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<br /> <br />Wetlands in riverine and coastal areas have <br />especially complex hydrological interactions <br />because they are subject to periodic water-level <br />changes, Some wetlands in coastal areas are <br />affected by very predictable tidal cycles, Other <br />coastal wetlands and riverine wetlands are more <br />affected by seasonal water-level changes and by <br />flooding. The combined effects of precipitation, <br />evapotranspiration, and interaction with surface <br />water and ground water result in a pattern of <br />water depths in wetlands that is distinctive. <br />Hydroperiod is a term commonly used in <br />wetland science that refers to the amplitude and <br />frequency of water-level fluctuations, Hydro- <br />period affects all wetland characteristics, including <br />the type of vegetation, nutrient cycling, and the <br />types of invertebrates, fish, and bird species <br />present. <br /> <br /> <br />A <br /> <br />Line of equal <br />hydraulic <br />head <br /> <br />COMPLEX FLOW FIELDS <br />Area favorable for <br />wetland formation <br /> <br />Direction of <br />ground-water <br />flow <br /> <br /> <br />B <br /> <br />Land surface <br /> <br />Areas favorable for <br />wetland formation water ~~e_ _1__ - '\-- <br />SEEPAGE FACE '" V~----~---l \\.....v- <br />BREAK IN SLO~a II \ \ <br /> <br />_--- I <br />-- -\ <br />Dir ctionlf gr7nd-water flow <br /> <br />, <br /> <br /> <br />c <br /> <br />Wetland <br /> <br />Land surface <br /> <br />..!'V2..t~~ble <br />-- <br /> <br /> <br />---- <br /> <br />D <br /> <br />Wetland <br /> <br /> <br />Land surface <br /> <br />\'3'0\8 __ <br />/~.;."~~ <br /> <br />Direction of ground-water flow <br /> <br />Figure 17, The source of water to wetlands can be <br />from ground-water discharge where the land surface <br />is underlain by complex ground-water flow fields (A), <br />from ground-water discharge at seepage faces and at <br />breaks in slope of the water table (B), from streams (C), <br />and from precipitation in cases where wetlands have no <br />stream inflow and ground-water gradients slope away <br />from the wetland (0), <br /> <br />20 <br />