The water need in the Northern area of Bandung City was predicted to be 2.49 m3/s in 2040. The government responded to this issue by planning the construction of several reservoirs in the Cikapundung watershed. A previous study suggested three potential locations, i.e., Cikukang 2, Cikawari 2A, and Cikawari 5A reservoir. Since Cikawari 2A and Cikawari 5A are located on the same Cikawari river, three construction alternatives, i.e., a single reservoir of Cikawari 2A, a single reservoir of Cikawari 5A, and cascade reservoir Cikawari 2A+5A are proposed. Each alternative has its own advantages and limitations, thus evaluation of the best construction alternative needs to be carried out. The evaluation was conducted based on their reliable service in supplying water to Bandung City. This evaluation was analyzed by comparing the projected water demand following population growth and water availability derived from the rainfall-runoff model, NRECA. The analysis was conducted using two variations of dam height and reservoir capacity for each alternative. Based on the analysis results, the single reservoir of Cikawari 2A with 45 m of dam’s height was chosen as the most suitable alternative. It can supply 0.56 m3/s of water and provide water for 30.4% of the citizens in 2020, and decrease to 30.15% in 2040. However, it was also found that the reservoir could only supply 0.44 m3/s of water during the dry period. These results showed that the construction of the reservoir itself could not meet the total water demand. Therefore, another alternative is required to closing the gap in water demand.Keywords: Cikapundung watershed, water supply, Cikawari reservoir, reservoir simulation, service reliability

This paper compares the results of direct runoff obtained by a numerical model of the shallow water equations (SWE) with the synthetic unit hydrograph (SUH) methods generally used in Indonesia. It is known that such SUH methods are still empirical, thus making it difficult for users to determine a representative method. Meanwhile, the hydrodynamic approach such as the SWE numerical model can achieve more accurate results in predicting the direct runoff compared to the SUH methods, because the model itself is derived mathematically based on the physical processes. The findings indicate that the direct runoff predicted using the SWE numerical model (HEC-RAS 5.0.7) produced more accurate results for the peak discharge with an average error of -0.07%, the peak time with an average error of 19.77%, and the shape of the hydrograph with the smallest Root Mean Square Error (RMSE) from all the cases tested. Therefore, it can be concluded that in the future the use of a hydrodynamic approach is highly recommended for the direct runoff prediction. This paper was also aimed to be used as a reference in the development of new, more accurate SUH method in the future.