This is the review of the paper titled "Compromise Programming Methodology for Determining Instream Flow under Multi-objective Water Allocation Criteria" by Jeng-Tzong Shiau and Fu-Chun Wu, in the Journal of the American Water Resources Association in October, 2006.
This paper is about implementing a quantitative assessment framework for determining the instream flow under multi-objective water allocation criteria using a the Range of Variability Approach (RVA) to evaluate hydrologic alterations caused by flow diversions. The resulting degrees of alterations for the 32 Indicators of Hydrologic Alterations (IHAs) are integrated into one overall degree of Hydrologic Alteration. The inclusion of this index in the objective function to optimize a water allocation scheme to minimize hydrologic alterations and water supply shortages using compromise programming is suggested.
The proposed methodology is applied to a case study of the Kaoping diversion weir in Taiwan that is designed to simultaneously assure the water supply reliability and sustain natural flow variability. The Kaoping Creek in southwestern Tainwan is 171 km long and has the largest drainage area(3,257 km2) on the island, the average annual runoff being about 8.5 billion m3. The creek supplies major proportions of the total water demand in this region. The Kaoping diversion weir with a design diversion capacity of 35 m3/s was completed in 1999, built to supply for the increasing municipal demands. The Kaoping Creek provides habitats for some endemic species and it is believed that agricultural withdrawals and municipal diversions both can effect the aquatic biota considerably dowstream of the Kaoping weir. Currently a minimum instream flow of 9.5 m3/s is being released at the weir but a minimum flow is unable to provide sufficient flow variation which is recognosed as a primary driving force for sustaining the integrity of aquatic ecosystems.
In RVA analysis, a range of variation for each IHA is determined from the prediversion flows. In this study the target range for each IHA was bracketed between 25th and 75th percentile values as suggested by Richter et al. (1998). The weir operations are aimed to make post diversion flow conditions reach the established RVA ranges at the same frequency as that of the prediversion flows.
This is a multi-objective decision making problem which involves the minimizing of the hydrologic impacts and water supply shortages as the operational goals for the Kaoping weir. The objective function can be expressed as a function of shortage ratio of the registered agriculural withdrawals, shortage ratio of the projected diversion for municipal supplies and the combined index for Hydrological Alterations whose definitions are provided in the article. All these can be expressed as the function of the instream flow value as decision variable.
The compromise programming algorithm is adopted as the authors believe its suited for the discrete problem and is still felixible for the preferences of the decision makers concerning the relative importance of each goal considered. Compromise programming identifies the optimal solution as the one that has the shortest distance to an ideal point where the multiple objectives simulatneously reach their minimum values. The ideal point is practically inachievable but may be used as a base point.The objective function involves the use of the base point and the worst point wrt each goal. It also involves the use of weights in order to decide the preferred goals.
The results indicate that the current realease of 9.5 m3/s as a minimum instream flow does not effectively restore the natural flow variations. Increasing the amount of instream flow release would reduce the overall degree of hydrologic alteration; however, this is achieved at the cost of increasing the water supply shortage ratios. An equal weighting to both water supply reliability and natural flow variability would suggest a minimum flow of 26 m3/s which is supported by the authors. The authors also suggest an improvement by including biological component into the current model for a better representation of ecological effects.
My views:
I like the approach and totally understand the use of a single index for hydrological alterations for reducing complexity of the model. Though I would suggest some alternative approaches like developing a pareto front and evaluate scenarios for different objects, trade-off analysis. I would also like to see a weighting introduced in the IHAs so as to recognize which IHAs have more effect on the downstream ecology.
This paper is about implementing a quantitative assessment framework for determining the instream flow under multi-objective water allocation criteria using a the Range of Variability Approach (RVA) to evaluate hydrologic alterations caused by flow diversions. The resulting degrees of alterations for the 32 Indicators of Hydrologic Alterations (IHAs) are integrated into one overall degree of Hydrologic Alteration. The inclusion of this index in the objective function to optimize a water allocation scheme to minimize hydrologic alterations and water supply shortages using compromise programming is suggested.
The proposed methodology is applied to a case study of the Kaoping diversion weir in Taiwan that is designed to simultaneously assure the water supply reliability and sustain natural flow variability. The Kaoping Creek in southwestern Tainwan is 171 km long and has the largest drainage area(3,257 km2) on the island, the average annual runoff being about 8.5 billion m3. The creek supplies major proportions of the total water demand in this region. The Kaoping diversion weir with a design diversion capacity of 35 m3/s was completed in 1999, built to supply for the increasing municipal demands. The Kaoping Creek provides habitats for some endemic species and it is believed that agricultural withdrawals and municipal diversions both can effect the aquatic biota considerably dowstream of the Kaoping weir. Currently a minimum instream flow of 9.5 m3/s is being released at the weir but a minimum flow is unable to provide sufficient flow variation which is recognosed as a primary driving force for sustaining the integrity of aquatic ecosystems.
In RVA analysis, a range of variation for each IHA is determined from the prediversion flows. In this study the target range for each IHA was bracketed between 25th and 75th percentile values as suggested by Richter et al. (1998). The weir operations are aimed to make post diversion flow conditions reach the established RVA ranges at the same frequency as that of the prediversion flows.
This is a multi-objective decision making problem which involves the minimizing of the hydrologic impacts and water supply shortages as the operational goals for the Kaoping weir. The objective function can be expressed as a function of shortage ratio of the registered agriculural withdrawals, shortage ratio of the projected diversion for municipal supplies and the combined index for Hydrological Alterations whose definitions are provided in the article. All these can be expressed as the function of the instream flow value as decision variable.
The compromise programming algorithm is adopted as the authors believe its suited for the discrete problem and is still felixible for the preferences of the decision makers concerning the relative importance of each goal considered. Compromise programming identifies the optimal solution as the one that has the shortest distance to an ideal point where the multiple objectives simulatneously reach their minimum values. The ideal point is practically inachievable but may be used as a base point.The objective function involves the use of the base point and the worst point wrt each goal. It also involves the use of weights in order to decide the preferred goals.
The results indicate that the current realease of 9.5 m3/s as a minimum instream flow does not effectively restore the natural flow variations. Increasing the amount of instream flow release would reduce the overall degree of hydrologic alteration; however, this is achieved at the cost of increasing the water supply shortage ratios. An equal weighting to both water supply reliability and natural flow variability would suggest a minimum flow of 26 m3/s which is supported by the authors. The authors also suggest an improvement by including biological component into the current model for a better representation of ecological effects.
My views:
I like the approach and totally understand the use of a single index for hydrological alterations for reducing complexity of the model. Though I would suggest some alternative approaches like developing a pareto front and evaluate scenarios for different objects, trade-off analysis. I would also like to see a weighting introduced in the IHAs so as to recognize which IHAs have more effect on the downstream ecology.
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