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The Preissmann slot model is one of the most widely used models to conceptualize both free-surface and pressurized flows in urban drainage systems. Despite its simplicity and wide range of applications, numerical solutions of the Preissmann slot model suffer from the spurious oscillations, especially when flow conditions switch from free-surface flow to pressurized flow. To overcome this problem, a new hybrid numerical flux solver of the Preissmann slot model is proposed herein, in which the upwind flux solver is combined with the centered flux solver. Numerical experiments are conducted for multiple flow conditions such as typical filling, pipe-filling, and transition-flow conditions. The numerical results indicate that the proposed scheme generally outperforms the conventional flux schemes for various hydraulic conditions and wave velocities. The proposed scheme should be useful to further enhance integrated urban water modeling in which transient mixed flow conditions significantly impact the simulation accuracy during extreme floods.

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An embankment raising project on 113 agricultural reservoirs in Korea was implemented in 2009 to increase water supply capacity for agricultural water and instream uses. This study evaluated the future water supply capacity of the Imgo reservoir at which the agricultural reservoir embankment raising project was completed, considering climate change scenarios. The height of the embankment of the reservoir was increased by 4.5 m, thereby increasing its total storage from 1,657.0 thousand to 3,179.5 thousand cubic meters. To simulate the reservoir water storage with respect to climate changes, two climate change scenarios, namely, RCP 4.5 and RCP 8.5 (in which greenhouse gas reduction policy was executed and not executed, respectively) were applied with bias correction for reflecting the climate characteristics of the target basin. The analysis result of the agricultural water supply capacity in the future, after the agricultural reservoir embankment raising project is implemented, revealed that the water supply reliability and the agricultural water supply increased, regardless of the climate change scenarios. By simulating the reservoir water storage considering the instream flow post completion of the embankment raising project, it was found that water shortage in the reservoir in the future is not likely to occur when it is supplied with an appropriate instream flow. The range of instream flow tends to decrease over time under RCP 8.5, in which the greenhouse gas reduction policy was not executed, and the restoration of reservoir storage was lower in this scenario than in RCP 4.5, in which greenhouse gas reduction policy was executed.