Question

11. A client requires a drainage design for a yard inlet. The area to be drained is a 400ft by 500ft area with an average slope of 2% from one corner to the other (diagonal across the rectangular area). The surface is comprised of grass with a Manning's roughness coefficient of 0.4. You may assume a runoff coefficient of 0.5. Compute the design discharge for a storm (in cfs) with a return interval of 1 year. Determine the size of a circular inlet with 66% clear area needed to handle this runoff.

Answer 1

solution, given data Rectongular for a area Size = 400x soo et bed slope (S) = 2% morning's Roughness coefficient Runoto coettient =0.5 -0.4 use in monning's that equation area to compute Rain ball R- YAR 3 A = 400 x 500 = 20 x 10 Gt² K noobt Perimeter 6 = Bray = 400 + (500XL) - 14000t. Hydraulic rean depth (R) - Ale

R = 20x104 .- 142.866t 1450 - they shoxo" y com.augub {178 Q = 193.23 x10 ft Rain bau . Area in this latement Q- 193.23 x 10 cta Raunott CoetG² = Rain off Rainball 0.5 = Rainoto 193-23X1ou Runoto (OR) - 96.624 104 cl bor due Design to as discharge storm the catch meter By using Rational burmale Qp = Yaxkx PCX A.

K= 0.5 Renbal (d) 1 Time Pied Rainfall 'lyar Time Period S2 Pc = 1/365 Xhuhr. = 1.14 X 10" (m / sec Area in hr 450 X 500 X (0.3048 x 10-4 ha Area = 1.86 ha Q1 = 1/36 10.5 x 1.14 X20" x 1.86 Qua 0-13 Xco-4 m/sec it we use circular inlet instead of Rectongular, one so 6.6%. clear area needed to handdle the run off. Area of circular inlet (A.) = 56/150 X 400 X 500

AC= WL X 100 6t² Size of the circular inlet Aca Tlux (Rc)2 = B2 XR03 Re- 489.36 bt с 10 БЕ