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THE IMPACT OF DIFFERENT CANAL CONFIGURATIONS ON THE DRAINAGE OF TROPICAL PEATLANDS A geohydrological model to predict drying of sloping peat aquifers in Central Kalimantan, Indonesia

Vonk, Erwin (2011) THE IMPACT OF DIFFERENT CANAL CONFIGURATIONS ON THE DRAINAGE OF TROPICAL PEATLANDS A geohydrological model to predict drying of sloping peat aquifers in Central Kalimantan, Indonesia.

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Abstract:Excessive drainage of tropical peatlands in the province Central Kalimantan is a major environmental problem of Indonesia. The intention was to transform tropical peat swamp forests into a food production and living area for the country’s rapidly growing population. Most well known example of these development schemes is the so called Mega Rice Project. Initiated around 1996, tropical rainforest were logged and a dense network of drainage canals constructed to prepare the area. But the project failed as the soil appeared not to be suitable for the rice agriculture it was intended for. Furthermore the dense drainage network caused the groundwater level to drop rapidly during the dry season, a decline that does not stop until the wet season commences again. Nowadays the site has a disrupted hydrological cycle and suffers many problems like drought, greenhouse gas emissions, fires and land subsidence. During this research project for LabMath-Indonesia a data-extensive geohydrological model was developed to predict the peatland drying process under various canal configurations. The model is specifically intended for predictions in poorly gauged basins. Key aspect is the distinguishing between different drying processes: diffusional flow, gravitational flow and evapotranspiration. Several canal configurations have been evaluated for their performance during relatively dry years. The first one is the current situation. Secondly, as a reference, the effects of a complete fill operation of all canals have been determined. Thirdly a hybrid solution has been studied, in which the so called contour canals are preserved and equipped with weirs at their intersections with remaining side slope canals. Currently the peatland is intersected with canals that have a spacing of approximately 80 m. On an average peat dome with a slope angle of 0.1 degrees this results in full drainage of the top layer (0-1 m below surface) within 80 days. Model outcomes show that evapotranspiration is the dominant process, while also canal spacing has great influence on the outflow. Even though diffusion is a relatively slow process, it starts to contribute significantly to the outflow when the canal spacing is small. In a situation where all canals would be completely filled, the remaining drainable storage is still 10% after 100 days. This can be approximated by constructing weirs in the contour canals at their intersection with the side slope canals. With a weir height of 0.75 m the water retention in the peatland can be increased by 20%, extending the drainage time from 80 till 100 days (compared to the current situation). The strategy seems promising, since it not only increases the water retention, but also allows for drainage during the wet season. Overall it can be concluded that the natural situation can be approximated by filling nearly all side slope canals, except an absolute minimum necessary for drainage during the wet season. It is recommended to construct weirs at the intersections between the remaining side slope canals and contour canals. The higher the weirs, the more effective the solution will be. However, the exact height is to be determined by also taking agricultural requirements into account.
Item Type:Essay (Bachelor)
Faculty:ET: Engineering Technology
Subject:43 environmental science
Programme:Civil Engineering BSc (56952)
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