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Modelling the Jakarta groundwater system : a sensitivity analysis

Roover, S.A.W. de (2015) Modelling the Jakarta groundwater system : a sensitivity analysis.

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Abstract:Jakarta suffers from land subsidence. The rate at which this happens is alarming. The subsidence causes much direct and indirect damage to buildings and both surface and subsurface infrastructure. Also the flood risk is increased since domestic, industrial and economic buildings have a higher probability of being flooded and damages will only increase with the (economic) growth of Jakarta. Another consequence of the subsidence is the disruption of the water management, since the gradients of surface water flows change. Groundwater abstractions play a major role in the land subsidence and it is important to schematise the Jakarta groundwater system. In this way also possible groundwater strategies, which could influence the subsidence rate, can be evaluated. Already similar models were developed, but for the current model there are now more possibilities due to technological advance and a continually growing database. The goal of this research was to support the modelling study with an analysis of the sensitivities of the model. Although a larger database was available compared to earlier models, still a vast lack of input data is present. Data collection is the solution, but to save resources it is of importance which input data have priority in the collection. Based on the sensitivity analysis in this study suggestions could be made on where what parameters have the largest influence on the model. In this way, with the data collection one can focus on improvement of quantity and/or quality of input data for certain parameters in certain areas. The research question which was answered in this study is to what extent the input parameters influence the model. This research question was elaborated in subquestions concerning which parameters are used in the model, what sensitivity is attributed to these parameters, and what sensitivity these parameters have in the model. The results present the outcomes of a univariate sensitivity analysis done with a selection of parameters. This selection consisted out of the parameters for the horizontal and vertical hydraulic conductivity, the recharge of groundwater, and the groundwater abstractions. This selection was made based on found sensitivities in literature. The results of the sensitivity analysis with these four parameters are shown as differences in groundwater heads compared to the original results from the model. These results are presented in tables and maps per model layer. The selected parameters each had their own influence on the model. Important is to notify that these influences are relative to each other and that thus on the influence of a sole parameter on the model nothing could be concluded. The horizontal hydraulic conductivity parameter had an overall influence on the model. The adjustment of the groundwater abstractions resulted in the largest sensitivities, but these were only present in the deeper layers in the northern part of the study area. Groundwater recharge also had a large overall influence on the model, but it is not certain of this statement could be made based on the found results. Changing the vertical hydraulic conductivity had the least influence when compared with the other parameters If Deltares will continue developing the current model and sampling data for it, then therefore some recommendations are proposed in the study. It is advised to carry out a detailed research for data on abstractions in the northern, industrial districts, as in this region the model reacted most to the variations in the abstractions parameter. Also is recommended for Deltares that for the overall model more research should be into horizontal hydraulic conductivity in the whole study area, with which a more detailed, layer specific map can be made to use as input for the horizontal hydraulic conductivity parameter.
Item Type:Essay (Bachelor)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering BSc (56952)
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