53:078 Principles of Hydrology (Spring 2004)
Problem #28
Rational Method to Predict Urbanization Effects
Use the Rational Method to evaluate the effect of a
proposed subdivision development on the 10-year peak discharge for a 92-acre subcatchment near Iowa City with the
characteristics listed below. The hydrologic soil group for the entire
subcatchment is B.
| Before Development | After Development |
| 65% Lawn (Fair condition) | 75% Single Family Home |
| 35% Undeveloped Areas | 25% Business (Neighborhood Area) |
| tc = 60 minutes | tc = 25 minutes |
Estimate the Rational Method runoff coefficient (C) using Iowa Urban Design
Standard Manual (Table 3.1).
Estimate rainfall intensity using the rainfall frequency atlas estimates for Iowa (class handout, Table 3.5 -- Section 6). [Hint: First interpolate the rainfall
depths for
the required duration. Then compute the rainfall intensities]
- Compute the 10-year return period peak discharge (in cfs) before development.
- Compute the 10-year return period peak discharge (in cfs) after development.
- Which effect of development has a greater influence on the peak discharge
for this case, the change in land cover or the change in tc?
Hint: Use the Rational Method to examine the two effects one-at-a-time.
Last changed on
04/22/04
by aab.