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<br />program. The basinlilas divided into 29 aubcatchmentareas (secFigure-2,Fage 14) <br />which averaged 300 acres in size. The model computed the runoff from each suh- <br />catchment and routed the flood through the basin. Runoff hydrographs were <br />developed for each subcatChmcnt based on a step by step accounting of raintall <br />infiltration losses, surface detention and flow concentration times. <br /> <br />The rainfall values for various frequencies were obtained from the <br />National Occanic and Atmospheric Administration's technical publication, <br />"Atlas 2; Volume III, Colorado"precipitation- frequency charts. Aone <br />hour storm duration was chosen as the MOst representative thundersrorm <br />duration for the area. <br /> <br />The"80ulderCountySoilSurvey",publishedbytheSoilConservation <br />Service. was used to estimate rainfall infiltration rates. Ten different <br />soil types are represented in the basin. The infiltration ratcs for tbese <br />soils vary from moderate to slow with tbe greatest percentage being in the <br />moderate range. Minimum infiltration rates of 0.4 to 0.5 inches per hour <br />were selected for each subcatchment based on the soils data. <br /> <br />TIle 5WMM program also ha. the capability to route floods through <br />reservoirs. This waS considered to be a key clement in the hydrologic <br />analysis, since a number of large reftervoirs are present in the upper <br />basin. Basic operation data, spillway sizes, and potential stora~e volumes <br />were obtained for five major reservoirs. Actual design and construction <br />plans from the r.olorado State Engineer's files were reviewed to deter~ine <br />the potential for flood storage in each reservoir. In the final analysis <br />each reservoir was assumed to be full to the level of the normal operation <br />spillway. Floods were routed through the reservoirs based on the surcharge <br />storage available above that elevation. The reservoir storage liIas found to <br />have a substantial effect in reducing peak flows. <br /> <br />D"taileJcompuc..tionsf,,' th"hydroJloJgic i1nalysis..."r" slibiuitte<l to the <br />technical committee as part of the technical addendum. The selected peak <br />flows for Dry Creek No. I at specified design points are presented in <br />Tabl"-4. <br /> <br />31 <br /> <br />, <br />I <br /> <br />TABLE-4 <br />DRY CREEK NO. 1 PEAK <br />(cis) <br /> <br />DISCHARGES <br /> <br />LOCATIOI' <br /> <br />REFERE)lCE <br />LIllE STATION(a) <br /> <br />Qs Ql0 <br /> <br />Q" <br /> <br />QIOO <br /> <br />Q500 <br /> <br />DRY CREEK NO.l <br /> <br />Upstream Limit <br />Above Lagerman Reservoir <br />confluence <br /> <br />Above fro~ Steele Lakes <br />tributary <br />Below Steel Lakes <br />tributary <br />Above Clover Basin <br />trib"tary <br />8elow Clover Basin <br />tributary <br />Above private road <br />cro9sing <br />At private road crossing <br />At Schlagel Street <br />AtlloverKoad <br /> <br />Diversion acrosS Nelson <br />Road at Hover Road <br />At Sunset Street <br /> <br />Diversioo across Nelson <br />Road at Sunset Street <br /> <br />Diversion to St. VrQin <br />Creek above S.H. 119 <br />Helo,," S.H. 119 <br /> <br />i\t Bo'~en Street <br /> <br />At Pratt Parkway <br />AtstteamOlouth <br /> <br />Steele Lakes Tributary <br />At 7,thStreet <br /> <br />374+00 <br /> <br />325..00 <br /> <br />271+00 <br /> <br />270+00 <br /> <br />238..00 <br /> <br />236+00 <br /> <br />211..00 <br />210+00 <br />154..00 <br />102..00 <br /> <br />102..00 <br />71..00 <br /> <br />71..00 <br /> <br />64..00 <br /> <br />62+00 <br />40..00 <br />25..00 <br />1..00 <br /> <br />hOO <br /> <br />1'0 <br /> <br />143 <br /> <br />'" <br /> <br />32' <br /> <br />m <br /> <br />'14 <br />'" <br />'" <br />1,43 <br /> <br />" <br />m <br /> <br />14 <br /> <br />no <br />m <br />143 <br />m <br />m <br /> <br />236 <br /> <br />" <br /> <br />181 <br /> <br />608 <br /> <br />'" <br /> <br />'" <br /> <br />1245 <br /> <br />1268 <br /> <br />14'" <br /> <br />1617 <br />1771 <br />1745 <br /> <br />1704 <br /> <br />14' <br />1719 <br /> <br />'" <br /> <br />'" <br />no <br />'" <br />'20 <br />m <br /> <br />963 <br /> <br />60' <br /> <br />9" <br /> <br />1716 <br /> <br />1726_ <br /> <br />2150 <br /> <br />2192 <br />2162 <br />2374 <br /> <br />2354 <br /> <br />14' <br />2315 <br /> <br />", <br /> <br />1170 <br />350 <br />560 <br />620 <br />60' <br /> <br />1165 1512 <br />CONTINUED <br /> <br />32 <br /> <br />M <br /> <br />m <br /> <br />'" <br /> <br />568 <br /> <br />'OJ <br /> <br />'" <br />'60 <br />m <br /> <br />691] <br /> <br />60 <br />no <br /> <br />no <br /> <br />360 <br />no <br />m <br />290 <br />no <br /> <br />1,9/, <br /> <br />1920 <br /> <br />1873 <br /> <br />Ig72 <br /> <br />3105 <br /> <br />3112 <br /> <br />3923 <br /> <br />3950 <br />4238 <br />4260 <br />4185 <br /> <br />'" <br />4172 <br /> <br />1630 <br /> <br />2127 <br />m <br /> <br />954 <br /> <br />1050 <br />1199 <br /> <br />2428 <br />