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<br /> <br />COASTAL TERRAIN <br /> <br />Coastal terrain, such as that along the east- <br />central and southern coasts of the United States, <br />extends from inland scarps and terraces to the <br />ocean (area C of the conceptual landscape, <br />Figure 2). This terrain is characterized by <br />(1) low scarps and terraces that were formed when <br />the ocean was higher than at present; (2) streams, <br />estuaries, and lagoons that are affected by tides; <br />(3) ponds that are commonly associated with <br />coastal sand dunes; and (4) barrier islands. <br />Wetlands cover extensive areas in some coastal <br />terrains (see Figure 18). <br />The interaction of ground water and surface <br />water in coastal terrain is affected by discharge <br />of ground water from regional flow systems and <br />from local flow systems associated with scarps and <br />terraces (Figure 23), evapotranspiration, and tidal <br />flooding. The local flow systems associated with <br />scarps and terraces are caused by the configura- <br />tion of the water table near these features (see <br />Box J). Where the water table has a downward <br />break in slope near the top of scarps and terraces, <br />downward components of ground-water flow are <br />present; where the water table has an upward <br />break in slope near the base of these features, <br />upward components of ground-water flow are <br />present. <br /> <br /> <br />Regional upland <br />/ <br /> <br />COASTAL TERRAIN <br /> <br />Water <br />table <br />~"'~~......, <br />~..... Terrace <br />. J'- --. ---- -----... Terrace 0 <br />.. 11 C... cean <br />\ . .?" 'J m_______" \ <br />,.JJ \ ----- <br />./ ""- <br />Direction of regional flow / J <br />Direction of local flow <br /> <br />Ffgure 23. In coastal terrain, small local ground-water <br />flow cells associated with terraces overlie more regional <br />ground-water flow systems. In the tidal zone, saline <br />and brackish surface water mixes with freslt ground <br />water from local and regional flow systems. <br /> <br /> <br />Coastal terrain in Maryland. (Photograph by <br />Robert Shedlock.) <br /> <br />---- <br /> <br />Evapotranspiration directly from ground <br />water is widespread in coastal terrain. The land <br />surface is flat and the water table generally is close <br />to land surface; therefore, many plants have root <br />systems deep enough to transpire ground water at <br />nearly the maximum potential rate. The result is <br />that evapotranspiration causes a significant water <br /> <br />42 <br />