Practice Question: Peak Runoff for Different Terrains
NCEES Civil PE Specification V.D.: Runoff analysis
Problem
A city block is divided between a park, a cemetery, and undeveloped land. Due to increased demand, the cemetery owner plans to purchase the undeveloped land and extend the cemetery boundaries 😞.
Given the parameters shown in the figure and a storm with peak intensity of 10 inches per hour occurs, determine the increase in peak runoff flow in cubic feet per second once the new cemetery limits are developed.
Select an Answer:
CORRECT 😃
INCORRECT 😟
% Students Correctly Answered:
61.4%
Solution
Answer: C) 0.75 cfs
Peak runoff flow can be calculated based on the rational formula:
$$ Q=C\ast\ I\ast\ A $$
Runoff flow prior to extending the cemetery:
$$ Q_{old}=\left(0.15\ast0.75\ ac+0.25\ast2.5\ ac+0.1\ast2\ ac\right)\ast10\frac{in}{hr}=9.38\ cfs $$
Runoff flow after extending the cemetery:
$$ Q_{new}=\left(0.25\ast\left(2.5\ ac+0.75\ ac\right)+0.1\ast2\ ac\right)\ast10\frac{in}{hr}=10.13\ cfs $$
Change in flow:
$$ \Delta Q=Q_{new}-Q_{old}=10.13\ cfs-9.38\ cfs=0.75\ cfs $$
