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1 1 1 1 1 1 The calculated capacity for the dischazge using the historic 25 yr. runoff is a 12" PVC pipe that is fitted with an orifice. The emergency spillway has been sized to handle the 100 yr. event and has the following dimensions: Description Feet Bottom of Ditch 2.50 Depth of Flow 1.00 Ditch Width -Top of Flow 7.50 Ditch Width - Top of Ditch 9.00 Freeboard 0.30 Ditch Side Slope 2.5:1 Velocity, fps 3.14 It is recommended that the emergency spillway be lined with a riprap having a Dso of 6 inches. A geotextile fabric should be placed between the soil and riprap. The estimated dimensions across the top of the detention pond aze 110 feet by 110 feet. The pond has been sized using a 3:1 slope. The existing ground slopes to the south from the Colorado River banks toward the gravel pits. On the south side of the pits the ground is essentially level or sloping to the northwest. Storm water runoff is expected to flow towazd the gravel pits. The sediment and erosion control for the gravel pits is expected to be accomplished by utilizing in pit ponds in the wet portion of the pit when practical. The small size of the detention ponds, less than '/: acre, when compared to the size of the pits 12 to S l acres indicates that sufficient room exists to provide detention volume to settle solids. The calculations aze included in the attached appendices. The runoff control structures described above provide design criteria. The specific design drawings will be prepared after the acceptance of the drainage study and prior to construction. Conclusions and Recommendations The following conclusions and recommendations are based on the information included in this report and field observations. The drainage basin for the project site includes the west end, Dry Creek, slough to east property line and west property line to horse fence mining areas and a small portion of the I-70 corridor adjacent to the Dry Creek mining area containing approximately 33.68 acres. 2. Runoff from the remaining portion of the I-70 corridor south of the project site, is intercepted by the slough or diverted azound proposed pits by existing irrigation ditches or topography. 3. Runoff from the bench area south of the interstate corridor and upgradient from the Last Chance Ditch is intercepted by the Last Chance Ditch and diverted to the west away from the project site.