FLOOD09429

• County: Statewide
• Basin: Statewide
• Title: Hydrologic Engineering Methods for Water Resources Development Volume 6
• Date: 7/1/1975
• Prepared For: US
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Educational/Technical/Reference Information

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Section 3.05. Significance of FloVl Type in Computerized Techniques

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TIle fact that surface water flows naturally as open channel

flow. but often is interrupted by the works of man so that pressure

flow exists, is of little concern when calculations are being done

manually. The engineer applies the appropriate procedures for obtain-

ing area. wetted perimeter and losses under the prevailing flow con-

ditions at each point. HO\'lever, "hen a computer program is being

developed for calculating water surface profiles, the capability to

distinguish between pressure flow and open channel flow should be

incorporated. This will permit automatic calculations to continue

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in the space remaining even though the mode of conveyance changes

back and forth between pressure and open channel flow. Calculating

area and wetted perimeter of flow, considering critical depth, and

including form losses, expansion losses and other losses besides

friction are primary problems in progralTVning the automatic computa-
tions.

No special program logic is required to identify the Reynolds

number in order to calculate friction loss, but one should be aware

of its significance on hydraulic roughness values and be prepared to

include such refinement if a problem warrants it. The classification

of steady flow profiles by bed slope and profile shape is not an

important feature in a computer program. but the program must distinguish

between subcritical and supercritical flow. i'toreover, it is important

to develop program logic so computations will continue ~Iithout manual

intervention.

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