53:078 Principles of Hydrology (Spring 2004)
Problem #22
Streamflow Prediction for Ralston Creek Using a
Synthetic Unit Hydrograph (July 1972 Flood)
Predict the streamflow hydrograph for the North
Branch Ralston Creek (drainage area of 3.01 square miles) during the flood
on July 17-18, 1972. The areal
average rainfall estimates (based on the Thiessen polygon method) are
available. You will also need to use the observed
streamflow
hydrograph for comparison with your prediction. Assume the following
basin characteristics:
- f-index is 0.59 in/hr for the storm.
- Time of concentration: 200 minutes
- Constant baseflow of 10 cfs
Use the NRCS triangular unit
hydrograph method.
- Compute the rainfall excess hyetograph (in inches)
- Develop the NRCS unit hydrograph (in cfs) [HINT: First determine
the effective duration (tr) required for prediction given
the rainfall excess in part a]. Use a time step of 0.5 hour for the unit
hydrograph values.
- Predict the direct runoff hydrograph (in cfs). Use a time step of 0.5
hour.
- Predict the streamflow hydrograph (in cfs). Use a time step of 0.5 hour.
- Plot the predicted vs. observed hydrographs
NOTE: Only
part (e) requires a graph. In parts (a)-(d) provide a table of the
values.
Last changed on
03/29/04
by aab.