2003-01-29_REVISION - M1992066 - Laserfiche WebLink

Home Browse Search

Floodplain Delineation Report Pa e 3 of 4 Hogue Pit g RESULTS Complete results are included in the attached Figures f-6. Results show that the ftoodway along this reach is fully contained within the riparian corridor of the Yampa River. Based on the width of the river (150-175 feet) and the slope (nearly one percent), this is a reasonable result. The floodplain is essentially contained within the channel until cross-section 3 (XS-3), where it spreads out into the adjacent pasture land on the right overbank area. The base flood elevation varies by cross-section. All elevations are indicated as Mean Sea Level, 1929 NVGD, elevations. Shallow overbank floodwaters can backflow into the mining operation at the southwest comer of the existing mine. When full, the elevation of water in the pit will equal the base flood elevation at the southwest comer, equal to the base flood elevation of 6567.5 at cross- section 2 (XS-2). Based on the existing site conditions, all areas upstream of cross-section 3 (XS-3), are above the 1 DO-year floodplain. The limits of the flcdway and floodplain are shown on Figure 2. The remainder of Figures 3-6 show the resul~f the HEC-RAS analysis for existing conditions. SUMMARY The results of thoodway and floodplain study indicate that the gravel mining operation is subject to floodi om shallow overbank flow backflowing into the southwest comer of the pit. Per discs' May 17, 2002 with John Eastman, Routt County Planning Department, ranter than bed southwest comer of the pit, an option is to allow the pit to Flood in an e~~me event' rs feasible, as the equipment in the pit is mobile, and can be moved in the event of ~srer levels. A second option would be b construct a small berm (one to three feet ~i9hvever, not constructing a berm will alleviate any potential concerns with modificatio *1 of~odplain within this reach of the Yampa River. Rev 1 - 17 _Ma} I W~RESOURGE CONSULT.WTS, LL-c