ETL 1110-2-367
31 Mar 95
area elevation-frequency and duration relationship using the
simultaneously. In this case, the pumps are assumed to stop
computed interior stage hydrograph.
when the gravity outlets are discharging.
3-8.
Analytical Procedures
e.
Interior pond routing parameters.
An overview of procedures used to perform the CSA and HEA
(1) The "Starting Pond Elevation" of Figure 3-23 is the
analyses are described in the following subsections.
interior storage pond elevation at the beginning of the analysis.
The starting pond elevation must be within the range of
a. Analytical procedures for CSA. HEC-IFH continuous
elevations specified in the pond elevation-surface area table. If
simulation analyses are performed in the following sequence:
the starting pond elevation is below the minimum elevation, or
above the maximum elevation, HEC-IFH adjusts the starting
(1) Rainfall. Enter continuous record rainfall data for a
elevation to the minimum or maximum value as appropriate. It
single gauge or several gauges. If appropriate, compute the
also writes a warning message to the plan message file.
composite basin average precipitation for a subbasin as the
weighted average of measurements for up to five individual rain
(2) The "Minimum Head of Gravity Outlet Operation"
gauges. Chapter 3 of the HEC-IFH user's manual describes
specifies the minimum positive differential head (interior minus
rainfall data entry.
exterior water surface elevation) necessary before the gravity
outlets will operate. Some levee systems close the gravity
(2) Rainfall excess. Compute subbasin rainfall excess
outlets when the exterior water surface elevation rises to a level
values using either the generalized runoff coefficients or the
close to the interior water surface elevation. The user may
initial-uniform recovery method. Chapter 4 of the HEC-IFH
specify gates on gravity outlets that require a small head
user's manual describes these methods.
differential before the outlet will open. Any value greater than
or equal to zero may be entered.
(3) Runoff. Transform rainfall excess into a runoff
hydrograph for each interior subbasin using user-defined unit
(3) The "Operate Pumps, Gravity Outlets Simultaneously?"
hydrograph methods. Add base flows to the computed runoff
option requires a "yes or no" response. If "Yes" is selected,
hydrographs. Chapter 4 of the HEC-IFH user's manual
then the pumps and gravity outlets operate independently. They
describes these methods.
may operate simultaneously at times during the analysis. If
"No" is selected, then pumps and gravity outlets do not operate
Figure 3-23. Pond starting conditions screen
3-18
Previous Page
