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<br />II <br />II. <br />II <br />11 <br />il <br />il <br /> <br />:1 <br />:1 <br />I <br />:1 <br />I <br />:1 <br />!I <br />I <br />II <br />:1 <br />:1 <br />11 <br />II <br /> <br />Lower Big Dry Creek Hydrologic Study <br /> <br />designs improve the effectiveness of natural systems rather than negate, replace <br />or ignore them. <br /> <br />8. In New Developments, Attempts Should Be Made to Reduce Storm water Runoff <br />Rates and Pollutant Load Increases After Development to the Maximum Extent <br />Practicable. The perviousness of the site should be maintained, to the extent <br />feasible. The rate of runoff should be slowed. Preference should be given to <br />stormwater management systems that use practices that maximize vegetative and <br />porous land cover. These systems will promote infiltration, filtering and slowing <br />of the runoff. It should be noted that, due to the principle of mass conservation, it <br />is virtually impossible to prevent increases in post-development runoff volumes <br />when an area urbanizes. However, existing stormwater regulations can require <br />control of peak flows to predevelopment levels to a maximum extent achievable. <br />Increased flow volumes may present no flooding problems if the watershed has a <br />positive outfall to a stream or river; however, these volumes may cause problems <br />for a small, enclosed watershed draining to a lake or into streams of limited <br />capacity. Pollution control is best accomplished by implementing a series of <br />measures, which can include source control, minimization of directly connected <br />impervious areas, and construction of on-site and regional facilities, to control <br />both runoff and pollution. <br /> <br />9. The Storm water Management System Should Be Designed Beginning With the <br />Outlet or Point of Outflow From the Project, Giving Full Consideration to <br />Downstream Effects and the Effects of Off-Site Flows Entering the System. <br />The downstream conveyance system should be evaluated to ensure that it has <br />sufficient capacity to accept design discharges without adverse backwater or <br />downstream impacts such as flooding, stream bank erosion, and sediment <br />deposition. In addition, the design of a drainage system should take into account <br />the runoff from upstream sites, recognizing their urban development potential. <br /> <br />10. The Storm water Management System Should Receive Regular Maintenance. <br />Failure to provide proper maintenance reduces both the hydraulic capacity and <br />pollutant removal efficiency of the system. The key to effective maintenance is <br />clear assignment of responsibilities to an established agency and a regular <br />schedule of inspections to determine maintenance needs and to ensure that <br />required maintenance is done. Local maintenance capabilities should be a <br />consideration when selecting specific design criteria for a given site or project. <br /> <br />11. Floodplains Need to Be Preserved Whenever Feasible and Practicable. Nature <br />has claimed a prescriptive easement for floods, via its floodplains, that cannot be <br />denied without public and private cost. Floodplains often provide a natural order <br />to the land sw1ace with drainageways that serve as outfalls for urban drainage, <br />bottomland for wildlife habitat, riparian corridors, and specialized vegetation. <br />Floodplain encroachment can occur only after competent engineering and <br />planning have been conducted to assure that flow capacity is maintained, risks of <br />flooding are defined and risks to life and property are strictly minimized. <br /> <br />971-179.092 <br />June 2005 <br /> <br />Wright Water Engineers, Inc. <br /> <br />Page 27 <br />