Question

Question 04 (20 pts) [will be graded] Use the NRCS (SCS) method to estimate rainfall excess for an area before and after development. The rainfall is estimated at 15 cm. The hydrologic soil type is A. The pre-development condition is open space with grass on above 50% of the area with fair condition. The post- development condition is residential with a 38% impervious cover. If the watershed were 10.1 ha, how many m3 of ponding is necessary to store all the rainfall excess from post-development?

Answer 1

Rainfall, P = 15 CM Hydrologic soil type A Pre- development condition open space with grass (50% ob circa) - bris, CNE 49 Post development condition, Residential with 38% impejuious, coves, CN=61 5- 1000 -10- 1000 -10 = 6.3934 in = 16.84 €) Za 5 0.88 = 0.276.3934 = 1.2 7868 in = 3.850" Q- R-Id)? (15-3.25) -4.9330m P-Iats 15-3.95 +16.24 CN Area = 10.1 ha= 10.1% 10" me Volume = Area x Q = 10.1X/0" x 4.933x 10-2 - 4982.33.m