Laserfiche WebLink
Subbasin P1-3 has an area of 37 acres and is completely captured within the gravel mine and thus <br />the peak flow was not calculated. Water collected in the mine will be pumped into a drainage swale <br />and conveyed to the Cache la Poudre River. The storm water capture reduces flow at DP8. <br />Subbasin P1-4 has an area of 13 acres and is completely captured within the gravel mine and thus <br />the peak flow was not calculated. Water collected in the mine will be pumped into the Cache la <br />Poudre River. The storm water capture reduces flow at DP8. <br />Subbasin P1-5 has an area of 11 acres and is completely captured within the gravel mine and thus <br />the peak flow was not calculated. Water collected in the mine will be pumped into the Cache la <br />Poudre River. The storm water capture reduces flow at DP8. <br />Subbasin P1-6 has an area of 4 acres. The imperviousness of the subbasin is 0 percent since the <br />subbasin will be unaffected by the gravel operations and will remain as grassland. The runoff <br />coefficient was calculated to be 0.365 for the 100-year storm. A time of concentration of 33 <br />minutes would result in a 100-year rainfall intensity of 4.12 inches per hour. Applying the rational <br />method produced a peak runoff of 5.3 cfs. Subbasin P1-6 returns to the Cache la Poudre River as <br />overland flow and contributes flow to DP8. <br />Subbasins P1-7 and P1-8 have a combined area of 10 acres. The imperviousness of each Subbasin <br />is 15 percent since the subbasins will be under mining operations. The runoff coefficient was <br />calculated to be 0.452 for the 100-year storm. A time of concentration of 29 minutes would result <br />in a 100-year rainfall intensity of 4.45 inches per hour. Applying the rational method produced a <br />combined peak runoff of 19.2 cfs. Subbasins P1-7 and P1-8 are collected in a dewatering trench <br />and routed off the property in the vicinity of historical overland flow discharges and contribute flow <br />to DP9. <br />Subbasin P1-9 has an area of 1 acre. The imperviousness of the subbasin is 10 percent since the <br />subbasin will be used only for temporary stockpiles. The runoff coefficient was calculated to be <br />0.416 for the 100-year storm. A time of concentration of 9 minutes would result in a 100-year <br />rainfall intensity of 7.83 inches per hour. Applying the rational method produced a peak runoff of <br />4.6 cfs. Subbasin P1-9 is routed off the property by overland flow in the vicinity of historical <br />overland flow discharges and contributes flow to DP9. <br />Subbasin P1-10 has an area of 6 acres and is completely captured within the gravel mine and thus <br />the peak flow was not calculated. Water collected in the mine will be pumped into a drainage swale <br />and conveyed to the Cache la Poudre River. The storm water capture reduces flow at DP9. <br />Subbasin P1-11 has an area of 9 acres and is completely captured within the gravel mine and thus <br />the peak flow was not calculated. Water collected in the mine will be pumped into the Cache la <br />Poudre River. The storm water capture reduces flow at DP9. <br />Subbasin P1-12 has an area of 2 acres. The imperviousness of the subbasin is 5 percent since the <br />subbasin will be partially under mining operations and partially unaffected. The runoff coefficient <br />was calculated to be 0.439 for the 100-year storm. A time of concentration of 27 minutes would <br />result in a 100-year rainfall intensity of 4.64 inches per hour. Applying the rational method <br />-8- Revised Preliminary Drainage Report.doca