Some Types of Coastlines A closer look at: Estuaries, Deltas and Barrier Islands

Estuary An estuary is a partly enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with tidal influences from the sea /ocean

Why are estuaries important? They are very productive ecosystems which provide habitats for wildlife To find shelter To find food As breeding grounds

Fig 20.22

Unique ecosystem: Salt marsh

Mangroves

Oyster bars

Mud flats

Horseshoe crab

Blue crab

Estuary Types (4) 1 Drowned river valley – Chesapeake

Ancient river channel is on the east side of the Bay.

Other Estuaries Bar-built – Sand bar blocks river Fjord – Flooded Glacial valley Tectonic – Land moved via regional tectonic activity

Bar Built Estuary

(sand) bar built estuary, Cape Hatteras NC

Fjord

Greenland fjords from satellite

Glaciers (depositional) As huge continental glaciers melt they leave behind sediment called moraines.

Tectonic Estuary

Baja Peninsula from satellite

Deltas Rivers deposit sediment at coast If more fluvial influence than ocean influence Bird’s foot delta If more ocean influence than river influence Arcuate delta FIG b

Nile River empties into the Mediterranean Sea Arc shaped delta, ocean forces dominates, think longshore transport reshaping the front edge

Mississippi Delta

Barrier Islands Detached linear islands of sand that run parallel to the shore Backed by a bay, lagoon, marsh Built by waves, wind and tides ier.html

Shape and Size Barrier islands occur in chains Chains are separated by inlets Storms produce inlets Tides keep them open Waves transport sediment that fills them in Width of the island is determined by amount of sediment supply

4000 km barrier islands on east coast and gulf coast

New Jersey Barrier Islands

s2005/photosets-santarosa.html

Origin of Barrier Islands At the end of the last Ice Age, sea level was a the edge of the continental shelf. The climate was much colder. Large dunes formed a beach ridge and were the natural shoreline

As sea level began to rise, the dunes were breached as the waves washed over them and a lagoon or bay began to fill in behind them. The beach ridge becomes a barrier island backed by a bay or lagoon

The barrier system migrates landward across the shelf as sea level continues to rise

Rising sea level pushes barrier island landward

s2005/photosets-santarosa.html

Oyster shells exposed here have been found to be 8000 years old. When they were alive this was the sound side of the barrier island

Ocean City in Winter

. From the period 2014 to 2044 at least 9 million cubic meters of sand will be required to maintain Ocean City beaches.

Interesting … There have been 16 sets of barrier islands in the past 2 million years. They come and go with the rise and fall of sea level during ice ages.

The Future of Barrier Islands Barrier islands need new sand input to continue to grow and rising sea level to keep the lagoon from filling with sand So, barrier islands may eventually disappear

Fig Oops, shouldn’t have put the house there (part 13)

Cape Hatteras Lighthouse (before)

Fig 20.C (after)

Hard stabilization Groin and groin field Perpendicular to shore Traps sand between groins Interrupts longshore current Jetty similar Built to protect harbor entrance Sand on upcurrent side

Breakwater Parallel to shore Offshore Deposition behind breakwater

Seawall Built on beach Parallel to beach Erosion enhanced seaward of wall Seawall destroyed Beach narrowed Fig

Alternatives to hard stabilization Limit construction near shore Relocate businesses/homes destroyed by wave erosion Beach replenishment

End of Chapter 11: The Coast: Beaches and Shoreline Processes