Japan-Jordan team develops prototype for turning flash floods into water resources
Establishing irrigated agriculture using renewable water resources is an urgent issue in arid areas of the Middle East and North Africa -- or MENA -- regions, where water scarcity and salt accumulation are prevalent. At the same time, flash flood incidence is increasing.
Koichi Unami of Kyoto University's Graduate School of Agriculture, in collaboration with Osama Mohawesh of Mutah University, Jordan, has launched a prototype of an irrigation scheme consisting of a flash flood harvesting system equipped with reservoirs, a solar-powered desalination plant, and a command area with a date palm garden.
The prototype is situated in the harshly arid Jordan Valley, a location chosen in order to demonstrate the feasibility of flash flood harvesting for water resource development in the MENA region.
"Flash floods in the desert are generally considered to be natural disasters. We want to turn them into water resources," says Unami.
"The nature of water resources is their uneven distribution and uncertainty," continues Unami. "Construction of reservoirs such as dams have been key to creating stable water resources. But the operation of such reservoirs is mostly based on intuition and empirical knowledge."
The research team tackled the question of scientifically rationalizing reservoir operation, namely to optimally control the flash flood harvesting system. Their methodology employs the framework of stochastic control theory, where the Hamilton-Jacobi-Bellman -- HJB -- equations and their viscosity solutions dominate optimal solutions. The paper presents a proof of unique existence of the viscosity solution to the HJB equation involved in a hydro-environmental model of the prototype under uncertainty.
"A reservoir operation strategy must be consistent with intuition and empirical knowledge," explains Unami. "Our 'unique viscosity solution' supports this thinking."
Interestingly, the team has found that an optimal operational strategy is determined by the uncertainty in occurrence of flash floods. In their next study, they plan to show that an arbitrary strategy becomes optimal in the absence of uncertainty.
"We plan to disseminate the concept of flash flood harvesting to the other parts of the MENA region," concludes Unami, "pioneering a new paradigm for flash flood control and sustainable development of water resources."
【KURENAI ACCESS URL】 http://hdl.handle.net/2433/229528
Koichi Unami & Osama Mohawesh (2018). A unique value function for an optimal control problem of irrigation water intake from a reservoir harvesting flash floods. Stochastic Environmental Research and Risk Assessment, 32(11), 3169-3182.