Topic 1-SP 1C - INFILTRATION AND RUNOFF ANALYSIS A storm with a rainfall pattern as shown below occurred over your watershed and you are asked to determine the runoff from the rainstorm. The rainfall pattern is shown: 30 min of rainfall, 30 minutes of no rain (infiltration recovery), followed by 60 minutes of rain at different amounts for each 30 min period. The infiltration rates are sketched in. They are not accurately plotted and are diagrammatic only. Depth, in 2 0.5 Data are as follows: 0 1.5 in Rainfall Item Infiltration - not to scale Rainfall period duration, each, min fo, in/hr fc, in/hr K, hr-¹(decay) Kr, hr¹ (recovery) Partial Recovery Interception Losses in 1st rainfall period only, in Depression Storage in 1st rainfall period only, in 0.75 in Rainfall Time, minutes 90 2.0 in Rainfall 120 Infiltration Rate, in/he Value 0.10 0.15 30 1.50 0.50 3 2 a) Calculate the actual infiltration rates, f, in/hr, at each 30 minute period, taking into account recovery and decay b) Calculate the amount of infiltration that occurred in each 30 minute rainfall period, F, in. c) Taking into account the interception and depression storage losses and the infiltration from b), determine the direct runoff in each of the 3 rainfall periods, in.

Fig: 1