FLOOD01888

• County: Statewide
• Title: River Hydraulics
• Date: 10/15/1993
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Educational/Technical/Reference Information

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.
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accurnte, but they do so with increased study effort.
They are also constrained by the modeler's experience
and ability to formulate and accurately solve the mathe-
matical expressions and obtain the data that represent the
important physical processes.

e. Hybrid modeling. The preceding paragraphs
described the four principal solution methods and some
of their advantages and disadvantages. Common practice
has been 10 use two or more methods jointly, with each
method being applied to that purlion of the study for
which it is best suited. For example, field data are usu-
ally used 10 define the most important processes and
verify a model that predicts hydrodynamic or sedimenta-
tion conditions in the river. Combining physical model-
ing with numerical modeling is referred to as hybrid
modeling. Combining them in a closely coupled fashion
that permits feedback among the models which is
referred 10 as an integrated hybrid solution. By devising
means to integmte several methods, the modeler can
include effects of many phenomena that otherwise would

EM 1110-2-1416
15 Oct 93

include effects of many phenomena that otherwise would
be neglected or poorly modeled, thus improving the
reliability and detail of the results. A hybrid modeling
method for stodying sedimentation processes in rivers,
estuaries and coastal waters has been developed by the
Waterways Experiment Station (WES) (McAnally et al.,
1984a and 1984b; JOhoson et al., 1991). The method
uses a physical model, a numerical hydrodynamic model,
and a numerical sediment transport model as its main
constituents. Other optional components inclode a wind-
wave model, a longshore current calculation, and a ship
handling simulator.

f Selection of procedure. Tables 3-2 and 3-3 give
suggestions, based on experience, regarding usage of the
various procedures in different phases of flood control
and navigation studies. This information should be
viewed as a starting point; it will change as computer
resources and the Corps' planning process and missions
evolve.

Table 3-2
Model Usage During Hydreullc Sludies For Flood Conlrol Prolecte

Stage Existing Data GVSF MB
& Criteria

GVUSF

Phys.'

x

Multi-D

Reconnaissance

x

1(1)
X(I)
X

FeasibililY

X

Rs-evaluation

X

General Design
Memo.

x

X

Feature Design
Memo.

Continuing
Authority

x

X

X(I)

X(2)
X

1

1

1

1

X

X(3)

X(3)

X(3)

X(3)

1

1

1

. Existing Data and Criteria = available reports. Corps criteria. regional relationships for depth-frequency, nonnal depth rating relationships,
elc.; GVSF = gradually varied, steady flow p.e. HEC-2, HEC (199Ob)l: MB = moble boundary analysis p.e. HEC-6. HEC (1991a)l; GVUSF =
gradually varied unsteady ftow [i.e. UNET, HEC (1991b): not inclueing hydrologic models like HEC-l, HEC (199Oa)); Multi-D = multidimen-
sional analysis [i.e. TABS-2, Thomas and McAnally (1985)): Phys_ = physical models (by WES or similar agency).

1 Possible. but very unusual- highly dependent on problem being analyzed.

(1) Sediment problems musl be addressed. bUllhe procedure at this stage may be qualitative or quantitative. depending on the type and
magnitude of the project.

(2) Use is possible. but unlikely, on most ftood control stueies.

(3) Typically employed 10 evaluale design perlormance for a short reach of river or in the immediate vicinity of a specific project compo-
nent. or 10 refine the hydraulic design of a project component.

3-3