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<br />There have been no f~ood protection neasures take~ on Dry <br />Creek or in the Loomiller Basin, exce~t for using <br />Loomiller Pond as a flood storage facility. Varicas <br />properties along the streets in ~oo~iller Basin have <br />low retaining walls alor.g the street frontage to ?reve~t <br />yard flooding. <br /> <br />In addition to the physical flood preventio~ measures <br />mentioned, t~e City of Long~ont initiated an ordinance <br />in ~ay o~ 1973 for flood plain regulation and has fol- <br />lowed with =lood plain nanagement policies outlined In <br />The St. Vrain Conprehensive Plan (Reference 1). <br /> <br />3.0 ENGIKEERING METEODS <br /> <br />For flooding sources studied in detail in the ccr.~unity, <br />standard ~ydrologic and hydraulic study methods were used ~o <br />determine the flood hazard data required for this study. <br />Floods having recurrence ir.tervals of 10-, 50-, 100-, and <br />500-years have been selected as having special signi=icance <br />for flood plain nanagement and for flooc insurar.ce ?re~i~~ <br />rates. T~e analyses reported here re=lect curre~t co~ditions <br />in the watersheds of the streans. <br /> <br />3.1 Hydrologic Analyses <br /> <br />Hydrologic analyses were carried out to establish the <br />peak discharge-frequency relationships for floods 0= tne <br />selected recurrence intervals for each strea~ s~udied <br />in detail in the conmunity. <br /> <br />Frequency-discharge data for two of the strea~s studied <br />in detail in the City of Longmont are based on infor~a- <br />tion published in the U.S. Army Corps o~ Engineers =lood <br />Plain I~~ornation Reports for the St. Vrain Creek and <br />Left Hand Creek (Re=erences 3 and 4). 7he 100-year <br />flood discharges on Lef~ Hand Creek and the St. Vrai~ <br />Creek are 4,250 (cfs) and :0,200 (cfs) res?ectively. <br />The SOD-year discharges for these two streaLS equal the <br />discharges for the standard project floods as published <br />in the Flood Plain Infornation Reports (References 3 <br />and 4). Ten-year and 50-year discharges for these two <br />streams were taken from the area versus discharge curves <br />in Figure 10. These relationships are based on a <br />log-Pearson Type III analysis of peak r~no=f data <br />recorded at gages on the St. Vrain Creek near Lyons, <br />Colorado and Platteville, Colorado (Reference 9). The <br />years 0= record vary from 79 years at t~e ~yons gage <br />to 47 years at the Platteville gage. <br /> <br />14 <br />