LONGSHORE DRIFT
WEST COAST INDIA
EAST COAST INDIA
Waves & Coastal Processes
Wave Breaking & Refraction · Erosion, Littoral Drift & Deposition · High Rocky vs. Low Sedimentary Coasts (28 Micro-Realms)
The Most Dynamic & Destructive Geomorphic Interface (NCERT Chapter 7)
Coastal processes are the most dynamic and hence most destructive. Most changes along the coast are accomplished by Waves, which break with great force onto the shore while churning bottom sediments. Assuming sea level to be constant, NCERT classifies coasts into two fundamental types: 1) High, Rocky Coasts (submerged retreating coasts where erosional features dominate—shaping cliffs, wave-cut platforms, and wave-built terraces, exemplified by India's West Coast), and 2) Low, Smooth, Gently Sloping Sedimentary Coasts (emerged advancing coasts where depositional features dominate—building bars, spits, and lagoons that fill into coastal plains, exemplified by India's East Coast).
I. Wave Kinematics, Shoaling, Breaking & Refraction Physics (NCERT)
Dynamic Wave Dominance
- Coastal processes are most dynamic
- And hence most destructive (NCERT)
- Waves accomplish most coastal changes
Wind Speed, Duration & Fetch
- Friction of wind over open ocean
- Fetch: Uninterrupted distance of water
- Determines wave height & wavelength ($L$)
Wave Base ($d = L / 2$)
- Water particles move in circular orbits
- Orbit diameter shrinks to zero at $L/2$
- Below Wave Base, seabed is undisturbed
Shoaling & Breaking Waves
- At depth $< L/2$, wave feels bottom friction
- Wavelength shortens; crest steepens & breaks
- Throws water with great force & churns bed
Swash vs. Backwash
(ONSHORE)
(OFFSHORE)
- Swash: Turbulent foaming rush up beach
- Backwash: Gravity-driven return downslope
- Balance governs beach build vs scour
Storm & Tsunami Waves
- Normal swell: Strong swash builds beaches
- Storm & Tsunami waves: Huge energy
- Cause far-reaching changes in hours (NCERT)
Wave Refraction on Headlands
- Waves slow down first off shallow headlands
- Wave crests bend & focus energy on headlands
- Disperses energy inside sheltered bays!
II. Marine Erosion (4 Modes), Littoral Drift Transport & Deposition
1. Hydraulic Action (Quarrying)
- Breaking waves slam tons of water into rock
- Compresses trapped air inside cliff joints
- Explosive decompression shatters rock blocks
2. Corrasion (Abrasion)
- Waves hurl pebbles, shingle & boulders
- Like artillery against base of sea cliffs
- Excavates basal wave-cut notches
3. Attrition (Rounding)
- Rock fragments ground against each other
- By incessant back-and-forth surf churning
- Turns angular blocks into rounded shingle/sand
4. Solution & Bio-Erosion
- Seawater dissolves coastal limestone & chalk
- Salt-spray wetting-drying tafoni fretting
- Boring molluscs, urchins & algae graze rock
Zig-Zag Beach Drift
- Waves hit shore at an oblique angle ($\theta$)
- Swash carries sand obliquely up beach (↗)
- Backwash pulls straight down by gravity (↓)
Longshore (Littoral) Drift
- Beach Drift + surf-zone Longshore Current
- Transports millions of tons of sand parallel
- To the coast — builds spits & bars (NCERT)
Rip Currents & Littoral Cells
- Piled-up surf water escapes seaward through
- Narrow, fast channels = Rip Currents
- Littoral Cell: River source $\to$ Drift $\to$ Canyon sink
III. High Rocky Coasts vs. Low Sedimentary Coasts (NCERT Core Classification)
2 Coastal Control Factors
FLOOR CONFIG
RETREATING
- Other than wave environment, coasts depend on:
- 1) Configuration of land and sea floor
- 2) Advancing (emerging) vs Retreating (NCERT)
1. High Rocky Coasts (Submerged)
- Submerged coasts with drowned rivers
- Highly irregular & indented coastline
- Fjord inlets & steep hillsides dropping into sea
Rocky Coast: Erosion Dominates
- Shores do NOT show any depositional
- Landforms initially; erosional features dominate
- Waves break with great force shaping cliffs
Wave-Cut vs. Wave-Built
- Receding cliff leaves a Wave-Cut Platform
- Debris gets ground & carried offshore to form
- A Wave-Built Terrace below water (NCERT)
2. Low Sedimentary Coasts
- Smooth & gently sloping emerged coasts
- Rivers extend length by building coastal plains
- And deltas; land slopes gently into water
Sedimentary: Deposition Rules
- Depositional features dominate (NCERT)
- Breaking waves churn bottom sediments
- Readily builds Bars, Barrier Bars, Spits, Lagoons
Lagoon → Swamp → Plain
- Exact NCERT coastal succession chain!
- Lagoon silts up & turns into a Swamp
- Swamp subsequently turns into a Coastal Plain
IV. Submerged vs. Emerged Coasts & India's West vs. East Coast Duality
Advancing vs. Retreating
EMERGING ↑
SUBMERGING ↓
- Advancing (Emerging): Uplift or progradation
- Retreating (Submerging): Subsidence or
- Post-glacial eustatic sea-level rise
Ria, Fjord & Dalmatian Coasts
- Ria: Drowned V-shaped river valley (⊥ coast)
- Fjord: Drowned U-shaped glacial trough
- Dalmatian: Drowned longitudinal folds (∥ coast)
Raised Marine Terraces
- Tectonic uplift or glacio-isostatic rebound
- Lifts old wave-cut platforms & beaches
- Above high-tide mark as stepped benches
West Coast of India (NCERT)
- West coast of our country is a
- High rocky retreating coast (NCERT Box)
- Erosional forms dominate (Konkan/Karwar)
East Coast of India (NCERT)
- East coast of India is a
- Low sedimentary coast (NCERT Box)
- Depositional forms dominate (Coromandel/Utkal)
Natural Harbours vs. Deltas
HARBOURS
BARS & DELTAS
- Submerged West: Deep natural ports (Mumbai, Marmagao, Karwar, Kochi)
- Emergent East: Shallow shelf & sandbars (Chennai artificial port)
Master Coastal Matrix
- Establishes Wave & Coastal framework
- Links directly to Realm 57 (Coastal Landforms)
- Cliffs, Caves & Stacks vs Beaches, Spits & Bars
Core Distinctions
• High, Rocky Coasts (Submerged / Retreating): Drowned rivers, highly irregular and indented coastline, steep hillsides drop sharply into water, shores show no depositional landforms initially; erosional features dominate (Cliffs, Wave-Cut Platforms, Wave-Built Terraces).
• Low, Smooth Sedimentary Coasts (Emerged / Advancing): Rivers extend length by building coastal plains and deltas, smooth coastline with lagoons and tidal creeks, gentle land slope, marshes and swamps abound, depositional features dominate (Bars, Barrier Bars, Spits, Lagoons).
"The west coast of our country is a high rocky retreating coast. Erosional forms dominate in the west coast. The east coast of India is a low sedimentary coast. Depositional forms dominate in the east coast." (Note: The Malabar coast in Kerala is an exception on the west coast, showing emergent features like Kayals/backwaters).
3. Wave-Cut Platform vs. Wave-Built Terrace (NCERT)As cliffs recede under constant wave pounding, they leave a rocky, gently sloping Wave-Cut Platform directly in front of the sea cliff. The material eroded off the cliff is ground into small fragments, carried offshore, and deposited below the low-water mark as a Wave-Built Terrace.
Waves & Coastal Matrix
NCERT Chapter 7 Master Comparison