deeper water moves faster, bending the wave crest to align parallel to the bottom contours (Snell's Law: $\frac{\sin α}{C} = \frac{\sin α_{0}}{C_{0}}$ ).
- Refraction Coefficient: $K_{r} = \sqrt{\frac{b_{0}}{b}} = \sqrt{\frac{\cos α_{0}}{\cos α}}$ (where $b_{0}, b$ are spacing between wave orthogonals/rays).
- Importance in Siting Marine Structures:
  - Over submarine ridges / headlands, wave rays converge ( $b < b_{0} ⟹ K_{r} > 1$ ), focusing wave energy and causing severe erosion/structural loads.
  - Over submarine canyons / bays, wave rays diverge ( $b > b_{0} ⟹ K_{r} < 1$ ), spreading energy out and creating calmer water ideal for harbors.

   CONVERGENCE AT HEADLAND (High H)        DIVERGENCE AT BAY / CANYON (Low H)
       |     |     |   Wave Rays               |       |       |   Wave Rays
        \    |    /  (b decreases)            /        |        \  (b increases)
         v   v   v                           v         v         v
       _.-""""""-._                        ""-._               _.-""
     .'  Headland  '.                           '-._  Bay  _.-'

Wave Diffraction ( $K^{'}$ ):
- Definition & Cause: Lateral transfer of wave energy along the wave crest into the geometric shadow zone behind an obstacle (breakwater tip, island, or harbor entrance) due to water surface elevation (pressure) gradients between the exposed wave region and the calm sheltered zone.

Q9.2 `[Theory & Math]`: State Green's Law, explain how wave height theoretically reaches infinity as depth $d \to 0$ vs. what happens in reality, and calculate tsunami wave height in shallow water.

Appeared in: 2023 (Q8a, 5m), 2024 (Q4a, 6m) (Rank #29)
Time & Length Budget: 4–5 mins (~75 words)
Reference: SA/Lec 09-10/EWC471_lecture 9 and 10.pdf

Answer:

Derivation & Statement of Green's Law: For long shallow-water waves (like tsunamis, where $C_{g} = C = \sqrt{g d}$ ) between two depths $d_{1}$ and $d_{2}$ with orthogonal spacing $b_{1}$ and $b_{2}$ , conservation of wave energy flux ( $\bar{E_{1}} C_{g 1} b_{1} = \bar{E_{2}} C_{g 2} b_{2}$ ) gives: $(\frac{1}{8} ρ g H_{1^{2}}) \sqrt{g d_{1}} b_{1} = (\frac{1}{8} ρ g H_{2^{2}}) \sqrt{g d_{2}} b_{2} ⟹ \frac{H_{2}}{H_{1}} = {(\frac{b_{1}}{b_{2}})}^{1 / 2} {(\frac{d_{1}}{d_{2}})}^{1 / 4}$ For straight parallel depth contours with no refraction ( $b_{1} = b_{2}$ ), Green's Law states: $\frac{H_{2}}{H_{1}} = {(\frac{d_{1}}{d_{2}})}^{1 / 4}$
Why $H \to \infty$ as $d \to 0$ & Real Fate of the Wave:
- Mathematically: In $H_{2} = H_{1} (d_{1} / d_{2})^{1 / 4}$ , as water depth approaches the shoreline ( $d_{2} \to 0$ ), the ratio $d_{1} / d_{2} \to \infty$ , so $H_{2} \to \infty$ .
- In Reality: Before depth reaches zero, wave height exceeds the depth-limited stability limit ( $H_{b} \approx 0.78 d_{b}$ ) and bottom friction increases. The wave becomes unstable and breaks, dissipating its energy as turbulence and swash runup.
Calculation Recipe (e.g., Tsunami Shoaling): Given deep-ocean tsunami height $H_{1}$ (e.g., 0.5 m or 1.0 m) at depth $d_{1}$ (e.g., 4000 m) entering shallow depth $d_{2}$ (e.g., 10 m), directly compute: $H_{2} = H_{1} {(\frac{d_{1}}{d_{2}})}^{1 / 4}, C_{2} = \sqrt{g d_{2}}, L_{2} = T \sqrt{g d_{2}}$

Q9.3 `[Math]`: Method to calculate shoaled and refracted wave height ( $H = H_{0^{'}} K_{s} K_{r}$ ) at intermediate/shallow depths.

Appeared in: 2021 (Q2b), 2023 (Q7c), 2024 (Q4b), 2025 (Q3b) (Rank #11)
Reference: SA/Lec 09-10/EWC471_lecture 9 and 10.pdf

Method to Follow:

Step 1 — Deep-Water Parameters: Given deep-water wave height $H_{0}$ , period $T$ , and deep-water approach angle $α_{0}$ : $L_{0} = 1.56 T^{2}, C_{0} = 1.56 T$
Step 2 — Wavelength ( $L$ ) and Celerity ( $C$ ) at Target Depth ( $d$ ): Find $L$ at depth $d$ using Q5.1, then compute $C = L / T$ and $k = 2 π / L$ .
Step 3 — Shoaling Coefficient ( $K_{s}$ ): $n = \frac{1}{2} [1 + \frac{2 k d}{\sinh (2 k d)}], K_{s} = \sqrt{\frac{C_{0}}{2 n C}} = \sqrt{\frac{1}{\tanh (k d) [1 + \frac{2 k d}{\sinh (2 k d)}]}}$
Step 4 — Wave Angle ( $α$ ) and Refraction Coefficient ( $K_{r}$ ): Using Snell's Law for straight parallel contours: $\sin α = (\frac{C}{C_{0}}) \sin α_{0} = \tanh (k d) \sin α_{0} ⟹ α = \arcsin (\frac{C}{C_{0}} \sin α_{0})$ $K_{r} = \sqrt{\frac{\cos α_{0}}{\cos α}}$ (Note: If $α_{0} = 0^{\circ}$ , i.e., wave crests are already parallel to bottom contours, then $K_{r} = 1.0$ , and unrefracted deep-water height is $H_{0^{'}} = H_{0} K_{r}$ ).
Step 5 — Local Wave Height ( $H$ ): $H = H_{0} K_{s} K_{r}$

SA / Lec 11-12 — Wave Breaking, Surf-Zone Currents (Longshore & Rip) & Wave Setup

Q11.1: Explain why waves break, why wave breaking is much more common in shallow water than deep water, and describe the 4 types of breaking waves.

Appeared in: 2019 (Q3d-i, 2.5m), 2022 (Q3b, 7m), 2023 (Q7a, 6m; Q7b-i,ii, 4m), 2024 (Q2a-iii,iv, 4m; Q3d, 5m) (Rank #4)
Time & Length Budget: 4–6 mins (~80–110 words + sketch)
Reference: SA/Lec 11-12/EWC471_lecture 11 and 12.pdf

Answer:

Why a Wave Breaks (Physical Mechanism):
1. Kinematic Instability: A wave breaks when the horizontal water particle velocity at the crest ( $u_{crest}$ ) exceeds the wave's forward propagation speed ( $C$ , celerity), causing the crest to overtake the wave form and topple forward.
2. Limiting Criteria (Miche / McCowan): Breaking occurs when wave steepness exceeds HL=17tanh(kd), which simplifies to:
  - Deep water: $\frac{H_{0}}{L_{0}} \approx \frac{1}{7} \approx 0.142$ (crest angle $< 120^{\circ}$ ).
  - Shallow water: $\frac{H_{b}}{d_{b}} \approx 0.78$ .
Why Breaking is Much More Common in Shallow Water than Deep Water:
- In deep water, only extreme local storm winds can push wave steepness above $H / L = 0.142$ (whitecapping).
- In shallow water, every wave eventually breaks because decreasing depth ( $d \to 0$ ) slows wave speed ( $C = \sqrt{g d}$ ), shortens wavelength ( $L$ ), and increases wave height ( $H$ ) via shoaling, while bottom friction retards the base of the wave.
Four Types of Breaking Waves (classified by Surf Similarity / Iribarren Number $ξ_{0} = \frac{m}{\sqrt{H_{0} / L_{0}}}$ , where $m = \tan β$ is beach slope):

1. SPILLING (xi_0 < 0.5)       2. PLUNGING (0.5 < xi_0 < 3.3)   3. SURGING (xi_0 > 3.3)
   Foam spills down front         Crest curls over air pocket      Base surges up steep beach
       _.-**(foam)                     _.-""-. (tube)                    _.-/
     .'      \                       .'   ( ) \                     _.-'   / Steep
   .'  Flat   \                    .'   Steep  \              _.-""       /  Slope

Spilling ( $ξ_{0} < 0.5$ ): Occurs on gentle/flat beaches with steep waves; foam and turbulence spill gently down the front face.
Plunging ( $0.5 < ξ_{0} < 3.3$ ): Occurs on moderate-to-steep beaches; the crest curls forward as a jet over an air pocket and crashes violently with high impact force.
Collapsing ( $ξ_{0} \approx 3.3$ ): Intermediate between plunging and surging; the lower face steepens and collapses into foam right at the shoreline.
Surging ( $ξ_{0} > 3.3$ ): Occurs on very steep beaches with low-steepness (long) waves; the wave base slides smoothly up and down the beach face with almost no curling crest.

Q11.2 `[Math]`: Method to estimate breaking wave height ( $H_{b}$ ), breaking water depth ( $d_{b}$ ), and breaker type on a given beach slope ( $m$ ).

Appeared in: 2021 (Q2b, 20m), 2023 (Q7c, 12m), 2024 (Q4b, 15m), 2025 (Q3b, 20m) (Rank #11)
Reference: SA/Lec 11-12/EWC471_lecture 11 and 12.pdf

Method to Follow:

Step 1 — Unrefracted Deep-Water Wave Height ( $H_{0^{'}}$ ):
- Given wave height $H_{1}$ and angle $α_{1}$ at depth $d_{1}$ (or deep-water $H_{0}, α_{0}$ ), compute $L_{0} = 1.56 T^{2}$ .
- If starting from intermediate depth $d_{1}$ , find $K_{s 1}$ and $K_{r 1}$ at $d_{1}$ (using Q9.3) to get equivalent deep-water height $H_{0^{'}} = \frac{H_{1}}{K_{s 1}} K_{r}$ . (If $α_{0} = 0^{\circ}$ , $K_{r} = 1$ and $H_{0^{'}} = H_{0}$ ).
Step 2 — Deep-Water Steepness Index: Compute $\frac{H_{0^{'}}}{g T^{2}}$ (dimensionless) or $\frac{H_{0^{'}}}{L_{0}}$ .
Step 3 — Breaking Wave Height ( $H_{b}$ ) (Weggel / SPM Nomogram or Formula):
- Using Nomogram (Fig. 7-3 / SPM): Enter the horizontal axis with $\frac{H_{0^{'}}}{g T^{2}}$ , move vertically to the curve for beach slope $m = \tan β$ , read $\frac{H_{b}}{H_{0^{'}}}$ on the vertical axis, and calculate: $H_{b} = (\frac{H_{b}}{H_{0^{'}}}) H_{0^{'}}$
- Using Empirical Formula (Komar & Gaughan, if no chart is needed): $H_{b} = 0.39 g^{1 / 5} {(T \cdot H_{{0^{'}}^{2}})}^{2 / 5}$
Step 4 — Breaking Water Depth ( $d_{b}$ ) (Weggel Nomogram or Equations):
- Using Nomogram (Fig. 7-2 / SPM): Enter the horizontal axis with $\frac{H_{b}}{g T^{2}}$ , move up to the beach slope curve $m$ , read $\frac{d_{b}}{H_{b}}$ on the vertical axis, and calculate $d_{b} = (\frac{d_{b}}{H_{b}}) H_{b}$ .
- Using Weggel's Analytical Equations: $a = 43.8 (1 - e^{- 19 m}), b = \frac{1.56}{1 + e^{- 19.5 m}}$ $\frac{d_{b}}{H_{b}} = \frac{1}{b - a (\frac{H_{b}}{g T^{2}})} ⟹ d_{b} = H_{b} (\frac{d_{b}}{H_{b}})$
Step 5 — Identify Breaker Type: Calculate the Surf Similarity Parameter ξ0=mH0′/L0 (or ξb=mHb/L0):
- $ξ_{0} < 0.5$ ( $ξ_{b} < 0.4$ ): Spilling breaker
- $0.5 < ξ_{0} < 3.3$ ( $0.4 < ξ_{b} < 2.0$ ): Plunging breaker
- $ξ_{0} > 3.3$ ( $ξ_{b} > 2.0$ ): Surging / Collapsing breaker

Q11.3: Explain why waves are the prime movers for littoral processes, sketch the nearshore current system (longshore current & rip current), and explain why rip currents are dangerous to swimmers.

Appeared in: 2022 (Q2a, 7m part), 2023 (Q5a, 6m; Q6a, 10m) (Rank #23)
Time & Length Budget: 5–7 mins (~100–120 words + sketch)
Reference: SA/Lec 11-12/EWC471_lecture 11 and 12.pdf

Answer:

   Oblique Wave Crests
      \       \       \
   ----\-------\-------\---- Breaker Line
        v               v
   ======>   <====   <====== Longshore Current (Feeder)
             || ||           Rip Neck (Fast narrow jet seaward)
            _||_||_
            \     /          Rip Head (Expands outside breaker zone)
             '---'
   ========================= Shoreline

Why Waves Are the Prime Movers for Littoral Processes:
1. Breaking waves release intense turbulence that lifts and suspends seabed sand (stirring action).
2. Oblique breaking waves transfer excess momentum (radiation stress) to generate longshore currents (transporting action) and swash/backwash (beach drift), moving millions of cubic meters of sand along the coast.
Nearshore Current System:
- Longshore Current: Flows parallel to the shoreline inside the surf zone, driven by oblique waves breaking at an angle $α_{b}$ to the beach.
- Rip Current: Narrow, strong seaward-flowing jet that returns water piled up inside the surf zone back out through a gap in the sandbar. Consists of feeder currents (parallel to shore), rip neck (narrow fast channel through the breakers), and rip head (mushroom-shaped plume seaward of breakers).
- Undertow: Near-bottom seaward return flow below trough level balancing onshore mass transport.
Why Rip Currents Are Dangerous to Swimmers:
- Rip necks reach speeds of 1–2.5 m/s, faster than even Olympic swimmers can swim against.
- Uninformed swimmers panic and exhaust themselves trying to swim straight back to shore against the jet.
- Escape Rule: Never swim against a rip current; swim parallel to the shoreline (20–30 m sideways) out of the narrow rip neck, then let the waves carry you back to shore.

Q11.4 `[Theory & Math]`: Define radiation stress, wave set-down, and wave setup; explain why wave setup contributes significantly to coastal flooding; and state the method to calculate set-down and setup.

Appeared in: 2023 (Q7b-iv, 2m; Q7d, 4m), 2025 (Q3c, 5m; Q4b, 15m) (Rank #17)
Time & Length Budget: 4–7 mins (~80–110 words + formulas)
Reference: SA/Lec 11-12/EWC471_lecture 11 and 12.pdf

Answer:

                                                     _.-"" Mean Water Level (MWL)
Still Water Level (SWL)                     _.-"""""       ^ Wave Setup (+eta_u)
------------------------------------._    .'-------------- | -------------------
                                      '--'  <- Max Set-down (-eta_d) at Breaker Line

Definitions:
- Radiation Stress ( $S_{x x}$ ): Excess depth-integrated horizontal momentum flux caused by the presence of waves: $S_{x x} = \bar{E} (2 n - \frac{1}{2}) = \frac{1}{8} ρ g H^{2} [\frac{2 k d}{\sinh (2 k d)} + \frac{1}{2}]$
- Wave Set-down ( $η_{d}$ ): Slight lowering of the Mean Water Level (MWL) below Still Water Level (SWL) just seaward of the breaker line because $S_{x x}$ increases as waves shoal ( $\frac{d S_{x x}}{d x} > 0$ ).
- Wave Setup ( $\bar{η}$ ): Superelevation (rise) of the Mean Water Level above SWL inside the surf zone toward the shoreline.
Why Wave Setup Contributes Significantly to Coastal Water Rise:
- Inside the surf zone, wave height $H$ rapidly drops due to breaking ( $H = κ d$ ), causing a sharp decrease in radiation stress ( $\frac{d S_{x x}}{d x} < 0$ ).
- To balance this onshore momentum force, the mean water surface tilts upward toward the beach ( $\frac{d \bar{η}}{d x} = - \frac{1}{ρ g (d + \bar{η})} \frac{d S_{x x}}{d x}$ ). During severe cyclone waves (H_b = 4–6 m), wave setup alone adds 0.5–1.5 m of extra static water depth on top of astronomical tide and storm surge, allowing larger waves to reach and overtop coastal embankments.
Calculation Method ([Math]):
1. First find breaking wave height $H_{b}$ and breaking depth $d_{b}$ (using Q11.2).
2. Wave Set-down at the Breaking Point ( $η_{b} = η_{d}$ ): $η_{b} = - \frac{H_{b^{2}} k_{b}}{8 \sinh (2 k_{b} d_{b})} \approx - \frac{H_{b^{2}}}{16 d_{b}} (or η_{b} = - \frac{κ^{2} d_{b}}{16} \approx - 0.038 d_{b} for κ = \frac{H_{b}}{d_{b}} \approx 0.78)$
3. Wave Setup Rise Across the Surf Zone ( $Δ η$ ): $Δ η = \frac{3 κ^{2} / 8}{1 + 3 κ^{2} / 8} d_{b} \approx 0.19 d_{b} \approx 0.24 H_{b} (orsimplifiedSPMformula [PARSE ERROR: Undefined("RBrace")] Δ η \approx 0.15 d_{b} to 0.23 H_{b})$
4. Net Wave Setup at the Shoreline ( $\bar{η_{\max}}$ ): $\bar{η_{\max}} = η_{b} + Δ η = - \frac{H_{b^{2}}}{16 d_{b}} + \frac{3 κ^{2} / 8}{1 + 3 κ^{2} / 8} d_{b} \approx 0.15 d_{b} \approx 0.19 H_{b}$

SA / Lec 13-14 — Wave Forces on Piles & Vertical Walls (Non-Breaking, Breaking & Broken)

Q13.1: Classify and illustrate wave force problems by type of wave action and structure, and write the Morison equation for horizontal wave force on a vertical pile.

Appeared in: 2019 (Q3a, 5m; Q4a, 5m), 2024 (Q4c, 3m) (Rank #20)
Time & Length Budget: 3–5 mins (~60–90 words)
Reference: SA/Lec 13-14/EWC471_lecture 13 and 14.pdf

Answer:

Classification of Wave Force Problems:
1. By Type of Wave Action (Water Depth at Structure):
  - Non-Breaking Waves (Standing Wave / Clapotis): Structure is in deeper water ( $d_{s} > 1.5 H_{i}$ ); wave reflects cleanly without breaking, exerting smooth hydrostatic + dynamic pressure.
  - Breaking Waves: Wave breaks directly against the structure ( $d_{s} \approx d_{b}$ ), trapping an air pocket and creating extreme short-duration shock/impact pressure (Minikin pressure).
  - Broken Waves: Structure is landward of the breaker line (very shallow water or dry beach); the turbulent broken surge hits the wall with dynamic velocity head + hydrostatic head.
2. By Type of Coastal Structure:
  - Slender Pile Structures ( $D / L < 0.05$ , e.g., jetty piles, offshore jacket legs): Drag + inertia forces (Morison Equation).
  - Vertical-Wall / Monolithic Structures (seawalls, caissons, bulkheads): Reflected/breaking pressure diagrams (Miche–Rundgren / Sainflou / Minikin).
  - Sloping Rubble-Mound Structures (breakwaters, revetments): Armor unit stability (Hudson Formula).
Morison Equation for Horizontal Wave Force on a Vertical Cylindrical Pile: For a slender vertical cylinder of diameter $D$ , the total force per unit length $f$ at elevation $z$ is the sum of Inertia Force ( $f_{i}$ ) and Drag Force ( $f_{d}$ ): $f = f_{i} + f_{d} = C_{M} ρ (\frac{π D^{2}}{4}) \frac{\partial u}{\partial t} + \frac{1}{2} C_{D} ρ D u | u |$ where $C_{M}$ is the inertia (mass) coefficient, $C_{D}$ is the drag coefficient, $ρ$ is water density, $u$ is horizontal water particle velocity, and $\frac{\partial u}{\partial t} = a_{x}$ is horizontal acceleration.

Q13.2 `[Theory & Math]`: Explain non-breaking wave pressure distribution on a vertical wall and state the Miche–Rundgren (Sainflou) method to calculate forces and overturning moments.

Appeared in: 2019 (Q3c, 10m), 2021 (Q3b, 20m), 2023 (Q8b, 20m), 2024 (Q1b, 24m), 2025 (Q1b, 21m; Q4a, 10m) (Rank #2)
Reference: SA/Lec 13-14/EWC471_lecture 13 and 14.pdf

Answer:

Non-Breaking Wave Pressure Distribution (Standing Wave / Clapotis):
- When an incident wave ( $H_{i}$ ) reflects off a vertical wall ( $χ = H_{r} / H_{i} [PARSE ERROR: Undefined("Command(\"le\")")] 1.0$ ), it forms a standing wave (clapotis) of height $H_{wall} = (1 + χ) H_{i} \approx 2 H_{i}$ .
- Because of finite-amplitude effects, the mean water level at the wall rises by $h_{0}$ above SWL:
  - Under Wave Crest: Water rises to $y_{c} = d_{s} + h_{0} + \frac{1 + χ}{2} H_{i}$ above the toe. Pressure increases from $0$ at the crest to $γ d_{s} + p_{1}$ at the toe (where $p_{1} = \frac{γ H_{i} (1 + χ)}{2 \cosh (k d_{s})}$ ).
  - Under Wave Trough: Water drops to $y_{t} = d_{s} + h_{0} - \frac{1 + χ}{2} H_{i}$ above the toe. Pressure at the toe drops to $γ d_{s} - p_{1}$ .

      CREST AT WALL                               TROUGH AT WALL
      |\                                          |
      | \  y_c = d_s + h_0 + H_i                  |
  ----|--\----------------------- SWL ------------|----------------------- SWL
      |   \                                       |\  y_t = d_s + h_0 - H_i
  d_s |    \                                  d_s | \
      |_____\                                     |__\
      Toe: w*d_s + p_1                            Toe: w*d_s - p_1

Step-by-Step Calculation Method (Miche–Rundgren Nomograms, SPM Figs. 7-90 to 7-93):
1. Step 1 — Input Dimensionless Ratios: Given incident wave height Hi, period T, water depth at wall ds, reflection coefficient χ (0.9 or 1.0), and unit weight of water w=γ (10.05 kN/m³ or 64 lb/ft³):
  - Compute deep-water steepness parameter $\frac{H_{i}}{g T^{2}}$ (and equivalent $H_{0^{'}}$ if not given).
  - Compute depth ratio $\frac{d_{s}}{H_{i}}$ .
2. Step 2 — Crest & Trough Elevations at Wall ( $y_{c}, y_{t}$ ):
  - Enter Fig. 7-90 (or 7-91) with $\frac{H_{i}}{g T^{2}}$ and $\frac{d_{s}}{H_{i}}$ to read $\frac{h_{0}}{H_{i}}$ , then calculate $h_{0}$ .
  - Compute crest and trough water elevations above the wall base: $y_{c} = d_{s} + h_{0} + \frac{1 + χ}{2} H_{i}, y_{t} = d_{s} + h_{0} - \frac{1 + χ}{2} H_{i}$ (Check if $y_{c}$ exceeds wall height $b$ ; if $y_{c} [PARSE ERROR: Undefined("Command(\"le\")")] b$ , no overtopping occurs).
3. Step 3 — Total Integrated Forces ( $F_{c}, F_{t}$ ) and Moments ( $M_{c}, M_{t}$ ) on the Seaward Face:
  - Enter Fig. 7-92 (Force Nomogram) with dsHi and HigT2 (using solid curves for Crest and dashed curves for Trough, interpolating between χ=1.0 and χ=0.9 if χ=0.95):
    - Read $\frac{F_{c}}{w H_{i^{2}}}$ and $\frac{F_{t}}{w H_{i^{2}}} ⟹$ calculate $F_{c}$ and $F_{t}$ (per unit width of wall).
  - Enter Fig. 7-93 (Moment Nomogram) similarly:
    - Read $\frac{M_{c}}{w H_{i^{3}}}$ and $\frac{M_{t}}{w H_{i^{3}}} ⟹$ calculate $M_{c}$ and $M_{t}$ about the wall base.
4. Step 4 — Critical Net Forces and Net Moments on the Wall:
  - Case A — Dry Landward Side (No water behind wall):
    - Seaward shoreward-pushing load is maximum under the Crest: $F_{net m a x} [PARSE ERROR: Undefined("RBrace")] = F_{c}, M_{net m a x} [PARSE ERROR: Undefined("RBrace")] = M_{c}$
  - Case B — Equal or Unequal Still Water Level ( $d_{land}$ ) on Landward Side (e.g., Curtain Wall / Breakwater):
    - Compute constant hydrostatic force and moment from the landward water of depth $d_{L}$ ( $d_{L} = d_{s}$ if SWL is equal on both sides): $F_{static} = \frac{1}{2} w d_{L^{2}}, M_{static} = \frac{1}{6} w d_{L^{3}}$
    - Under Crest (Net Landward Push): $F_{net c r e s t} [PARSE ERROR: Undefined("RBrace")] = F_{c} - F_{static}, M_{net c r e s t} [PARSE ERROR: Undefined("RBrace")] = M_{c} - M_{static}$
    - Under Trough (Net Seaward Pull): $F_{net t r o u g h} [PARSE ERROR: Undefined("RBrace")] = F_{t} - F_{static}, M_{net t r o u g h} [PARSE ERROR: Undefined("RBrace")] = M_{t} - M_{static}$
    - Compare $| F_{net c r e s t} [PARSE ERROR: Undefined("RBrace")] |$ vs. $| F_{net t r o u g h} [PARSE ERROR: Undefined("RBrace")] |$ and $| M_{net c r e s t} [PARSE ERROR: Undefined("RBrace")] |$ vs. $| M_{net t r o u g h} [PARSE ERROR: Undefined("RBrace")] |$ to report the governing design force and moment.

Q13.3 `[Theory & Math]`: Draw the Minikin breaking wave pressure diagram with the toe moment equation, and state the method to calculate broken wave force on a vertical wall.

Appeared in: 2019 (Q1d, 5m), 2022 (Q2c, 16m) (Rank #30 & #44)
Time & Length Budget: 4–7 mins (~80–110 words + diagram)
Reference: SA/Lec 13-14/EWC471_lecture 13 and 14.pdf

Answer:

Part A — Minikin Breaking Wave Pressure Diagram & Toe Moment (2019 Q1d):

   Wall
    |\   H_b / 2
    | \
 ---|------------> p_m (Max Dynamic Impact Pressure at SWL)
    | / \  H_b / 2
    |/   \
 d_s|     \
    |______\
   Toe      w*d_s + (w * H_b / 2)

Peak Dynamic Pressure at SWL ( $p_{m}$ ): $p_{m} = 101 w \frac{H_{b}}{L_{D}} \frac{d_{s}}{D} (D + d_{s})$ (where $H_{b}$ = breaking wave height, $d_{s}$ = depth at wall toe, $D$ = depth at one wavelength seaward of wall, and $L_{D}$ = wavelength in depth $D$ ).
Dynamic Force ( $R_{m}$ ) & Hydrostatic+Wave Force ( $R_{s}$ ): $R_{m} = \frac{p_{m} H_{b}}{3} a c t s a t S W L, l e v e r a r m [PARSE ERROR: Undefined("RBrace")] d_{s} [PARSE ERROR: Undefined("RBrace")]$ $R_{s} = \frac{w H_{b}}{2} (d_{s} + \frac{H_{b}}{4})$
Overturning Moment about the Toe ( $M_{toe}$ ): $M_{toe} = R_{m} d_{s} + M_{s} = \frac{p_{m} H_{b} d_{s}}{3} + \frac{w H_{b}}{2} [\frac{d_{s^{2}}}{2} + \frac{d_{s} H_{b}}{4} + \frac{H_{b^{2}}}{24}]$ (Note: Include $\frac{1}{6} w d_{s^{3}}$ if uncompensated hydrostatic water pressure acts on the seaward side only).
Part B — Broken Wave Force & Moment on a Vertical Wall (2022 Q2c):
1. Step 1 — Breaking Wave Height ( $H_{b}$ ) and Depth ( $d_{b}$ ): From deep-water $H_{0}, T$ and beach slope $m$ , find $H_{b}$ and $d_{b}$ using Q11.2.
2. Step 2 — Broken Wave Surge Height at the Wall ( $h_{c}$ ):
  - Case 1 (Wall Seaward of Shoreline, water depth $d_{s} [PARSE ERROR: Undefined("Command(\"le\")")] d_{b}$ ): hc=0.78Hb
    - Dynamic pressure (uniform from SWL to $h_{c}$ ): $p_{d} = \frac{1}{2} ρ C_{b^{2}} = \frac{w d_{b}}{2}$
    - Hydrostatic surge pressure (triangular from $0$ at $d_{s} + h_{c}$ to $w (d_{s} + h_{c})$ at toe): $p_{s} = w (d_{s} + h_{c})$
    - Forces & Moments: $R_{d} = p_{d} h_{c} = \frac{w d_{b} h_{c}}{2}, R_{s} = \frac{w (d_{s} + h_{c})^{2}}{2}$ $F_{total} = R_{d} + R_{s}, M_{toe} = R_{d} (d_{s} + \frac{h_{c}}{2}) + \frac{R_{s} (d_{s} + h_{c})}{3}$
  - Case 2 (Wall Landward of Shoreline at distance $x_{1}$ up the dry beach of slope $m$ , where maximum runup reaches $x_{2} = R / m$ ): $h_{c} = 0.78 H_{b} (1 - \frac{x_{1}}{x_{2}})$ $p_{d} = \frac{w d_{b}}{2} {(1 - \frac{x_{1}}{x_{2}})}^{2}, p_{s} = w h_{c}$ $R_{d} = p_{d} h_{c}, R_{s} = \frac{1}{2} w h_{c^{2}}, F_{total} = R_{d} + R_{s}, M_{toe} = R_{d} (\frac{h_{c}}{2}) + R_{s} (\frac{h_{c}}{3})$

SA / Lec 17-18 — Shoreline Dynamics, Beach Profile, Coastal Features & Estuaries

Q17.1: "The shoreline is a dynamic interface" — explain the statement in the context of coastal morphological and geological processes.

Appeared in: 2022 (Q1b, 7m) (Rank #42)
Time & Length Budget: 4–5 mins (~85 words)
Reference: SA/Lec 17-18/EWC471_lecture 17 and 18.pdf

Answer:

Triple Boundary: The shoreline is the meeting point of three dynamic spheres—lithosphere (land), hydrosphere (ocean/rivers), and atmosphere (wind/storms)—and is never static.
Continuous Energy Input: Waves, astronomical tides, wind, and river flows constantly deliver kinetic energy that erodes, sorts, and redistributes sediment along and across the coast.
Multi-Timescale Changes:
1. Short-term (Hours to Seasons): Tides shift the waterline twice daily; winter/storm waves strip sand from the berm to build offshore bars (storm profile), while calm summer swells push sand back onto the berm (swell profile).
2. Medium-term (Years to Decades): Longshore drift builds spits, tombolos, and barrier islands while eroding headlands and shifting river mouths.
3. Long-term (Centuries to Geological): Tectonic uplift/subsidence, delta building, and eustatic sea-level rise continuously reshape the entire coastline.

Q17.2: Draw a neat sketch of a typical cross-shore beach profile and identify all salient features.

Appeared in: 2019 (Q2a, 6m), 2024 (Q4d, 6m) (Rank #18)
Time & Length Budget: 4–5 mins (~70 words + labeled sketch)
Reference: SA/Lec 17-18/EWC471_lecture 17 and 18.pdf

Answer:

|<--- OFFSHORE --->|<------- NEARSHORE ------->|<-- FORESHORE -->|<-- BACKSHORE -->|<- COAST ->|
                   |<- Breaker ->|<-- Surf --->|<-- Swash -->|
                                                                  _______  _.-""-.   /|
                                                          _.-""""|  Berm |' Dunes './ | Cliff
~~~~~~~~~~~~~_.-._~~~~~~~~~~~~~~~_.-._~~~~~~~~~~~~~_.-""""Scarp  |       |         |  |
----------------HWL----------------------------------------------|-------|---------|-----------
~~~~~~~~~~~~~     ~~~~~~~~~~~~~~~     ~~~~~~~~_.-""              |       |         |
----------------LWL---------------------_.-"""                   |       |         |
                    _.-""-._      _.-"""
_________.---------'  Bar   '----' Trough

Cross-Shore Zones & Features:
1. Coast (Upland): Landward of the beach, marked by seacliffs or coastal sand dunes.
2. Backshore: Extends from the dune/cliff base to the berm crest; remains dry under normal waves and is submerged only during severe storms. Contains flat berms (storm berm, normal berm) and beach scarps (steep step cut by wave erosion).
3. Foreshore (Beach Face): Sloping zone between High Water Line (HWL) and Low Water Line (LWL) subjected to daily swash and backwash.
4. Nearshore: Extends from the LWL out to the breaker line; includes the breaker zone, surf zone, longshore trough, and submerged longshore sandbar.
5. Offshore: Seaward of the breaker zone out to the edge of the continental shelf.

Q17.3: Define and sketch key coastal features (Coastline, Tombolo, Barrier Spit, Barrier Island, Headland, Coastal Dune, Tidal Flats) and explain how barrier islands and coastal dunes are formed.

Appeared in: 2019 (Q3d-ii, 2.5m), 2021 (Q1a, 10m), 2022 (Q2a, 7m part), 2023 (Q1a, 10m part), 2025 (Q1a-i,iii, 6m) (Rank #7)
Time & Length Budget: 2–6 mins (write only the features asked in the question)
Reference: SA/Lec 17-18/EWC471_lecture 17 and 18.pdf, SB/Topic 01/EWCE 471_LEC-01 & 02_Introduction to Coastal Engineering, Coast and Coastal Features.pdf

Answer:

   TOMBOLO                       BARRIER SPIT                  BARRIER ISLAND
  ========= Mainland            ========= Mainland            ========= Mainland
     | |   Sand Neck               \                          ~~~ Lagoon / Bay ~~~
    ( O )  Offshore Island          '---> Spit Hook            [======]  [======] Islands

Definitions:
1. Coastline: The line forming the boundary between the coast (upland) and the shore/beach, usually marked by the foot of seacliffs or permanent coastal dunes (the landward limit of extreme storm wave action).
2. Tombolo: A narrow sand or gravel bar built by wave refraction and diffraction that connects an offshore island (or detached breakwater) to the mainland.
3. Barrier Spit: A long, narrow ridge of sand or shingle attached to the mainland at one end and terminating in open water at the other, formed where longshore drift continues past a bend or inlet in the coastline.
4. Barrier Island: An elongated, narrow ridge of sand lying parallel to the mainland coast and separated from it by a shallow lagoon, bay, or tidal marsh.
  - How Formed: Built by (i) breaching of a long barrier spit during storm surges, (ii) upward growth (emergence) of offshore sandbars, or (iii) drowning of coastal dune ridges during post-glacial sea-level rise.
5. Headland: A high, rocky projection of resistant land jutting out into the sea, flanked by bays where softer rock has eroded away.
6. Coastal Dune: Mounds or ridges of wind-blown (aeolian) sand formed immediately behind the backshore.
  - How Formed: Require three conditions: (i) an abundant supply of dry beach sand exposed at low tide, (ii) strong onshore winds to blow the sand landward, and (iii) obstacles/vegetation (e.g., dune grass, driftwood) that trap the moving sand and anchor the mound.
7. Tidal Flats: Broad, nearly horizontal muddy or sandy plains along low-energy estuaries and lagoons that are alternately submerged at high tide and exposed at low tide.

Q17.4: Define an estuary, classify estuaries, differentiate between tide-dominated and wave-dominated estuaries, and explain mixed estuarine systems.

Appeared in: 2019 (Q1f, 5m), 2025 (Q1a-ii, 3m; Q3a, 5m) (Rank #21)
Time & Length Budget: 3–5 mins (~60–85 words)
Reference: SA/Lec 17-18/EWC471_lecture 17 and 18.pdf

Answer:

Definition of Estuary: A semi-enclosed coastal body of water having a free connection with the open sea, within which seawater is measurably diluted by freshwater from land drainage (rivers).
Classifications of Estuaries:
1. By Geomorphology: (i) Drowned river valleys (coastal plain), (ii) Lagoon-type / bar-built, (iii) Fjord-type (glacially carved), (iv) Tectonically produced.
2. By Salinity & Water Circulation: (i) Salt-wedge (river-dominated, sharp halocline), (ii) Partially mixed (moderate tidal turbulence), (iii) Well-mixed / Vertically homogeneous (strong tidal currents), (iv) Fjord / Inverse.
3. By Dominant Coastal Energy: (i) Wave-dominated, (ii) Tide-dominated, and (iii) Mixed energy.
Tide-Dominated vs. Wave-Dominated Estuaries:

Feature	Tide-Dominated Estuary	Wave-Dominated Estuary
Dominant Force	Strong tidal currents (macrotidal range) exceed wave energy.	Strong ocean wave action exceeds tidal current energy.
Mouth Geometry	Funnel-shaped (wide mouth) with elongated linear tidal sand ridges/bars aligned parallel to flow.	Constricted entrance partially closed off by a barrier spit or barrier island at the mouth.
Central Basin	Energetic braided tidal channels bordered by broad mudflats/salt marshes.	Calm, low-energy central lagoon behind the barrier spit where fine mud settles.

Mixed Estuarine Systems:
- Hydrodynamically (Partially Mixed): Both river outflow and tidal currents are significant; turbulence mixes fresh and salt water vertically so salinity increases gradually both seaward and from surface to bottom.
- Morphologically (Mixed Wave–Tide Energy): Influenced by both moderate waves and moderate tides, producing short barrier islands broken by numerous wide tidal inlets and well-developed flood/ebb tidal deltas.

2. Section B Lecture Materials (`EWCE 471/SB/`)

SB / Topic 01 — Coast, Sea vs. Lake, Ocean & Sea Level Rise (SLR) in Bangladesh

Q1.1 (SB): How do you distinguish a lake from a sea, and when is a sea called an ocean? Justify with examples.

Appeared in: 2019 (Q5a, 6m) (Rank #32)
Time & Length Budget: 4–5 mins (~85 words)
Reference: SB/Topic 01/EWCE 471_LEC-01 & 02_Introduction to Coastal Engineering, Coast and Coastal Features.pdf

Answer:

Distinguishing a Lake from a Sea:
1. Connection to the World Ocean: A lake is a completely landlocked body of water surrounded by land on all sides, whereas a sea is directly connected to the open ocean (via straits or wide openings) and shares its mean sea level.
2. Salinity & Bed Crust: Lakes are typically freshwater sitting on shallow continental crust (e.g., Lake Superior, Lake Baikal), while seas are saline (saltwater) bodies sitting over continental margins or oceanic crust (e.g., Arabian Sea, Mediterranean Sea).
3. Historical/Geological Exception: A few landlocked saltwater bodies are called "seas" by convention (e.g., Caspian Sea, Dead Sea), but hydrologically they are saline endorheic lakes (the Caspian is a remnant of the ancient Tethys Ocean).
When a Sea is Called an Ocean:
- A Sea is a smaller subdivision of saltwater partially enclosed by land, island arcs, or submarine ridges along the margin of a continent (e.g., Bay of Bengal, Red Sea, South China Sea).
- It is called an Ocean when it forms one of the five vast, continuous, interconnected global basins of saltwater (Pacific, Atlantic, Indian, Southern, and Arctic Oceans) resting on deep basaltic oceanic crust (average depth ~3,700 m) that separates entire continents and drives global thermohaline circulation.

Q1.2 (SB): Discuss the impacts of Sea Level Rise (SLR) and the adaptation measures against SLR impacts in Bangladesh.

Appeared in: 2023 (Q1b, 15m) (Rank #47)
Time & Length Budget: 9–10 mins (~160–180 words)
Reference: SB/Topic 01/EWCE 471_LEC-01 & 02_Introduction to Coastal Engineering, Coast and Coastal Features.pdf, SB/Topic 05/EWCE 471_LEC 13 _Bangladesh Delta Plan (BDP) 2100.pdf

Answer:

Impacts of Sea Level Rise (SLR) in Bangladesh:
1. Permanent Coastal Inundation: A 1 m rise in sea level threatens to submerge ~15–17% of Bangladesh's low-lying coastal land, displacing millions of people (climate refugees).
2. Salinity Intrusion: Saltwater pushes deeper into coastal rivers and aquifers (up to 100+ km inland during the dry season), ruining drinking water and agricultural soil.
3. Drainage Congestion & Waterlogging: Higher sea levels block gravity drainage through polder sluice gates at low tide, causing severe waterlogging inside southwestern polders (e.g., Khulna, Satkhira, Jessore).
4. Amplified Cyclone Storm Surges: Higher base water depth reduces bottom friction, allowing higher storm surges and larger breaking waves to overtop coastal embankments.
5. Accelerated Coastal Erosion: Faster shoreline retreat along exposed islands (Sandwip, Bhola, Hatiya) and beaches.
6. Loss of Sundarbans Ecosystem: Rising salinity and submergence threaten freshwater-dependent mangrove species (Sundari trees) and royal Bengal tiger habitat.
Adaptation Measures Against SLR in Bangladesh:
1. Upgrading Coastal Polders & Embankments: Raising crest elevations of the 139 coastal polders, adding slope armor/revetments, and installing two-way tidal regulators.
2. Tidal River Management (TRM): Temporarily cutting selected polder embankments to let sediment-laden tidal water enter low-lying beels, naturally raising land elevation by 1–2 m through siltation while keeping river channels deep.
3. Coastal Greenbelt (Mangrove Afforestation): Planting mangrove buffer belts along the foreshore of embankments to attenuate wave energy and trap sediment.
4. Climate-Resilient Agriculture & Aquaculture: Adopting salt-tolerant and submergence-tolerant rice varieties (e.g., BRRI dhan47/67), floating vegetable gardens, and crab/shrimp farming.
5. Freshwater Harvesting & Storage: Rainwater harvesting, pond sand filters (PSF), Managed Aquifer Recharge (MAR), and freshwater reservoirs/barrages.
6. Land Reclamation via Cross-Dams: Building closure dams in the Meghna Estuary to accelerate new char accretion.

SB / Topic 02 — Tides, Tidal Datums, Tidal Bores & Bangladesh Tidal Characteristics

Q2.1 (SB): Discuss and illustrate with graphical representations the different types of daily tidal cycles (Semidiurnal, Diurnal, and Mixed).

Appeared in: 2021 (Q6a-i, 3m), 2023 (Q2b, 10m part), 2024 (Q6b, 12m) (Rank #22)
Time & Length Budget: 3–8 mins (~50–120 words + 3 quick graphs)
Reference: SB/Topic 02/EWCE 471_LEC-02-04_Tides and Currents.pdf

Answer:

1. SEMIDIURNAL (2 equal HW, 2 equal LW)   2. DIURNAL (1 HW, 1 LW per day)   3. MIXED (2 unequal HW, 2 unequal LW)
Height                                    Height                            Height    HHW
  |   /\      /\                            |       /""\                      |   /\  /  \  LHW
--|--/--\----/--\--                       --|------/----\------             --|--/--\/----\/--\--
  |      \  /    \  /                       |  \__/      \__/                 |      HLW   \  / LLW
  +------------------ Time (24h 50m)        +------------------ Time          +------------------ Time

Semidiurnal Tide:
- Pattern: Two high waters (HW) and two low waters (LW) each lunar day (24 hr 50 min), with successive high tides (and low tides) of nearly equal height.
- Period: 12 hr 25 min per cycle.
- Occurrence: East coast of North America, most of Europe, and the Bangladesh coast (Bay of Bengal).
Diurnal Tide:
- Pattern: Only one high water and one low water each lunar day.
- Period: 24 hr 50 min per cycle.
- Occurrence: Gulf of Mexico, parts of the South China Sea / Java Sea.
Mixed Tide:
- Pattern: Two high waters and two low waters per lunar day, but with markedly unequal heights (diurnal inequality)—producing a Higher High Water (HHW), Lower High Water (LHW), Higher Low Water (HLW), and Lower Low Water (LLW).
- Occurrence: US Pacific Coast (West Coast), parts of the Arabian Sea and Australia.

Q2.2 (SB): Define and explain standard tidal levels (Height of Tide, Mean Sea Level, MHWS, MLWS, MHWN, MLWN, HAT, LAT), Chart Datum, and changes in sounding datum.

Appeared in: 2019 (Q5b-ii, 7m), 2021 (Q6a-iii, 3m), 2022 (Q6a-i,ii, 2m) (Rank #24)
Time & Length Budget: 2–5 mins (~40–90 words + datum diagram)
Reference: SB/Topic 02/EWCE 471_LEC-02-04_Tides and Currents.pdf

Answer:

   ================== HAT (Highest Astronomical Tide)
   ------------------ MHWS (Mean High Water Springs)
   ------------------ MHWN (Mean High Water Neaps)
   ================== MSL (Mean Sea Level)                 ^
   ------------------ MLWN (Mean Low Water Neaps)          | Height of Tide (above Chart Datum)
   ------------------ MLWS (Mean Low Water Springs)        |
   ================== LAT / Chart Datum (Sounding Datum) --v--
                      |
                      | Charted Depth (Sounding)
                      v
   /////////////////////////////////////////////////////// Seabed

Key Tidal Level Definitions:
- Mean Sea Level (MSL): The average surface level of the sea over all stages of the tide measured over a long period (ideally 18.6 to 19 years, one full lunar nodal cycle).
- Chart Datum (CD / Sounding Datum): The low-water reference plane below which charted water depths (soundings) on nautical charts are measured, and above which Height of Tide is predicted in tide tables. Modern charts set CD at LAT (or MLWS) so actual water depth is almost never less than the charted depth.
- Height of Tide: The vertical distance at any given instant between the water surface and Chart Datum (CD). ( $ActualWaterDepth = ChartedDepth + HeightofTide$ ).
- MHWS & MLWS (Mean High / Low Water Springs): The long-term average height of the two successive high waters (or low waters) occurring during spring tides (every fortnight).
- MHWN & MLWN (Mean High / Low Water Neaps): The long-term average height of high waters (or low waters) occurring during neap tides.
- HAT & LAT (Highest / Lowest Astronomical Tide): The highest and lowest tidal levels that can be predicted to occur under average meteorological conditions and any combination of astronomical alignments over an 18.6-year cycle.
Changes in Sounding Datum: Along funnel-shaped estuaries and rivers, tidal range changes rapidly with distance upstream. Therefore, the sounding datum (Chart Datum) is stepped or sloped along the river channel rather than kept as a single horizontal plane, so charted depths always reflect true local low-water clearance.

Q2.3 (SB): Why does a tidal bore occur? Write down its principal characteristics.

Appeared in: 2022 (Q6b, 5m) (Rank #50)
Time & Length Budget: 3.5 mins (~65 words)
Reference: SB/Topic 02/EWCE 471_LEC-02-04_Tides and Currents.pdf

Answer:

Why a Tidal Bore Occurs: A tidal bore is a steep, breaking wall of water that surges upstream against a river's current on the incoming flood tide. It occurs when three conditions meet:
1. Large Tidal Range: Macrotidal spring tide range (typically > 5–6 m).
2. Funnel-Shaped Estuary: Wide mouth that narrows rapidly inland, compressing and amplifying the flood wave.
3. Shallow, Gently Sloping Riverbed: Shallow water slows the toe of the tide ( $C = \sqrt{g d}$ ) while the deeper crest behind overtakes it, steepening the front into a moving hydraulic jump.
Principal Characteristics:
- Asymmetric Tide Profile: Very rapid water rise (flood lasts only 1–3 hours) followed by a long, slow fall (ebb lasts 9–10 hours).
- High Speed & Turbulence: Travels upstream at 15–30 km/h with a roaring noise, intense sediment suspension/scour, and hazardous impact on small boats and riverbanks (e.g., Meghna/Sandwip Channel bore ("Ban") in Bangladesh, Qiantang River in China).

Q2.4 (SB): Define tidal stream and tidal flow, and describe the tidal characteristics and tidal range zones of the Bangladesh coast.

Appeared in: 2019 (Q6c, 7m part), 2023 (Q2b, 10m part; Q4a, 10m) (Rank #14)
Time & Length Budget: 5–7 mins (~100–130 words)
Reference: SB/Topic 02/EWCE 471_LEC-02-04_Tides and Currents.pdf

Answer:

Definitions:
- Tidal Stream (Tidal Current): The periodic horizontal movement of water caused by the vertical rise and fall of the tide—flowing shoreward/upstream as the Flood Stream and seaward as the Ebb Stream, separated by brief periods of Slack Water.
- Tidal Flow (Tidal Discharge / Prism): The volume rate of water ( $Q$ , in $m^{3} / s$ ) moving through a coastal inlet or estuarine channel cross-section during the flood and ebb cycles.
Three Tidal Range Zones of Bangladesh Coast:
1. Microtidal Zone (Range < 2 m): Tetulia River to Chandpur (0.5–2 m).
2. Mesotidal Zone (Range 2 – 4 m): Most of the Western (Sundarbans / Hiron Point) and Southern (Cox's Bazar) coast (2–4 m).
3. Macrotidal Zone (Range > 4 m, up to 6–7 m): Sandwip Channel, Hatiya, and Chittagong at the funnel head of the Bay of Bengal.
Key Tidal Characteristics of the Bangladesh Coast (10 Points from BIWTA / Topic 02):
1. Predominantly Semidiurnal: Two high waters and two low waters every 24 hr 50 min across the entire coast.
2. Funnel Amplification: As the tide travels northward up the shallow Bay of Bengal, the narrowing funnel geometry increases tidal range from ~2 m at Cox's Bazar/Hiron Point to 6–7 m around Sandwip.
3. Submarine Canyon Effect (Swatch of No Ground): Deep water in the Swatch speeds up tidal propagation toward the Sundarbans compared to the shallower Meghna flats.
4. Diurnal Inequality: Slight height difference between the two daily high waters (0.1–0.4 m).
5. Seasonal Mean Water Level Variation: Monsoon river flood + southwest monsoon wind piles water up, making monsoon Mean Sea Level 0.6 to 1.2 m higher than dry-season (winter) MSL.
6. Tidal Distortion in Shallow Estuaries: In shallow channels, flood duration is shorter (~4–5 hrs) and faster than ebb duration (~7–8 hrs).
7. Tidal Bores: Strong breaking tidal bores occur during spring tides in the Sandwip and Hatiya channels.

SB / Topic 03 — Ports and Harbors

Q3.1 (SB): Define a harbor (including harbor of refuge and locked basin), explain its features/components, explain the role and remedies of littoral drift in harbor layout, and sketch a typical harbor layout and the Madras Harbor layout.

Appeared in: 2019 (Q5c, 10m), 2021 (Q6a-iv, 3m; Q6b, 15m), 2022 (Q6a-iv,v, 2m; Q6c, 5m; Q6d, 15m), 2023 (Q2c, 6m), 2024 (Q6a, 12m) (Rank #3)
Time & Length Budget: 5–10 mins (write only the sub-parts asked)
Reference: SB/Topic 03/EWCE 471_LEC-07_08_Ports and Harbors.pdf

Answer:

Definitions:
- Harbor: A partly enclosed, sheltered coastal water area—either natural or protected by artificial breakwaters—where ships can safely anchor, moor, load/unload cargo, or weather storms protected from open-sea waves and currents.
- Harbor of Refuge: A harbor sited along a stormy coastline specifically to provide emergency shelter and safe anchorage for vessels caught in severe storms, rather than for commercial cargo trade (requires wide, easy all-weather entrance and good holding ground).
- Locked Basin (Wet Dock): An enclosed harbor basin separated from the tidal sea by entrance locks / lock gates that keep water inside at a nearly constant high depth, allowing ships to stay afloat and load/unload comfortably where external tidal ranges are very large (macrotidal).
Ten Principal Features / Components of a Harbor:
1. Approach Channel: Dredged deep waterway guiding ships from the open sea to the harbor entrance.
2. Harbor Entrance: Opening between breakwaters wide enough for safe ship passage (typically 0.7–1.0 × ship length) but narrow enough to block waves.
3. Breakwaters: Protective arms (rubble-mound or vertical wall) that absorb/reflect ocean waves.
4. Turning Basin: Central water area with sufficient diameter (≈ 2.0 × length of largest ship) for vessels to turn around.
5. Anchorage Area: Sheltered deeper zone where ships wait at anchor before berthing.
6. Berthing Structures (Quays, Wharves, Piers, Jetties): Platforms along which ships tie up to load/unload.
7. Mooring Accessories: Bollards, fenders, dolphins, and buoys that secure vessels and absorb berthing impact.
8. Navigational Aids: Lighthouses, channel buoys, beacons, and radar/VTS systems.
9. Dry Docks / Slipways: Facilities for ship repair and maintenance.
10. Onshore Apron & Transit Sheds: Cargo cranes, storage yards, and road/rail links.
Sketches — (A) Typical Harbor Layout & (B) Madras Harbor Layout:

(A) TYPICAL HARBOR LAYOUT                     (B) MADRAS HARBOR LAYOUT (Sand Drift & Remedy)
         Open Sea / Waves                                         North
         |   Approach   |                                           ^
      _.-'   Channel    '-._                                        |      [Outer Dock]
    .'  \   Entrance   /    '.                              +---------------+-------+
   /     '===>    <==='       \  Breakwaters                |               |Sheltering
  |        ( Turning )         |                            |   MADRAS      |  Arm (New
  |         ( Basin )   [Pier] |                            |   HARBOR      |  North Ent.)
  | Anchorage           [Pier] |                            |   BASIN       +   <-- Entrance
  |____________________________|                        ====|               |
  ======== Quay / Wharf ========                 Accretion  +---------------+
         Onshore Port Area                       (Updrift)  ^ Sand Drift (South -> North, ~1M tons/yr)

Role of Littoral Drift in Harbor Layout & Madras Harbor Case Study:
- The Problem: Breakwaters extending across the surf zone act like a giant groin, blocking natural longshore sediment transport (littoral drift). This causes severe sand accretion (shoaling) on the updrift side—which eventually creeps around the breakwater tip to choke the harbor entrance with a sandbar—and severe beach erosion on the downdrift coast.
- Madras (Chennai) Harbor Example: Strong littoral drift (~1 million tons/year moving South to North) accumulated against the South Breakwater, advanced seaward, and silted up the original eastern entrance. Engineers had to close the eastern entrance, open a new northern entrance protected by an eastern sheltering arm, and later add a northern Outer Dock plus regular sand dredging.
- Engineering Remedies for Littoral Drift at Harbors:
  1. Sand Bypassing: Pumping sand across the entrance from an updrift sand trap to the downdrift eroding beach (via fixed jet pumps or hopper dredgers).
  2. Offshore/Detached Sand-Trap Breakwater: Creating a calm deposition basin updrift of the entrance where a dredge can safely operate.
  3. Orienting the Entrance: Placing the harbor entrance on the downdrift (lee) side in deep water beyond the active surf zone.

Q3.2 (SB): Write down five differences between ports and harbors.

Appeared in: 2025 (Q8c, 10m) (Rank #54)
Time & Length Budget: 5 mins (~95 words)
Reference: SB/Topic 03/EWCE 471_LEC-07_08_Ports and Harbors.pdf

Answer:

Feature	Harbor	Port
1. Core Purpose	Provides safe shelter, parking, and anchorage for ships against waves, winds, and currents.	Provides commercial trade, cargo loading/unloading, customs, and passenger transfer between sea and land.
2. Origin (Natural vs. Artificial)	Can be completely natural (e.g., Sydney Harbor, Trincomalee) or artificially enclosed by breakwaters.	Always man-made / developed with engineered commercial and logistics infrastructure.
3. Onshore Facilities	Does not require cranes, warehouses, customs offices, or railway/highway terminals.	Must have quays, container cranes, warehouses, customs, cold storage, and road/rail/inland links.
4. Relationship / Scope	A harbor is the sheltered water component inside a port. "Every port contains a harbor, but not every harbor is a port."	A port is the broader economic & transport hub that includes one or more harbors plus landside terminals.
5. Revenue & Activity	Can exist purely as a non-commercial harbor of refuge or naval anchorage.	Operates as a revenue-generating commercial gateway for imports, exports, and industrial zones.

SB / Topic 04 — Coastal Processes, Coastal Erosion & Longshore Sediment Transport

Q4.1 (SB): Explain what natural coastal processes occur at a coast, how waves, tidal currents, and longshore currents transport material and change a beach (with sketches), how they affect human settlements, and how coastal developments affect coastal processes.

Appeared in: 2019 (Q8a, 7m), 2021 (Q7b, 10m), 2022 (Q7a, 5m; Q7c, 5m), 2023 (Q1c, 5m), 2025 (Q5a, 5m) (Rank #12)
Time & Length Budget: 4–7 mins (~80–120 words + sketch)
Reference: SB/Topic 04/EWCE 471_LEC 08-10_Coastal Processes and Sediment Transport.pdf, SB/Topic 04/Coastal Processes_252-253.pdf

Answer:

   ZIGZAG BEACH DRIFT & LONGSHORE TRANSPORT
   ======================================== Dry Beach
        /\      /\      /\    <- Swash (up beach at wave angle alpha)
       /  \    /  \    /  \   <- Backwash (straight down beach by gravity)
   ---/----\--/----\--/----\--------------- Shoreline
   ========>  Longshore Current & Net Sediment Transport ======>
      \       \       \
       \       \       \  Oblique Incoming Wave Crests

Three Main Natural Coastal Processes:
1. Erosion (Wearing Away): Waves and currents strip rock and sand from cliffs, dunes, and beaches.
2. Transportation (Movement): Littoral drift moves sediment parallel (longshore) and perpendicular (cross-shore) to the shore.
3. Deposition (Accretion): Sediment settles in low-energy bays, estuaries, and spits to build beaches, bars, and deltas.
How Waves, Longshore Currents & Tides Move Material and Change a Beach:
- Sawtooth / Zigzag Beach Drift: Oblique waves push sand diagonally up the beach (swash) at angle $α$ , while gravity pulls water and sand straight down the slope (backwash), moving sand in a zigzag path along the shore.
- Longshore Current: Inside the breaker zone, oblique breaking waves drive a shore-parallel current that carries suspended sand alongshore.
- Cross-Shore Seasonal Shift: Calm constructive swells push sand onshore to build up the beach berm (accretion), whereas steep destructive storm waves comb sand offshore into submerged bars (erosion).
- Tidal Currents: Scour tidal inlets and carry fine silt/clay into tidal flats and estuaries.
Mutual Impacts with Human Settlements & Coastal Developments:
- How Coastal Processes Affect Settlements: Shoreline erosion undermines coastal homes, roads, and hotels; siltation blocks fishing harbors and drainage sluices; storm surges flood low-lying communities.
- How Coastal Developments Disrupt Natural Processes:
  - Upstream River Dams: Trap river sediment, starving deltas and beaches of sand.
  - Groins, Jetties & Breakwaters: Block longshore drift, starving downdrift beaches and accelerating downdrift erosion.
  - Dune Leveling & Mangrove Clearing: Removes natural sand reservoirs and wave buffers, worsening storm damage.

Q4.2 (SB): List the input datasets required for modeling physical processes in the coastal zone of Bangladesh.

Appeared in: 2022 (Q7b, 5m) (Rank #51)
Time & Length Budget: 3.5 mins (~65 words)
Reference: SB/Topic 04/EWCE 471_LEC 08-10_Coastal Processes and Sediment Transport.pdf

Answer:

Bathymetric & Topographic Data: High-resolution seabed soundings (including the Swatch of No Ground and Meghna flats), river cross-sections, digital elevation models (DEM), and polder embankment heights.
Hydrodynamic Boundary Data:
- Upstream: Daily water discharge ( $Q$ ) and water level time series from the Ganges, Brahmaputra, and Upper Meghna rivers.
- Offshore: Astronomical tidal constituents (amplitude & phase) along the open Bay of Bengal boundary.
Offshore Wave Climate: Time series of significant wave height ( $H_{s}$ ), peak period ( $T_{p}$ ), and wave direction ( $θ$ ).
Meteorological / Cyclone Forcing: Wind speed and direction fields ( $U_{10}$ ), and central atmospheric pressure drop ( $Δ P$ ) for storm surge modeling.
Sediment & Water Quality Data: Bed grain-size distribution ( $D_{50}$ ), suspended sediment concentration (SSC), bed roughness (Manning's $n$ ), and salinity profiles.

Q4.3 (SB): Define coastal erosion, explain the processes of coastal erosion, and describe methods to reduce erosion (including how wetlands/mangroves protect the shoreline).

Appeared in: 2019 (Q6c, 8m part), 2022 (Q8a, 5m), 2024 (Q8b, 10m) (Rank #13)
Time & Length Budget: 4–7 mins (~80–120 words)
Reference: SB/Topic 04/EWCE 471_LEC 08-10_Coastal Processes and Sediment Transport.pdf, SB/Topic 04/Coastal Processes_252-253.pdf

Answer:

Definition: Coastal erosion is the wearing away of coastal land and the net removal of beach, dune, or cliff sediments by wave action, tidal currents, wind, or human interference, causing landward retreat of the shoreline.
Six Physical Processes of Coastal Erosion:
1. Hydraulic Action: Direct pounding force of breaking waves against rock faces and soil slopes.
2. Compressed Air (Cavitation): Waves trap and compress air pockets inside cliff cracks; when the wave recedes, the air expands explosively, shattering the rock.
3. Abrasion (Corrasion): Waves hurl sand, pebbles, and boulders against the cliff base like sandpaper, undercutting a wave-cut notch.
4. Attrition: Rock fragments and pebbles collide against each other in the surf, grinding down into smaller, smoother, rounded sand grains.
5. Corrosion (Solution): Weak acids in seawater chemically dissolve soluble rocks such as limestone and chalk.
6. Wave Refraction Concentration: Wave rays converge on headlands, focusing destructive wave energy.
Methods to Reduce Coastal Erosion:
- Hard Engineering Structures: Seawalls & Revetments (armor the shoreline slope), Groins (trap longshore sand drift), and Detached Breakwaters (create a sheltered wave shadow zone).
- Soft / Nature-Based Engineering: Beach Nourishment (pumping imported sand onto the beach), Sand Dune Stabilization (fencing + grass planting), and Coastal Wetlands / Mangrove Greenbelts.
How Wetlands & Mangroves Protect Against Erosion:
1. Wave Attenuation: Dense aerial roots (pneumatophores), trunks, and marsh stems create drag that dissipates 50–80% of incoming wave and surge energy.
2. Sediment Trapping: Slowed water flow inside the wetland lets suspended silt and clay settle out, vertically building up the mudflat.
3. Soil Binding: Interlocking root mats bind soft coastal mud and prevent waves from scouring the bank.

Q4.4 (SB): Write down the differences between constructive and destructive waves.

Appeared in: 2024 (Q6c, 6m) (Rank #37)
Time & Length Budget: 4 mins (~75 words)
Reference: SB/Topic 04/EWCE 471_LEC 08-10_Coastal Processes and Sediment Transport.pdf, SB/Topic 04/Coastal Processes_252-253.pdf

Answer:

Feature	Constructive Waves	Destructive Waves
1. Net Beach Effect	Build up the beach (accretion) by pushing sand onshore onto the berm.	Erode the beach by combing sand offshore into submerged bars.
2. Wave Steepness & Height	Low, flat waves ( $H / L$ is small; typically $< 1 m$ high) with long wavelength ( $L$ up to `100 m`).	High, steep waves ( $H / L$ is large) with short wavelength.
3. Wave Frequency	Low frequency (`6 – 8 waves/minute`); long period ( $T$ ).	High frequency (`10 – 14 waves/minute`); short period ( $T$ ).
4. Breaker Type	Gently spilling breakers.	Violently plunging breakers.
5. Swash vs. Backwash	Strong swash, weak backwash (long time between waves allows water to percolate into beach sand).	Weak swash, very strong backwash (saturated beach + crashing plunging jet drags sand seaward).
6. Weather Condition	Calm summer weather / distant ocean swell.	Local storms / monsoon cyclones.

Q4.5 `[Math]`: Method to calculate potential longshore sediment transport rate ( $I_{l}$ and $Q_{l}$ ) using the Energy Flux Method.

Appeared in: 2024 (Q8a, 8m), 2025 (Q5b, 10m) (Rank #25)
Reference: SB/Topic 04/EWCE 471_LEC 13-14_Coastal Processes and Sediment Transport Copy.pdf

Method to Follow:

Step 1 — Breaking Wave Parameters ( $H_{s b}, C_{g b}, α_{b}$ ):
- Given significant breaking wave height $H_{s b}$ (or $H_{b}$ ), breaking depth $d_{b}$ (where $d_{b} = H_{b} / κ \approx H_{b} / 0.78$ ), and breaking wave crest angle $α_{b}$ :
- Compute shallow-water group velocity at breaking: $C_{g b} = C_{b} = \sqrt{g d_{b}} = \sqrt{\frac{g H_{s b}}{κ}} (typically κ = 0.78)$
Step 2 — Longshore Energy Flux Factor ( $P_{l s}$ ): Calculate the shore-parallel component of wave energy flux per unit length of beach at breaking: $P_{l s} = (\bar{E} C_{g})_{b} \sin α_{b} \cos α_{b} = (\frac{1}{8} ρ g H_{{s b}^{2}}) C_{g b} \sin α_{b} \cos α_{b} = \frac{1}{16} ρ g H_{{s b}^{2}} C_{g b} \sin (2 α_{b}) (inW m o r N / s [PARSE ERROR: Undefined("RBrace")])$ (where $ρ \approx 1025 kg m {[PARSE ERROR: Undefined("RBrace")]}^{3}$ for seawater).
Step 3 — Dimensionless Coefficient ( $K$ ): Use the CERC / SPM empirical coefficient $K = 0.39$ (when using significant wave height $H_{s b}$ , or $K = 0.77$ if using root-mean-square wave height $H_{rms, b}$ ).
Step 4 — Immersed-Weight Longshore Transport Rate ( $I_{l}$ ): $I_{l} = K \cdot P_{l s} (inN s [PARSE ERROR: Undefined("RBrace")])$
Step 5 — Volumetric Longshore Sediment Transport Rate ( $Q_{l}$ ): Convert immersed weight rate Il into bulk volume rate Ql using sediment density ρs≈2650kgm[PARSE ERROR: Undefined("RBrace")]3 and in-place sand porosity p≈0.40: Ql=Il(ρs-ρ)g(1-p)=K·Pls(ρs-ρ)g(1-p)(inm3/s)
- To express in $m^{3} / year$ , multiply $Q_{l} m {[PARSE ERROR: Undefined("RBrace")]}^{3} / s [PARSE ERROR: Undefined("RBrace")]$ by $3.1536 \times 10^{7} s y e a r [PARSE ERROR: Undefined("RBrace")]$ (or use the direct CERC shortcut: $Q_{l} m {[PARSE ERROR: Undefined("RBrace")]}^{3} / yr [PARSE ERROR: Undefined("RBrace")] \approx 1290 P_{l s} W / m] [PARSE ERROR: Undefined("RBrace")]$ ).

SB / Topic 05 — Deltas & Bangladesh Delta Plan (BDP) 2100

Q5.1 (SB): Discuss the process and 3 stages of delta formation with figures, and describe how gravel, sand, silt, and clay are deposited into Topset, Foreset, and Bottomset beds.

Appeared in: 2024 (Q7a, 12m), 2025 (Q6a, 10m; Q6b, 12m) (Rank #18)
Time & Length Budget: 6–9 mins (~110–150 words + sketch)
Reference: SB/Topic 05/EWCE 471_LEC 11-12_Deltas and Its Characteristics (1).pdf

Answer:

   CROSS-SECTION OF DELTA BEDS (GILBERT PROFILE)
   River Flow ===>  [====== Topset Beds (Gravel & Coarse Sand, Horizontal) ======]
   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~\~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Sea Level
                                \  Foreset Beds (Sand & Silt, Steep 10-25 deg Slope)
                                 \
                                  '=================================================
                                    Bottomset Beds (Flocculated Clay, Flat Offshore)

Basic Process of Delta Formation:
1. Jet Expansion & Deceleration: When a sediment-laden river enters a standing body of water (sea or lake), confinement ends, the flow spreads out, and velocity ( $V$ ) drops sharply.
2. Loss of Competence & Sorting: Because carrying capacity depends on velocity, sediment drops out in order of grain size—gravel and coarse sand first at the mouth, medium/fine sand on the delta front slope, and fine silt and clay farthest offshore.
3. Clay Flocculation: When negatively charged river clay particles mix with saline seawater electrolytes ( ${Na}^{+}, {Mg}^{2 +}$ ), surface charges neutralize and clays clump into heavier flocs that settle onto the seabed.
Three Internal Sedimentary Beds (Bottomset, Foreset, Topset):
1. Bottomset Beds: Thin, horizontal layers of fine silt and flocculated clay carried farthest seaward by suspension and deposited on the flat prodelta floor ahead of the advancing delta.
2. Foreset Beds: Thick, inclined layers (5°–25° slope) of sand and coarse silt that roll down the delta front like an underwater avalanche, building the main body of the delta seaward over the bottomset beds.
3. Topset Beds: Nearly horizontal layers of gravel, coarse sand, and floodplain mud deposited on top of the foreset beds by shifting distributary channels and marshes as the delta emerges above sea level.
Three Evolutionary Stages of Delta Growth:
- Stage 1 (Subaqueous Initiation & Mouth Bar): Sediment drops at the river mouth to form a submerged river-mouth bar; Bottomset and Foreset beds start building.
- Stage 2 (Channel Bifurcation / Splitting): The growing mouth bar blocks the main flow, forcing the river to split (bifurcate) into two distributary channels around the bar, creating a triangular delta island (char).
- Stage 3 (Subaerial Progradation & Delta Plain): Repeated channel splitting, natural levee building, and crevasse splays merge islands into a broad subaerial delta plain crossed by a network of distributaries advancing into the sea.

Q5.2 (SB): Compare and discuss with sketches and examples the classification and geometry of deltas based on shape and depositional controls.

Appeared in: 2019 (Q8b, 8m), 2021 (Q6a-ii, 3m; Q7c, 10m), 2022 (Q8b, 5m), 2023 (Q3c, 8m), 2024 (Q7b, 8m) (Rank #5)
Time & Length Budget: 4–7 mins (~80–120 words + sketches)
Reference: SB/Topic 05/EWCE 471_LEC 11-12_Deltas and Its Characteristics (1).pdf

Answer:

1. ARCUATE (Fan-Shaped)     2. DIGITATE / BIRD'S-FOOT     3. CUSPATE (Tooth-Shaped)    4. TIDE-DOMINATED
      _.-"""""-._                   \  |  /                      _..---.._                |  ||  ||  |
    .'  /  |  \  '.               ---+-+--+---                 .'    |    '.              |  ||  ||  | Linear
===+===+===+===+===+===              / | \                 ==='      |      '===         /   ||  ||   \ Tidal
       |River|                         |                             |                  /    ||  ||    \ Bars
    (Nile / Niger)               (Mississippi)                    (Tiber)               (Ganges-Brahmaputra)

Delta Type	Controlling Process	Plan Geometry & Characteristics	Real-World Examples
1. Arcuate Delta	Balanced river supply + moderate wave action.	Smooth, convex fan/arc-shaped shoreline (`triangle Δ`) with many branching distributaries and barrier beaches.	Nile Delta (Egypt), Niger Delta, Rhine Delta.
2. Digitate (Bird's-Foot / River-Dominated)	River discharge & sediment supply dominate over very weak waves and small tides ( $T_{R} < 2 m$ ).	Long, narrow natural-levee fingers (`distributary channels`) jutting far into the sea like a bird's foot.	Mississippi River Delta (USA).
3. Cuspate (Wave-Dominated)	Strong ocean waves & longshore currents redistribute sediment along the shore away from the single mouth.	Pointed, tooth-shaped (`V-shaped`) projection with smooth flanking beach ridges on both sides.	Tiber Delta (Italy), São Francisco Delta (Brazil), Ebro Delta.
4. Tide-Dominated Delta	Macrotidal currents rework river sediment into channels.	Funnel-shaped mouth filled with elongated linear tidal sand bars/islands aligned parallel to tidal flow.	Ganges–Brahmaputra–Meghna (GBM) Delta (Bangladesh), Fly Delta.
5. Estuarine Delta	River empties into a long, drowned valley or tectonic bay before reaching the open coast.	Delta fills the interior estuary basin with sandbars and mudflats without protruding into the open ocean.	Seine Delta (France), Ob, Mackenzie.
6. Gilbert-Type Delta	Coarse bedload stream entering a deep, quiet lake or fjord.	Steep foreset slope (`up to 25°`) with distinct Topset, Foreset, and Bottomset beds.	Lake Bonneville fossil deltas, mountain lake deltas.

Q5.3 (SB): Bangladesh Delta Plan (BDP) 2100 — Explain the need for an integrated plan and Bangladesh's delta challenges; define "Hotspots" and list the 6 Hotspots and their issues; and state the National-level and Coastal Zone Hotspot strategies.

Appeared in: 2019 (Q8c, 15m), 2021 (Q7a, 10m), 2023 (Q2a, 10m; Q3b, 15m; Q4c, 10m), 2024 (Q7c, 10m), 2025 (Q6c, 8m) (Rank #2)
Time & Length Budget: 6–9 mins (write only the sub-parts asked)
Reference: SB/Topic 05/EWCE 471_LEC 13 _Bangladesh Delta Plan (BDP) 2100.pdf

Answer:

Why Bangladesh Needs an Integrated Long-Term Delta Plan (Challenges):
1. Extreme Hydro-Climatic Vulnerability: Peak monsoon floods submerge 20–70% of the country, while dry-season transboundary flows drop sharply, causing droughts and salinity intrusion.
2. Climate Change & Sea Level Rise: Rising sea levels, stronger cyclones, and erratic rainfall threaten food security and GDP growth (costs ~2% of GDP annually without action).
3. Sectoral Fragmentation: Past projects (embankments, roads, agriculture, water supply) were planned in isolation without considering long-term morphological feedback (such as polder waterlogging). BDP 2100 provides an Adaptive Delta Management (ADM) framework combining water safety, food security, and economic growth up to 2100.
Definition of "Hotspots" & The 6 Hotspots of BDP 2100:
- Definition: Hotspots are broad, hydrologically and geomorphologically homogeneous regions (districts/upazilas) that share similar water and climate hazard risks.
- The 6 Hotspots & Their Key Issues:
  1. Coastal Zone (27,738 km²): Cyclone storm surges, salinity intrusion, polder waterlogging/drainage congestion, coastal & island erosion, and freshwater scarcity.
  2. Barind & Drought-Prone Areas (22,848 km²): Severe dry-season droughts, falling groundwater table, and surface water scarcity.
  3. Haor & Flash Flood Areas (16,574 km²): Pre-monsoon flash floods destroying Boro rice crops, wave erosion of village mounds (hati), and poor drainage.
  4. Chattogram Hill Tracts (13,295 km²): Hill slope erosion, landslides, flash floods, and acute dry-season drinking water shortage.
  5. River Systems & Estuaries (35,204 km²): Severe riverbank erosion, channel shifting, char instability, and navigation siltation.
  6. Urban Areas (19,823 km²): Urban drainage congestion/waterlogging, river water pollution, groundwater depletion, and waste management.
National-Level Strategies (2 Core Pillars):
- Strategy FR 1 (Flood Risk Management):
  - FR 1.1: Protect economic/industrial zones, major cities, and critical infrastructure to high flood safety standards.
  - FR 1.2: Improve river flood conveyance and warning systems (dredging, embankments, flood forecasting).
  - FR 1.3: Revitalize internal drainage channels (khals) and floodplains.
- Strategy FW 1 (Fresh Water Availability):
  - FW 1.1: Ensure dry-season water availability (Ganges & Brahmaputra barrages/reservoirs, transboundary cooperation, rainwater harvesting).
  - FW 1.2: Protect water quality and treat industrial/municipal wastewater (ETPs, CETPs).
Coastal Zone Hotspot Strategies (3 Core Strategies):
1. Strategy CZ 1 — Combat Storm Surge & Salinity Intrusion via Effective Embankments & Polders: Rehabilitate and raise sea-facing polders, repair sluice gates, plant mangrove greenbelts, and construct multipurpose cyclone shelters.
2. Strategy CZ 2 — Resolve Waterlogging & Drainage Congestion: Implement Tidal River Management (TRM), excavate silted tidal rivers/khals, and upgrade tidal regulators.
3. Strategy CZ 3 — Land Reclamation, Conservation of Sundarbans & Freshwater Supply: Build Meghna Estuary cross-dams to accelerate new land (char) accretion, maintain freshwater flows (Gorai/Madhumati restoration) to protect the Sundarbans from high salinity, and develop coastal freshwater reservoirs.

SB / Topic 06 — Tidal Theories (Static & Dynamic), Spring/Neap Tides & Tide Prediction

Q6.1 (SB): Explain Newton's Static (Equilibrium) Theory and Laplace's Dynamical Theory of tide generation, state the limitations of the Static Theory, and justify mathematically why the Moon has a greater tide-generating influence than the Sun.

Appeared in: 2019 (Q5b-i, 7m), 2022 (Q8d, 15m), 2025 (Q7a, 10m) (Rank #19)
Time & Length Budget: 5–8 mins (~100–130 words + derivation)
Reference: SB/Topic 06/EWCE 471_LEC 13-14_Tidal Theories and Tide Prediction.pdf

Answer:

   EQUILIBRIUM TIDE (TWO BULGES)
        Centrifugal Force               Gravitational Attraction
        <---  _.-""""""-._  --->
       <--- .'   EARTH    '. --->       ( Moon )
        <--- '-._      _.-' --->
       Bulge B   '""""'    Bulge A (Facing Moon)
   (Opposite Moon)

1. Newton's Static (Equilibrium) Theory (1687):
- Assumption: Assumes the Earth is covered by a uniformly deep, frictionless ocean with no continents, and the water surface responds instantaneously to gravitational and centrifugal forces.
- Mechanism: The Earth–Moon system revolves around a common center of mass (barycenter), creating a uniform outward centrifugal force everywhere on Earth equal to the average gravitational pull of the Moon.
  - On the near side facing the Moon (Bulge A), lunar gravity exceeds centrifugal force, pulling water toward the Moon.
  - On the opposite side (Bulge B), centrifugal force exceeds lunar gravity, pushing water outward.
  - As the Earth rotates through these two stationary bulges in 24 hr 50 min, any point experiences two high tides and two low tides per day.
- Limitations of Static Theory: Neglects (i) continental landmasses blocking the bulges, (ii) finite shallow ocean depth (wave speed C = √gd ≈ 200 m/s cannot keep up with Earth's equatorial rotation of 465 m/s), (iii) water inertia and seabed friction, and (iv) Coriolis force.
2. Laplace's Dynamical Theory (1775):
- Treats tides as forced long-period shallow-water waves moving inside real ocean basins bounded by continents.
- Accounts for ocean depth variations, fluid inertia & bottom friction, basin resonance (natural period), and Coriolis deflection—causing tidal waves to rotate around central nodal points (amphidromic points where tidal range is zero) via co-tidal and co-range lines.
3. Mathematical Justification: Why Moon's Tide Force > Sun's Tide Force:
- The differential tide-generating force ( $Δ F$ ) across Earth's radius ( $R$ ) is the gradient of gravitational attraction $F_{g} = \frac{G M}{d^{2}}$ : $Δ F = \frac{d}{d d} (\frac{G M}{d^{2}}) R \propto \frac{M R}{d^{3}}$ Thus, tide-generating force is inversely proportional to the CUBE of the distance ( $d^{3}$ ), not the square ( $d^{2}$ ).
- Comparing Sun vs. Moon:
  - Mass ratio: $\frac{M_{Sun}}{M_{Moon}} \approx 2.7 \times 10^{7}$
  - Distance ratio: $\frac{d_{Sun}}{d_{Moon}} = \frac{150 \times 10^{6} km}{384, 400 km} \approx 390 ⟹ {(\frac{d_{Sun}}{d_{Moon}})}^{3} \approx (390)^{3} \approx 5.93 \times 10^{7}$
- Ratio of Tide-Generating Forces: $\frac{Δ F_{Sun}}{Δ F_{Moon}} = (\frac{M_{Sun}}{M_{Moon}}) {(\frac{d_{Moon}}{d_{Sun}})}^{3} = \frac{2.7 \times 10^{7}}{5.93 \times 10^{7}} \approx 0.46 ⟹ Δ F_{Moon} \approx 2.17 Δ F_{Sun}$ Because the Moon is 390 times closer, its distance-cubed advantage outweighs the Sun's huge mass, making the Moon's tide-generating effect 2.17 times stronger than the Sun's.

Q6.2 (SB): Explain with figures: (i) Priming and lagging of tide, and (ii) Spring and neap tides.

Appeared in: 2023 (Q2d-i, 2m), 2025 (Q7c, 10m) (Rank #30)
Time & Length Budget: 2–5 mins (~40–90 words + sketches)
Reference: SB/Topic 06/EWCE 471_LEC 13-14_Tidal Theories and Tide Prediction.pdf

Answer:

(i) SPRING & NEAP TIDES                          (ii) PRIMING & LAGGING OF TIDE
   SPRING (Syzygy: 0 / 180 deg)                      ( Moon: 1st Octant, 45 deg )
   [SUN] ---> (Earth) <--- (Moon)                          /  Resultant Crest (Ahead of Moon = PRIMING)
   High Highs + Low Lows (Max Range)                      /  /
                                                   [SUN] ---- (Earth)
   NEAP (Quadrature: 90 deg)                                \  \
   (Moon)                                                    \  Resultant Crest (Behind Moon = LAGGING)
     |                                                     ( Moon: 3rd Octant, 135 deg )
   (Earth) <--- [SUN]   (Min Range)

(i) Spring and Neap Tides:
- Spring Tide: Occurs twice a month at New Moon and Full Moon (Syzygy) when the Sun, Moon, and Earth align in a straight line (180° or 0°). Solar and lunar tidal bulges reinforce each other constructively ( $M_{2} + S_{2}$ ), producing higher high waters, lower low waters, and maximum tidal range.
- Neap Tide: Occurs twice a month at First and Third Quarter Moon (Quadrature) when the Sun and Moon pull at 90° right angles relative to Earth. Solar and lunar bulges partially cancel each other ( $M_{2} - S_{2}$ ), producing lower high waters, higher low waters, and minimum tidal range.
(ii) Priming and Lagging of Tide:
- Priming of the Tide: Between New Moon and First Quarter (and between Full Moon and Third Quarter), the solar tidal bulge lies slightly ahead of the lunar bulge. The combined resultant high-tide crest is shifted ahead of the Moon, so high water occurs earlier than usual, shortening the tidal day below 24 hr 50 min.
- Lagging of the Tide: Between First Quarter and Full Moon (and between Third Quarter and New Moon), the solar bulge pulls behind the lunar bulge. The resultant high-tide crest lags behind the Moon, so high water occurs later than usual, lengthening the tidal day above 24 hr 50 min.

Q6.3 `[Theory & Math]`: Explain the Non-Harmonic and Harmonic methods of tide prediction, define non-harmonic constants (Age of tide, Lunitidal interval, Mean & Vulgar establishment), and state the method to calculate afternoon high-water time and height of tide.

Appeared in: 2021 (Q6a-v, 3m), 2022 (Q6a-iii, 1m), 2023 (Q3a, 7m; Q4b, 10m), 2025 (Q7b, 10m) (Rank #12)
Time & Length Budget: 4–6 mins (~80–110 words + calculation recipe)
Reference: SB/Topic 06/EWCE 471_LEC 14-15_Tidal Theories and Tide Prediction.pdf

Answer:

Non-Harmonic Constants & Method:
- Applies empirically observed time/height corrections to the Moon's meridian transit time:
  1. Lunitidal Interval: Time elapsed between the Moon's transit across the local meridian and the next following High Water (or Low Water).
  2. Vulgar Establishment (High Water Full & Change — HWF&C): The lunitidal interval observed specifically on the day of Full Moon or New Moon.
  3. Mean Establishment: The average of all high-water lunitidal intervals measured throughout a full semi-lunation (14.77 days).
  4. Age of the Tide: Time lag (typically 1 to 2 days) between the astronomical New or Full Moon and the actual occurrence of the maximum Spring Tide at a port, caused by ocean friction and inertia.
Harmonic Method of Tide Prediction:
- Represents the real tide at any port as the sum of simple cosine waves (harmonic constituents), each having a known astronomical speed ( $ω_{i}$ , deg/hr) and locally measured amplitude ( $H_{i}$ ) and phase lag ( $g_{i}$ ): $h (t) = Z_{0} + \sum_{i = 1}^{N} f_{i} H_{i} \cos (ω_{i} t + V_{0 i} + u_{i} - g_{i})$
- Major Constituents:
  - Semidiurnal: $M_{2}$ (Principal Lunar, T = 12.42 hr), $S_{2}$ (Principal Solar, 12.00 hr), $N_{2}$ (Larger Lunar Elliptic), $K_{2}$ (Luni-Solar).
  - Diurnal: $K_{1}$ (Luni-Solar Diurnal, 23.93 hr), $O_{1}$ (Principal Lunar Diurnal, 25.82 hr), $P_{1}$ (Principal Solar Diurnal).
  - Shallow-Water Overtides: $M_{4}, M S_{4}$ (account for shallow-water wave distortion).
Step-by-Step Calculation Recipes ([Math]):
- Problem Type A — Afternoon High-Water Time (2023 Q3a): Given morning High Water time THWam[PARSE ERROR: Undefined("RBrace")] (e.g., 07:10 AM):
  - Add one semidiurnal tidal period 12 hr 25 min (half a lunar day of 24 hr 50 min): $T_{HW p m} [PARSE ERROR: Undefined("RBrace")] = T_{HW a m} [PARSE ERROR: Undefined("RBrace")] + 12 hr 25 min$ (Example: 07:10 AM + 12 hr 25 min = 19:35 or 07:35 PM; Low Water occurs halfway in between at + 6 hr 12.5 min).
- Problem Type B — Height of Tide at Any Intermediate Time (2023 Q4b, Cosine Formula): Given High Water time t1 with height HHW, and Low Water time t2 with height HLW, to find the Height of Tide H at any time t between t1 and t2:
  1. Duration of Fall (or Rise): $D = | t_{2} - t_{1} |$
  2. Range of Tide ( $r$ ): $r = H_{HW} - H_{LW}$
  3. Mean Tide Level ( $h$ ): $h = \frac{H_{HW} + H_{LW}}{2} = H_{LW} + \frac{r}{2}$
  4. Phase Angle ( $θ$ in degrees) measured from High Water time $t_{1}$ : $θ = (\frac{t - t_{1}}{D}) \times 180^{\circ}$
  5. Height of Tide ( $H$ ) at time $t$ : $H = h + \frac{1}{2} r \cos θ$

SB / Topic 07 & Topic 08 — Coastal Structures, Failure Modes & Revetment/Seawall Design

Q7.1 (SB): Name different types of coastal structures, state their objectives and principal functions, describe physical and functional characteristics of seawalls, revetments, bulkheads, groins, detached breakwaters, submerged sills, and storm surge barriers, and state the design criteria for groins and breakwaters.

Appeared in: 2019 (Q6a, 7m), 2022 (Q7d, 15m; Q8c, 5m), 2023 (Q2d-ii,iii, 4m), 2024 (Q5a, 10m), 2025 (Q8a, 10m) (Rank #5)
Time & Length Budget: 4–8 mins (write only the structures asked)
Reference: SB/Topic 07/EWCE 471_LEC 16-17_Types and Functions of Coastal Structures.pdf, SB/Topic 07/Types & Functions_of_Coastal_Structures.pdf

Answer:

Five Core Objectives of Coastal Protection Works:
1. Protect exposed land and cliffs against wave erosion.
2. Prevent coastal flooding and overtopping of low-lying hinterland (sea dikes, surge barriers).
3. Stabilize or widen recreational and protective beaches (groins, nourishment, detached breakwaters).
4. Provide calm water for harbors and navigation channels (harbor breakwaters, entrance jetties).
5. Stabilize river mouths and tidal inlets.
Comparison of Coastal Structure Types & Functions:

Structure	Alignment & Location	Principal Function & Physical Characteristics
1. Seawall	Shore-parallel, along the waterline.	Heavy, massive self-supporting structure (vertical concrete caisson, curved-face wall, or rubble mound) built to withstand full storm wave impact and prevent coastal flooding/erosion; reflects high energy, which can scour the beach at its toe.
2. Revetment	Shore-parallel, laid directly on an existing soil slope.	Sloping armor facing (quarrystone riprap, concrete blocks, gabions over a filter layer) supported by the embankment behind it; absorbs and dissipates wave energy on its rough slope with minimal reflection.
3. Bulkhead	Shore-parallel, in sheltered/low-wave areas.	Vertical soil-retaining wall (steel/vinyl sheet piles or timber anchored by tie-rods to deadmen); primary job is holding back upland earth fill rather than resisting heavy ocean breakers.
4. Groin	Shore-perpendicular, extending from backshore across the surf zone.	Narrow finger structure (sheet pile, timber, rubble) that traps part of the longshore sand transport (`littoral drift`) to build or widen a beach on its updrift side (causes erosion downdrift if not pre-filled with sand).
5. Detached Breakwater	Shore-parallel, offshore at a distance $X$ from shore.	Absorbs/diffracts incoming waves before they reach the beach, creating a calm shadow zone behind it where longshore drift slows down and deposits sand to form a Salient or Tombolo.
6. Submerged Sill (Artificial Reef)	Shore-parallel, underwater crest below SWL.	Trips and breaks the largest storm waves offshore while preserving an open ocean view; also used as a perched beach toe to hold nourished sand in place.
7. Storm Surge Barrier	Across an estuary mouth or tidal inlet.	Movable floodgates (e.g., Maeslantkering, Thames Barrier) that stay open under normal conditions for navigation and tidal flushing, and close only during extreme storm surges.

Design Criteria for Groins & Breakwaters:
- Groins:
  1. Length ( $L_{g}$ ): Extend across 60–100% of the normal breaker zone (avoid extending too far offshore, which diverts sand into deep water).
  2. Spacing ( $S$ ): Space adjacent groins at $S = 2 to 3 \times L_{g}$ .
  3. Height & Permeability: Keep crest low (0.5–1.0 m above beach profile) or permeable so excess sand can bypass over/through to feed downdrift beaches.
  4. Artificial Nourishment: Pre-fill groin compartments with sand right after construction.
- Detached Breakwaters:
  1. Length-to-Offshore Distance Ratio ( $L_{s} / X$ ): Use $L_{s} / X < 1.0$ to form a Salient (allowing sand to keep bypassing behind it) or $L_{s} / X > 1.5 – 2.0$ to form a connected Tombolo.
  2. Armor & Foundation Stability: Size armor stones ( $W_{50}$ by Hudson formula) and wide toe protection against wave scour.

Q7.2 (SB): State the features of the different layers of a conventional multilayer rubble-mound breakwater, explain what design factor governs Tombolo vs. Salient formation, and draw neat sketches of: (i) beach with groins, (ii) detached breakwaters (Tombolo & Salient), (iii) sea dike, (iv) vertical-front seawall, and (v) conventional rubble-mound breakwater.

Appeared in: 2019 (Q6b, 8m), 2021 (Q5a-ii, 3.33m), 2022 (Q5a, 5m; Q5b, 5m), 2024 (Q8c, 12m) (Rank #10)
Time & Length Budget: 4–8 mins (draw only the sketches requested)
Reference: SB/Topic 07/EWCE 471_LEC 16-17_Types and Functions of Coastal Structures.pdf, SB/Topic 07/Types & Functions_of_Coastal_Structures.pdf

Answer:

Layers of a Conventional Multilayer Rubble-Mound Breakwater:
1. Core (Quarry Run): Central body made of fine, graded quarry waste ( $W \approx W_{50} / 200 to W_{50} / 4000$ ) that provides bulk volume and blocks wave transmission through the breakwater.
2. Filter / Underlayer (Secondary Armor): 1 or 2 intermediate stone layers ( $W \approx W_{50} / 10 to W_{50} / 15$ , thickness $r = 2$ stones) that prevent fine core material from washing out (piping) through the large voids of the outer armor.
3. Primary Cover / Armor Layer: Two layers ( $n = 2$ ) of heavy natural quarrystones or interlocking concrete units (Tetrapods, Dolos, Accropodes, weight $W_{50}$ ) that directly resist wave impact and uprush/downrush forces.
4. Toe Berm & Bedding Blanket: Supports the bottom of the armor slope and prevents seabed scour and settlement.
5. Crown Wall / Superstructure: Concrete cap at the crest that reduces wave overtopping and provides a roadway.
Design Factor Governing Tombolo vs. Salient Behind a Detached Breakwater:
- Governed by the dimensionless ratio of breakwater length ( $L_{s}$ ) to offshore distance from the original shoreline ( $X$ ):
  - Tombolo Formation ( $\frac{L_{s}}{X} > 1.5 to 2.0$ ): Long breakwater placed close to shore; diffracted waves deposit sand all the way out to touch the breakwater, blocking longshore drift.
  - Salient Formation ( $\frac{L_{s}}{X} \approx 0.5 to 1.0$ ): Shorter breakwater placed farther offshore; shoreline bulges seaward into a bell shape without touching the structure, allowing sand to keep bypassing behind it.
Five Standard Exam Sketches:

(i) BEACH CONFIGURATION WITH GROINS          (ii) DETACHED BREAKWATERS (TOMBOLO vs. SALIENT)
     Littoral Drift ====>                         [=== L_s ===]                  [== L_s ==]
        ||            ||                              |   |  X                       ^  X
        ||            ||  Groins                     /     \                        / \
    _.-"||        _.-"||                       _.-""'Tombolo'""-._            _.-""Salient""-._
==='Accr||==='Eros    ||==='               ==='                   '==='   ==='                 '==='

(iii) SEA DIKE CROSS-SECTION                      (iv) VERTICAL-FRONT SEAWALL WITH TOE PROTECTION
                        Crown / Road                           Wave Deflector (Curved Lip)
                       .------------.                           _.-""|
         Outer Slope  /              \ Inner Slope             |     |  Concrete Caisson / Wall
  SWL ~~~(1:4-1:8)~~~/   Sand Core    \ (Grass)         SWL ~~~|     |================== Upland Fill
        /Revetment  /  with Clay Cover \                       |     |   Weep Hole + Gravel Filter
       / + Berm    /                    \               .[Toe].|_____|__________________
  ====+===========+======================+====          ==================================
  Toe Protection                          Drain          Rubble Bedding Layer + Toe Stones

(v) CONVENTIONAL MULTILAYER RUBBLE-MOUND BREAKWATER
                         [Concrete Crown Wall]
                       _.-+-----------------+-._
                     .'  /  Underlayer       \  '.
                    /   /  (W_50 / 10)        \   \  Primary Armor Layer (W_50)
  SWL ~~~~~~~~~~~~~/   /     .-----------.     \   \~~~~~~~~~~~~~ Harbor Side
      .------.    /   /     /  Core       \     \   \    .-----.
     /  Toe   \  /   /     / (Quarry Run)  \     \   \  /  Toe  \
  ==+==Berm====++===+=====+=================+=====+===++=========+==
     [============== Quarry-Run Bedding / Filter Blanket =========]

Q7.3 (SB): Define coastal structure failure, state the general reasons for failure, and explain/sketch the failure modes of rubble-mound breakwaters, rear-side overtopping erosion, slip surface failure of rubble foundations, hydraulic instability & breakage of armor units, and pressure blowout of slab elements.

Appeared in: 2019 (Q7a, 10m), 2021 (Q5a-i,iii, 6.67m), 2022 (Q5c, 5m), 2025 (Q8b, 10m) (Rank #13)
Time & Length Budget: 4–7 mins (~80–120 words + sketches)
Reference: SB/Topic 07/EWCE 471_LEC 16-17_Types and Functions of Coastal Structures.pdf, SB/Topic 07/Types & Functions_of_Coastal_Structures.pdf

Answer:

Definition of Failure: Damage that leads to reduced structural performance or complete loss of engineering function (either Serviceability Failure where wave transmission/overtopping becomes excessive, or Ultimate Collapse where the structure breaches).
Four General Reasons for Failure:
1. Design Errors: Underestimating wave loads, poor filter design, or overlooking liquefaction/toe scour.
2. Load Exceedance: Extreme storm waves or storm surges exceeding the design return period (overload).
3. Construction Deficiencies: Poor armor interlocking, wrong stone grading, or out-of-tolerance placement.
4. Material Deterioration: Rock weathering, freeze-thaw cracking, concrete spalling, or steel corrosion.
Key Failure Modes & Mechanisms (with Sketches):

(A) RUBBLE-MOUND BREAKWATER FAILURE MODES          (B) REAR-SIDE OVERTOPPING EROSION
       Overtopping -->  _.-+---+-._                     Wave Overtopping Jet ===>
     Armor Displacement/  /  |  \  \ Rear Slope              _.-+[Crown Cap]+-._
   SWL ~~~~~~~~~~~~~~~/  /   |   \  \Sliding           ~~~ .'   |___________|   '. ===> Scours
     .---.           /  /Core|    \  \                    /                \      \     Rear Armor!
    /Toe  \         /  /Wash |Slip \  \                  /  Seaward Slope   \Core  \ (Uncovered)
  =+Erosion+=======+==+======+ Circle==+==              +--------------------+------+-----------
  (Scour Hole)        (Seabed Liquefaction)

(C) SLIP SURFACE IN RUBBLE FOUNDATION              (D) PRESSURE BLOWOUT OF SLAB ELEMENT
         Wave Push ===> |       |                        Wave Downrush (Low External Pressure)
                        |Caisson|                                   ^   ^   ^
                        |_______|                                  /   /   /  Slab Lifted Out!
                      .'    :    '.                               /  [SLAB]  /
                    .'  _..---.._  '.  Rubble Mound              /          /  <-- High Uplift
  ================='==='========= '==='=====>          ~~~~~~~~~/          /       Pore Pressure
                       '--_____--'  Slip Circle!

Hydraulic Instability & Breakage of Armor Units: Wave uprush and downrush exert drag and lift forces that rock, roll, or pull armor units out of the slope (hydraulic displacement). For slender concrete units (Dolos, Tetrapods), rocking impacts snap the concrete limbs (structural breakage), rapidly unraveling the armor layer and washing out the core.
Erosion of Rear-Side Slope by Wave Overtopping (Sloping-Front Breakwater with Capping): Large waves overtopping the concrete crown wall plunge as a high-velocity water jet directly onto the upper rear (harbor-side) slope, stripping away rear armor stones and undermining the back of the crown cap.
Slip Surface Failure of Rubble Foundation: Horizontal wave impact and overturning moment on a vertical caisson transfer high shear stress into the underlying rubble bedding mound and soft seabed, causing a rotational or circular shear slide (slip circle) through the rubble foundation.
Pressure Blowout of Impermeable Slab Elements: During wave downrush (trough) on a pitched-block or concrete-slab revetment, external water pressure on top of the slab drops suddenly while trapped high hydrostatic/wave pore water pressure underneath pushes upward, blowing the slab out of the slope.
Toe Scour & Seabed Liquefaction: Reflected waves scour a trench at the toe, causing the entire armor face to slide downward (unbuttoning).

Q7.4 `[Design Math]`: Step-by-Step Design Method for a Quarrystone (Riprap) Revetment and a Rubble-Mound Seawall.

Appeared in:
- Revetment Design: 2021 (Q5b, 20m), 2022 (Q5d, 15m), 2024 (Q5b, 20m) (Rank #16)
- Seawall Design: 2019 (Q7b, 20m), 2025 (Q5c, 15m) (Rank #33)
Reference: SB/Topic 07/EWCE 471_DESIGN OF REVETMENTS, SEA WALL, BULKHEADS.pdf, SB/Topic 07/Graph for Revetment Design.pdf, SB/Topic 08/Graph for Seawall Design.pdf, SB/Topic 08/Seawall Design.JPG

Method to Follow (USACE EM 1110-2-1614 Procedure — Identical Core Steps for Both):

   DESIGN CROSS-SECTION (REVETMENT / RUBBLE-MOUND SEAWALL)
                                                           Crest Elevation = DWL + R_max
                                                      _.-+----------------+-._
                                                    .'  /  Filter Layer    \
      Design Water Level (DWL)                    .'   /  (r_f = min 1 ft)  \
   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.'    /                      \
       <-- Apron Width (B >= 3-6 ft) -->      .'     /   Primary Armor (W_50) \
       .-------------------------------.    .'      /    Thickness = r         \
      /  Toe Protection (W_toe = W_50)  \ .'       /     Slope = 1V : cot(theta)H
   ==+===================================+========+==============================
      Water Depth at Toe = d_s            Geotextile / Bedding Layer

Step 1 — Design Water Depth at Toe ( $d_{s}$ ): Given Design Still Water Level ( $DWL = HighTide + StormSurge$ ) and seabed/beach toe elevation $z_{toe}$ : $d_{s} = DWL - z_{toe}$
Step 2 — Design Breaking Wave Height ( $H_{b}$ ) at the Structure Toe:
- Given wave period $T$ and nearshore bottom slope $m$ in front of the structure:
- Compute $\frac{d_{s}}{g T^{2}}$ .
- From Breaking Wave Nomogram (Graph for Revetment/Seawall Design): Enter with $\frac{d_{s}}{g T^{2}}$ and bottom slope $m$ to read $\frac{H_{b}}{d_{s}}$ , then calculate: $H_{b} = (\frac{H_{b}}{d_{s}}) d_{s} (Note i f n o c h a r t i s u s e d, [PARSE ERROR: Undefined("RBrace")] H_{b} \approx 0.78 d_{s} to 0.90 d_{s})$
- Use $H = H_{b}$ (or the lesser of offshore $H_{s}$ and depth-limited $H_{b}$ ) as the design wave height.
Step 3 — Select Structure Slope ( $\cot θ$ ) and Stability Coefficient ( $K_{D}$ or $K_{R R}$ ):
- Choose a stable seaward slope: typically 1V : 2H ( $\cot θ = 2.0$ ) or 1V : 3H ( $\cot θ = 3.0$ ) (1V : 1.5H for compact seawalls).
- For rough angular quarrystone (2 layers, random placement, breaking waves):
  - Uniform stone ( $W_{50}$ by Hudson formula): $K_{D} = 2.0$ (breaking waves).
  - Graded riprap ( $W_{50}$ ): $K_{R R} = 2.2$ .
Step 4 — Median Armor Stone Weight ( $W_{50}$ ) (Hudson Formula): Given unit weight of rock γr (e.g., 165 lb/ft³ or 25.9 kN/m³) and water γw (64 lb/ft³ or 10.05 kN/m³):
- Compute specific gravity relative to water: $S_{r} = \frac{γ_{r}}{γ_{w}}$ (typically 165/64 = 2.58).
- Compute median armor stone weight: $W_{50} = \frac{γ_{r} H^{3}}{K_{D} (S_{r} - 1)^{3} \cot θ}$
- Armor Gradation Limits:
  - For Uniform Quarrystone Armor: $W_{\min} = 0.75 W_{50}$ to $W_{\max} = 1.25 W_{50}$ .
  - For Graded Riprap: $W_{\min} = 0.125 W_{50}$ to $W_{\max} = 4.0 W_{50}$ .
- Equivalent Median Stone Diameter ( $D_{50}$ ): $D_{50} = {(\frac{W_{50}}{γ_{r}})}^{1 / 3}$
Step 5 — Armor Layer Thickness ( $r$ ) and Number of Stones ( $N_{r}$ ): For $n = 2$ layers of rough angular quarrystone (layer coefficient $k_{Δ} = 1.00$ , porosity $P = 37 %$ ): $r = n k_{Δ} {(\frac{W_{50}}{γ_{r}})}^{1 / 3} = 2.0 D_{50} (forgradedriprap [PARSE ERROR: Undefined("RBrace")] r = 2.0 D_{50} or 1.5 D_{100, \max})$ $Numberofstonesperunitarea A : \frac{N_{r}}{A} = n k_{Δ} (1 - \frac{P}{100}) {(\frac{γ_{r}}{W_{50}})}^{2 / 3}$
Step 6 — Wave Runup ( $R_{\max}$ ) and Crest Elevation (Freeboard):
- Compute deep-water wavelength $L_{0} = \frac{g T^{2}}{2 π}$ (5.12 T² in ft, or 1.56 T² in m) and structure Surf Similarity Parameter ( $ξ$ ): $ξ = \frac{\tan θ}{\sqrt{H / L_{0}}} = \frac{1 / \cot θ}{\sqrt{H / L_{0}}}$
- Compute rough-slope Wave Runup ( $R_{\max}$ ) using the Ahrens & McCartney empirical formula (or read $\frac{R}{H}$ from the Runup curve): $\frac{R}{H} = \frac{a ξ}{1 + b ξ} (where a = 0.956, b = 0.398 forquarrystone)$ $R = H (\frac{R}{H})$
- Crest Elevation (for zero overtopping): $CrestElevation = DWL + R$
Step 7 — Filter / Underlayer Design:
- Use a geotextile filter cloth overlaid by a crushed stone bedding/underlayer of median weight: $W_{filter} = \frac{W_{50}}{10} to \frac{W_{50}}{15} (orgrainsizecriterion \frac{D_{15, armor}}{D_{85, filter}} < 5)$
- Minimum filter layer thickness: $r_{filter} = \max (2 D_{50, filter}, 1.0 ftor 0.30 m)$ .
Step 8 — Toe Protection & Crest Width:
- Crest Width ( $B_{crest}$ ): At least $3$ stones wide ( $B_{crest} = 3 k_{Δ} D_{50}$ ).
- Toe Apron: Use stones of weight $W_{toe} = W_{50}$ , thickness $= r$ , and horizontal apron width $B_{toe} = \max (2 r, 3 to 6 ft or 1 to 2 m)$ (or embed toe below maximum scour depth $\approx 1.0 H_{b}$ ).
Step 9 — Draw the Labeled Cross-Section Sketch: Always finish by drawing the cross-section above showing DWL, Crest Elevation, Slope ( $1 V : \cot θ H$ ), Armor ( $W_{50}, r$ ), Filter ( $W_{filter}, r_{f}$ ), and Toe Apron.

3. Unmapped / Earlier-Syllabus Past Exam Questions (`SA / Lec 02` & `SA / Lec 15-16`)

U.1: Define secondary coasts and list the types of marine deposited coasts under secondary coasts.

Appeared in: 2019 (Q2b, 6m) (Rank #34)
Time & Length Budget: 4 mins (~75 words)
Reference: Shepard's Classification of Coasts (formerly in SA / Lec 02)

Answer:

Definition of Secondary Coasts: Under Shepard's Coastal Classification, Secondary Coasts are coastlines that have been shaped and modified primarily by present-day marine processes (ocean waves, longshore currents, tides) or marine organisms, rather than by terrestrial/land processes (rivers, glaciers, volcanoes, or faults, which form Primary Coasts).
Three Main Categories of Secondary Coasts:
1. Wave-Erosion Coasts: Wave-straightened cliffs and irregular headlands/bays.
2. Marine-Deposited Coasts (built by waves and currents).
3. Coasts Built by Organisms: Coral reefs, mangrove swamps, and salt marshes.
Types of Marine-Deposited Coasts under Secondary Coasts:
1. Barrier Coasts: Barrier beaches, barrier islands, and barrier spits enclosing lagoons.
2. Cuspate Forelands: Large triangular sandy projections built out from the coast by converging longshore drift.
3. Beach Plains: Prograding sandy beach ridges built along a flat coast.
4. Mudflats / Tidal Marshes: Low-energy coastal plains built up by fine tidal sediment deposition.

U.2: Write short notes on: (i) Ring of Fire, and (ii) DART.

Appeared in: 2022 (Q3a, 7m) (Rank #43)
Time & Length Budget: 4.5 mins (~85 words)
Reference: Tsunami Generation & Warning Systems (SA / Lec 02–03)

Answer:

(i) Ring of Fire (Circum-Pacific Belt):
- Definition: A 40,000 km horseshoe-shaped tectonic belt rimming the basin of the Pacific Ocean (from New Zealand, Indonesia, Philippines, and Japan up through Alaska and down the west coast of North and South America).
- Significance: Driven by oceanic plate subduction trenches (Nazca, Pacific, Philippine plates). It contains 75% of the world's active volcanoes, produces 90% of the world's earthquakes, and generates over 80% of destructive global tsunamis.
(ii) DART (Deep-Ocean Assessment and Reporting of Tsunamis):
- Definition: A real-time early-warning buoy system developed by NOAA to detect tsunamis in the deep ocean long before they strike coastlines.
- How It Works (Two Components):
  1. Bottom Pressure Recorder (BPR): Anchored on the deep ocean floor (3000–6000 m depth) to sense tiny hydrostatic pressure changes (as small as 1 cm of water-column change) caused by a passing tsunami wave.
  2. Surface Mooring Buoy: Receives data from the BPR via acoustic telemetry and transmits real-time tsunami alerts via satellite to Tsunami Warning Centers.

U.3 `[Theory & Math]`: Storm Surge definitions (wind stress, moving wind field, triangular wind velocity, fetch length), procedure for estimating storm surge height in enclosed Langhaar-shape basins, and continental shelf storm surge height calculation.

Appeared in: 2022 (Q4a, 7m; Q4b, 7m; Q4c, 16m) (Rank #46)
Time & Length Budget: 4–8 mins (~90–130 words + formulas)
Reference: Storm Surge Theory (formerly in SA / Lec 15-16)

Answer:

Part A — Definitions (2022 Q4a):
1. Wind Stress ( $τ_{s}$ ): Horizontal frictional shear force per unit surface area exerted by blowing wind on the sea surface, driving surface drift and piling water up against the coast: $τ_{s} = ρ_{a} C_{D} U_{10^{2}} or \frac{τ_{s}}{ρ g} = k U^{2} (where k \approx 3.0 \times 10^{- 6} s^{2} / m)$
2. Moving Wind Field: A cyclonic storm system whose wind field translates forward at speed $V_{f}$ across the water body; if $V_{f}$ approaches the shallow-water wave speed $C = \sqrt{g d}$ , dynamic resonance dramatically amplifies the surge height.
3. Triangular Wind Velocity Distribution: Idealized cyclone wind profile where wind speed increases linearly from zero at the storm eye (r = 0) to a peak maximum wind ( $U_{\max}$ ) at the Radius of Maximum Winds ( $R$ ), and then decays linearly (or exponentially) outward toward the storm periphery.
4. Fetch Length ( $F$ ): The horizontal distance of open water over which wind blows continuously with reasonably constant speed and direction to generate waves and wind setup.
Part B — Procedure for Estimating Storm Surge in Enclosed Langhaar-Shape Basins (2022 Q4b):
1. Idealize the enclosed lake/bay of length $L$ and average depth $d$ under steady wind speed $U$ blowing along its axis.
2. Compute the basic 1D wind setup gradient: $\frac{d S}{d x} = \frac{τ_{s} + τ_{b}}{ρ g (d + S)} = \frac{n τ_{s}}{ρ g d}$ (where $n \approx 1.15 – 1.25$ accounts for bottom return-flow shear stress $τ_{b}$ ).
3. Calculate the fundamental seiche period of the basin $T_{n} = \frac{2 L}{\sqrt{g d}}$ and compare it with the effective duration of the wind storm $t_{d}$ .
4. Apply Langhaar's planform shape factor ( $f_{s}$ ) (which accounts for converging or diverging bay width from the windward to leeward end) and dynamic response factor ( $m$ ) to obtain maximum wind setup at the leeward shore: $S_{\max} = f_{s} \cdot m \cdot \frac{k U^{2} L}{2 g d}$
Part C — Continental Shelf Storm Surge Height Calculation ([Math], 2022 Q4c): For a cyclone blowing perpendicular to a continental shelf of width F (fetch length), uniform depth d (or sloping from d1 at the shelf edge to d2 at the coast), wind speed U, and central pressure drop ΔP=P∞-P0 (in hPa or mbar):
1. Step 1 — Inverted Barometer (Pressure) Setup ( $S_{p}$ ): Water rises by ~1 cm for every 1 mbar (hPa) drop in atmospheric pressure: $S_{p} = \frac{Δ P}{ρ g} \approx 0.0104 Δ P i n m e t e r s, f o r [PARSE ERROR: Undefined("RBrace")] Δ P inmbar [PARSE ERROR: Undefined("RBrace")]$
2. Step 2 — Wind Stress Setup Across the Continental Shelf ( $S_{w}$ ):
  - For Constant Shelf Depth ( $d$ ): $S_{w} = \frac{n k U^{2} F}{g d} (using n k \approx 3.3 \times 10^{- 6}, g = 9.81 m s {[PARSE ERROR: Undefined("RBrace")]}^{2})$
  - For Linearly Sloping Shelf from Depth $d_{1}$ (offshore) to $d_{2}$ (nearshore) over Distance $F$ : $S_{w} = \frac{n k U^{2} F}{g (d_{1} - d_{2})} \ln (\frac{d_{1}}{d_{2}})$
3. Step 3 — Total Storm Surge Height ( $S_{total}$ ): $S_{total} = S_{p} + S_{w}$

U.4: Describe the environmental conditions required for coral survival.

Appeared in: 2025 (Q4c, 5m) (Rank #52)
Time & Length Budget: 3.5 mins (~65 words)

Answer:

Reef-building corals (hermatypic corals living in symbiosis with photosynthetic zooxanthellae algae) require six strict environmental conditions:

Warm Water Temperature: Optimal range of 20°C to 29°C (68°F–84°F); temperatures below 18°C prevent reef growth, while sustained temperatures above 30°C cause coral bleaching.
Shallow, Sunlit Water (Photic Zone): Depth < 25–50 m so abundant sunlight can reach the symbiotic algae for photosynthesis.
Clear, Sediment-Free Water: Low turbidity and suspended silt (heavy river mud smothers coral polyps and blocks sunlight, which is why only St. Martin's Island in Bangladesh supports corals, far from the muddy Meghna mouth).
Normal Marine Salinity: Stable ocean salinity of 32 to 40 ppt (PSU); freshwater dilution from major river mouths kills corals.
Hard, Stable Substrate: Rocky seabed or old limestone skeleton for free-swimming coral larvae (planulae) to attach and grow.
Moderate Wave Action & Circulation: Gentle waves and currents continuously supply dissolved oxygen and planktonic food while flushing away waste.

ewce09.azraftaohid.me/L4T1/EWCE 471/Question Answer - by Gemini Argon on Antigravity.md

Created: 2026/11/03 05:05

EWCE 471 — Exam-Ready Question & Answer Guide (2019–2025)

How to Use This Guide

Table of Contents

1. Section A Lecture Materials (EWCE 471/SA/)

SA / Lec 01 — Introduction to Coastal Engineering & Bangladesh Coast

Q1.1: Define Coastal Engineering and explain why it is different from other ocean-related studies.

Q1.2: What are the basic information needed for oceanology, and what are their applications?

Q1.3: Give a physical description of the coastal zone of Bangladesh and explain how it is managed against cyclones and storm surges.

SA / Lec 03 — Wave Classification, Basic Wave Parameters & Transformation Overview

Q3.1: Define and differentiate between Swell, Seiche, and Tsunami with respect to wave generation and water level variation.

Q3.2: Differentiate between pure oscillatory waves and finite-amplitude waves.

Q3.3: Define basic wave parameters: Wave Height (H), Wave Number (k), Relative Depth (d/L), Wave Steepness (H/L), and Sinusoidal Wave Profile.

Q3.4: Differentiate between deep-water, transitional, and shallow-water waves and sketch water particle displacement / velocity profiles.

Q3.5 & Q3.6: Overview of Wave Transformation & Wave Breaking

SA / Lec 04 — Derivations & Assumptions of Small-Amplitude (Airy) Wave Theory

Q4.1: State the basic physical and mathematical assumptions made to derive Small-Amplitude (Airy / Linear) Surface Wave Theory.

SA / Lec 05-06 — Wave Celerity, Wavelength, Orbital Kinematics & Wave Energy

Q5.1 [Math]: Method to calculate Wave Celerity (C) and Wavelength (L) across deep, transitional, and shallow water depths.

Q5.2 [Math]: Method to calculate water particle velocities (u,w), accelerations (ax,az), displacements (ξ,ζ), wave energy (E), and wave power (P).

SA / Lec 07-08 — Group Velocity, Subsurface Pressure, Finite-Amplitude Waves & Wave Statistics

Q7.1 [Theory & Math]: Define group velocity (Cg), state its relation with wave celerity (C) in deep and shallow water, and explain its physical significance in wave energy conservation.

Q7.2 [Theory & Math]: Explain subsurface pressure under a progressive wave and outline the method to calculate surface wave height (H) from an underwater pressure gauge.

Q7.3: Compare Airy (Linear), Stokes Finite-Amplitude, Cnoidal, and Solitary wave theories.

Q7.4 [Math]: Method to calculate statistical wave parameters (Hs,Ts,H1/10,T1/10,Hrms) from a wave train record.

SA / Lec 09-10 — Wave Shoaling, Refraction, Green's Law & Diffraction

Q9.1: Explain the necessity of studying wave transformation, wave shoaling, wave refraction, and why wave diffraction occurs in shallow water.

Q9.2 [Theory & Math]: State Green's Law, explain how wave height theoretically reaches infinity as depth d→0 vs. what happens in reality, and calculate tsunami wave height in shallow water.

Q9.3 [Math]: Method to calculate shoaled and refracted wave height (H=H0′KsKr) at intermediate/shallow depths.

SA / Lec 11-12 — Wave Breaking, Surf-Zone Currents (Longshore & Rip) & Wave Setup

Q11.1: Explain why waves break, why wave breaking is much more common in shallow water than deep water, and describe the 4 types of breaking waves.

Q11.2 [Math]: Method to estimate breaking wave height (Hb), breaking water depth (db), and breaker type on a given beach slope (m).

Q11.3: Explain why waves are the prime movers for littoral processes, sketch the nearshore current system (longshore current & rip current), and explain why rip currents are dangerous to swimmers.

Q11.4 [Theory & Math]: Define radiation stress, wave set-down, and wave setup; explain why wave setup contributes significantly to coastal flooding; and state the method to calculate set-down and setup.

SA / Lec 13-14 — Wave Forces on Piles & Vertical Walls (Non-Breaking, Breaking & Broken)

Q13.1: Classify and illustrate wave force problems by type of wave action and structure, and write the Morison equation for horizontal wave force on a vertical pile.

Q13.2 [Theory & Math]: Explain non-breaking wave pressure distribution on a vertical wall and state the Miche–Rundgren (Sainflou) method to calculate forces and overturning moments.

Q13.3 [Theory & Math]: Draw the Minikin breaking wave pressure diagram with the toe moment equation, and state the method to calculate broken wave force on a vertical wall.

SA / Lec 17-18 — Shoreline Dynamics, Beach Profile, Coastal Features & Estuaries

Q17.1: "The shoreline is a dynamic interface" — explain the statement in the context of coastal morphological and geological processes.

Q17.2: Draw a neat sketch of a typical cross-shore beach profile and identify all salient features.

Q17.3: Define and sketch key coastal features (Coastline, Tombolo, Barrier Spit, Barrier Island, Headland, Coastal Dune, Tidal Flats) and explain how barrier islands and coastal dunes are formed.

Q17.4: Define an estuary, classify estuaries, differentiate between tide-dominated and wave-dominated estuaries, and explain mixed estuarine systems.

2. Section B Lecture Materials (EWCE 471/SB/)

SB / Topic 01 — Coast, Sea vs. Lake, Ocean & Sea Level Rise (SLR) in Bangladesh

Q1.1 (SB): How do you distinguish a lake from a sea, and when is a sea called an ocean? Justify with examples.

Q1.2 (SB): Discuss the impacts of Sea Level Rise (SLR) and the adaptation measures against SLR impacts in Bangladesh.

SB / Topic 02 — Tides, Tidal Datums, Tidal Bores & Bangladesh Tidal Characteristics

Q2.1 (SB): Discuss and illustrate with graphical representations the different types of daily tidal cycles (Semidiurnal, Diurnal, and Mixed).

Q2.2 (SB): Define and explain standard tidal levels (Height of Tide, Mean Sea Level, MHWS, MLWS, MHWN, MLWN, HAT, LAT), Chart Datum, and changes in sounding datum.

Q2.3 (SB): Why does a tidal bore occur? Write down its principal characteristics.

Q2.4 (SB): Define tidal stream and tidal flow, and describe the tidal characteristics and tidal range zones of the Bangladesh coast.

SB / Topic 03 — Ports and Harbors

Q3.1 (SB): Define a harbor (including harbor of refuge and locked basin), explain its features/components, explain the role and remedies of littoral drift in harbor layout, and sketch a typical harbor layout and the Madras Harbor layout.

Q3.2 (SB): Write down five differences between ports and harbors.

SB / Topic 04 — Coastal Processes, Coastal Erosion & Longshore Sediment Transport

Q4.1 (SB): Explain what natural coastal processes occur at a coast, how waves, tidal currents, and longshore currents transport material and change a beach (with sketches), how they affect human settlements, and how coastal developments affect coastal processes.

Q4.2 (SB): List the input datasets required for modeling physical processes in the coastal zone of Bangladesh.

Q4.3 (SB): Define coastal erosion, explain the processes of coastal erosion, and describe methods to reduce erosion (including how wetlands/mangroves protect the shoreline).

Q4.4 (SB): Write down the differences between constructive and destructive waves.

Q4.5 [Math]: Method to calculate potential longshore sediment transport rate (Il and Ql) using the Energy Flux Method.

SB / Topic 05 — Deltas & Bangladesh Delta Plan (BDP) 2100

Q5.1 (SB): Discuss the process and 3 stages of delta formation with figures, and describe how gravel, sand, silt, and clay are deposited into Topset, Foreset, and Bottomset beds.

Q5.2 (SB): Compare and discuss with sketches and examples the classification and geometry of deltas based on shape and depositional controls.

Q5.3 (SB): Bangladesh Delta Plan (BDP) 2100 — Explain the need for an integrated plan and Bangladesh's delta challenges; define "Hotspots" and list the 6 Hotspots and their issues; and state the National-level and Coastal Zone Hotspot strategies.

SB / Topic 06 — Tidal Theories (Static & Dynamic), Spring/Neap Tides & Tide Prediction

Q6.1 (SB): Explain Newton's Static (Equilibrium) Theory and Laplace's Dynamical Theory of tide generation, state the limitations of the Static Theory, and justify mathematically why the Moon has a greater tide-generating influence than the Sun.

Q6.2 (SB): Explain with figures: (i) Priming and lagging of tide, and (ii) Spring and neap tides.

Q6.3 [Theory & Math]: Explain the Non-Harmonic and Harmonic methods of tide prediction, define non-harmonic constants (Age of tide, Lunitidal interval, Mean & Vulgar establishment), and state the method to calculate afternoon high-water time and height of tide.

SB / Topic 07 & Topic 08 — Coastal Structures, Failure Modes & Revetment/Seawall Design

Q7.4 [Design Math]: Step-by-Step Design Method for a Quarrystone (Riprap) Revetment and a Rubble-Mound Seawall.

3. Unmapped / Earlier-Syllabus Past Exam Questions (SA / Lec 02 & SA / Lec 15-16)

U.1: Define secondary coasts and list the types of marine deposited coasts under secondary coasts.

U.2: Write short notes on: (i) Ring of Fire, and (ii) DART.

U.3 [Theory & Math]: Storm Surge definitions (wind stress, moving wind field, triangular wind velocity, fetch length), procedure for estimating storm surge height in enclosed Langhaar-shape basins, and continental shelf storm surge height calculation.

U.4: Describe the environmental conditions required for coral survival.

1. Section A Lecture Materials (`EWCE 471/SA/`)

Q3.3: Define basic wave parameters: Wave Height ( $H$ ), Wave Number ( $k$ ), Relative Depth ( $d / L$ ), Wave Steepness ( $H / L$ ), and Sinusoidal Wave Profile.

Q5.1 `[Math]`: Method to calculate Wave Celerity ( $C$ ) and Wavelength ( $L$ ) across deep, transitional, and shallow water depths.

Q5.2 `[Math]`: Method to calculate water particle velocities ( $u, w$ ), accelerations ( $a_{x}, a_{z}$ ), displacements ( $ξ, ζ$ ), wave energy ( $E$ ), and wave power ( $P$ ).

Q7.1 `[Theory & Math]`: Define group velocity ( $C_{g}$ ), state its relation with wave celerity ( $C$ ) in deep and shallow water, and explain its physical significance in wave energy conservation.

Q7.2 `[Theory & Math]`: Explain subsurface pressure under a progressive wave and outline the method to calculate surface wave height ( $H$ ) from an underwater pressure gauge.

Q7.4 `[Math]`: Method to calculate statistical wave parameters ( $H_{s}, T_{s}, H_{1 / 10}, T_{1 / 10}, H_{rms}$ ) from a wave train record.

Q9.2 `[Theory & Math]`: State Green's Law, explain how wave height theoretically reaches infinity as depth $d \to 0$ vs. what happens in reality, and calculate tsunami wave height in shallow water.

Q9.3 `[Math]`: Method to calculate shoaled and refracted wave height ( $H = H_{0^{'}} K_{s} K_{r}$ ) at intermediate/shallow depths.

Q11.2 `[Math]`: Method to estimate breaking wave height ( $H_{b}$ ), breaking water depth ( $d_{b}$ ), and breaker type on a given beach slope ( $m$ ).

Q11.4 `[Theory & Math]`: Define radiation stress, wave set-down, and wave setup; explain why wave setup contributes significantly to coastal flooding; and state the method to calculate set-down and setup.

Q13.2 `[Theory & Math]`: Explain non-breaking wave pressure distribution on a vertical wall and state the Miche–Rundgren (Sainflou) method to calculate forces and overturning moments.

Q13.3 `[Theory & Math]`: Draw the Minikin breaking wave pressure diagram with the toe moment equation, and state the method to calculate broken wave force on a vertical wall.

2. Section B Lecture Materials (`EWCE 471/SB/`)

Q4.5 `[Math]`: Method to calculate potential longshore sediment transport rate ( $I_{l}$ and $Q_{l}$ ) using the Energy Flux Method.

Q6.3 `[Theory & Math]`: Explain the Non-Harmonic and Harmonic methods of tide prediction, define non-harmonic constants (Age of tide, Lunitidal interval, Mean & Vulgar establishment), and state the method to calculate afternoon high-water time and height of tide.

Q7.4 `[Design Math]`: Step-by-Step Design Method for a Quarrystone (Riprap) Revetment and a Rubble-Mound Seawall.

3. Unmapped / Earlier-Syllabus Past Exam Questions (`SA / Lec 02` & `SA / Lec 15-16`)

U.3 `[Theory & Math]`: Storm Surge definitions (wind stress, moving wind field, triangular wind velocity, fetch length), procedure for estimating storm surge height in enclosed Langhaar-shape basins, and continental shelf storm surge height calculation.