The Brantas River Basin has been developed under a stage-wise approach, with an evolving institutional set-up that has paved the path for the continuous development of water resources potentials within the basin. Following the maxim of 'One river, One plan, One management', the basin has profited from consistent steps of development, initially under the Brantas Project, into a service-based river basin organisation, namely Jasa Tirta I Public Corporation (PJT-I), established in 1990 and based on the principle of cost recovery. Capacity development in the basin is driven by challenges and has been reformulated several times to meet these challenges. During the development stage, the Brantas Project not only built the dam and other infrastructures, but also helped to establish the designer, planners and technicians for dam development in Indonesia. Nowadays, the sustainability of PJT-I depends on the trust of the Government and the satisfaction of the users who receive the services rendered. Key success factors of capacity development are strong leadership, incentive schemes and, most importantly, the spirit of innovation, the willingness to learn and the eagerness to take on new challenges.
Wlingi and Lodoyo reservoirs in the Brantas River basin, Indonesia, provide numerous benefits including reliable irrigation water supply, flood control, power generation, fisheries and recreation. The function of both reservoirs particularly in relation to flood control has declined due to severe sedimentation that has reduced their storage capacities. The sedimentation in Wlingi and Lodoyo reservoirs is mainly caused by sediment inflow from the areas most affected by ejecta from eruptions of Mt. Kelud, one of the most active volcanoes in Indonesia. The main objective of this research is to assess the sedimentation problem in Wlingi and Lodoyo reservoirs, particularly as they are affected by eruptions of Mt Kelud. We performed reservoir bathymetric surveys and field surveys after the most recent eruption of Mt. Kelud in February 2014 and compared the results with surveys undertaken before the eruption. The assessment revealed that both reservoirs were severely affected by the 2014 eruption. The effective storage capacity of Wlingi reservoir in March 2013 was 2.01 Mm3and the survey in May 2015 indicated that the effective storage of Wlingi reservoir had decreased to 1.01 Mm3. Similarly, the effective storage capacity of Lodoyo reservoir in March 2013 was 2.72 Mm3, reduced to 1.33 Mm3in May 2015. These findings underpin the analysis of the impacts of the secondary disaster due to reservoir sedimentation following the volcanic eruption and the implications for mitigating and managing the risks for sustainable use of reservoirs to control floods, supply water, generate electricity, etc. To cope with the extreme sedimentation problem in Wlingi and Lodoyo reservoirs, diverse sediment management strategies have been applied in these reservoirs and their catchments. However sediment disaster management strategies for both reservoirs, an integral part of the Mt. Kelud Volcanic Disaster Mitigation Plan, require continuous maintenance and recurrent operations, and ongoing evaluation and improvement.
This paper presents a study carried out to assess the accuracy of several sediment transport functions commonly applied in HEC-RAS 4.0 against data from the sediment flushing of Wlingi reservoir in 2016. Another aim of this assessment is to evaluate the viability of selected transport equations to simulate riverbed changes during the sediment-flushing event. Thus, the best scenario of sediment flushing could be determined according to their efficiencies. The overall accuracy of the transport function indicated by RMSE values in descending order were those of Laursen-Copeland, Ackers and White, Meyer-Peter and Müller, and Wilcock formulas, when applied to the observed data. The study also indicated that Laursen-Copeland formula had parameters that were commonly well-characterized by the riverbed of Wlingi reservoir. Further, it was suitable to be utilised to assess the achievement of sediment flushing in Wlingi reservoir, while others seem less satisfactory.
The sedimentation in reservoirs is mainly caused by sediment inflow from land erosion, riverbank erosion and volcanic eruption. The objectives of this research are to study reservoir sedimentation using the average end-area method for reservoir volume calculation, and to study sediment management in reservoirs and their catchments. This research was conducted in Wlingi and Lodoyo reservoirs, located near Mt. Kelud, one of the most active volcanoes in Indonesia. The assessment reveals that both reservoirs are severely affected by eruptions of Mt. Kelud. The total remaining capacity of Wlingi reservoir in 2015 was 2·20 million m3, which corresponds to 9·2% of the initial capacity. The total remaining capacity of Lodoyo reservoir in 2015 was 1·33 million m3, which corresponds to 25·8% of the initial capacity. Sediment management strategies of both reservoirs consist of methods to reduce sediment inflow from upstream, methods to minimise sediment trapping, and methods to recover the reservoirs’ storage.
Volcanoes erupt in many parts of the world, producing abundant sediment that is rapidly delivered to deposition sites. Where a reservoir is located near an active volcano, the sedimentation will be very severe. Wlingi and Lodoyo reservoirs are severely affected by eruptions of Kelud volcano, one of the most active volcanoes in Indonesia. After the February 2014 eruption, the capacity of Wlingi and Lodoyo reservoirs decreased dramatically to 2.20 million cubic meter (Mm 3 ) and 1.33 Mm 3 , respectively, just 46 and 49% of their pre-eruption capacities and 19.42 and 26.60% of their initial capacities. To cope with the extreme sedimentation problems in Wlingi and Lodoyo reservoirs, diverse sediment management strategies have been applied in these reservoirs and their catchments. Construction of many on-stream sediment control facilities (sabo works) and a sediment bypass channel has reduced sediment inflow to the reservoirs. Removal of deposited sediment by dredging and hydraulic flushing in Wlingi and Lodoyo reservoirs has also resulted in storage capacity recovery. These measures are an integral part of the Mt. Kelud Volcanic Disaster Mitigation Plan.
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