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<br />230 <br /> <br />c. H. THEILlNG <br /> <br />f---- PRE-DAM ----I <br /> <br />POST.DAM <br /> <br />E <br />r-... <br />....: <br />C\J <br />E <br />0 <br />U: <br />c <br />.Q ,1 <br />Cii <br />'5 .2 <br />Q) <br />0 <br /> -3 <br /> ,4 <br /> <br /> <br />1890 1930 <br /> <br />1940 <br /> <br />1950 <br /> <br />1960 <br /> <br />1970 <br /> <br />19BD <br /> <br />1990 <br /> <br />Year <br /> <br />Figure 2. Long-term monthly average deviation from the elevation necessary to maintain navigation (127,7 m) at the confluence of the <br />Illinois and Mississippi Rivers <br /> <br />Backwater isolation projects <br />Projects isolating backwaters (29 locations indicated by circles in Figure I) are designed to reduce <br />sediment inputs and allow water level manipulations. Projects usually include levee construction, dredging <br />and installing water control structures. Pumps are installed in projects where complete dewatering of <br /> <br /> <br />Figure 3. Example of introduced flow habitat rehabilitation and enhancement projects <br />