EP 1110-2-9
31 Jul 94
each alternative or component. The results provide exist-
c.
Alternative evaluation and selection.
ing and future, with-project information for each alterna-
tive to be evaluated.
(1) Alternative evaluation and selection is an iterative
process, requiring continuous exchange of information
(2) Most structural components are usually modeled
between a variety of disciplines. An exact work flow or
by modifying storage-outflow relationships at the compo-
schematic is not possible for most projects, thus Para-
nent location and/or modifying hydraulic geometry
graph D-7 could be relatively straightforward for one or
through the reach under consideration.
two components or quite complex, requiring numerous
reiterations as more cost and design information is known
(a) Reservoirs--adjust storage-outflow relationships
and project refinements are made. Paragraph D-7 is usu-
based on spillway geometry and height of dam.
ally the area of the HEMP requiring the most time and
cost contingencies.
(b) Levees--adjust cross-section geometry based on
proposed levee height(s). Evaluate effect of storage loss
(2) For the selected alternative, provide hydrologic
behind levee on storage-outflow relationships and deter-
information to environmental engineers for use in studies
mine revised discharge- and stage-frequency relationships
concerning the effects of the recommended project.
downstream, if considered significant. Develop uncer-
D-9. Hydraulic Design
tainty relationship for the revised stage-discharge function.
(c) Channels--adjust cross-section geometry based on
This paragraph and Paragraph D-8 are partly intertwined,
proposed channel dimensions. Evaluate effect of channel
as hydraulic design must be included with the sizing of
cross section and length of channelization on floodplain
the various components, both to operate hydrologic engi-
storage, modify storage-outflow in reach, and determine
neering models and to provide sufficient information for
revised downstream discharge-frequency relationships, if
design and costing purposes. Perform hydraulic design
considered significant.
studies commensurate with the level of detail of the study
process.
(d) Diversions--adjust hydrology model for reduced
flow downstream of the diversion and to identify where
diverted flow rejoins the stream (if it does).
way cross section, outlet works (floor elevation, length,
appurtenances, etc.), scour protection, pool guidetaking
(e) Pumping--adjust hydrology model for various
line, etc.
pumping capacities to be analyzed.
b. Levees. Levee design profile, interior flood control
(3) Evaluate the effects of potential components on
requirements, etc.
the sediment regime. Refer to guidance given in
EM 1110-2-4000.
c. Channels. Channel geometry, bridge modifica-
tions, scour protection, channel cleanout requirements,
(a) Qualitatively--for initial screening.
channel and bridge transition design, etc.
(b) Quantitatively (where necessary)--for final
d. Diversions. May be similar to channel design
selection.
activities, also would include diversion control (weir,
gates, etc.). Where the diversions are tunnels, open chan-
b. Nonstructural components.
nel flow and pressure conduit hydraulic analyses may be
necessary, depending on tunnel capacity and range of
(1) Floodproofing/structure raises--elevations of
possible discharges.
design events primarily.
e. Pumping. Capacities, start-stop pump elevations,
(2) Flood forecasting--development of real-time
sump design, outlet design, scour protection, etc.
hydrology model, determination of warning times, etc.
D-6
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