Water Potential in Petanu River Estuary and Model of Water Resources Management for Sustainable Agriculture in Gianyar Regency Bali Province

Water needs in the province of Bali from year to year increase along with the rise of population and tourism activities. A study conducted by the Ministry of Environment (2009) stated that Bali is already experiencing water deficit during the dry seasons since 1995 as many as 1.5 billion m3 / year. To overcome this water deficit issue, it will require researching on the potential water resources in Bali. Along the Petanu River, there are 25 irrigation weirs on a 4475.5 ha of land. Research was carried out in in Saba village, Gianyar Regency, Bali, along The Petanu River up to its estuary. The data collected from the research included primary and secondary data, namely: water quality, water quantity (water volume) in Petanu River estuary, precipitation, climate, and environmental conditions of the Petanu river. The data collected from the research site and the secondary data, the water quality was tested on the reseacrh site and  in the laboratory before it was analyzed. The model used to detect water presence (the water system) along the Petanu River up to its estuary was procesed using a software called RIBASIM (River Basin Simulation). The result showed that there is a potential water source (water volume) on the estuary of the Petanu River estuary during the dry season as much as 6.16 million m3 and during the rainy season as much as 43.79 million m3. Water quality in terms of physics (smell, taste, temperature, color, turbidity and salinity), meet the quality standards of class IV (for irrigation). Based on the simulation results on the RIBASIM software, the water resources in the Petanu River estuary can potentially be managed as irrigation water for horticulture agriculture along the coast of Saba. The potential water sources can be contained by building dams / reservoirs that are placed ± 300 m from the shoreline of Saba village in Gianyar regency. The water management model for the water sources in Petanu River to support sustainable agriculture can be put to use through water and soil conservation by controlling land use and cropping patterns that involve the community using the subak system.