Author(s): Ulrike Feistel; Thomas Grischek; Doan Thu Ha; Hong Nam Nguyen; Nguyen Cao Don
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Keywords: Bank Filtration; Flood Protection; Flood Relief Wells; Land Heaves; Land Subsidence
Abstract: The Dresden University of Applied Sciences (HTW Dresden) has a long record of successfully implementing and investigating river bank filtration (RBF) schemes for drinking water supply in various countries including Germany, India, Thailand, Brazil, and Egypt. RBF is a sustainable, low-cost technique to meet the increasing drinking water demand that has developed in many countries over the last decades. By using wells installed on the banks of perennial rivers, RBF combines the advantage of easy access to large volumes of surface water with the benefit of natural filtration during aquifer passage. This produces high-quality pre-treated water and helps to mitigate the water quality problems associated with solely using surface water or groundwater. Encouraged by the recent activities in Thailand, the HTW Dresden, and the Water Resources University Vietnam (WRU) are currently preparing a research and development project to assess the feasibility of RBF in Vietnam. During the preparatory stages of this project, one particular aspect emerged which could potentially expand the use of the RBF technique beyond its original purpose of water abstraction for drinking water supply. Behind a dyke system along the Red River in Hanoi, the unconfined groundwater rises during floods causing land heaves thereby compromising the stability of the flood protection dykes. To manage the risk, flood relief wells have been constructed delivering the relief water to a drainage system. Specifically designed RBF wells for continuous water abstraction for drinking water supply could be used as flood relief wells, too. Continuous abstraction would potentially allow increasing storage prior to flood events thereby reducing the flood risk and at the same time addressing the increasing water demand. Furthermore, as the wells are located behind the dykes, they would be effectively protected from potential contamination during flooding, a problem to be considered when planning RBF sites. In order to assess the feasibility of RBF wells as elements both for flood protection and water supply, groundwater flow and transport modeling is required complemented by other methods to determine the portion of bank filtrate and respective travel times. Groundwater modeling has to be accompanied by geophysical and geotechnical investigations as transport of fine sand has been observed at some wells, which may pose a risk to the dyke stability if water is pumped continuously. The paper is intended to present the approach of a combined use of wells for dyke protection and water supply; first of all to get feed-back on the idea and secondly to discuss practical issues that might occur and need to be addressed such as the water quality problems (e.g. iron, manganese and arsenic), the transport of fine sand and others.
Year: 2014