Pusat Penyelidikan Kejuruteraan Sungai dan Saliran Bandar (REDAC) - Tesis

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    Assessing sustainability index of water resources system for lombok river basin
    (2022-05-01)
    Wit Saputra, Anggara Wiyono
    River basin sustainability is vital for the fulfilment of water demands, but the majority of river basins worldwide, including those in Indonesia, are increasingly being severely degraded, leading to their unsustainability. The Lombok river basin at Nusa Tenggara Barat province, Indonesia, is currently experiencing such problems. Water balance in the Lombok river basin is closely affected by climate conditions, which in turn affects the availability of water. In addition, the basin is experiencing shrinking reservoir storage due to sedimentation, deterioration of river headworks structure, and irrigation efficiency reduction, all of which have a reverse effect on maintaining the sustainability of the water resources system. This study focuses on the Lombok river basin, which experiences unique climate characteristics and conditions in variability which has generally affected water availability and its distribution. Interbasin transfer conveys water from the western area, which has surplus water, to the central and eastern parts of the river basin. This study aims to assess the water resources system sustainability in light of the availability of streamflow and fulfilment of water demand in the Lombok river basin to provide information for the stakeholders and decision-makers. The methodology includes simulation and optimization of the water resources system to assess the water resource system performance indicators (reliability, resilience, and vulnerability) and sustainability index for various system improvement scenarios. The SWAT model was employed to simulate the Lombok streamflow with the corresponding land use and soil map data based on historical data as the required inputs. Calibration and validation processes using SUFI-2 were done to get the appropriate parameters used in SWAT model. By applying simulated streamflow as an input, the MODSIM model was used to simulate and optimize water allocation in the system to predict performance indicators at each headwork for irrigation and domestic demand. The results show that the smallest watershed sustainability index for irrigation was in the Renggung watershed and the Palung watershed was the smallest domestic watershed sustainability. The results show that the smallest watershed sustainability index for irrigation was in the Renggung watershed at 0.188 in 2017-2025, which decreased to 0.177 in the climate change period (2032-2040). Babak watershed was the smallest domestic watershed sustainability index at 0.884 and down to 0.812 in the climate change period. Watershed index with the same weight of 0.50 for domestic and irrigation demand, respectively, showed the highest was Jangkok watershed followed by Dodokan, Meninting-Midang, Renggung, Babak, Palung, Rere Penembem, and Pare Ganti. Results from this study indicated that the operation of the new dams and improvement of irrigation efficiency enhanced the water sustainability index at most simulation scenarios. These results indicate that careful constructing of suitable new dams and improvement of irrigation efficiency is justified in the Lombok river basin as they contribute towards the enhancement of water sustainability in the river basin.