How and Why does Caustal constraction effect the shorline by distributing the longshore current?

Question

How and Why does Caustal constraction effect the shorline by distributing the longshore current?

Answer 1

The longshore current is a very important part to any coastal area.  The current usually travels south to north and transports sand in the same direction.  This is the main process responsible for coastal erosion as well as accumulation.  It doesnt become apparent how important it is until a Nor' Easter storm (I am from NJ in the USA) or a hurricane hits because those storms normally reverse the longshore current and erode beaches very very severely.  

The longshore current/drift is responsible for every coastal landform...take New Jersey for example, it has barrier islands in the central part of the state, very heavily eroded beaches to the south and a spit (Sandy Hook) to the north.  

What the problem is is that the coast is becoming so over built that our structures are also affecting this current.  When we build a jetty, boardwalk, pier, or groin that runs perpindicular to the shoreline and goes out into the water those structures will cut off the current.  What you get is sand being deposited on the south side (current runs south to north) and then the beach being eroded on the north side.  These structures also affect beaches very far away by cutting off the sand and sediment source right at its source.  Also by building mroei mpervious surfaces as well as more houses and buioldings we effect how water drains in these areas and thus how the currents move.  By far the most devastating stuctures to this current are the jetties groins and other structures that run right out into the water perpindiculair with the shoreline....