Mawiti Infantri Yekti, De Dwi Saptarahadi, I Putu Gustave Suryantara Pariartha, Bart Schultz, Wil van der Krogt, Tri Hayatining Pamungkas, I Gusti Ngurah Hesa Respati Haditama, Ida Bagus Gede Indrayana, Luh Ayu Putri Wedayanti Pulasari
This study evaluates optimal water allocation within the Subak Bali irrigation system in the Petanu River Basin, focusing on return flow dynamics known locally as “natak tiyis.” The objective was to enhance water availability for downstream irrigation while ensuring system sustainability under increasing water scarcity. A synthetic rainfall-runoff model was employed to derive dependable discharge (Q80), and net field water requirements were calculated for irrigation area behind each weir, considering both the existing cropping pattern and a shift in planting start periods. Eight allocation scenarios were simulated using DSS-RIBASIM (Decision Support System - River Basin Simulation Model), varying return flow percentages incrementally. Optimal performance was assessed using a multi-criteria framework based on reliable water supply (Q80), water availability gain, irrigation equity, and system sustainability. Results indicate that the eighth scenario, with a 31.7% return flow, achieved the highest performance, increasing water availability by and expanding irrigable areas downstream. This improvement supports agricultural resilience without requiring structural modifications, demonstrating that optimizing traditional water reuse mechanisms can serve as a sustainable, nature-based solution in UNESCO-recognized cultural landscapes. The findings underscore the value of integrating indigenous knowledge with hydrological modelling for climate-resilient water governance. © The Author(s) 2026.
Master’s Program in Civil Engineering, Faculty of Engineering, State University of Yogyakarta, Yogyakarta, Indonesia; Directorate General of Water Resources, River Basin Organization of Bali Penida, Ministry of Public Works, Bali, Indonesia; Study Program of Civil Engineering, Faculty of Engineering, Udayana University, Bali, Denpasar, Indonesia; Professor Emeritus of Land and Water Development, IHE-Delft, Lelystad, Netherlands; Sustainable Use of Water and Soil, Deltares, Delft, Netherlands; Study Program of Civil Engineering, Faculty of Science and Technology, Ngurah Rai University, Bali, Denpasar, Indonesia; Study Program of Civil Engineering, Faculty of Engineering and Planning, Warmadewa University, Bali, Denpasar, Indonesia
