Shiau JT, Wu FC (2006) Compromise programming methodology for determining instream flow under multiobjective water allocation criteria, JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, 42(5), pp. 1179-1191.
Instream flow is one of the most challenging issues in water resources systems. Using a multiobjective optimization criterion, this study implements a framework to allocate water for three different uses: agriculture, urban and instream flow. The methodology considered three objectives: overall degree of hydrological alteration, shortage ratio for agriculture withdrawals, and shortage ratio for municipal uses. The degree of hydrological alteration was assessed using the Range of Variability Approach (RVA), which use 32 indicators of hydrological alteration (IHA) to evaluate hydrological impacts. The decision variable is instream flow release, considered to be constant during time.
The methodology was applied in Kaoping watershed in southern Taiwan. A weir operation diverts a maximum of 35 m³/s for municipal uses but more than that is also diverted to irrigation districts.
Results indicate that actual 9.5 m³/s instream flow is not enough to restore the natural flows variability. Weighting the three objective functions equally, optimal instream flow discharge of 26 m³/s could reduce hydrological alterations from a high to moderate state. A discharge of 93 m³/s would bring the hydrological regime to a low alteration state.
Discussion
This paper presents a very important study for water resources management. It combines shortage ratios and hydrological alteration statistics to perform a multiobjective optimization. The degree of hydrological alteration considered a kind of average value of the 32 IHA to represent the overall alteration. Future improvements could consider each of 32 indicators or the five groups of IHA. Considering variable instream flow releases would also be a interesting application.
The variable instream flow releases would be interesting to incorporate for this program. Andrew pointed out in his discussion that the TWDB has already tackled a program that does just this, however what form of optimization that was implemented in the program would be interesting to look into.
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