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Compromise Programming Methodology for Determining Instream Flow under Multiobjective Water Allocation Criteria
By Jenq-Tzong Shiau and Fu-Chun Wu

Journal of the American Water Resources Association
October 2006

Summary

The purpose of this paper is to quantitatively address “the problem of compromises between human water demand and instream flow requirements.” To illustrate this problem, the authors choose to model the Kaoping diversion weir in southwestern Taiwan. The diversion weir was designed to “simultaneously assure the water supply reliability and sustain the natural flow variability.” However the second objective was not meet (at least not at an acceptable standard), since the weir flow often varied significantly from the naturally flow. There are three primary demands placed on the flows of Kaoping Creek: 1) Instream flow releases; 2) Agriculture water withdraws; 3) Municipal uses. The water allocation priorities are in the same order as listed.

In an effort to optimize this multiobjective system, the authors utilize the Range of Variability Approach (RVA) to evaluate the hydrologic alterations. The RVA resulted in 32 Indicators of Hydrologic Alterations, which are integrated into a single index that allows for the optimization of the multiple conflicting objectives. The optimal operation scheme was “then determined using the compromise programming among multiple conflicting objectives.” The objective function was to minimize both hydrologic impacts and water supply shortages.

The model determined “that the current minimum flow release of 9.5 m3/s does not effectively serve to restore the natural flow variations.” It was found that if the water releases were increased the overall stream flow variations would be reduced; however, the increase in flow releases would simultaneously increase the water supply shortage ratios. If equally weighting was given to the natural flow variability and water supply reliability, the optimal instream flow is 26 m3/s.


Discussion

Did anyone else find it a little peculiar that the registered agricultural water withdraws remained nearly constant for the entire year but the diversions for municipal use was extremely variable? Typically it is the opposite. Do these people find it beneficial to irrigate all year around but consider bathing and drinking only important from May to December? I’m assuming they have some other water source, but still.