Laserfiche WebLink
<br />. <br /> <br />For each stream studied In detal I, the boundaries of the 100- <br />year and the 500-year flood have been del ineated on the Flood <br />Insurance Rate Maps using the flood elevations determined at <br />each cross section; between cross sections, the boundaries were <br />extrapolated using topographic maps at a scale of 1:24,000 <br />with a contour interval of 40 feet (Reference 21) or in limited <br />portions of the County topographic maps at a scale of 1:600 or <br />1: 1,200 with a contour interval of 2 feet (Reference 28 and 5 <br />respectively). In cases where the 100-year and the 500-year <br />flood boundaries are close together, only the lOa-year boundary <br />has been shown. <br /> <br />For each stream studied by the approximate method, the boundaries <br />of the lOa-year flood have been del ineated on the Flood Insurance <br />Rate Maps using the flood elevations approximated by the re- <br />gression .equations described in the Hydraulic Anaiysis section <br />of this report. <br /> <br />Areas subject to shal low flooding where a clearly defined channel <br />does not exist and where the path of flooding is unpredictable <br />and indeterminate are included in Zone B on Exhibit 2. <br /> <br />Smal I areas within the flood boundaries may I ie above the flood <br />elevations and therefore not be subject to flooding; owing to <br />limitations of topographic information and the map scale, such <br />areas are not shown. <br /> <br />4.2 Proposed Floodways <br /> <br />. <br /> <br />Encroachment on flood plains, such as artificial fi I I, reduces the <br />flood carrying capacity and increased flood heights, thus increas- <br />ing flood hazards in areas beyond the encroachment itself. One <br />aspect of flood plain management involves balancing the economic <br />gain from flood plain development against the resulting increase <br />in flood hazard. For purposes of the Flood Insurance Program, <br />the concept of a floodway is used as a tool to assist local <br />communities in this aspect of flood plain management. Under this <br />concept, the area of the lOa-year flood is divided into a pro- <br />posed floodway and a floodway fringe. The floodway is the channel <br />of a stream plus any adjacent flood plain areas that must be kept <br />free of encroachment in order that the laO-year flood be carried <br />without substantial increases in flood heights. Criteria adopted <br />by the Federal Insurance Administration I imit such increases in <br />flood heights to 1.0 foot, provided that hazardous velocites are <br />not produced. The floodways in this report are proposed to local <br />agencies as minimum standards that can be adopted or that can be <br />used as a basis for additional studies. <br /> <br />18 <br />