Role of Human Activities: Transportation
Shipping has always played a vital role in our nation's economy and it was for that reason that shallow coastal waters were deepened in the 1800s to create or enlarge major ports and harbors that were busy centers of commerce. Abnormally high rates of land loss occur along ship channels and service canals as well as along natural tidal channels that are frequently used as transportation routes. Bow waves of large ships and wakes of smaller vessels alternately raise and lower water levels generating local waves and currents that erode the banks and enlarge the navigation channels. Periodic dredging of the Intracoastal Waterway that stretches from Maine to Texas is necessary because the channel shoals from the material eroded from the banks by bow waves. Even commercial and recreational boating in tidal creeks of coastal marshes can cause bank erosion and enlargement of channels such as those crossing the marshes of the Mississippi Delta and the Eastern Shore of Virginia.
Rates of land loss caused by these artificial processes are typically controlled by the amount of boat traffic, channel age, channel-bank composition, and channel setting. Land loss rates are greatest where boat traffic is high, channels are relatively new, and channel banks are steep and composed of sandy sediments. Land loss rates are also unusually high where channels are narrow and restricted by high banks that cause wave and current energy to be dissipated against the channel banks. As an example, maintenance dredging of a federal anchorage in Wells, Maine has been halted by the State in part because of the wetlands losses associated with the artificially deepened channel.
U.S. Department of the Interior, U.S. Geological Survey
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Last modified: 23:13:02 Sat 12 Jan 2013
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