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<br />Lakes <br /> <br />Lakes, both natural and human made, <br />are present in many different parts of the land- <br />scape and can have complex ground-water-flow <br />systems associated with them. Lakes interact with <br />ground water in one of three basic ways: some <br />receive ground-water inflow throughout their <br />entire bed; some have seepage loss to ground <br />water throughout their entire bed; and others, <br /> <br />A <br /> <br />High <br /> <br />Infr uenthi h <br /> <br />Fre uenthi h <br /> <br />z <br />Q <br />~ <br />~ <br />w <br /> <br />Minimumavera e <br /> <br />Fr uenllow <br /> <br />Infre uentlow <br /> <br />Littoral Zone , <br /> <br />L~ <br /> <br />B <br /> <br />High <br /> <br />z <br />o <br />~ <br />~ <br />w <br /> <br /> <br />Infrequent high \ <br />\ <br />Frequent high <br /> <br />Minimum average <br /> <br />Low <br />o <br /> <br />perhaps most lakes, receive ground-water inflow <br />through part of their bed and have seepage loss to <br />ground water through other parts. Lowering of <br />lake levels as a result of ground-water pumping <br />can affect the ecosystems supported by the lake <br />(Figure 16), diminish lakefront esthetics, and have <br />negative effects on shoreline structures such as <br />docks. <br /> <br /> <br />-g <br />i <br />I <br />0::: <br /> <br />rr <br />.,~ <br /> <br />/ <br /> <br /> <br />/ <br />Frequenllow <br /> <br />20 40 60 80 <br />PERCENTAGE OF TIME LAKE LEVELS ARE EXCEEDED <br /> <br />'00 <br /> <br />Figure 16. Setting minimum water levels in Florida lakes. (Modified from McGrail and others, 1998.) <br /> <br />As part of efforts to prevent significant undesirable environmental consequences from water-resources develop- <br />ment, water-management agencies in Florida are defining minimum flows and water levels for priority surface <br />waters and aquifers in the State. For lakes, the minimum flows and water levels describe a hydrologic regime that is <br />less than the historical or optimal one but allows for prudent water use while protecting critical lake functions. As <br />an example, five possible minimum water levels defined for a lake are shown in A. All elevation and a percentage of <br />time the level is exceeded characterize each of these levels. The upper curve in B shows the percentage of the time that <br />the lake is historically above each corresponding level. The goal is to ensure that water withdrawals and other water- <br />resource management actions continue to allow the lake water levels to be at or above the minimum levels shown by <br />the lower curve in B for the percentage of time shown. <br /> <br />40 <br />