2008-10-07_PERMIT FILE - C1981047

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n ~~ • PEAK FLOW CALCULATIONS FOR DITCHES AREA A AREA B AREA C AREA D AREA E DRAINAGE AREA (ACRES) 5.5 3.8 10.9 3.9 4.5 CURVE NO. 74 74 73 73 73 STORM EVENT _YR., 24 HR. 100 100 100 10 10 STORM EVENT in. 2.4 2.4 2.4 1.7 1.7 RUNOFF in. 0.55 0.55 0.51 0.20 0.20 WATERSHED SLOPS 0.31 0.75 0.70 0.68 0.74 SLOPE ADJUSTMENT FACTOR 1.09 1.17 1.17 1.17 1.17 LENGHT OF WATERSHED 400 700 1600 950 950 EQUIVALENT DRAINAGE AREA 3.0 7.5 30 12 12 PEAK FLOW efs/in FiR D-2 6.25 13 35 18 18 ADJUSTED PEAK FLOW 7.02 4.26 7.72 1.30 1.50 The design of Dive rsion BC is present ed on page C-6. Thi s diversion ditch is designed to handle the 100 y ear event from areas B & C w hich is shown to be 18.7 CFS on page C-6. The peak flow calc ulated above from a reas B & C is 11.98 CFS. Diversion BC is therefore sized appropriately. The design of the collection ditch along the north aide of the mine bench is presented on page C-11. This ditch is designed to handle the 100 year event from areas B k C which is shown to be 18.7 CFS on page C-11. The peak Plow calculated above from areas B & C is 11.98 CFS. The collection ditch along the north side of the mine bench is therefore sized appropriately. The design of Ditch A is presented on page C-11. This ditch is designed to handle the 100 year event from areas A, B & C which is shown to be 29.1 CFS on page C-11. The peak flow calculated above from areas A, B & C is 19.00 CFS. Ditch A is therefore sized appropriately. The design of Ditch D is presented on page C-5. This ditch is designed to handle the 10 year event from Area D which is shown to be 3.2 CFS on page C-5. The peak flow calculated above from areas D & E is 2.8 CFS. Ditch D is therefore sized appropriately. • ,.~ C-17 3-29-91