Laserfiche WebLink
<br />I <br /> <br />I <br /> <br />-11- <br /> <br />Tech.u.co...t StuckM <br /> <br />I <br /> <br />Water surface profile deterreinations were made using standard SCS <br /> <br />I <br /> <br />automatic data processing progr~.5 to establish elevation-discharge <br /> <br />I <br /> <br />relationships. There are no streamflaw records for Sand Creek. Synthe- <br /> <br />tic rainfaIl.runoff evaluation procedures were used in deter~ining the <br /> <br />I <br /> <br />flows for various frequency storms. <br /> <br />R <br /> <br />1\;0 hydrologic analyses were made: (1) using runoff compl\tations <br /> <br />I <br /> <br />based on existing land use and cover conditions in the watershed as of <br /> <br />March 1972. and (2) computations reflecting the runoff conditions with <br /> <br />I <br /> <br />projected developments expected by the year 1990. Information regarding <br /> <br />the tyPe and location of existing and projected land USeS was provided <br /> <br />I <br /> <br />by the El Paso County Planning Department in a study conducted in coopera- <br /> <br />I <br /> <br />tion with this Flood Hazard Analyses. <br /> <br />I <br /> <br />Floo<l r<Jutings Were cornputerprogTal11lJled todeterminepeak-<li5charg e <br /> <br />frequency relationships for both existing and projected conditions. The <br /> <br />I <br /> <br />10-, 25-, 50-, 100-, and SOO-year frequency flood events were analyzed. <br /> <br />I <br /> <br />These floods have an average occurrence ofcnce in the nUl:lber of year sas <br /> <br />indicated. For example, the laO-year flood occurs once in 100 years On <br /> <br />I <br /> <br />the average, and ha~ a one percent chance of being equaled Or exceeded 1n <br /> <br />any given year. <br /> <br />I <br /> <br />I <br />I <br /> <br />I <br /> <br />Water surhc,," profiles ~'ere plotted sho~'ing the elevations of the <br /> <br />selected flood events at each cross section under existing conditions. <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />-12. <br /> <br />Flood lines for the 100- and SOO-year floods were located on the aerial <br />mosaics using the water surface elevations, cross section data, and by <br />interpolating between the cross sections. Recognizing that aerial photo- <br />graphs are subject to displaccITent due to ground relife, the photographic <br />image does not match the delineated flood lines in all areas. l~e location <br />of flood lines at road crossings were computed using the normal openings of <br />bridges and culverts. Because of the multitude of possible events in which <br />sedi~ent and debris could cause blockage of bridges and culverts, these consi- <br />derations were not inCluded in the study. <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />STUVYRESULTS <br /> <br />Ex.u,.ting COIld.{.UOn,s <br /> <br />I <br /> <br />I <br /> <br />Because of urbanization near the Sand Cree~ flood plain, several land use <br />changes have oecurred during the time this study was beinp:conduc ted. Changes <br />whiCh have altered the Ion.' ~^"f'g '1 ^ I d .. d <br />~..~ ~~ ~ ur~ i~n inc u e graU1ng, roa crossings, and <br />channellT.odification. Maps, drawings, and other technical data labeled Existing <br />Cvnditi~a are valid as of March 1972. The effects of new road crossings, con- <br />structed between March and ~ovember 1972, were inCluded in the hydraulic studies. <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />ForplanninJ<andfloodzoneregulationl'"Tposes,theIOO_yearfloodis used <br />locally as the basI' flood. Floodsofhigherfrequency,suchastheSOO_year <br />flood, are also considered in the planning and management of flood-prone areas. <br />The 100-year and SOO-year events were chosen for delineation on the flood hazard <br />maps. In many instances the laO-and SOO-year floods will appear as one lin eOn <br />them,,!,s. This is due to the topographic relief and slight difference inclevat ion <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br />