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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />14 <br /> <br />SUMMARY <br /> <br />graphically shown on the drawings. <br /> <br />Floodways have also been computed for each stream. A floodway <br /> <br /> <br />represents that part of the flood plain which is required to pass <br /> <br /> <br />a 100-year flood event without raising the flood profile more than <br /> <br /> <br />an acceptable amount and which represents hazards to personal <br /> <br /> <br />safety and welfare. In this study, the floodway represents that <br /> <br /> <br />portion of the flood plain where the 100-year flood velocities <br /> <br /> <br />exceed 2 to 3 feet per second or the water surface profile would <br /> <br /> <br />not increase more than 0.5 feet after encroachment. Floodway <br /> <br /> <br />widths, representing the limits of encroachment into the flood- <br /> <br /> <br />plain at each point in the stream, are tabulated in Tables 6 <br /> <br /> <br />through 9. The water surface elevations to be expected after <br /> <br /> <br />encroachment are also tabulated. <br /> <br />This report has identified the probable flooding limits of the <br /> <br /> <br />100-year flood. As mentioned previously, floods of greater <br /> <br /> <br />magnitude can occur and flooding beyond the extent of the limits <br /> <br /> <br />shown in the report can also occur due to other factors, such as <br /> <br /> <br />tributary flow and new developments within the flood plain and <br /> <br /> <br />basin not presently anticipated. The replacement of some key <br /> <br /> <br />crossing structures with crossings that will pass the 100-year <br /> <br /> <br />flood would eliminate much of the potential road crossing damage. <br /> <br /> <br />Both structural and non-structural methods may be used to alleviate <br /> <br /> <br />the flood problems. The non-structural measures consist of flood <br /> <br /> <br />proofing, building permits, land use regulations and flood plain <br /> <br /> <br />zoning. <br /> <br />Flood Velocities <br /> <br />Presently the four streams are considered to have a moderate to <br /> <br /> <br />low flood damage potential. The preservation and protection of <br /> <br /> <br />the flood plains and adjoining lands will serve to maintain and <br /> <br /> <br />even reduce the present flood hazard. <br /> <br />Average flow velocitiees during a 100-year flood for each creek <br /> <br /> <br />are provided on the Flood Hazard Area Delineation Drawings. The <br /> <br /> <br />channel velocities would average between 7 to 11 feet per second <br /> <br /> <br />for a 100-year event in the four study areas. OVerbank velocities <br /> <br /> <br />would average between 1 to 5 feet per second in the study areas. <br /> <br />Water flowing at a rate of 6 to 8 feet per second or greater will <br /> <br /> <br />cause severe erosion of strearnbanks and is capable of transporting <br /> <br /> <br />large rocks. Velocities in the range of 6 to 8 feet per second <br /> <br /> <br />could erode fill around bridge abutments. Water flowing at about <br /> <br /> <br />2 feet per second or less will deposit debris and silt. <br />