53:078 Principles of Hydrology (Spring 2004)
Problem #31
Design Storm Approach for Flood Frequency Estimation on Ralston Creek (HEC-HMS)
In this assignment, you will be using the Hydrologic Modeling System
(HEC-HMS) Version 2.2.1 to simulate streamflows on the North Branch Ralston
Creek. Before you begin, please review the following:
Predict the 2-, 10-, and 100-year return period peak
discharges for the North Branch Ralston Creek using the design storm approach
(SCS Type II 24-hour design storms), and compare the estimates with those
based on flood frequency analysis of the streamgage flows (EV-1 distribution). Design floods should be predicted using the SCS method with a runoff curve
number (CN) for antecedent moisture conditions II (AMC-II), which was
determined for the North Branch Ralston Creek in Problem
14 (answers).
Design storms have been created for the 2- and 10-year return period, and
have been entered into the HEC-HMS data base for North Branch Ralston Creek.
You will need to enter the 100-year 24-hour SCS design storm that was
constructed in Problem 30.
- Use HEC-HMS to simulate the streamflow for the 2-year 24-hour design storm
for North Ralston Creek (Run 2). Make a printout
of the Summary Table for the North Branch. Highlight the predicted peak discharge.
This is the estimated 2-year return period peak discharge.
- Use HEC-HMS to simulate the streamflow for the 10-year 24-hour design storm
for North Ralston Creek (Run 3). Make a printout
of the Summary Table for the North Branch. Highlight the predicted peak discharge.
This is the estimated 10-year return period peak discharge.
- Enter the 100-year 24-hr SCS Type II design storm into HEC-HMS (see How
to make HEC-HMS work for instructions). Use HEC-HMS to simulate the
streamflow for the 100-year 24-hour design storm for North Ralston Creek. Make a printout
of the Summary Table for the North Branch. Highlight the predicted peak discharge.
This is the estimated 100-year return period peak discharge.
- Plot the 2-, 10-, and 100-year return period peak discharge estimates versus
the EV1 reduced variate for both the design
storm approach and the flood frequency analysis of streamgage flows (one
plot). Use the flood frequency estimates from Problem 26 (answers). (You might wish to notice the
differences in the two estimates to gain some insight on the uncertainties in
estimating design flows).
Hint: For the streamflow simulation with HEC-HMS, be
sure to enter the correct parameters for the
North Branch subbasin, a 120-min SCS lag for the SCS Transform, and the correct curve number (CN) for the SCS method.
(Note: Assume that the initial loss and the percent
impervious area are zero. However, be sure to leave the Initial Loss box
blank for the SCS Curve Number method (it won't work right otherwise).
Last changed on
04/27/04
by aab.