Coastal & Harbor Engineering

A structured learning path from coastal processes through advanced harbor and marine structure design. Master wave mechanics, shoreline protection, and port engineering.

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Level 1

Beginner — Coastal Processes and Wave Mechanics

Start here if you are new to coastal engineering.

Water Wave Theory

Surface waves are the primary drivers of coastal processes. Linear (Airy) wave theory describes small-amplitude waves: wave length L = gT²/2π (deep water), wave celerity C = L/T, and the dispersion relation ω² = gk·tanh(kh). In deep water (h/L > 0.5), waves are dispersive — longer waves travel faster. In shallow water (h/L < 0.05), wave speed depends only on water depth: C = √(gh). As waves approach shore, shoaling increases wave height (H ∝ 1/√(C_g) where C_g is group velocity).

Nonlinear wave theories (Stokes, cnoidal, solitary) apply as wave steepness H/L increases. Wave breaking occurs when the wave height reaches a critical fraction of depth (H/h ≈ 0.78 for spilling breakers). Breaking types (spilling, plunging, surging, collapsing) depend on the surf similarity parameter (Iribarren number) ξ = tanβ / √(H/L₀). Plunging breakers (ξ = 0.5-3.0) produce the most energetic breaking and greatest potential for scour and structural damage.

Coastal Sediment Transport

Sediment transport in the coastal zone occurs as longshore transport (driven by waves approaching the coast at an angle) and cross-shore transport (driven by wave asymmetry and undertow). The longshore transport rate Q = K·P_b^n, where P_b is the longshore wave power per unit length of beach (derived from breaking wave height and angle). The CERC formula gives Q = 0.023·H_b²·C_b·sin(2α_b) in m³/second (where H_b is breaking wave height, C_b is breaking wave celerity, α_b is breaking wave angle).

Sediment grain size affects transport rates: coarse sand (0.5-1.0 mm) moves primarily as bedload, fine sand (0.125-0.25 mm) moves predominantly as suspended load. The fall velocity w_s determines whether grains are suspended or remain near the bed. The Dean number Ω = H_b/(w_s·T) classifies beach type: Ω < 1 reflective beaches (coarse sand, steep profile), Ω > 6 dissipative beaches (fine sand, flat profile), and intermediate types between. Understanding sediment transport is fundamental to shoreline management and harbor siltation prediction.

Tides, Storm Surges, and Sea Level Rise

Tides (diurnal, semi-diurnal, or mixed) are astronomical oscillations with predictable amplitude and phase from harmonic analysis (over 40 tidal constituents — M₂, S₂, K₁, O₁ dominant). The tidal range controls harbor access, mooring design, and coastal flooding. Storm surge is the meteorological rise in water level due to wind setup and inverse barometer effect — a 1 mbar pressure drop gives 1 cm rise (static). Dynamic surge modeling (SLOSH, ADCIRC) simulates hurricane-induced flooding.

Sea level rise (currently ~3-4 mm/year globally, accelerating) has major implications for coastal infrastructure design life. IPCC projections for 2100 range from 0.3-1.0 m under different emission scenarios. Adaptation strategies include: raising coastal defenses, managed retreat (relocation), beach nourishment (replacing eroded sand), and nature-based solutions (mangrove restoration, oyster reefs, dune stabilization). Design return periods range from 50-year (harbor facilities) to 200+ year (nuclear plants, major coastal defenses).

Level 2

Intermediate — Shoreline Protection and Harbor Design

Build on fundamentals with protection and harbor structures.

Shoreline Protection Structures

Coastal defense structures manage erosion and flooding. Seawalls (vertical or recurved) reflect wave energy and prevent upland erosion but can cause toe scour. Revetments (sloping, rock-armored or concrete block-armored) absorb wave energy and protect the shoreline. Groins (perpendicular to shore) trap longshore sediment to build beaches updrift but cause downdrift erosion. Breakwaters (offshore, parallel to shore) reduce wave energy reaching the coast. Headland breakwaters and artificial headlands create cremulated shorelines with stable pocket beaches.

Hard structural solutions are increasingly supplemented by soft approaches. Beach nourishment adds compatible sand from offshore or upland sources — the typical renourishment interval is 3-10 years depending on erosion rate. Dune restoration with native vegetation provides natural defense against storm surge. Living shorelines combine structural elements (coir logs, oyster reef balls) with vegetation for habitat enhancement. The choice between hard, soft, and hybrid approaches depends on erosion rate, wave climate, sediment supply, environmental sensitivity, and cost.

Breakwater Design

Breakwaters create sheltered water areas for harbors. Rubble-mound breakwaters consist of: armor layer (large rock or concrete units — 2-3 layers for single layer systems like Core-Loc, Xbloc, or Accropode), filter layers (graduated sizes preventing winnowing of core), core (quarry run material), and toe protection. The Hudson formula determines armor weight: W = ρ_sg·H³/(K_D·(S_r-1)³·cotα) where ρ_s is stone density, S_r = ρ_s/ρ_w, cotα is slope angle, and K_D is stability coefficient.

Caisson breakwaters (vertical composite) use large concrete caissons filled with sand or rock, founded on a rubble-mound mattress. They reflect rather than absorb wave energy. Sliding and overturning stability are checked against extreme wave loads. Van der Meer formulas and Goda's wave pressure formulas are used for design. Overtopping (mean overtopping discharge q in l/s/m) must be limited to acceptable levels — typically q < 50 l/s/m for structural safety and q < 5 l/s/m for pedestrian safety behind the crest.

Port and Harbor Layout

Harbor planning requires integration of: approach channel (depth = design vessel draft + underkeel clearance + wave allowance + siltation allowance — typically 1.5 m clearance), turning basin (1.5-2.0 times vessel length), berthing area (wharves, quays, jetties, or dolphins), and navigational aids. Channel alignment should minimize cross-currents and wave penetration — typically oriented within 30° of prevailing wave direction to reduce sediment infill.

Mooring analysis (static or dynamic, using ship-mooring analysis software like OPTIMOOR) checks: line tensions (all lines within safe working load — typically 50% of MBL for nylon, 40% for wire), fender compression (fender reaction within rated capacity — rubber pneumatic, foam-filled, or solid rubber fenders), and vessel motions (surge, sway, heave, roll, pitch, yaw within operational limits). Design vessel dimensions (LOA, beam, draft, displacement) determine quay length and dredged depth. Service life: 50-100 years for major port infrastructure.

Level 3

Advanced — Marine Infrastructure and Coastal Management

For senior students and practicing engineers.

Marine Structures: Piers, Wharves, and Dolphins

Marine structures are classified as: gravity structures (caissons, blockwork, or sheet-piled) cantilevering or anchored, and open-piled jetties with steel or concrete piles. Piled jetty design: vertical and batter piles (1:6 to 1:4 pitch) resist lateral loads from vessel berthing and mooring, wave forces, and seismic loads. Deck elevation = design high water level + wave runup + freeboard + settlement (typically 3-5 m above MHWS for cargo handling areas).

Berthing energy E = 0.5·M_v·v_b²·C_e·C_m·C_s·C_c, where M_v is vessel mass, v_b is berthing velocity (typically 0.1-0.15 m/s for tug-assisted berthing), C_e is eccentricity factor, C_m is added mass coefficient (typically 1.3-1.8), C_s is softness coefficient, and C_c is configuration coefficient. This energy is absorbed by fenders — rubber or foam-filled fenders at 4-8 m spacing. Mooring loads (wind and current on moored vessel) are computed per OCIMF or PIANC guidelines.

Dredging and Reclamation

Dredging maintains navigable depths in harbors and approach channels. Types: capital dredging (initial excavation for new facilities), maintenance dredging (recurring removal of accumulated sediment), and remedial dredging (removal of contaminated sediments). Equipment selection: trailing suction hopper dredgers (TSHD — for open water, transporting dredged material in hopper), cutter suction dredgers (CSD — for compacted or cohesive materials with mechanical cutterhead), backhoe dredgers (for precision work near structures).

Dredged material management follows the waste hierarchy: minimize, reuse, recycle, treat, dispose. Beneficial uses: beach nourishment, land reclamation, habitat creation (wetlands, reefs), and construction fill. Land reclamation techniques: hydraulic fill (pumping dredged sand slurry into contained areas with settlement and consolidation), dry fill (trucking fill material), and staged construction with prefabricated vertical drains (PVDs) accelerating consolidation. Ground improvement (dynamic compaction, vibroflotation, stone columns) achieves required bearing capacity for port facilities.

Coastal Zone Management

Integrated Coastal Zone Management (ICZM) balances economic development (ports, tourism, aquaculture) with environmental protection and hazard mitigation. Shoreline management plans (SMPs) define strategic policies: hold the line (maintain existing defense), advance the line (build seaward), managed realignment (set back defenses), limited intervention (monitor and accept change). Setback lines control coastal development based on erosion projections (typically 30-100 year planning horizon).

Environmental impact assessment (EIA) for coastal projects covers: habitat loss (seagrass, mangroves, coral reefs), water quality (turbidity from dredging, thermal discharge), marine ecology (fish spawning, cetacean migration), and landscape/visual impact. Mitigation hierarchy: avoid, minimize, restore, offset. The Marine Spatial Planning (MSP) framework allocates coastal space among competing uses. Climate change adaptation integrates sea level rise, increased storm intensity, and changing wave climates into long-term coastal infrastructure planning with regular review cycles.

Practice Exercises

Exercise 1: Wave Transformation

A deep-water wave with height H₀ = 3 m, period T = 8 s, and direction 20° (relative to shore normal) propagates toward shore. Compute the wave height and direction at the 10 m depth contour assuming straight, parallel depth contours. Determine the breaking wave height and depth (use γ = H_b/h_b = 0.78).

Exercise 2: Rubble Mound Breakwater

Design the armor layer for a rubble mound breakwater in a water depth of 12 m with significant wave height H_s = 5.5 m, peak period T_p = 12 s. Use quarry stone with density 2,650 kg/m³, slope 1:2, and K_D = 4 for the trunk. Compute the required armor weight using Hudson's formula. Determine the crest elevation (allow overtopping q < 10 l/s/m) and armor thickness.

Exercise 3: Berthing Energy

A 50,000 DWT container vessel (displacement 60,000 tonnes, LOA 250 m, beam 32 m) berths at a ferry pier with berthing velocity 0.12 m/s. Calculate the berthing energy assuming eccentricity factor C_e = 0.6, added mass coefficient C_m = 1.5, softness C_s = 1.0, and configuration C_c = 1.0. Select an appropriate fender type and spacing (8 m center-to-center) from manufacturer data.

Exercise 4: Longshore Sediment Transport

A beach has a breaking wave height of 1.2 m, breaking angle of 8°, and sediment grain size d₅₀ = 0.3 mm. Using the CERC formula with K = 0.77, calculate the annual longshore sediment transport rate. A groin field of 3 groins at 200 m spacing is proposed — estimate the beach response and fillet volume per groin cell.

References

USACE. Coastal Engineering Manual (CEM). U.S. Army Corps of Engineers, 2002.
Dean, R.G. and Dalrymple, R.A. Coastal Processes with Engineering Applications. Cambridge, 2002.
Sorensen, R.M. Basic Coastal Engineering. 3rd ed., Springer, 2006.
PIANC. Maritime Navigation Commission Guidelines.
OCIMF. Mooring Equipment Guidelines (MEG4). Oil Companies International Marine Forum, 2018.
Civil Engineering Handbook — Coastal engineering chapter with design guidance.
Engineering Formula Library — Wave mechanics and coastal formulas.
Engineering Standards Reference — PIANC, USACE coastal standards.
Engineering Glossary — Definitions of coastal engineering terms.