Problem 6-1

Rain falls on a 15-ha urban catchment with an average intensity of 2.5 cm/h and duration of 2 h. The catchment is divided into (1) industrial district (with 72% impervious area), soil group B, covering 25% of the area; and (2) residential district, with 1/4-ac average lot size (with 38% impervious area), soil group C, covering 75%. Determine the total runoff volume, in cubic meters, assuming AMC II antecedent moisture condition.

Problem 6-2

The following rainfall distribution was observed during a 24-h storm:

Time (h)	Intensity (mm/h)
0-3	5
3-6	8
6-9	10
9-12	15
12-15	12
15-18	10
18-21	5
21-24	2

The φ-index is 3 mm/h. Calculate the runoff curve number.

Problem 6-3

Calculate a set of Snyder synthetic unit hydrograph parameters for the following data: catchment area A = 520 km²; L = 25 km; L_c = 14 km; C_t = 1.5; and C_p = 0.62.

Problem 6-4

Calculate an SCS synthetic unit hydrograph for the following data: catchment area A = 11.2 km²; runoff curve number CN = 82; hydraulic length L = 4.2 km; and average land slope Y = 0.02. Plot the calculated unit hydrograph using a spreadsheet.