Analysis of Water Availability in the Upper Siak Basin Using the GR2M Model Application

The Siak watershed is one of the critical watersheds, where natural disasters such as floods, landslides and erosion often occur in this area. The Siak watershed has 4 main sub-watersheds, namely the Tapung Kanan sub-watershed, the Tapung Kiri sub-watershed, the Mandau sub-watershed and the Siak Hilir sub-watershed. The existence of these 4 sub-watersheds is also not able to meet the water needs of the community due to the rapid development of the region which will then cause the demand for water to continue to increase in line with the rate of population growth, especially in the Siak watershed area. Fulfillment of food needs and population activities is always closely related to the need for water. These demands cannot be avoided, but must be predicted and planned for the best possible use. The purpose of this study is to describe the application of the GR2M modeling and the amount of raw water availability in the Upper Siak Watershed. The research method used is descriptive quantitative with data collection techniques in the form of map data, rain data, climatology data and field discharge data. And the research location is in the Upper Siak Watershed, namely the Tapung Kiri Sub-watershed. The results of the study show that 1) GR2M modeling can be applied to the Tapung Kiri Sub-watershed with an R2 performance of 0.41 with a satisfactory interpretation, a correlation coefficient (R) of 0.67 with a strong interpretation, and an efficiency coefficient (CE) of 0.59 with sufficient optimization interpretation. The reliable discharge obtained based on the GR2M modeling data for the availability of drinking water (Q99%) in the Siak Hulu watershed is 15.69 m3/second.