FLOOD01888

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

EM 1110-2.1416
15 Oct 93

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hydrograph for a reach subject to a given inflow hydro-
graph at its upstream end, the hydraulic methods compute
water surface elevations and discharges at a sequence of
stations in the interior of the reach. The desired hydro-
graph is computed along with all interior hydrographs,
and stages in the reach are routinely determined as part
of the solution. In another example, the calculated
advance of a darn-break flood wave is a by-product of
calcutations of flow conditions in the interior of the
wave.

(b) In the limit, as the number of distance steps
increases indefmitely, while the size of each is
correspondingly reduced, the governing physical prin-
ciples lead to partial differential equations in distance
along the channel and time. The dependent variables are
the time dependent proftles of depth and discharge (or

5-22

depth and discharge hydrographs at all stations in the
reach). These partial differential equations are generally
solved numerically, algebraically, in finite-sized distance,
and time steps with the aid of high-speed electronic
computers.

(7) The hydrologic techniques are often easi,er to
. apply than the hydraulic techniques and are usually asso-
ciated with quicker, less troublesome, computations.
Hydraulic methods require a description of the geometry
and roughness of the reach usually defmed by cross
sections and reach lengths. Those hydrologic methods
which use past flood hydro graph records to estimate the
response of the reach bypass such detailed analysis of the
physical characteristics of the reach; the lumped effect of
its physical characteristics is assumed to be incorporated

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