Laserfiche WebLink
<br />In cases where the 100- and 500-vear flood houndaries are close <br />together, only the 100-year flood boundary has been shown. <br /> <br />Approximate flood boundaries in some portions of the study area <br />were taken from the Federal Insurance Administration's Flood Hazard <br />Boundan- Map (Reference 12). <br /> <br />Flood boundar ies for the 100- end 500-vear floods are shown on <br />the Flood Boundary and Floodway Map (Exhibit 2). <br /> <br />Small areas within the flood houndaries may lie ahove the flood <br />elevations and, therefore, not be Rubject to floodinq; owinQ to <br />limitations of the map scale, such areas are not shown. <br /> <br />4.2 Floodwavs <br /> <br />Encroachment on flood plains, such as artificinl fill, reduces <br />the flood-carrying capacity and increases flood heights, thus <br />increasinq flood hazards in areas beyond the encroachment itself. <br />One aspect of flood plain management involves balancinq the economic <br />gain from flood plain development against the re~ultinq incfPase <br />in flood hazard. For purposes of the National Flood Insurance <br />Program, the concept of a floodway is used as a tool to assist <br />local communities in this aspect of flood plain management. Under <br />this conceot, the area of the 100-vear flood is divided into a <br />floodway and a floodway fringe. The floodway is the channel of <br />a stream, plus any adjacent flood plain areas, that must he kept <br />free of encroachment in order that the 100-year flood be carried <br />without substantial increases in flood heiqhts. As minimum stano- <br />ards, the Federal Insurance Administration limits such increases <br />in flood heiahts to 1.0 foot, orovide<'l that hazardous velocities <br />are not produced. <br /> <br />The floodway presented in this study was comouted on the hasis <br />of equal-conveyance reduction from each side of the flood plain. <br /> <br />The results of these computations are tabulated at selected cross <br />sections for the stream segment for which a floodway is computed <br />(Table 2). <br /> <br />As shown on the Flood Boundarv and Floodwav Map (Exhibit 2), the <br />floodway boundaries were determined at cross sections; between <br />cross sections, the boundaries were interpolated. In cases where <br />the floodway and 100-year flood boundaries are close together, <br />only the floodway boundary has been shown. <br /> <br />The area between the floodway and the boundary of the 100-year <br />flood is termed the floodway frinqe. The floodwav frinqe thus <br /> <br />9 <br />