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<br />Flooded Areas and Flood Damage, The study areas subject <br /> <br /> <br />to flooding by the lOO- and 500-year floods are shown on Plate 4 <br /> <br /> <br />through 8. Plate 3 is an index map showing the relative location <br /> <br /> <br />of the flooded area plates in the study area. Limits of the over- <br /> <br /> <br />flow areas may vary from those shown on the Flooded Area plates <br /> <br /> <br />because of variation between map contours presented herein and <br /> <br /> <br />actual locations of ground contours. <br /> <br /> <br />Depths of flow for any location along a stream can be <br /> <br /> <br />estimated from the flood profiles shown on Plates 10 through l6 and <br /> <br /> <br />from the flood elevation lines shown on the flooded area plates. <br /> <br /> <br />Floodwater elevations determined in any particular area are not <br /> <br /> <br />always indicative of the depths actually attained, often flood- <br /> <br /> <br />water becomes isolated and trapped in overbank areas resulting in <br /> <br /> <br />depths greater than those shown on the various plates and table$. <br /> <br /> <br />Obstructions. Maintaining the channel and overbank capac- <br /> <br /> <br />ity .of a stream to convey floodwater through the community without <br /> <br /> <br />causing serious flood damage should be of major concern. Restrict- <br /> <br /> <br />ing the floodway by bridges and their approach embankments, roadbeds, <br /> <br /> <br />levees, or otherwise changing channel and overbank capacities will <br /> <br /> <br />impede floodflows and cause greater backwater depths with conse- <br /> <br /> <br />quent increase in flooded areas. The growth of vegetation, obstruc- <br /> <br /> <br />tive new developments or land filling in a stream's f100dway can <br /> <br /> <br />be a major factor in multiplying the adverse effects described. For <br /> <br /> <br />study purposes herein, it has been assumed that limited clogging of <br /> <br /> <br />bridges and culverts will occur and that they would stand intact <br /> <br /> <br />during the 100- and SOO-year frequency floods. Significant changes <br /> <br /> <br />in this premise could alter the flood crests and flood limits shown <br /> <br /> <br />in related plates and tables. <br /> <br /> <br />Ysidrio Avenue bridge has several wooden piers that are <br /> <br /> <br />close together and may be subject to severe clogging causing in- <br /> <br /> <br />creased backwater that may inundate some residences currently not <br /> <br /> <br />in the 100-year flood plains. The Ysidrio Avenue bridge is very <br /> <br />l4 <br /> <br />