ETL 1110-2-367
31 Mar 95
(4) Auxiliary flows. Determine auxiliary flows such as
(3) Runoff. Transform rainfall excess into a runoff
diversions from the upper interior drainage area, overflow from
hydrograph for each interior subbasin. Unit hydrographs may
an adjacent lower area, or seepage through the levee. Chapter 9
be entered directly, or computed using the Clark, Snyder, or
of the HEC-IFH user's manual discusses auxiliary flows.
SCS Dimensionless unit hydrograph methods. Compute base
flow and base flow recession. Chapter 4 of the HEC-IFH user's
(5) Channel routing. Route the total discharge hydrograph
manual discusses the available unit hydrograph methods.
from the upper portion of the interior area to the interior
ponding area using the modified Puls, Muskingum, or Lag
(4) Auxiliary flows. Determine auxiliary flows such as
methods. Chapter 4 of the HEC-IFH user's manual discusses
diversions from the upper interior area, overflow from an
channel routing.
adjacent lower area, and levee seepage. Chapter 9 of the HEC-
IFH user's manual describes auxiliary inflows and diversions.
(6) Exterior stages. Define exterior stage data using an
exterior stage hydrograph or an exterior discharge hydrograph
(5) Channel routing. Route the total discharge hydrograph
and channel rating curve. Exterior discharge hydrographs may
from the upper portion of the interior area to the interior
also be computed using the same rainfall-runoff methods
ponding area. The modified Puls, Muskingum, Muskingum-
described for interior discharge hydrographs. Chapter 8 of the
Cunge, or Lag methods are available. Streamflow routing is
HEC-IFH user's manual describes exterior stage data.
discussed in Chapter 4 of the HEC-IFH user's manual.
(7) Pond routing. Route interior inflow through the ponding
(6) Exterior stages. Define exterior stage data using an
area and discharge it through the line-of-protection via the
exterior stage hydrograph or an exterior discharge hydrograph
gravity outlets and/or pumping stations. Seepage and auxiliary
and channel routing curve. Exterior discharge hydrographs may
flows into or out of the ponding area are included in the pond
be computed using the same methods described for interior
analysis. Chapter 5 of the HEC-IFH user's manual describes the
discharge hydrographs. Chapter 8 in the HEC-IFH user's
interior pond module, while Chapter 10 describes the interior
manual describes exterior stage data.
pond routing computations. The gravity outlet rating curve, the
pump outlet capacity, and seepage and overflows are described
(7) Pond routing. Route interior inflow through the ponding
in Chapters 6, 7, and 9, respectively, in the user's manual.
area and discharge it through the line-of-protection via the
gravity outlets and/or pumping stations. Include seepage flows
(8) Results analysis.
Develop elevation-frequency
through the line-of-protection, as well as overflows from the
relationships, duration of flooding, and other pertinent
ponding area. Gravity outlet rating curves, pump station
hydrologic information from the analysis results. Chapter 11 of
capacity, seepage/diversions, and interior pond routing
the HEC-IFH user's manual documents the program results,
computations are described in Chapters 6, 7, 9, and 10,
output tables, and plots.
respectively, in the HEC-IFH user's manual.
b. Analytical procedures for HEA. HEC-IFH program
(8) Analysis results. Determine the interior elevation-
frequency relationships and other results from the computation
procedures for hypothetical event analysis are performed in the
outputs of the HEC-IFH program.
following sequence:
3-9.
Analysis Summaries
(1) Rainfall. Enter hypothetical storm depth-duration-
frequency data for individual or multiple hypothetical events
HEC-IFH has extensive reporting capabilities. Table 3-1
historic storms and/or for the SPS. Hypothetical frequency
provides an overview of the output capabilities for both the CSA
storms are balanced storm distributions with total rainfall
and HEA options. Figures 3-24 and 3-25 show the hydrologic
amounts consistent with specific exceedance frequencies or
analysis summary screens, from which the user may view the
recurrence intervals. The program can consider the 0.2-percent
output and print results. Chapter 12 of the HEC-IFH user's
(500-year), 1-percent (100-year), 2-percent (50-year), 4-percent
manual provides a detailed description of the output summary
(25-year), 10-percent (10-year), 20-percent (5-year), and
capabilities of HEC-IFH.
50-percent (2-year) frequency storms. The SPS is determined
according to the criteria discussed in EM 1110-2-1411.
3-10.
Plan Comparison
Chapter 3 of the HEC-IFH user's manual describes rainfall data
entry.
The HEC-IFH program enables users to compare the
performance of various plans in tables and graphically.
(2) Rainfall excess. Compute rainfall excess for each
Figures 3-26 and 3-27 show users options for plan comparison
interior subbasin using SCS curve number, Holtan, Green-
for the CSA and HEA. Chapter 13 of the HEC-IFH user's
Ampt, or the Initial-Uniform methods. Chapter 4 of the HEC-
manual provides details on the plan comparison capabilities.
IFH user's manual describes these methods.
3-19
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