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I I II ill III .11 II' Page Fourteen Battlement Nesa Development storm Drainage and Flood Plain Study II It is recommended that no encroachment be made into the existing channel cross section without careful en9ineering analyses. The velocity of flow in the main channel ranges betvleen 6 feet per second and 12 feet per second. The velocity of flow in the overbank areas is highly dependent upon the depth of flow and the degree of roughness exhibited by the characteristic grOlvth in the overbank. Generally, the velocities in significant areas of overbanl: flow are less than 3 feet per second. The velocities of the main channel are highly erosive when contacting silt-type deposits which form the banks in many areas. The result is the steep cutbanks and meanderinq characteristics of the river. The water surface profile as calculated by HEC-2, utilizing field cross sections, should be accurate within 0.2 feet. The floodplain width at each actual surveyed cross section shoulcJ be accurate within 5 feet horizontally. Between the actual cross section locations, the accuracy of the water surface profile remains within 0.2 feet. The floodplair limits, however, become less precise, as it is necessary to interpolate elevations from available mapping to locate the edge of the flood plain. II For the above reasons, the elevation of the water surface profile, as srown on Drawing 926.010, Flood Plain Plan and Profile, shoulcJ be considered as the governing criteria for establishing flood hazarcJ. The elevation datum for the profile is V.S.C. & G.S. as establishecJ by the primary vertical control network utilized for the Battlement Mesa project. X. Summary - Flood Plain Study 111 II The flood plain limits determined by the study have been recognized by the development plan and no development is proposed for Ccny areas subject to inundation by the lOa-year flood. II II II II II II II Although a wide flood plain exists for the Colorado River throughout the majority of the area borderinq the project, the flood plain has little effect on the project area. All proposed land uses on the site are located above the 100- year flooe profile. The existing Grand Valley bridge, which provides the primary access to the site, is located approxi- mately five fE~et above the 100-year flood profile. II