31 Mar 95
therefore, interior ponding elevation.
materials of the levee and pumping tests of interior relief wells
for an existing levee project, or estimated from a similar project
(b) Exterior stage hydrographs may be entered directly,
(preferably in the same river basin). On a potentially large
computed from discharge hydrographs and rating curves, or
study, money may be available for subsurface investigation early
computed from rainfall-runoff as defined in a PRECIP and
enough to coordinate with the geotechnical engineer to have a
RUNOFF module (exterior subbasin) and rating curve. The
pump test at one or more boring locations. Generally seepage
latter is used where there is a high degree of dependence and
is lagged 1 day to simulate the flow rate along the seepage path.
coincidence between exterior and interior events.
(b) Auxiliary inflow. Auxiliary inflows provide means to
(c) HEC-IFH can transfer exterior stages (such as from a
enter hydrographs from adjacent areas or to compute them using
nearby gauge) to another upstream or downstream location
methods other than in HEC-IFH. For example, a more detailed
using river transfer relationships. Figure 3-20 illustrates the
analysis of a complex system (more than two subbasins) may be
concept of relating data from the index location to another
performed using HEC-1 or another program and the
location based on the slope in the water surface profiles.
hydrographs imported into HEC-IFH from HEC-DSS. HEC-1
Evaluation of interior systems with outlets on a tributary to the
may be used to compute hypothetical runoff hydrographs using
main stem where the exterior stages at the outlet are affected by
the kinematic wave in an urban area. Similarly, a continuous
the main stem backwater may also be performed. Chapter 8 of
runoff record generated from a more detailed moisture
the HEC-IFH user's manual describes the EXSTAGE module
accounting program could be imported and used in HEC-IFH.
and data entry options in detail.
Data for the PRECIP and RUNOFF modules would not be
required in these cases. Another application of auxiliary inflow
(7) AUXFLOW module. The AUXFLOW module defines
is to import overflow from an adjacent interior area into HEC-
external flow into the system, overflow and diversion out of the
IFH for the area under study. This would be applicable where
system, and seepage inflow from the exterior river to the interior
adjacent subbasins have a cascading effect and are analyzed as
area. Chapter 9 of the HEC-IFH user's manual describes in
separate interior areas. Appendix D provides a case example
detail the AUXFLOW module.
application that uses auxiliary inflows.
(a) Head-versus-seepage relationships. A secondary inflow
(c) Diversions. Diversions transfer all or portions of the
into the ponding area is seepage through or under the line-of-
runoff from one location to another. Diversions may be made to
protection during high exterior river stages. A relationship of
remove flow from an upper subbasin to the exterior river via a
seepage rate versus differential head between the interior pond
pressure conduit. They may be designed to alter all flows or to
and the exterior river stage is generally estimated by the
convey flows above or below some target value.
geotechnical member of the study team. It is based on soil
Figure 3-20. Main river transfer concept: slope-profile