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Cingery Associates, Inc. '~t--)/\j.s'(....J!...J/:\.,-- E^/(~'INCE!-7S ~ . "I ~lJ-t:1'v t.. IV IV ~ , PRINC/PALS OERYL W GINGERY LARRy A MULLER FLOYD E. MONTGOMERY JOHN W CASKEY DOUGLAS C. STOVALL {sUo 2840 SOUTH VAUEJO STREET ENGLEWOOD, COLORADO 80110 TELEPHONE 303 761~4860 I 8R4NCH OFFICE GRAND JUNCTION. COLORADO 81501 TELEPHONE 303 245~0621 September 25, 1979 Mr. E. I. Jcncsok Colorado Water Conservation Board 823 Centennial Building 1313 Sherman Street Denver, Colorado 80203 Re: Floodplain Designat:~ons for Breckenridge, Silverthorne, Gypsum, Eagle, Frisco, and Red Cliff Dear Gene: This letter is in response to your letters of August 28 and September 5, 1979, to Wayne Graham of the FE,deral Emergency Management Agency (FEMA), regarding recent Flood Insurance St.udies completed by Gingery Associates. The letter of August 28, 1979, addresses the Breckenridge Flood Insurance Study. As you have indicated, the water surface elevations from this study do not match those of thE "Breckenridge Floodplain Information Report" pre- pared by Leonard Rice Corsulting Engineers and designated by your office. As you are aware, the Town cf Breckenridge was not diligent in their enforcement of floodplain regulations in the years following this initial study. As a result, there were numerous instances of cut and fill, and construction within the Blue River floodplain that altered che topography and/or the floodplain hydraulics. In addition, the Town has also initiated some floodplain improve- ments which include new culvert crossing structures at several locations on the Blue River and its tributaries. The extent of these floodplain disturbances required that our firm survey many new cross sections throughout the Blue River study reach, and re-evaluate the water surface elevations and the floodplain delineation for the Blue River. The tributary streams of Lehman Gulch, Illinois Gulch and Sawmill Gulch were also re-analyzed for the FEMA study and do not match the previous water surface profiles. For these streams, the water surface elevations were hand calculated in the earlier study, and therefore no HEC-II runs were available. Without a HEC-II model setup, flo~dways for these streams would be extremely difficult and costly to determine. In addition, the earlier study had ignored all culverts, considering them to be totally blocked by debris. FEMA policy is generally to consider these culverts open to convey flood discharges. The water surface pro- files on these streams were therefore recomputed using HEC-II with conveyance available through culverts. These water surface profiles cannot be expected to match the previous study. CIVIL ENGINEERING f INOUSTRIAL & MINE FACILITIES I LAND SURVEYING I STORM DRAINAGE / STRUCTURAL I WATER & SANITATION