Question

[2] 7.7.8 The Gimlet Creek watershed at Sparland, Illinois, has a drainage area of 5.42 mi; the length of the main stream is 4.45 mi and the main channel length from the watershed outlet to the point opposite the center of gravity of the watershed is 2.0 mi Using c -2.0 and C-0.625, determine the standard synthetic unit hydrograph for this basin. What is the standard rain duration? use Snyder's method to determine the 30-minute unit hydrograph for this watershed

Answer 1

Data from the given question is drainage Area = 5.42 Mi^2. Length of main stream = 4.45 Mi. Center of gravity = 2.0 Mi. C_t = 2.0 C_P = 0.625. Lag time (or) Basin lag tP = C_t (L times L_C)^0.3 = 2(4.45 times 2)^0.3 = 2(8.9)^0.3 = 2 times 1.9267 tP = 3.8534 hr Peak discharge QP = 2.78 times C_P times (A/tP) = 2.78 times 0.625 times (5.42/3.8534) QP = 2.44386 m^3/sec. \r\n Base time tb = 3 + tP/8 = 3 + 3.8534/8 = 3 + 0.481675 tb = 3.481675 tb = 3.48 days. w_50 = 5.87 times (q_P/A)^-1.08 = 5.87 times (2.443/5.42)^-1.08 = 5.87 times 2.3646 = 13.88 w_75 = w_50/1.75 = 13.88/1.75 = 7.9316. 0.5 QP = 0.5 (2.443) = 1.2215 m^3/sec. \r\n 0.75 QP = 0.75 (2.443) = 1.83225 m^3/sec. D = tP/5.5 = 3.853/5.5 = 0.70054 hr.