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Colowyo, C1981-019, PR3 adequacy No. 2 20 April 22, 2011 <br />• The locations of some ditches and areas on the maps look like they could be errors (or if <br />correct, then the purpose of the structures appears uncertain): <br />o On Map 41B, some watershed boundaries are stream channels (Jubb Creek, Collom <br />Gulch). It is unclear why watershed boundaries are shown this way. <br />o Some ditches are on ridges (e.g., Porcupine Draw and Cougar Draw). <br />o Area A3 extends over a ridge. <br />• Detailed mapping of culvert locations is limited or non-existent. <br />Please address these deficiencies. <br />Regarding the SEDCAD model documentation for the worst-case scenario (Exhibit 7, Item 23), <br />many of the issues previously noted were addressed by Colowyo, however additional <br />deficiencies in the revised model and documentation need to be addressed as noted in the <br />following items. <br />4. The floating siphon proposed in the sediment control plan is not included in the drawings and <br />may not be the best design at this site due to climate. Please provide additional text narrative <br />and drawings, as necessary, to describe the operation of the siphon, including during winter <br />conditions when the pond surface is frozen. <br />Please remove all references to the floating siphon, for example page A-l. <br />5. The ditch downstream of Area 3 does not extend around the ridgeline on Figures Al and El <br />(Exhibit 7, Item 23) as it does on Map 41B (see Little Bear Draw). Please explain or revise <br />figures. On Figure Al, should area A3 extend to west? Also on Figure El, the scale bar <br />appears to be wrong. <br />6. The Structure Networking table indicates which areas drain to which channels for a few of the <br />channels (for example Structure 6 is fed by Area A-35), but not for most channels. Please <br />provide this information for all channels. <br />7. It is stated in the text of Exhibit 7, Item 23 that Table 1, Part A will be used for CN values used <br />in all current modeling. This table gives a CN value of 91 for bare soil, but the values in the <br />Subwatershed Hydrology Detail table are 85. Please address this discrepancy for bare soil and <br />for any other applicable land use categories. <br />8. On the SEDCAD model overview sketch (figure entitled Network Sketch 7-23A), should the <br />long natural channel drain to structure 5 rather than structure 6? <br />9. Regarding the Subwatershed Hydrology Detail table, the following questions/comments should <br />be addressed: <br />a) It appears that subwatersheds for structures 5 and 6 were interchanged. In