Conjunctive management methodology considering stream-aquifer systems and reservoir operations
Date
2007
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Abstract
The purpose of this research was to develop a methodology to determine whether conjunctive surface water and groundwater management integrated with reservoir operation could significantly reduce deficits in a river basin with a relatively limited alluvial aquifer. The Geum River basin is one of major river basins in South Korea. The upper region of the Geum River basin is typical of many river basins in Korea where the shape of river basin is narrow with small alluvial aquifer depths from 10m to 20m and where most of the groundwater pumped comes quickly from the steamflow. The basin has two surface reservoirs, Daecheong and Yongdam. The most recent reservoir, Yongdam, provides water to a trans-basin diversion, and therefore reduces the water resources available in the Geum River basin. After the completion of Yongdam reservoir, the reduced water supply in the Geum basin resulted in increasing conflicts between downstream water needs and required instream flows, particularly during the low flow season.
Historically, the operation of groundwater pumping has had limited control and is administered separately from surface water diversions. Further, the operation of the two reservoirs has only considered the surface water demands and instream flow requirements in the development of operational policies. Given the limited size of the alluvial aquifer, it is apparent that groundwater pumping is essentially taking its water from the stream. Therefore, the operation of the surface water withdrawals and groundwater pumping must be considered together.
The major component of the proposed methodology is a goal-programming based, multi-objective optimization model that simultaneously considers reservoir release surface water withdrawals, groundwater pumping and instream flow requirements. A 10-day time step is used in the model for a 24 year period of record. The interactions between groundwater pumping and the stream are handled through the use of response and lag coefficients. The impacts of pumping on streamflow are considered for multiple time periods. The model is formulated as a large linear goal-programming problem that is solved with the commercial LINGO optimization software package. The model was used to determine reservoir releases and groundwater pumping rates for a 10-day time step for a 24 year period of historical data from 1981 to 2004.
The results of the optimization model were analyzed and reservoir and groundwater pumping operational rules were developed by linear regression. The developed operational rules were tested using the KMODSIM simulation model, which had been previously developed for the Geum river basin. The results of simulating various scenarios confirmed that the developed operation rules were able to yield an improved operation of the system, that is, meet the demands in the Geum river basin and reduce the deficits to the trans-basin diversion by as much as 15% as compared to a non-integrated operation.
In general this study was able to show that even though the aquifer system is small, there are possibilities to reduce deficits in the system through appropriate, integrated surface water withdrawal, groundwater pumping and reservoir release strategies.
Historically, the operation of groundwater pumping has had limited control and is administered separately from surface water diversions. Further, the operation of the two reservoirs has only considered the surface water demands and instream flow requirements in the development of operational policies. Given the limited size of the alluvial aquifer, it is apparent that groundwater pumping is essentially taking its water from the stream. Therefore, the operation of the surface water withdrawals and groundwater pumping must be considered together.
The major component of the proposed methodology is a goal-programming based, multi-objective optimization model that simultaneously considers reservoir release surface water withdrawals, groundwater pumping and instream flow requirements. A 10-day time step is used in the model for a 24 year period of record. The interactions between groundwater pumping and the stream are handled through the use of response and lag coefficients. The impacts of pumping on streamflow are considered for multiple time periods. The model is formulated as a large linear goal-programming problem that is solved with the commercial LINGO optimization software package. The model was used to determine reservoir releases and groundwater pumping rates for a 10-day time step for a 24 year period of historical data from 1981 to 2004.
The results of the optimization model were analyzed and reservoir and groundwater pumping operational rules were developed by linear regression. The developed operational rules were tested using the KMODSIM simulation model, which had been previously developed for the Geum river basin. The results of simulating various scenarios confirmed that the developed operation rules were able to yield an improved operation of the system, that is, meet the demands in the Geum river basin and reduce the deficits to the trans-basin diversion by as much as 15% as compared to a non-integrated operation.
In general this study was able to show that even though the aquifer system is small, there are possibilities to reduce deficits in the system through appropriate, integrated surface water withdrawal, groundwater pumping and reservoir release strategies.
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Subject
conjunctive management
groundwater pumping
reservoirs
stream-aquifer
environmental engineering