Assessment of Sedimentation in Wlingi and Lodoyo Reservoirs: A Secondary Disaster Following the 2014 Eruption of Mt. Kelud, Indonesia

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 Mm 3 and the survey in May 2015 indicated that the effective storage of Wlingi reservoir had decreased to 1.01 Mm 3 . Similarly, the effective storage capacity of Lodoyo reservoir in March 2013 was 2.72 Mm 3 , reduced to 1.33 Mm 3 in 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.