Rainwater Harvesting System Scenario Analysis on Runoff Reduction Potential in Surabaya, Indonesia: A Geospatial Analysis for Brantas Hilir Watershed

Global warming has become an environmental concern over the past several decades and its impact on the water cycle is very crucial to the well-being of the human population. In the hydrological cycle, water evaporates by the heat of the sun and atmosphere, where it is accumulated in the atmosphere via clouds and it then falls as rain. With warmer temperatures, more intensive evaporation and downpours occur. In addition, impervious surfaces are increasing as a result of urban development. Those surfaces cause more water to flow faster into open water bodies, creating more extensive flooding, and additionally reducing water quality. In this study, the amount of runoff volume (streamflow) that can be reduced by harvesting rainfall in residential systems is explored. Rainfall harvesting can be accomplished by installing storage tanks under roofs of residential homes. The harvested rainwater can be later used to augment domestic water demands. It also reduces the peaks of storm runoff, thereby reducing downstream flooding. The investigation on the impact of rainfall storage has been done using the USDA-Soil Conservation Service Curve Number (SCS-CN) method that estimates rainfall-runoff as a function of the imperviousness of the land surface, including structures. Soil maps, land use/land cover, and precipitation data were used as input to the process. Surabaya is the second largest city in Indonesia, with a 2.843 million population based on 2017 demographics. The city has large residential areas as noted from land use/land cover maps. The buildings that cover this city can be a promising opportunity to harvest the rainfall, and supports water management in Surabaya. One of the objectives of this study was to develop and assign rainfall-runoff curve numbers based on fractions of lawn, buildings and other impervious systems to residential, government and commercial buildings with and without rainfall harvesting practices. These developments can help to model suitable rainwater harvesting potentials for the future. Advisor: Ayse Kili