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Comment Response Page 4 <br />Response: CDRMS requested additional support for the control factors we selected for <br />topsoiled and seeded conditions and the 1 to 2 year growth conditions. The following describes <br />the technical basis for values we selected: <br />Control factor values assigned to the topsoiled and seeded conditions and the 1 to 2 year <br />growth conditions were 0.45 and 0.042, respectively. These values were selected from the <br />internal SEDCAD tables for control factors and based on a reasonable vegetative cover that <br />could be achieved by each reclamation category. The topsoiled and seeded conditions <br />assumed that no appreciable canopy and no ground cover had been established. The 1 to 2 <br />year growth conditions assumed that no appreciable canopy had yet established, but that 60% <br />ground cover had been achieved. These vegetative cover conditions are reasonable and <br />attainable for the defined reclamation categories. <br />As a reasonableness check, control factor values from an independent reference (Haan, 1994) <br />were investigated and compared to the Colowyo selected values. Control factor values for <br />construction, mining, and forest lands show newly seeded conditions, with a prepared seedbed, <br />at a control factor of 0.40, which is lower than the 0.45 value selected by Colowyo. Control <br />factor values for sites with no canopy, but notable ground cover establishment were consistent <br />with values from the internal SEDCAD tables. The 0.042 value selected by Colowya for the 1 to <br />2 year growth conditions assumes 60% ground cover by grasses (not weeds), however, it does <br />not factor in any shrub growth that establishes, which would serve to increase interception by <br />above-ground cover and by subsurface effects and therefore reduce the appropriate control <br />factor. <br />Note: Comments No. 49 through 51 apply to Section 29 pond. which has been eliminated. <br />However. Comments No. 52 and 53 apply to the other ponds as well and were not repeated for <br />all other ponds. Therefore answers are provided here. <br />This concludes the general comments regarding the SEDCAD runs and input parameters. Specific items for <br />each pond design run are noted below in addition to those general comments above. Three SEDCAD runs were <br />reviewed for each proposed pond using rainfall values for the 10-year, 100-year, and 50% of PMP, 24-hour <br />events. <br />Section 29 Pond <br />49. Although the second SEDCAD run is titled 100-year storm event, the storm information page <br />and the output indicate it is actually a 50% PMP run, identical to the third run [or this pond. <br />Please correct this discrepancy. <br />Response: CDRMS noted that the SEDCAD run entitled 100-year storm event was a repeat <br />of the 50% PMP run. The SEDCAD runs for Section 29 pond are no longer applicable since <br />Section 29 pond has been eliminated. <br />50. The Division does not concur with the flow paths used to determine the time of concentration. <br />The time of concentration for each subwatershed is the longest flow path to the subwatershed <br />outlet. The Division also does not agree with the some of the land use designations, especially <br />selection #1, forest with heave around litter and hav meadow for disturbed areas with a curve <br />number of 91. Parameter selection should be discussed with the Division to resolve this issue. <br />Response: CDRMS stated non-concurrence with the flow paths used to determine time of <br />concentration and noted that the longest flow path to the subwatershed outlet must be used. <br />Colowyo agrees that the longest flow path must be used and the SEDCAD modeling utilized the <br />longest flow path for all calculations. <br />