Fuzzy optimization model for integrated management of total nitrogen loads from distributed point and nonpoint sources in watershed |
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| Authors: | Shigeya Maeda Toshihiko Kawachi Koichi Unami Junichiro Takeuchi Tomoki Izumi Syunsuke Chono |
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| Institution: | (1) Graduate School of Agriculture, Kyoto University, Kitashirakawa-oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan |
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| Abstract: | A fuzzy optimization model is developed to allocate allowable total nitrogen (T-N) loads to distributed nonpoint sources (NPSs)
and point sources (PSs) in a watershed for river water quality management using the linear programing technique. The watershed
is divided into uniform grid cells on which T-N loads issuing from NPSs such as paddy fields, upland crop fields and cities
are controlled. A geographic information system integrated with the digital elevation model facilitates computation of route
lengths of surface and subsurface flows from cells to a river running through the watershed. The T-N loads discharged from
their sources are assumed to decay, subject to distance-related first-order kinetics. As management goals, maximizations of
total allowable NPS loads, total allowable PS loads and total yield of rice are considered from environmental and economic
viewpoints. A prime constraint is an effluent limitation standard for the aggregate amount of loads that arrive at the downstream
end of the river. The fuzzy sets theory helps appropriately describe vague attitudes of decision-makers (i.e., stakeholders
and management authorities) in terms of constraints and conflicting goals. An application of the fuzzy optimization model,
developed as an improvement over our last nonfuzzy model, to a real watershed in Shiga prefecture, Japan, demonstrates that
the fuzzy model embodies our last model, and is capable of creating management alternatives for T-N load allocation in a more
practical and flexible manner. |
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| Keywords: | Watershed management River water quality Pollutant load allocation Fuzzy sets Decision support model |
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