Design Criteria, Methods, Objectives

• Primary Design Criteria (4)– Maintain necessary freeboard at maximum flow– Maintain modular (critical) flow at minimum and

maximum flow (ensure free flow)– Froude number at maximum flow must be less than 0.5

• Secondary Design Criteria (2)– Control section must produce sufficient head to provide a

user-specified level of discharge-measurement precision at both minimum and maximum flow, based on the precision of the device used to measure upstream water level.

Control Section Adjustment Methods

Head Loss Objectives

• Minimum head loss

• Maximum head loss

• Intermediate head loss

• Match head loss to drop in canal invert at site

WinFlume’s Design Procedure• User chooses one of the four methods of contraction change, and

an increment at which to evaluate designs (e.g. evaluate designs at sill height increments of 0.1 ft).

• WinFlume brackets the range of possible designs by evaluating flume performance at the maximum design flow:

– The maximum possible throat-section contraction is that needed to produce a maximum upstream water level equal to channel depth.

– The minimum contraction is that which produces an upstream Froude number of 0.5 or less at maximum discharge, and an upstream water level that is at least as high as the downstream tailwater at maximum discharge.

• WinFlume builds and evaluates designs of “virtual” flumes between the lower and upper contraction limits at the interval specified by the user.

Design Procedure (continued)• Results are presented to the user, who may choose to accept one of the

designs or discard the results of the analysis.– Only designs meeting the four primary design criteria (freeboard,

Froude number, no submergence at minimum and maximum flow) are presented to the user, unless there are no acceptable designs.

– Designs that meet the four primary criteria, but do not meet measurement precision requirements may be improved by the user by specifying a better water level measurement method.

• Acceptable designs that have minimum head loss, maximum head loss, intermediate head loss, or head loss matching the bed drop at the site are listed in the output, along with any other acceptable designs. The user can evaluate the different head loss characteristics of the possible designs and then choose the design that best meets their needs.

If An Acceptable Design Is Not Found On The First Trial

• If contraction increment is too large, or if design criteria are too limiting, no acceptable design may be found.

• WinFlume searches for two adjacent designs for which the unsatisfied criteria in each design are satisfied in the adjacent design.– An acceptable design may exist between those two designs– Analysis is repeated using a smaller increment of

contraction change within that range.

• If no region of acceptable designs is found, then the results of the analysis are presented to the user, with suggestions for how to relax the design criteria or change the initial design so that an acceptable design can be found.