# Travel >> Transportation >> Boats

Why Beaches Accumulate Sand: The 5 Processes That Build Shorelines

Beaches are sediment budgets in dynamic equilibrium. Five processes deposit material; erosion removes it. Net accumulation = deposition > erosion.

1. Wave Onshore Transport (Swash/Backwash Asymmetry)

Waves break → swash (uprush) moves sediment landward faster than backwash returns it. Net onshore flux. Coarser grains deposit higher (steeper swash); finer grains stay suspended longer.

2. Longshore Drift (Littoral Drift)

Oblique wave approach → alongshore current (longshore current). Sediment zigzags downcoast. Groins, jetties, headlands interrupt drift → updrift accretion, downdrift erosion. Classic "sand starvation" problem.

3. Aeolian (Wind) Transport

Dry beach sand → saltation → foredune formation. Vegetation (sea oats, ammophila) traps sand → dune growth. Dunes = sand reservoir for storm recovery. Blowouts = dune breaches.

4. Tidal Pumping

Flood tide transports sediment over intertidal flats; ebb tide returns less. Net landward flux in macrotidal (>4 m range) environments. Tidal creeks import sediment on flood, export less on ebb.

5. Human Placement (Beach Nourishment)

Dredged offshore sand pumped onto beach. US: $1B+/yr (Florida, NJ, NC, CA). Temporary fix—renourishment cycles 5-10 years. Grain size match critical (too fine = muddy; too coarse = steep, uncomfortable).