Sedimentation Problem

EFFECT OF VOLCANIC ERUPTION ON RESERVOIR SEDIMENTATION PROBLEM

Case Study of Mt. Kelud in Brantas River Basin, East Java - Indonesia

ABSTRACT

Mt. Kelud with a summit elevation at 1,724 m above sea level is the active member of a volcanic cluster in East Java - Indonesia, located at about 35 km east of Kediri City and 24 km north of the repeatedly lahar-stricken city of Blitar.This volcano lies between the volcanic massif of Mt. Wilis (2,169 m) to the West and the complex of Mt. Kawi (2,639 m) and Mt. Butak (2,868 m) to the East around which Brantas River (320 km length) that is the second largest stream in Java Island is swirling. More than 30 eruptions of Mt. Kelud had been recorded in historical times with 3 to 30 years interval or 15 years on an average, resulted tremendous damage over the area.

Mt. Kelut Crater Lake (before erupts)

Mt. Kelud has such a particular morphology as forming a deep crater lake, which always stores several to ten mil. cubic meter of rainwater. Retained water in the crater was used to be the prime mover at every time of the eruption, which had brought hazardous hot debris flows, mixed the ejection with lake water. The primary lahar mostly flowed down along the slope of western half of volcanic area via dissected stream radiating from the crater, and then deposited on the slope thickly with the ash fallen becoming major source of the hazardous secondary lahar, which will be moved by surface runoff.

Based on the Master Plan for Mt. Kelud Volcanic Debris Control, many sabo facilities had been constructed since 1970. Some of the structures had fulfilled with the sediment, and most of them couldn’t retain the material and then will flow directly to Brantas River through its tributaries and finally deposit in Wlingi Multipurpose Dam and cause heavy reservoir sedimentation there. Although the reservoir also planned to have a function of trapping debris flows but the sediment rate is much higher than the expected value. In order to maintain the reservoir storage capacity, bypass channel was constructed and sediment removal measures by hydraulic flushing and dredging were carried out regularly.

Wlingi Multipurpose Dam

In the future, to prevent and mitigate sediment related disaster in this area, it is essential to develop integrated sediment management by conducting rehabilitation of the existing facilities, constucting additional sabo facilities, extending the bypass channel and providing new dredging system.

Key words: volcano, eruption, sedimentation, reservoir, and sabo

Presented on MPMD-2005, International Conference on Monitoring, Prediction and Mitigation of Water-Related Disaster, January 12-15, 2005, Clock Tower Centennial Hall, Kyoto University, Japan, by:

- Director of Technical Affairs, Perum Jasa Tirta I,

- Head of Research and Development Bureau, Perum Jasa Tirta I,

- Staff of Research and Development Bureau, Perum Jasa Tirta I.

After this article created and presented, on Nov 2007, Mt. Kelut Show its eruption activity which showed by increasing temperature of crater lake, increasing frequency of treamor earthquake.

on November 2007, Mt. Kelut Shows its Eruption Activity

But, big explosion doesn’t happened as predicted before. Eruption activity only makes tremor earthquake with over schale. That acticaty makes big heap shows up on the existing crater lake.

big heap shows up on existing crater lake