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<br />Mr. Frank M. Akers <br />September 23, 1991 <br />Page 3 <br /> <br />. A slight increase in the 1991 profile from the existing conditions profile <br />was due to the channel invert elevation used upstream of the existing <br />weir crest. In the COE design, the channel invert upstream of the weir <br />crest was constructed a few feet below the crest elevation of 5290.5. <br />The channel bottom, however, has silted in over the intervening years. <br />This is especially true along the west bank, opposite the city of <br />Englewood intake structure. The higher channel invert elevation today <br />results in a slightly higher water surface elevation. However, the effect <br />of this increase disappears immediately upstream of the Union Avenue <br />bridge as shown on sheet 4 of the construction drawings. <br /> <br />Another comment indicated that "the loo-year water surface profile for the design reach <br />from the physical model study should be shown for comparison." Only the upper portion <br />of the project reach was modeled. The loo-year water surface profile elevations from the <br />US Bureau of Reclamation model study are shown on sheet 4 of the construction drawings. <br />This profile is labeled as "modeled Qloo W.S." <br /> <br />The erosion potential downstream of the last drop structure was investigated. The final <br />downstream structure will be buried in the channel bed at the time of construction. Its <br />purpose is to provide for future channel degradation. The amount of degradation is set by <br />the downstream control elevation of the southerly Oxford Avenue drop structure. The bury <br />depth of the final embankment was designed for this downstream control. The embankment <br />is riprapped for its full depth. <br /> <br />The comments of O.P. Patney, Structural, are addressed below. Comment numbers are <br />taken from Mr. Patney's engineering review comment sheets. <br /> <br />Comment No. <br /> <br />Brown and Caldwell Reply <br /> <br />1, lA, 1B <br /> <br />Structural calculations requested are attached as Appendix B. <br /> <br />2 <br /> <br />The sheet that is referenced in this comment, sheet 7, is a demolition <br />drawing. Refer to sheet 8 for the new concrete placement. The <br />minimum concrete thickness in the new concrete is 4 inches. <br /> <br />3 <br /> <br />The sheet referenced, sheet 7, is a demolition drawing. Sheet 8 shows <br />the new concrete and the anchorage of the new to old concrete is <br />shown. <br /> <br />Brown and Caldwell <br />Consultants <br /> <br />21-5993/js <br />