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<br />'" <br /> <br />, <br />I <br />r~ <br /> <br />Box Elder Creek Hydrology <br /> <br />., <br />~' <br />11 <br />~ <br />j <br />{ <br /> <br />i. <br />'i <br />~ <br /> <br />I. <br />If' <br />& <br />I <br />, <br />ii' <br />;r <br /> <br />The hydrologic portion of the study was submitted to FEMA in 1957 for review as a <br />Letter of Map Revision (LOMR). To date, FEMA has not acceptec. the hydrologic <br />analyses prepared for the Box Elder Creek watershed. The remainder of this report will <br />present the justification necessary to allow FEMA to accept the hydrology and utilize it in <br />the preparation of updated FIRMs for the three local governments. <br /> <br />FEMA Requirements <br />FEMA's requirement for review is contained in 44 CFR 65. FEMA's guidance for <br />acceptance of hydrologic analyses is contained in the publication FEMA 37 "Flood <br />Insurance Study Guidelines and Specifications for Study Contractors" dated January, <br />1995. The guidelines are written specifically for a study contractor (SC) working under <br />the direction of a FEMA Project Officer (PO). However, to ensure that revisions to <br />FIRMs are consistent with technical standards for studies funded by FEMA, the SC <br />Guidelines are also used to review studies by others. <br /> <br />~ <br />l> <br />.. <br />~; <br />~. <br /> <br />" <br /> <br />For ungaged streams, which is the case with the Box Elder Creek watershed, the SC is <br />directed to "make use of any valid existing flood flow frequency analysis conducted by a <br />Federal, State, or local agency that authoritatively establishes the discharges for an <br />ungauged stream under consideration or the discharges in published Flood Insurance <br />Studies (FIS). In the case of Box Elder Creek, Flood Insurance Studies for Adams <br />County and Arapahoe County included a discharge for Box Elder Creek at their common <br />border (also the location ofI-70) of26,500 cfs as determined by USGS Water Supply <br />Paper 1680. (Note: The published Adams County FIS had a discharge of 13,900 cfs <br />which was a typographic error in the "Summary of Discharges" Table in the FIS and was <br />later corrected by FEMA) <br /> <br /> <br />Pages 2 and 3 of Attachment No. I, a memorandum prepared by CH2M Hill, demonstrate <br />why regression equations are not appropriate for determining peak discharges for Box <br />Elder Creek within the study reach. Brian Hyde, a staff member with the Colorado Water <br />Conservation Board (CWCB) and the Association of State Floodp.ain Managers <br /> <br />CTC8.doc <br /> <br />4 <br />