Page - 1278 - in Book of Full Papers - Symposium Hydro Engineering

tunnel. The water quality was monitored on BOD (biochemical oxygen demand), COD (chemical oxygen demand) and DO (dissolved oxygen) parameters from 2013 to 2017. Those BOD, COD, and DO parameters met the standard. 3.2. HYDROLOGY Spillway design of Lahor dam based on design flood with 1000 years time period and resulted inflow debit 790 m3/second with spillway capacity 399 m3/second. Flood routing with initial elevation of water table +272,70 m obtained maximum flood elevation +274,11 m for 1000 years time period (Q1000) and +277,09 m for QPMF. The elevation of parapet is +279,00 m. 3.3. INSTRUMENTATION Some instruments (pore pressure meter, V-Notch, and observation well) was installed in Lahor dam. The pore water pressure at each location is always up and down as the reservoir water level changes. Based on the monitoring results of the seepage discharge shows normal conditions, no significant fluctuations occur, the magnitude is still below the maximum threshold. The amount of seepage discharge depends on reservoir water level and rainfall. The maximum of seepage discharge on toe dam is 1,105.20 liter/minute, the maximum seepage discharge that occured in toe dam is 896,99 liter / min (April 25, 2017) at water level +273,21 m with seepage water condition looks clear. The amount of spring water discharge at the right bank and left bank (including on the rail way) was fluctuated, because it was influenced by rainfall that occurs. The ground water level conditions also fluctuate along with the water level of the reservoir 3.4. SEDIMENTATION Based on echo sounding measurement that was carried out in 2016, the dead storage capacity of Lahor reservoir is 3.38 million m3 or 50.45% of the initial dead storage capacity (6.70 million m3). The effective capacity is 28.73 million m3 or 97.72% of the initial effective storage capacity (29.40 million m3) and the total storage capacity is 32.11 million m3 or 88.95% of the initial total storage capacity (36.10 million m3). Sedimentation rates in the Lahor Reservoir from 1977 to 2017 is ± 99,750 m3/year or 0.623 mm/year. 3.5. GEOLOGY Geological structure (unconformity and fault) around the dam caused several problems during construction. There are agglomeratic tuff as the rock basement, grey clay layer at the middle, and tuffaceous loam as overburden. Those condition lead to land slide around the reservoir. Therefore, in the foundation was carried out rim grouting along the dam axis (433 m). This method could solve the probem effectively. 4. CONCLUSION Based on formal investigation result in Lahor dam can be concluded that its condition was normal and ready to be operated. There is no anomaly on each inspection parameter. 1278