COASTAL PROCESSESIntroduction to Watershed

ScienceMerritt College

Marc Epstein, Instructor

The edge of the sea is a strange and beautiful place. All through the long history of Earth it has been an area of unrest where waves have broken heavily against the land, where the tides have pressed forward over the continents, receded, and then returned. For no two days is the shoreline precisely the same. Not only do the tides advance and retreat in their eventual rhythms, but the level of the sea itself is never at rest. It rises or falls as the glaciers melt or grow… Today a little more land may belong to the sea, tomorrow a little less. Always the edge of the sea remains an elusive and indefinable boundary

Rachel Carson

COASTAL SYSTEM COMPONENTS

•Winds

•Weather

•Ocean currents

•Waves

•Climate

•Rocks

•Gravity

THE COASTAL ZONE

•On land - The highest water line that occurs on shore during a storm

•Seaward – Point at which waves can no longer move sediments on the seafloor

ESTUARIES AND THE COAST

• Estuary – Body of Estuary – Body of water along the water along the coastlinecoastline

• Open to the sea Open to the sea effected by tideseffected by tides

• Mix of fresh and Mix of fresh and salt watersalt water

TIDES

• Sea level oscillations (twice each day)

• Caused by gravitational influences of the sun and moon

• Moons influence is double that of the sun

• Partially enclosed waterways have greatest differences in tides

WAVES

•Energy moving through water

•Primarily caused by wind•Waves are not water

moving•Transferring energy from

molecule to molecule•Water molecules move

forward slightly in circular pattern

COASTAL ZONE WAVE MOTION

•Waves of transition – Both energy and water move forward

•Breakers – Wave height exceeds vertical stability

•Slope of shore •Steep = plunging breakers •Shallow = spilling breakers

LANDFORM INTERACTION

• Wave refraction – Results in coastal straightening

• Headlands – Protruding landforms of resistant rock

• Approaching waves focus energy around headlands

• Dissipate energy in coves and bays

SEDIMENT TRANSPORT AT THE SHORELINE

• Longshore or Littoral Current

• Beach Drift – Movement of particles

• Swash – Pushes sediment upslope

• Backwash – Pulls sediment downslope (undertow)

BEACH STABILIZATION

•Construction of groins or jetties

•Causes deposition up-current

•Causes erosion down-current

ESTUARY CLASSIFICATIONS

•Drowned river mouths

•Fjord type – glacier mouths

•Bar-built – barrier islands

•Tectonic processes – indentations from faulting

ESTUARY CIRCULATION

•Wind

•Tidal Flow

•River Flow

•Saltwater Wedge or Tidal Prism

•Zone of Intermixing

ESTUARY TYPES

• Wetland – Water dominates in soil development

• Lagoon – Between barrier island and mainland or shallow estuary isolated from the ocean

• Slough – Shallow where large areas of the bottom are exposed during low tide

• Salt Marsh – Protected from ocean waves

HUMAN IMPACTS ON ESTUARIES

•Flood Control

•Water Diversion

•Water StorageThese actions change the natural

flow of fresh water resulting in changes of the mixing with salt water changing the levels of salinity