Abstract
In this paper, a many-objective optimization algorithm was developed using SPEA2 for a system of four reservoirs in the Karun basin, including hydropower, municipal and industrial, agricultural, and environmental objectives. For this purpose, using 53 years of available data, hedging rules were developed in two modes: with and without applying fuzzy logic. SPEA2 was used to optimize hedging coefficients using the first 43 years of data and the last 10 years of data were used to test the optimized rule curves. The results were compared with those of non-hedging methods, including the standard operating procedures (SOP) and water evaluation and planning (WEAP) model. The results indicate that the combination of fuzzy logic and hedging rules in a many-objectives system is more efficient than the discrete hedging rule alone. For instance, the reliability of the hydropower requirement in the fuzzified discrete hedging method in a drought scenario was found to be 0.68, which is substantially higher than the 0.52 from the discrete hedging method. Moreover, reduction of the maximum monthly shortage is another advantage of this rule. Fuzzy logic reduced 118 million cubic meters (MCM) of deficit in the Karun-3 reservoir alone. Moreover, as expected, the non-hedging SOP and WEAP model produced higher reliabilities, lower average storages, and less water losses through spills.
Highlights
Iran is part of the arid and semi-arid regions of the world, with an average annual precipitation of about 250 mm, which is less than one-third of the world’s average annual rainfall
The time series studied in this paper were monthly data during the 1961–1962 to 2013–2014 water years, from which the initial 43 years were considered for optimization of decision parameters and the last 10 years were used for testing the performance of the optimized rule curves
It was compared to the non-hedging methods of standard operating procedures (SOP) and water evaluation and planning (WEAP) using a four-reservoir system in the Karun basin in Iran with four objective functions related to meeting municipal, agricultural, environmental, and hydropower water demands
Summary
Iran is part of the arid and semi-arid regions of the world, with an average annual precipitation of about 250 mm, which is less than one-third of the world’s average annual rainfall. Combining fuzzified hedging policies optimized with the SPEA2 optimization algorithm is a useful method in occurrence of severe and frequent droughts and can improve reservoir operation rules and aid water supply operators in coping with the risk of dramatic water deficiencies to the users This is a new strategy for optimal operation of multiple reservoirs by combining discrete hedging and fuzzy theory during drought and water scarcity for a multi-reservoir, many-objective systems. It proposes water supply policies in the form of a rule curve and reduces drought effects in meeting demands.
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