2014-02-07_REVISION - M1979094HR

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Whetstone Associates Technical Memorandum permeability alluvial fans would occur throughout the storm event. The Paradox Valley is a unique terrain not typically modeled by urban drainage planners, and requires site - specific consideration of hydraulic processes. 6 Section 5. 0, Model Results. Please note that the DRMS is only interested in the runoff volume from the l0 year, 24 -hour design storm for pond storage requirements and the peak flow from the 100 year, 24 -hour design storm for channel and spillway capacity and stability analyses. All hydrologic modeling other results are unnecessary. Cotter response: Only results for the 10 -yr 24 -hr storm and 100 -yr 24 -hr storm are presented in the revised DDP. 7. Section 5.3 and Table 21, pp. 47 -48. To reiterate the inadequacy of using "average cross sections "for hydraulic analyses, the 1.55 ft stage for PitDivW (Table 21) does not have the I ft of freeboard stated at the end of the paragraph on p. 47 in top cross section of Figure 14 (p. 32). Cotter response: The diversion channels have been evaluated based on reach - specific gradients and channel geometries. The proposed improvements will result in a consistent prismatic geometry for all or most engineered diversion channels. The scour analysis and hydraulic capacity analysis was performed using the specific slope and geometry for various segments within each reach, as shown in Section 5.4 of the revised DDP. 8. Section 5.5, p. 49. The "negligible outflow "from Catchment OOIB -A South demonstrates insufficient storage capacity requiring re- design. Please provide design drawings for both Catchments 001 B -A South and 001 B -A North. Cotter response: Design drawings for Catchment OO113-A North and OO111-A South are provided as Plate 3 in the revised DDP. 9. Section 63.2 (p. 63) and Plate 2. According to Figure HS -I -Probable Range of Drop Choices and Heights (UDFCD 2008) vertical drop structures are not acceptable if they are over 3 feet in height. Please limit the vertical hard drop height to 3 feet or less. Cotter response: Natural "drop structures" in the area exceed 7 feet in height on the Monogram Mesa escarpment, as shown in Figure 35 (Page 64) of the original DDP. Constructed drop structures for the Planned Pit Diversion East (PDEP) will be limited to three feet, in accordance with Urban criteria, to the extent practical during construction. The PDEP will be constructed in bedrock using excavators and heavy equipment, however, blasting of bedrock is not planned. 10. Plates I through 4. Pursuant to Rule 6 4.21(10)(a) of Mineral Rules and Regulations of the Colorado Mined Land Reclamation Board for Hard Rock, Metal, And Designated Mining Operations, design specifications shall be certi red by a licensed professional engineer for all Environmental Protection Facilities. Pursuant to Rule 3.2.3 of the Bylaws and Rules of The (Colorado) State Board of Licensure for Architects, Professional Engineers and Professional 4149A.140207