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Colowyo, C1981-019, PR3 adequacy No. 2 21 April 22, 2011 <br />particular, it appears that Area A-2c was erroneously included in portion of model <br />for structure 6 and Area A-35 was erroneously included in portion of model for <br />structure 5. <br />b) Was Area A-39a excluded from the model? Perhaps it should be included in portion <br />of model for structure 43. <br />c) Area A-30 should extend to Structure 39 (aka D7/D8). <br />d) The undisturbed portion of Area A-6 appears to have been excluded from the model. <br />Please clarify or add this portion to model. <br />10. Regarding the Subwatershed Time of Concentration Details table, it appears that subwatersheds <br />for structures 5 and 6 were interchanged (related to issue above). This error impacts the times <br />of concentration. <br />11. Regarding Figure A-1, the following questions/comments should be addressed, and any <br />associated changes in the SEDCAD model should be made: <br />a) It appears that Structure 40 (aka D1) and its drainage area do not extend far enough <br />to the west. On the figure, the channel is truncated at the ridgeline, however, the <br />disturbed area extends beyond the ridgeline, and runoff from part of the disturbed <br />area would not be captured by the drainage system and would not be treated by the <br />sediment pond. <br />b) Why is the ditch in area A26 labeled D15? Is this a mistake? <br />c) It appears that a small area that drains to Structure 19 is missing on the figure. The <br />Subwatershed Hydrology Detail table lists two small tributary areas but only one is <br />shown on the figure. <br />d) For mountain brush areas, the legend in Figure A-1 should indicate a CN of 41, not <br />57. <br />e) For juniper areas, the legend in Figure A-1 should indicate a CN of 73, not 63. <br />f) For bare areas, the legend in Figure A-1 should indicate a CN of 91, not 85. <br />g) The area that drains to ditch D7/D8 (Area A-30) needs to extend to north. <br />12. In the design details in Table 7-23C-1, some of the details for the perforated riser for the Little <br />Collom Pond (namely the barrel diameter, barrel length, and barrel slope) do not match these <br />details in the Structure Detail for Structure #1 in the SEDCAD report. <br />13. Within Exhibit 7, Item 26, on the Little Collom Pond Design Drawing, Figure 1, please address <br />the following errors: