A triangular direct runoff hydrograph due to a storm has a time base of 90 hours. The peak flow of 60 m3/s occurs at 20 hours from the start of the storm, the area of catchment is 300 km2. The rainfall excess of the storm (in cm), is

Concept:Direct Runoff Hydrograph: It is a plot of discharge vs time past a specific point DUE to the direct runoff coming from the catchment without including any contribution from Baseflow.Area of Direct Runoff Hydrograph = Rainfall excess × Area of catchmentRainfall excess is the part of PRECIPITATION that reaches the stream SOON after the rainfall.Calculation:Given:Using the property explained above,\(\FRAC{1}{2} \times 60 \times 90 \times 3600 = \left( {R.E} \right) \times {A_{catchment}}\)⇒ 30 × 90 × 3600 = (R.E) × (300 × 106)⇒ R.E = 0.0324 m= 3.24 cm Since it is a direct runoff hydrograph, the discharge at time t = 0 is 0. For a hydrograph that has baseflow contribution, discharge at t = 0 is not zero.