Compute the rainfall excess (direct runoff) for the North Branch Ralston Creek watershed (drainage area of 3.01 sq mi) for 17-18 July 1972 storm using the NRCS method. Use the areal-average precipitation estimated using the Thiessen Polygon method (this is provided). Assume that the NRCS runoff curve number (CN) is 82. Compute the following:

1. Total storm precipitation (in inches)
2. Cumulative rainfall hyetograph (in inches) (i.e., the mass curve)
3. Rainfall excess (P_e) hyetograph (in inches) [round-off to 2 decimal places]
4. Cumulative abstraction (I_a+F_a) (in inches)
5. Depth of direct runoff (r_d) (in inches)
6. Volume of direct runoff (V_d) (in acre-feet)
7. Effective storm duration (t_r) (in hr)
8. Runoff coefficient (C)

Hint: I recommend that you set this up with an Excel spreadsheet — it will make Problem #23 much easier. Be sure to make the CN an input variable, and use the spreadsheet to compute the potential maximum storage retention S, the intial abstraction I_a, and the rainfall excess calculations based on the CN value.