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<br />",0 FLOOO <br />",I'- 00 <br /> <br />! ]f~~ ~ <br />~ lID i2 <br />o 0 <br />'Vi>- 'yC;- <br />&/in . tel\'O <br /> <br />Board of Directors <br />Executive Committee: . <br />0 <br />~ <br /> "' <br />Cathy Reynolds N <br />Chairman c <br />~ <br />City/County of Denver 0 <br />0 <br /> ~ <br />Debra Vickrey ~ <br />0 <br />Chairman Pro-Tern ~ <br />0 <br />Arapahoe County u <br />cO <br />Paul Danish w <br />> <br />Secretary z <br />w <br />Boulder County 0 <br />Gretchen Cerveny rn <br />Treasurer ~ <br />City of Wheal Ridge <br />Elaine Valente '" <br />5 <br />Member at Large w <br />Adams County w <br />~ <br /> Z <br /> w <br />Members: ~ <br /> ~ <br />Steve Burkholder ~ <br />~ <br />City of Lakewood ~ <br />Noel Busck c <br />~ <br />City of Thornton ~ <br />Ken Fellman <br />City of Arvada ~ <br />Stephanie Foote ~ <br />CitylCounty of Denver , <br />Kathy Green , <br />, <br />City of Aurora <br />B. H. Hoffmaster c <br />Engineer rn <br />~ <br />Michelle Lawrence "' <br />~ <br />Jefferson County ~ <br />c <br /> r <br />Kathleen MacKenzie x <br />City/County of Denver ~ <br />W. Mike Maxwell <br />Douglas County <br />Jim McShane <br />Town of <br />Columbine Valley <br />Deborah Ortega <br />City/County of Denver <br />Art Patton <br />Engineer <br />Susan Spence <br />Town of Superior <br />Karen Stuart <br />City/County <br />of Broomfield <br /> <br />L. Scott Tucker, Executive Director <br /> <br />September 24, 2002 <br /> <br />Kevin Long, Water Resource Engineer <br />Federal Emergency Management Agency <br />Hazard Identification Branch - Mitigation Directorale <br />Federal Center Plaza, Room 437 <br />Washington, D,C. 20472 <br /> <br />Dear Kevin: <br /> <br />As we discussed in Breckenridge last week, I am sending a copy of "Ralston/Leyden <br />Creeks Hydrology Report" dated August, 2002, to Michael Baker, Jr. for transmittal to <br />you, The hydrology study documented in this report was undertaken by the District and <br />the City of Arvada, with staff support from Jefferson County, for two reasons: <br /> <br />1. To convert the hydrology model for the Ralston Creek Watershed from the <br />MITCA T model to the District's CUHP/SWMM hydrology model. <br /> <br />2. To recognize the effects of two major reservoirs, which were not included in <br />past hydrology studies, on the discharges, <br /> <br />The study methodology is fully outlined in the report, However, a few introductory <br />comments are in order. The discharges from the MITCA T model are the discharges <br />published in the Arvada Flood Insurance Study (FIS) and the draft Jefferson County FIS, <br />Our approach was to calibrate the CUHP/SWMM model to those discharges published in <br />the FIS, Once the model was calibrated, the two reservoirs were inserted into the model <br />and the model was mn to determine the effects of the reservoirs on downstream <br />hydrology, <br /> <br />Our next step will be to prepare a new Flood Hazard Area Delineation study (FHAD) for <br />Ralston Creek from its confluence with Clear Creek up to the Arvada Reservoir, and for <br />Leyden Creek from its confluence with Ralston Creek up to the Leyden Lake Reservoir. <br />We have obtained new topographic mapping at a scale of I.inch = IOO.feet with 2-foot <br />contour intervals, The mapping is registered to Arvada's GIS monumentation and is <br />NA VD88 datum, The completed FHAD product will be easily transferable to FEMA's <br />current DFIRM specifications, <br /> <br />CTP Task Agreement I.Hydrologic and Hydraulic Data Preparation and Review includes <br />recognition by FEMA of the CUHP/SWMM model as the basis for establishing flood <br /> <br />""__..i\L.:,,\,-___~ <br />