STUDY OF THE EFFECTIVENESS OF UPGRADING AND OPERATIONS & MAINTENANCE (O & M) RINJANI CHECK DAM ON FLOOD EARLY WARNING SYSTEM AND LEAD TIME ON THE BATU MERAH RIVER IN AMBON CITY

• Main Author: Tri Bunai, Putit
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/62721
• Institution: Institut Teknologi Bandung

The history of the flood disaster that occurred in Ambon City in 2012 and 2013 caused the highest loss of life and material loss to the community. The natural condition of Ambon City which is an archipelago with steep areas is one of the physical factors that causes many landslides to occur. This avalanche material is washing away into sediment in the river flow, which reduces the flow capacity of the river. What's more, the community around the river flow builds buildings on the river border. When it rains with high intensity, it can cause flooding due to inadequate river reservoirs. The Batu Merah River is one of the rivers that flows through the basin of Ambon City with a length of ±7km2 and a length of ±7km. One and a half km of the Batu Merah River flows through commercial and residential areas. With the disruption of the Batu Merah watershed due to community activities and the unavailability of an early flood warning system, it can increase the risk of flooding that occurs. Some of handling that has been done by Maluku River Basin Organization is the form of the physical building of flood control and sediment in the form of Yakobus Check dam, Petra Check dam and Upgrading of Rinjani Check dam. The purpose of this study is to assess the effectiveness of upgrading the Rinjani Check dam on the flood early warning system and lead time on the Batu Merah River. Type the flooding that occurred in the Batu Merah River is a flash flood with a time travel short. This study was conducted with the aim of knowing how effective the construction and rehabilitation of several checkdams was in increasing the lead time for flooding. The method used is to perform hydrological and hydraulic analysis as well as analysis of the reservoir capacity of the checkdam. Modeling using software Hec-HMS with 3 scenarios. The first scenario is in the initial conditions, the second scenario is with an empty checkdam and the third scenario is with a checkdam full of sediment. By using SCS method if the check dam empty condition then additional lead time on Batu Merah river is for 19 minutes and the reduction of peak discharge of 13 m3/ s while when check dam filled with sediment then the addition of lead time is 13 minutes with a reduction in peak discharge of 7.93 m3/ s. The hydraulic analysis found the manning roughness value of 0.051. The results of the flood analysis stated that after modeling with the checkdam there was a decrease in the water level of 1.12 m. Land erosion that occurred in the Batu Merah watershed using the USLE method obtained an average erosion rate of 2325.77 tons/ha/year or 3 mm/year. The history of landslides that occurred in the Batu Merah watershed was caused by the accumulation of rain with a range of 157 mm-712 mm. River degradation occurred at 1.4 km downstream of 47 cm/year with erosion of 6397.18 tons/year. To maintain the check dam function, checkdam maintenance must be carried out once a year.