University of Twente Student Theses


Modelling the water balance of Sembakkamlake, Chennai, India and evaluating low impact developments

Brink, J.M. van den (2019) Modelling the water balance of Sembakkamlake, Chennai, India and evaluating low impact developments.

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Abstract:This study aimed to propose management options for the improvement of water issues at Sembakkam lake. There are three major concerns in this study area. First, there is severe water scarcity during the dry period of the year in the catchment area. Second, flooding occurs during the wet period in the catchment area. Third, untreated sewage inflow contaminates the lake through the year. This study focused on the problems related to water quantity by proposing and evaluating two Low Impact Developments (LIDs) at the household level: percolation pits and cisterns. In order to evaluate their impact on Sembakkam lake, a hydrological model of the water balance of the lake was established using SWMM software. The runoff was estimated using GIS data and a literature research. Climate data of evaporation and precipitation and local arbitrary measurements of the dry weather inflow and overflow were used. Human consumption was estimated by literature review and making assumptions and in the end the seepage at the lake was arbitrarily calibrated. Moreover, the drainage network, infiltration parameters and dry weather inflow were found to be sensitive and uncertain parameters, which makes the results for infiltration and overflow volume uncertain. Further research and data collection should be carried out in order to increase the reliability of the results. Furthermore, the amount of percolation pits and cisterns was estimated based on the three scenarios that 5, 15 and 25% of households in the catchment area implement these LIDs. The dredging of the lake, proposed by experts from IITM, was also evaluated for different post-development hydraulic conductivities of the lake bed. The dry weather inflow appeared to be a major inflow of Sembakkam lake (26-38%). The outflows are overflow (68-78%), seepage (12-18%), evaporation (5-7%) and human extraction (1-4%). Moreover, the lake is always full throughout the year, resulting in the inability to store the runoff caused by rainfall events higher than 2 mm/hr. Therefore it is suggested to empty the lake during dry season by lowering the weir to create free storage capacity. The results indicated that the implementation of cisterns and percolation pits would not effect the runoff enough to have an impact on the water balance of Sembakkam lake. Implementing these LIDs in the quantities used in this study is therefore not recommended. Percolation pits however can increase the infiltration volume in the catchment by 5-25%. Although the increase in infiltration volume is too little to mitigate the water scarcity during dry season, implementing this LID could be effective for increasing the small infiltration volume at the catchment, especially in larger quantities than modelled in this study. Further research should be done on the water quality of the runoff infiltrating and its effect on the groundwater quality. More research could also be done on the question if cisterns are a cost-effective option for water supply since they can provide 5-9% of a households yearly water demand. Another subject for future research could be the impact of cisterns on local flooding. The dredging of the lake could increase the lake’s seepage by 150-200%, leading to a reduction in total overflow volume of 30-45%. Dredging the lake bed is therefore recommended, but it is important to find solutions for the lake’s detoriating water quality before dredging to prevent groundwater pollution. Also, further research on the downstream effects of an increase in groundwater and a decrease in overflow from Sembakkam lake is suggested.
Item Type:Essay (Bachelor)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering BSc (56952)
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