Abstract
Multifunctional weirs can be used to maintain water supply during dry seasons and to improve downstream water quality during drought conditions through discharge based on retained flux. Sixteen multifunctional weirs were recently constructed in four river systems as part of the Four Rivers Restoration Project. In this study, three multifunctional weirs in the Geum River Basin were investigated to analyze the environmental effects of multifunctional weir operation on downstream flow. To determine seasonal vulnerability to drought, the basin was evaluated using the Palmer Drought Severity Index (PDSI). Furthermore, the downstream flow regime and the effect on water quality improvement of a coordinated dam–multifunctional weir operation controlled by: (a) a rainfall–runoff model; (b) a reservoir optimization model; and (c) a water quality model, were examined. A runoff estimate at each major location in the Geum River Basin was performed using the water quality model, and examined variation in downstream water quality depending on the operational scenario of each irrigation facility such as dams and weirs. Although the water quality was improved by the coordinated operation of the dams and weirs, when the discharged water quality is poor, the downstream water quality is not improved. Therefore, it is necessary to first improve the discharged water quality on the lower Geum River. Improvement of the water quality of main stream in the Geum River is important, but water quality from tributaries should also be improved. By applying the estimated runoff data to the reservoir optimization model, these scenarios will be utilized as basic parameters for assessing the optimal operation of the river.
Highlights
Droughts, which are affected by insufficient precipitation, and by several other factors, including dams, rivers, and underground water storage, cause demands on water resources that exceed existing supply capacity
Securing the availability of a sufficient quantity of water through reservoir operation is crucial for ensuring the water quality at major facilities, such as intake stations, because an appropriate level of water quality can be maintained through discharge when the water quality of the river deteriorates under drought conditions
The Palmer Drought Severity Index (PDSI) was calculated using floodgate data for 1983 to 2008 at seven weather observation weather observation stations located in the Geum River Basin, while 2008 was selected as the year of stationsthe located in the Geum River Basin, while 2008 was selected as the year of the drought event
Summary
Droughts, which are affected by insufficient precipitation, and by several other factors, including dams, rivers, and underground water storage, cause demands on water resources that exceed existing supply capacity. To overcome the effects of droughts, non-structured short-and long-term plans incorporating the operation of reservoir groups, while considering water volume and quality, are required. This study examines: (a) an alternative water supply plan; (b) a structural plan to improve the operational efficiency of basin and reservoir groups that considers water volume and quality; and (c) a redevelopment plan that incorporates conversion of existing dams, redistribution of reservoir capacities, and raising dams. Previous studies have examined runoff, reservoir operation, and water quality separately, they did not evaluate the effect of the operation of reservoir groups and irrigation facilities on water quality of a river during drought conditions using an integrated method. Examination of the variation in water quality under each operational scenario, considering discharge flow and branch inflow, was used as the basis for the assessment of the optimal operation of the river
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