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<br />storage basin. After a flood peaks, water is released or pumped out at a [)te that <br />can be handled downstream. Reservoirs are most efficient in deep valleys with <br />more room to store water, or on smaller rivers where there is less water to store. <br />A diversion is a new channel, overflow weir, or tunnel that sends flood <br />waters to a different location, thereby reducing flooding along a watercourse. <br />During IIOrrnallIows, thci water staYIl in the old channel. During flood flows, the <br />stream spills over to the diversion channel or tunnel, which carries the excess <br />water to a lake or another river. . <br />Reservoirs and diversions should be implemented after a thorough <br />watershed analysis that identifies the most effective and efficient location for one <br />or more structures and to ensure that they will not increase flooding somewhere <br />else. Because they involve more than one community and are so expensive, they <br />are typically implemented with the help oestate or federal agencies, such as the <br />U.S. Army-Corps of Engineers or the Natural Resources Conservation Service. <br />To F'md Out More .. .. The U.S. Army Corps of Engineers":the Natural <br />Resources Conservation Service, and state natural or water resources agencies can <br />provide information on construction criteria and funding assistance. In western <br />states, the Bureau of Reclamation can help. <br /> <br />. <br /> <br />Channel and drainage modifications <br />When the conveyance of a channel, drainage ditch, or storm sewer is increased, <br />more water can be carried away. However, care must be taken to not increase a <br />flooding problem doWnstream. <br />Oumnel modifications include making a cltannel wider, deeper, <br />smoother, or straighter. Some smaller channels can be lined with concrete or even <br />enclosed in underground pipes. <br />Dredging is one form of channel modification. It is often too expensive to <br />be practical because the dredged material must be disposed of somewhere and the <br />stream will usually fill back up with sediment in a few years. Dredging is usually <br />undenaken only on larger rivers to maintain a navigation cltannel. <br />Drainage modifications include human-made ditches and storm sewers <br />that help drain areas where the surface drainage system is inadequate or where <br />underground drainageways are s.afer or more attractive than above-ground ones. <br />Drainage and storm sewer projects usually are designed to carry the runoff from <br />smaller, more frequent storms. They are particularly appropriate for depressions <br />and low spots that will not drain naturally. <br />Storm sewer improvements can increase the sewer's capacity or prevent <br />overloading from flooding in certain areas. These measures include installing new <br />sewers, enlarging pipes, modifying storm sewer inlets, and preventing back flow. <br />Street modifications may help because streets in many developments are <br />used as part of the drainage system to convey runoff to a receiving sewer, ditch, <br />or stream. Streets can also be designed to store water from larger, less frequent <br />storms. Allowing water to stand in the streets and then draining them slowly can <br />be more effective and less expensive than building bigger sewers and ditches. <br />To F'md Out More .. .. The U.S. Army Corps of Engineers and the Natural <br />Resources Conservation Service can provide information on projects for larger <br />channels. Public works departments and engineers are the best sources of <br />information on local drainage and sewer projects. <br /> <br />. <br /> <br />. <br /> <br />24 <br />