Page - 281 - in Book of Full Papers - Symposium Hydro Engineering

Note: 1) The volume reservoir between 1977 and 1996 was obtained from "The Brantas River Rehabilitation Project, Supporting Report 1, Evaluation of River Dredging Works for Wlingi and Lodoyo Reservoirs, December 1996" between 2001 and 2004 based on the HV curve prepared by PJT-1. 2) NA = Not Available. (Source: Jasa Tirta I Public Corporation) Mount Kelud last eruption was happened in February 2014, but the last eruption has no significant impact on the Wlingi Reservoir. But the eruption of Mount Kelud in February 1990 had a very significant impact on the Wlingi Reservoir. Wlingi Reservoir is fully with sediment. Many efforts have be done as corrective measurements to increase reservoir capacity such as dredging and flushing. It can recovered to 4.42 million m3 reservoir capacity or 18.4% of the initial capacity of 24.0 million m3. Total volcanic eruption in 1990 (estimated by the Volcanic Directorate of the Department of Energy and Mineral Resources) was approx. 125 million m3, which 22.3 million m3 of it deposited at Wlingi Reservoir through the Lekso, Semut, Jari, Putih and Kali Abab rivers. RIVER BED DEGRADATION Wlingi Dam is located in Brantas River where upper reach occurs sedimentation, but in the middle and lower reach occurs river bed degradation. This degradation occurs due to illegal sand mining. Regularly controlled by the local government in cooperation with Jasa Tirta I Public Corporation, has not been able to reduce the number of people mining sand along Brantas River. The volume of sand mining conducted by 6,280 workers along Brantas River is 2,695,000 m3 / year with details as shown in the Table 2. Table 2 Volume of Sand Mining Brantas River in 179 Location Location (City) Volume of Sand Mining (m3/year) Number of Workers (person / day) Manual Pump Total Sidoarjo 42,500 - 42,500 150 Mojokerto 151,500 111,000 262,500 1,060 Jombang 822,600 168,200 990,800 3,220 Nganjuk 267,100 383,000 650,100 720 Kediri 200,800 135,700 336,500 510 Kediri city 47,900 182,800 230,700 220 Tulungagung - 183,900 181,900 400 Total 1,532,400 1,164,600 2,695,000 6,280 As a result of excessive illegal sand mining leads to degradation of the river bed. The decrease in the riverbed ranges from 2 - 8 m below the initial river bed. Even at a certain point the river decline reaches 11 m in the area of KB 80. The following illustrates the long section of the river bed at Kali Brantas. 281