2011-12-16_REVISION - M1977572 (71)

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4.3.2 Riprap The proposed Berm A inlet will be protected with angular rock riprap at the top, bottom, and sides of the inlet. Several flooding conditions were analyzed to develop hydraulic parameters to determine the stable riprap size. Two likely flow conditions indicate a maximum D50 of 12 to 14 inches while a worst case scenario specified a D50 of 16 to 18 inches. The analyses assume uniform flow across the riprap blanket and do not account for turbulent hydraulic forces which may be present on spillways and around bridge piers. Therefore, a riprap gradation with a minimum D50 of 18 inches is recommended. Documentation supporting the determination of the riprap size is provided in Appendix E.2. The recommended gradation for the riprap is on the design plans located in Appendix C. 4.4 Outlet Pipe Design The outlet pipes in each pit were designed to release the volume of water captured by the pit after a flood recedes. The elevation of the normal water surface elevation in the pit will, over a period of time, vary with the stage of the river. The minimum normal water surface elevation was assumed to be within one -foot of the general river invert along each pit (see Appendix D.1). The maximum normal water surface elevation in the pit was assumed to be represented generally by the river water surface elevation which is not exceeded more than approximately 30 percent of the time during the irrigation season (May to August). Documentation supporting the determination of the minimum normal high water surface elevation is provided in Appendix D.2. The outlet pipe invert from each pit was set to drain the captured volume of water above the maximum normal water surface elevation in less than 72 hours after the water surface elevation in the main channel recedes. The evaluation documented in Appendix D.2 indicates that Pits 1, 3, and 4 will require outlet pipes with diameters of 12, 18, and 24 inches respectively. COVALCOO1_Phase 11 Report_082211.docx 4.4 ANdERSON CONSULTING ENGINEERS, INC.