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<br />HABITAT REHABILITATION <br /> <br />233 <br /> <br /> <br />-l <br />W <br />Z <br />Z <br /><( <br />I <br />U <br />Z <br /><( <br />~ <br /> <br />o Spoil III Land <br /> <br />o Water <br /> <br />. Rock <br /> <br />Figure 6. Schematic diagram of chevron dikes. The width of the flow arrows indicates relative flow distribution in the hydraulically <br />effected areas <br /> <br />Off-bankline revetmentsJFigure 5) were designed to reduce bank stabilization costs and increase habitat <br />diversity in main channel environments. They differ from standard revetment in that the rip-rap is placed <br />several metres away from the bank in areas where there is a gradually sloping river bed. The result is the <br />creation of artificial backwaters adjacent to the main channel. Fish movement is allowed through notches in <br />the revetment. <br />Results were positive from the point that the structures created lentic environments and also maintained <br />the other benefits associated with revetments (Farabee, 1986; Baker et af., 1991). Aquatic habitats between <br />dikes and natural banks are subject to high rates of sedimentation, however, due to their proximity to the <br />main channel. Some have filled with sediments and converted to terrestrial habitats. Observations of off- <br />bankline revetments constructed during three staggered time periods show complete terrestrial conversion in <br />the oldest (20 years), moderate terrestrial conversion with some aquatic area remaining in the next oldest (10 <br />years) and greater than I m depths throughout the newest structures (5 years). The newest structures <br />sometimes support submersed aquatic vegetation (Theiling, pers. obs.), which is rare in channel habitats in <br />the southern reaches of the Upper Mississippi River (Peck and Smart, 1986). A management scenario might <br />entail construction of many structures in stages and the use of prescribed dredging within them to enhance <br />lentic habitat availability and manage plant succession. Alternatively, refined hydraulic design may produce <br />projects that are more self-sustaining. <br /> <br />Chevron dikes <br /> <br />Side-channel closing dikes are used to prevent flow through secondary channels. The goal is to divert flow <br />towards the main channel to maintain high water surface elevations and increase scour in the main channel <br />