Laserfiche WebLink
<br />38 <br /> <br />Step 3 - Obta i n stage-frequency _<::~!,_ves_f()!,__e_ach.--,^~a.ch_!~()Ill.J1y~I^olQ'Li_c! <br />~draulic analysis <br /> <br />As an input to BCA, flood hazard areas under existing and pro- <br /> <br />jected future development conditions must be defined. The magnitude <br /> <br />of potential damage and the cost of preventive and corrective measures <br /> <br />all depend on the estimates of flood flows and flood plain limits and <br /> <br />the most reliable techniques consistent with the scope of the project <br />and the basic data available should be utilized in the hydrologic and <br /> <br />hydraulic analyses. <br /> <br />The BCA requires the computation of the flood hydrology for <br /> <br />existing and future tributary basin conditions for a range of recur- <br /> <br />rence intervals. The recurrence intervals should be chosen to give a <br /> <br />representative spread in the peak flows, i.e., low, medium and high. <br /> <br />The difference between existing and future hydl^ology reveals the <br /> <br />hydrologic effect of urbanization. <br /> <br />Development of the future hydrology will require estimation of <br /> <br />the future land development in the tributary basin. Existing land use <br /> <br />plans should be consJlted. If they are not available, the engineer <br /> <br />must make his own prediction, perhaps with the help of local planners <br /> <br />who are familiar with the existing development, local subdivis'on regu- <br /> <br />lations, community preferences and other factors that will affect the <br /> <br />type of development. <br /> <br />It must be recognized that the flood hazard for each year is a <br /> <br />function of the tributary basin and flood plain development for that <br /> <br />year. The most accurate assessment of the future hazards will therefore <br /> <br />discount to the present year-by-year development of both the tributary <br /> <br />basin and the flood plain area. It is not ~ormally practical, however, <br /> <br />to make this assessment for each year 0& the planning period. <br />