Laserfiche WebLink
<br />-11- <br /> <br />-12- <br /> <br />T,,-chy..{cal. S-tu.rli~J, <br /> <br />Flood lines for the 100- and SOO-year floods were located On the aerial <br />rnosaicsu.singthewatersurfaceelevations,crosssectiond"t",andby <br />interpolating between the cross sections. Recognizin~ that aerial photo- <br />graphs are subject to displacement due to ground relife, the photographic <br />irnag" does not match the delineated flood lines in all areas. Tho location <br />of flood lines at road crossings Were computed using the normal openings of <br />bridges and culverts. Becauseofthemultltudeofpos.ibleeventsinwhich <br />sediment and debris could cause blockage of bridges and culverts, these consi- <br />derations werc not included in the study. <br /> <br />Water surface profile determinations were mnde using standard SCS <br />automatic data processing programs to establish elevation-di,chargc <br />relationships. There are nO streamflow records for Sand Creek. Synthe- <br />tic rainfall-runoff evaluation procedures were used in determining the <br />flows for various frequency storms. <br /> <br />Two hydrologic analyses were made: (1) using runoff conputations <br />based on existing land use and cover conditions in the watershed as of <br />March i972, and (2) computations reflecting the runoff conditions with <br />projecteddeveloprnentse:<pectedbytheyearl990. Informationregarding <br />the type and location of existing and projected land uses was provided <br />by the E1 Paso County P1annin~ Department in a study conducted in coopera- <br />tion with this Flood Hazard Analyses. <br /> <br />STUVYRfSULTS <br /> <br />Ex.h.tA.ng COJ'trlitimu; <br /> <br />Becau.se of urbanization near the Sand Creek flood plain, several land USe <br />changes have occurreJ during the tirne this study was beingconJltC ted. ChanR.es <br /> <br />Flovo.l .outln&~ ~ef" "omp"ter p,'ogra"ur.e<1 to uderllliJle peak.,Jh~har!:e <br /> <br />;,'~.ich ',.,.... "l.~.."'d .,'". ,n_~ ~~~, , . d d. d <br />u. ~ ,~.~. c, . ~,,~ ~VH 'lgura ion InC,U e gra lng, roa crossings, and <br /> <br />fTequencyrelationshipSforbothexistingandprojectedconditions. The <br />10-, 25-, 50-, 100-, and sOO-year froqueney flood events were analy:ed. <br />lhese flood. have an average occurrence of once in the number of years as <br />Indicated. For example, the laO-year flood occurs once in 100 years on <br />the average, and has a One percent chance ot helng equaled or exceeded lr. <br />any giwn year. <br /> <br />channel modification. Map~, drawings, and other technical data labeled Exi8tir.~ <br />C'onditi""s are valid as of ~1arch 1972. TIle effecb of new road crossings, con- <br />structed bet\Oeen ~!arch an" NOV,,"ber 1972, ;,'ere included in the hydraulic stu"ics. <br /> <br />~'"ter surface prof! les ....(.re p lotted ~ho....iny' the e I evat j ons of the <br />selected flood event, at each crnss section under existing conditions. <br /> <br />Forphnnlng and flood zone regulation purposes, the lOa-year flood is uscd <br />locally as the base flood. flOods of higher frcquency, such as the SOO-year <br />flood,arealsoconsideredintheplanningandmanagementofflooc_prone areas. <br />The lOO-yearand SDO-rear cvents Were chosen for delineation unt hefloodha;:ard <br />maps. In many instances the 100_ and SOO-year floods will appear as one line o~ <br />the maps. This is due to the topogr~phic relief and slight diffcrence in elevation <br /> <br />I <br />