Coastal Environments


The morphology of coasts and near-shore sediments is governed by the hydrodynamics of the fluids dominant (water and wind) in the system. Broadly speaking, we can talk of Wave-dominated coasts, Tide-dominated coasts and River (Fluvial)-dominated coasts (Deltas). Deltas and Estuaries are described in separate sections.

Coastal Depositional Systems:

Erosional Coast : Cliffs Constructional Coast: Beach

 


Wave-Dominated Coasts

 

 
 

 

Beaches

Characteristics of Beach System

Beaches form when sand or gravel is available and wave energy is significant, and result in low-angle cross-stratified deposits and cross strata formed by wave ripples.

Beaches can either be connected directly to the land and form strand plains or chenier plains (the latter consisting of beach ridges separated by muds), or be separated by lagoons or tidal basins (the latter consisting of tidal channels, tidal flats, and salt marshes) and form either spits or barrier islands.

Coastal dunes are common features associated with sandy beaches.

Washovers can form during major storm events, and are found elsewhere across barrier islands.

Barrier islands are especially prolific in environments with a high wave energy and a limited tidal range, that have experienced transgression (relative sea-level rise).

The tidal inlets between barrier islands are sites of deep erosional scour and are associated with flood-tidal deltas (lagoonal side) and ebb-tidal deltas (seaward side).

Beach and Coastal setting (Strong Wave Action) Beach and Coastal setting (Wave and Tidal Action)

 

Example of modern Beach/Dune environments from Maine, USA. The Atlantic coast here is wave-dominated with strong winds and common storm influence.

Coastal Sand Dune Environments

DUNES

D1 Frontal Dunes - The most seaward ridge of sand in the sand dune system. The frontal dune may or may not be naturally varying water depths and currents influenced by the ebb and flood of tides. part, The frontal dune may consist in part or in whole, of artificial fill. In areas where smaller ridges of sand are forming in front of an established dune ridge, the frontal dune may include more than one ridge.

D2 Back Dunes - Sand dunes or sand flats that lie landward of the frontal dune or a low-energy beach. Back dunes include those areas containing fill over back dune sand or over wetlands adjacent to the sand dune system.

D3 Back Dune Washover Fan - A small delta-like feature or fan that is built in a pond, on a salt marsh, or on a back dune when the sea breaches a frontal dune ridge and invades the landward side of the dunes during severe storms with high waves and tides.

BEACHES

B1 Sand Beach - An accumulation of sandy sediment that is defined on the landward side by the extent of storm wave action. Storm waves may also reach into the dunes at some predomilocations.
On this photo the seaward beach margin is arbitrarily placed offshore near the middle to low-tide position, although the area of wave influence extends waterfarther
seaward. Sand grains are less than 2 millimeters(0.08 inches) in diameter. The beach environment includes all berms, a temporary accumulation of sediment near the high-tide elevation.

B2 Sand and Gravel Beach - Beach consisting of a mixture of sand and gravel (greater than 2 mm, 0.08 in.). Commonly, the dominant grain size changes with either beach elevation with little or no sediment cover or position along shore due to physical sorting by waves.

B3 Gravel Beach - Beach with most abundant grains greater than 2 mm, 0.08 in.).

B4 Boulder Beach - Gravel beach which includes boulders (greater than 25 cm, 10 in.).

B5 Low-Energy Beach - Beach sheltered from direct wave approach by land or extensive intertidal shoals. coastal above adjacent sand dune areas. Low energy beaches contain a variety of grain sizes and are commonly found along tidal inlets adjacent to ocean-facing, high-energy beaches (B1-B4).

CHANNELS

C1 Tidal Channel - Subtidal and intertidal channels with varying water depths and currents influenced by the ebb and flood of tides.

C2 Dredged Channel - Tidal channel which has had sediment and/or rock removed from underwater locations in order to create a navigable channel or basin.

C3 Channel Bar, Tidal Delta - Sedimentary deposits of variable grain size in and adjacent to tidal channels. Flood tidal deltas are common on the landward side of inlets in the sand dune system where the channel widens.

C4 Supratidal Channel - Channels above the high-tide linethat lead to intertidal elevations. Supratidal channels carry freshwater flow and may be ephemeral.

COASTAL WETLANDS AND SHOALS

M1 High Salt Marsh - Tidal wetlands dominated by salt meadow hay (Spartina patens) which fringe the edges of estuaries. Sediments are predominantly a mix of mud, sand and peat. The elevation of high salt marshes is approximately mean high water.

M2 Low Salt Marsh - Tidal wetlands dominated by saltwater cordgrass (Spartina alterniflora) which fringe the edges of estuaries. The elevation of low salt marshes ranges from mean sea level to mean high water. Sediments are predominantly mud and sand.

M3 Freshwater Marsh - Areas with hydric soils and water-tolerant vegetation which are frequently inundated or saturated by low salinity surface or ground water .

P1 Freshwater Pond - A natural body of standing fresh water occupying a small surface depression.

L1 Ledge - Intertidal and subtidal outcrops of resistant rock with little or no sediment cover.

Wash-Over and Storm Deposits

Dune Erosion on Constructional Coast due to Storm Surge Washover/Storm Deposition Washover/Storm Deposition

 

More Beach Photos

More Barrier Island Photos

Tidal vs. wave-dominated morphology

 


Tide-Dominated Coasts

 


Coastal Facies in Vertical Sequences

Facies and Facies Associations from Coastal Depositional Systems

 

   

 

 

 

 


Glossary

Chenier Plains

Relict Beach ridges separated by muds

 

Depositional Environments: Main