Final answer:
Using the Rational Method, the peak flow rate for an area of 5 acres with a runoff coefficient of 0.30 and a rainfall intensity of 1.2 inches per hour is 1.8 cfs. This is determined by converting the area to square feet, the rainfall intensity to feet per hour and then using the Q = CiA formula to calculate Q, the peak discharge rate. The correct option is c).
Step-by-step explanation:
The question asks to determine the peak flow rate using the Rational Method for an area of 5 acres given a runoff coefficient of 0.30 and a rainfall intensity of 1.2 inches per hour.
The Rational Method equation can be expressed as Q = CiA, where Q is the peak discharge rate in cubic feet per second (cfs), C is the dimensionless runoff coefficient, i is the rainfall intensity in inches per hour, and A is the drainage area in acres.
First, we need to convert the drainage area from acres to square feet (1 acre = 43,560 square feet):
A = 5 acres * 43,560 square feet/acre = 217,800 square feet
Next, we multiply all the values together to get the peak flow rate:
Q = 0.30 * 1.2 inches/hour * 217,800 square feet
However, we should convert the intensity from inches/hour to feet/hour as we work in cfs:
Q = 0.30 * (1.2 inches/hour / 12 inches/foot) * 217,800 square feet
Q = 0.30 * 0.1 feet/hour * 217,800 square feet
Q = 6534 cubic feet/hour
To convert the peak flow rate to cfs:
Q = 6534 cubic feet/hour / 3600 seconds/hour = 1.8 cfs
Therefore, the peak flow rate of an area of 5 acres with a runoff coefficient of 0.30 and a rainfall intensity of 1.2 inches per hour is 1.8 cfs. Option c) is the correct one.