Effects of Climate Change and Land Subsidence on Hydro-topographical Conditions in Tidal Lowlands. Case Study Telang I, South Sumatra

Water management zoning in tidal lowlands is an approach to design and implement proper water management. Water management zoning is defined as the determination of zones that have similar water management characteristics, based on their physical characteristic. The impacts of climate change and land subsidence on water management zoning deserve careful analysis, since they may have an important influence on success of agriculture in tidal lowlands. This study is dealing with the effects of climate change - especially sea level rise - and land subsidence on water management zoning in tidal lowlands. Results of this study may be useful to support development of lowlands, particularly in Indonesia, including of measures to be taken to deal with climate change and land subsidence. Data for the study were based on the conditions in the Telang I area, South Sumatra. Hydrodynamic modelling by using DUFLOW in combination with the Model Builder of ARCGIS was used in this research. Land subsidence in Telang I was calculated or modelled in compartments of soil in each layer. Samples were taken from two locations representing category A and B or B/C hydro-topographical conditions of the standard classification of tidal lowland areas in Indonesia (secondary block P8-12S and P6-3N). Results show that land subsidence has a relation with the groundwater fluctuation that varies in the area from 3 - 7 mm/year. In low areas where the groundwater level is near the surface land subsidence is about 3 mm/year, while for higher areas it is about 7 mm/year. Land subsidence during the reclamation period was higher than the present subsidence, about thirty years after reclamation. It can be concluded that the impacts of climate change and land subsidence on water management zoning in future will be significant. Land subsidence has more impact on water management zoning than sea level rise. The impacts can be positive and negative for the development of the tidal lowlands of the study area, as well as of similar areas in Indonesia. Water management zoning in the wet season is primarily dependent on the tidal fluctuation and rainfall, which is also related to the hydro-topographic conditions, tidal irrigation and drainability. Sea level rise and land subsidence make the potential of tidal irrigation larger and significant. The area with tidal depth of 0 - 25 cm or > 25 cm will increase. This change in water management zoning from dryland crops in the present condition to tidal irrigated wetland rice and from tree crops to dryland crops due to the reduced potential of drainage by gravity. Preventive efforts to control land subsidence are needed to overcome negative impacts which may occur in future, while for climate change there needs to be wider concern to minimize or to reduce its rate. Therefore, structural and non structural measures are needed