Impacts of Low Flows on the Alluvial Rivers of the Southwest Region of Bangladeshby Daryl B. Simons, (F.ASCE), Simons & Associates, Inc, Fort Collins, United States,
Abstract: The Ganges River, which flows out of China through Nepal and India and finally into Bangladesh, has been subjected to continuous scrutiny as conflicts regarding the diversion of water have intensified, mainly between India and Bangladesh. There has been a continual reduction of low flows, an alteration in the supply of sediment, and an incisement of the low-flow channel during the past several decades within Bangladesh as a consequence of upstream development related to expanding agriculture and associated irrigation activities, extraction of water for municipal and industrial use, and the construction and operation of the Farakka Barrage which is located approximately 11 miles upstream from the Bangladesh border. It has been concluded by both technical analysis and political action that a grave crisis has arisen for Bangladesh on account of the unilateral action taken in diverting the water of the Ganges River at Farakka. This extremely complex political and technical background establishes the need to consider geomorphic impacts that have been and will be imposed on the Ganges River within Bangladesh. Major geomorphic responses to imposed low flows recognize that there will be changes in channel regime, as well as changes in bed form. The normally experienced bar formations may adopt a totally different pattern. With the changes in bar location, the low flow channel will adopt an alignment different than the historic alignment that will cause numerous problems. The impacts on low-flow navigation will be severe. The creation of a new, ever-changing, low flow alignment will reduce the ability to divert water for irrigation. Also, with changes in low flow channel alignment and incisement of the flow into the bed of the channel, existing bank revetment, pump stations, etc., may be endangered. These changes will also significantly affect wildlife habitat, will reduce and, in some cases, eliminate wetlands, and will allow a greater degree of salt water intrusion. All of these factors are expected to have a significant impact upon fisheries and wildlife in the Ganges River area. In addition, the changing environment could result in the development of environmental conditions that would be very adverse to public health. Geomorphic changes in the channel system will continue in response to further reduction in minimum flows. As Bangladesh looks forward to present and future food requirements, it is essential to establish a magnitude of reliable base flow conditions. More importantly, Bangladesh must recognize the serious problems developing as a consequence of population expansion that makes it increasingly difficult to accommodate public health needs and food requirements regardless of water availability.
Subject Headings: Developing countries | Channel flow | Low flow | Rivers and streams | River flow | Water flow | Alluvial channels | Public health and safety | Streamflow | Asia | Bangladesh | India | Nepal | China
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