Assignment 9

Shiau JT, Wu FC (2006) Compromise programming methodology for determining instream flow under multiobjective water allocation criteria, Journal of the American Water Resources Planning and Management, 42(5), pg. 1179-1191

Summary
This report discusses at multi-objective water allocation criteria approach which determines instream flows. The case study of this methodology was the Kaoping diversion weir located in Taiwan. This research was unique in that it was considered one of the few studies that studies the compromises necessary to human water demand in order meet instream flow requirements on a quantitative level.

The objective of this report was to design the diversion weir to create a good tradeoff relationship between the water supply reliability and to sustain the natural flow variability to the best outcome. The three primary demands (constraints) for Kaoping Creek included instream flow releases, agriculture water withdrawals, and a constraint on municipal uses. The water allocation priorities are in the same order as listed. The authors of the report utilized the Range of Variability Approach. The RVA assesses the hydrologic impacts, using 32 meters of Hydrologic Alterations. These HAs that were produced were then integrated into one index that allowed one scheme among many to be optimized in lieu of the others. The RVA would work to minimize the impacts of natural hydrologic variability and ecology. The authors came up with a compromised algorithm because it was accurate for the problem in a discrete setting, and also flexible in incorporating decision makers’ inputs for each operation goal. The authors stated that compromise programming will find the optimal solution as the one with the shortest distance to an ideal point in which the multiple objectives will concurrently achieve their minimum values.

Currently, the minimum release rate from the weir does not efficiently restore the natural flow variations. The authors found that the instream flow release must be increased in other to decrease the overall rate of hydrologic variability. But the effect of increasing instream flow release means that the water supply shortage rates will also be increased. Therefore the RVA worked to minimize the overall degree of hydrologic alteration, and treated it as the same as minimizing ecological impacts. It weighs the natural flow change and water supply reliability equally in the model.

Discussion
I find multiobjective programming very interesting. Very few situations does water resource problem only have one single objective, whether it may be similar to this case study, or include a variety of other objectives. Therefore their research is definitely generic in my opinion, and models can be modeled similarly to this one, minus the decision makers’ inputs to the model. The authors claimed that their future research will include an implementation of a biological component into the RVA and optimization model. This would be very interesting to see the outcome of this model and the differences between the results of this model and the future model containing the biological input; furthermore, how the release rate would react.

One problem I have with the research, however, is the variations of agricultural and municipal water withdrawals. I know that this varies widely with respect to climate, land use, etc. However, it seemed that the agricultural demand was constant, and municipal was variable. It seems that in a usual case, the municipal withdrawal is more constant throughout the year than the seasonally variable agriculture demands. Was there a limit of withdrawal from the supply source? The authors claimed that municipalities wouldn’t receive diversions of water between January and April due to the dry season, yet agricultural withdrawal still remained constant.