Page - 517 - in Book of Full Papers - Symposium Hydro Engineering

2.4. Stage 3. Main Embankment – Third and Final Construction Season At the beginning of the final construction season, the soil cover over the DMSI columns will be removed, the tops of the DMSI columns will be trimmed smoothly of their excess material and a geotextile GeoGrid will be placed on top of the columns. After which, conventional soil embankment will be built layer by layer until the crest is reached. The embankment will be finished with riprap slope protections and top driving surface for maintenance access. 3. NEW SPILLWAY GATES Construction of New Spillway Gates (2 fixed rollergates; width = 7.50 m; height = 5.60 m) will serve several function as the following: 1. Sediment materials trapped in the sediment reservoir will be flushed down through the new spillway gates into the upper solo river. 2. New spillway gates will provide additional spillway capacity, which will increase safety against emergency situations (probable maximum floods). 3. This will also provide an opportunity to increase operationalwater level (NHWL) by 1 meter (from +136 to +137), which will generate 76 millions m3 additional reservoir storage. 4. CONCLUSION 1. Sedimentation become a serious problem to dam reservoir in Indonesia, it will decrease reservoir capacity and also the dam function. 2. Prevent the sedimentation rate is a difficult step due to rapid land development on upper side of the catchment area. 3. It needed a new innovation to restore the capacity of dam reservoir during operation, use proper method such as development of closure dike with DMSI. 4. Operational of the new spillway gates will provide an opportunity to increase normal high water level (NHWL) by 1 m, which will generate 76 millions m3 additional reservoir storage. 5. ACKNOWLEDGEMENT The authors would like to thank to Bengawan Solo River Basin Authority, Dam Center and Dam Safety Unit, Directorate General of Water 517