53:119 Hydrology
Problem #30
Time of Concentration Based on the NRCS Velocity Method

Compute the NRCS time of concentration a hydraulically most distant flow path with the following segements:

Segment Flow Path Slope Length (ft)
A Sheet Flow (Short-grass prairie) 0.02 100
B Shallow Concentrated Flow (Grassed waterway) 0.05 600
C Channel Flow (Triangular channel with 1v:3h side slopes and 1 foot depth; n=0.04) 0.015 1500
D Channel Flow (Rectangular channel with 7 foot width and 3 foot depth; n=0.05) 0.005 3000

Assume a 2-year 24-hour precipitation depth of 3.06 inches (for Iowa City area).

  1. Compute the travel time for segment A (in min).
  2. Compute the travel time for segment B (in min).
  3. Compute the travel time for segment C (in min).
  4. Compute the travel time for segment D (in min).
  5. Estimate the time of concentration (tc) (in min).
Last changed on 11/05/13 by aab.