MAY2011
Oceanography Ch # 10
THE COAST; BEACHES AND SHORELINE PROCESSES.
10 – 1. Coastal Regions
Shore – Lowest to Highest tide lines
Coast – Absolute farthest point inland affected by the Ocean
Coastline - Boundary between shore and coast.
Beach Terminology

Beach – lowest tide to coastline

Shoreline – water’s edge.
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Nearshore : 1st. breakers to low tide

Foreshore - low tide to high tide
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Backshore – hi tide to coast line
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Offshore – beyond the breakers
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Longshore bars/ Longshore Troughs

Beach – includes Berm and Beach face to longshore bars.
(see p.286)
Beach Composition and Slope relationship
Steep beach face result from coarse grain texture , sediments derived locally.
Flat beach – is covered with silt and mud, transported by streams and longshore
currents
Biological material indicated that there are no rivers
Black to green sand beaches – result from Volcanics
Slope angles range from 24 Deg. (cobble covered) to 9 – 3 Deg (Sand covered) to <1 Deg (Clay
and silt)
10 – 2. Sand movement on Beaches ( See p.288)
Perpendicular – low wave activity. Beach is swash dominated, net sand movement is up
the beach face. High wave activity - beach is dominated by back wash and erosion. Sand bars
are deposited offshore.
Parallel - Sand moves in a zig zag pattern along the coast. Sheet flow indicates Rip
currents, a very fast flow (7 to 8 km/hr.). A surface flow, perpendicular to the beach.
10 – 3. Erosion and Depositional type shores. (See p. 289 & 291)
Both processes are present but one dominates.
Erosional features : Sea caves; blow holes; sea arches, stacks; headlands; terraces; cliffs
and caves.
Depositional features : Sand is moved by longshore currents and redistributed by waves.
Spits; Bay mouth bars; tombolos and Barrier bars.
Lagoons separate the barrier islands from the main land. Peat deposits are associated with the
presence of salt marshes.
Deltas indicate that streams are carrying more sediments than the longshore currents can
redistribute.
Beach Compartments- composed of:
Rivers that supply sand to beach
Beach
Offshore submarine canyons.
Coast Classification.
Shepherd’s classification – Primary non-marine (Drowned, depositional or Tectonic
related)
Secondary marine coast lines.
10 – 4. Emerging and Submerging coastlines – are based on the position of MSL.
Terraces, stranded beach deposits – Emerging; Drowned valleys or sand dunes.
Tectonism or Isostatic adjustment may result in emerging or submerging coasts.
Tectonic Processes include folding, faulting, tilting and subsidence of the earth’s crust.
Crustal Isostatic adjustment can be the result of ice, sediment or volcanic debris removal.
Eustatic rise or drop in MSL may be due to water volume change or change in capacity of the
ocean basin.
Sea level-Greenhouse effect relationship. CO2 in the atm has increased 30% in the last 200
years. Temp increased 0.6 Deg C. in 130 years and MSL up 0.1 inch.
10 – 5. Characteristics of US Coastlines
Changes are due to coastal bedrock, wave activity, tidal range, tectonism, isostatic and eustatic
changes.
Atlantic Coast – Glacial (Drowned) NY to Maine; Barrier Islands to the Carolinas; and Biologic
influenced to Florida
Gulf Coast – Delta (Subsidence)
Pacific – Tectonic uplift and rivers are dammed.
10 – 6. Hard Stabilization
Structures built to protect the coastline: Groins (Groin fields and Rip Rap) / Jetties/ Break
waters and Sea Walls
10 – 7. Alternatives to hard stabilization
Restrict construction
Relocation.
Beach Replenishment (sand is added to the beach). Cost is $5 to $10/cub yard.
Beach replenishment