Colorado River Division 5 Palisades Whitewater Park Correspondence

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attraction flows provided at the fish passage structures. However,in the situation at the proposed Palisade Whitewater Park where there is not a dam but GSSs, it is unknown what appropriate attraction flow might be at the proposed fish bypass channel. You need to incorporate an adaptive management component into your alternative that considers this uncertainty. The following is a list of additional issues that need to be addressed; figure and page numbers refer to the report provided on September 19 titled"Addendum to the Palisade Whitewater Park Hydraulic Analysis for Fish Passage." 1. We are concerned that the base mapping used for the site provided by Mesa County does not provide the topography of the river channel(bathymetry); it only provides topography above the surface of the water. It is essential for project design and evaluation to know the specific river bathymetry and all land forms in the project area. This information must be obtained by taking measurements from cross sectional profiles of the river within the project site. Confirming elevations and water surface elevations is not adequate to determine the bathymetry of the river bottom. 2. Your report states that the fish passage structures and the fish bypass channel are designed at a lower elevation than the Iow-flow channels of each GSS and are the first channels to receive water during low flows. Our concern is that the downstream elevations of these fish passage features should match the elevation of the invert of the river channel. Because measurements of the river channel inverts have not been provided,it is not possible to determine the difference in elevations. 3. As discussed at our September 19,meeting, it is not appropriate to use the Cameo stream flow gage for the Palisade site. The stream gage just downstream of the proposed site is the appropriate gage to use(USGS#09106150). REP committed to provide information with the appropriate hydrology. 4. We are concerned that the cross sections used for the HEC--RAS model were simulated and that actual measured cross sections were not conducted. Therefore,the bathymetry of the river is unknown,making the results of the HEC-RAS model based on simulations instead of actual river conditions. Also,because HEC-RAS interpolates bathymetry between two measured cross section profiles,the cross sections need to be of suitable density to capture the river's complex bathymetry. 5. Figure 2 is a plot of the channel invert elevations;however,we understand that actual channel invert elevations have not been measured, but were simulated to create the profiles. 6. Page 3 states that"elevation drop is compounded at the drop structures by excavating the channel downstream of the structure in the area of the proposed scour pool." It is important to know the existing river bathymetry, and the proposed river bathymetry, 3 •