4. Local-Level Water Conservation Assessment in the Upstream Watershed Based on Land-Use Scenarios

To assess the effects of differences in land use in a mountainous sub-watershed on water conservation, namely, hydrological services like flood control and groundwater recharge, first, this chapter aims to present a water balance analysis in two sub-watersheds located upstream of the Saba River watershed. Specifically, the Titab and the Busungbiu-Tunju were compared. An annual water balance analysis in the two sub-watersheds in 2013 and 2014 revealed that the ratio of base flow to the total discharge was larger in the Titab, which has a lower areal percentage of clove plantation, a higher percentage of coffee plantation, and a slightly higher percentage of natural forest than the Busungbiu-Tunju. Second, by applying the International Center for Water Hazard and Risk Management/Public Works Research Institute (ICHARM/PWRI) distributed hydrological model, discharges under the present land use and three scenarios of changed land use were predicted. By converting all coffee plantations to clove plantations, base flow decreased, direct runoff increased, and the peak discharge increased. By converting clove plantations at high elevation to coffee plantations, base flow increased, direct runoff decreased, and the peak discharge decreased when compared with the present. In converting all land uses to natural forests, base flow was the largest, direct runoff was the smallest, and the peak discharge was the smallest of all cases. Comparison between the three land uses, coffee plantations, clove plantations, and natural forests, revealed that the clove plantation has the highest possibility of causing a flood disaster, the coffee plantation has a possibility of preventing a flood disaster and increasing groundwater, and the natural forest has the highest possibility of preventing a flood disaster and increasing groundwater.