Question
CIVENG 411. Water Resources Engineering Exam 1 Fall 2017 A storm with constant rainfall intensity (i0.4 inch per urs) precipitates on a soil surface with an initial moisture hour, duration 70 4 ho o 25 The conductivity and the wetting front suction head of the soil are = 34, 0.3 in/hr and =0.6 in, respectively. (1) Please (2) estimate the time it takes for water to pond on the surface. Estimate the cumulative infiltration depth at the ponding time. (3) Estimate the time it takes to infiltrate an additional 0.5 inch after ponding.
Explanation / Answer
1. By Green and ampt model
time for ponding = tp = K*Phi*(initial moisture deficit)/i*(i-K) = (0.3 in/hr * 0.6 in * 0.25) / (0.4 in/hr * (0.4-0.3) in/hr)
hence, tp = 0.045 / 0.04 = 1.125 hrs
2. Cumulative infilteration depth F = i*tp = 0.4 in/hr * 1.125 hr = 0.45 in