EP 1110-2-9
31 Jul 94
C-3. Development of Basin Model Hydrologic
Appendix C
Engineering Center (HEC-1)
Initial Hydrologic Engineering Manage-
ment Plan (HEMP) for a Flood Damage
Reduction Feasibility Study
gage data, develop unit hydrograph and loss rate parame-
ters for use in the study.
C-1. Scenario
b. Delineation of subareas. Subdivide study water-
shed based on the need for discharge-frequency informa-
a. The study objective is the development of a flood
tion at specific locations: major tributaries, damage index
protection plan for a community experiencing periodic
points, routing reaches, project sites, etc.
flooding from a stream draining a few hundred square
miles. The reconnaissance-phase study was based primar-
c. Subarea rainfall-runoff analysis of historic events.
ily on flood insurance study data and an abbreviated
Develop historic storm events, and subarea loss rate and
hydrologic engineering analysis. The study has deter-
unit hydrograph data for ungaged areas.
mined that a levee project is economically feasible. The
community is willing to be the cost-sharing local sponsor
d. Channel routing characteristics. Determine based
and would like a minimum certifiable level of protection
on information in Appendix D (Paragraph D-3d).
of a 1 percent chance event. A gage with 15 years of dis-
charge data is available at the site, with additional, short-
e. Assemble, debug HEC-1 model.
record gages located elsewhere in the watershed.
C-4. Hydraulic Studies
b. The feasibility phase will establish existing and
future without-project conditions. After discussions with
a. Prepare Water Surface Profile Data--Code HEC-2
the interdisciplinary study team and local sponsor, it was
model of study reach, after receipt of surveys. Estimate
decided that three heights of levee will be studied, along
"n" values, section locations, bridge routines applicable,
with six combinations of levee height and channel
effective flow areas. Debug model.
improvements to develop the economic optimum plan. A
total of nine alternatives will be evaluated. As all the
b. Calibrate HEC-2 model to gage data and high-
levee alternatives are along a similar alignment, a detailed
water marks from recent floods.
interior flood analysis will be evaluated for only the
National Economic Development Plan (NED) levee or
c. Develop storage-outflow relationships and flood
levee and channel plan. The hydrologic engineer must
wave travel time, by routing reach, for information
prepare an initial Hydrologic Engineering Management
required in Paragraph C-3d above.
Plan (HEMP) for the hydrologic engineering cost estimate
for the feasibility phase.
C-5. Calibration of Models to Historic Events
c. This sample initial HEMP represents what one
Calibrate the HEC-1 and -2 models to recorded events
might develop at the end of the reconnaissance-phase
and high-water marks. Make preliminary selection of
study for a time and cost estimate for use in the initial
hydrologic and hydraulic model parameters for hypotheti-
project management plan.
cal flood event analysis.
C-2. Preliminary Investigations/Initial Preparation
C-6. Frequency Analysis for Existing Land Use
Conditions
Finalize study objectives; confer with the study team
members on hydrologic engineering information require-
a. Perform statistical analysis of gaged data for
ments, study constraints, development information needs,
peak discharge-frequency relationship. Also estimate
and field reconnaissance; prepare survey data request;
prepare detailed HEMP.
C-1
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