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Closure of o ff takes in Bangladesh Causes and assessment of remedial measures
| Content Provider | Semantic Scholar |
|---|---|
| Author | Santamaria, Raffaele |
| Copyright Year | 2017 |
| Abstract | Bangladesh is characterised by its complex river system, which includes the downstream ends of two of the largest rivers in the world: the Ganges and Brahmaputra. Extremely variable flows and fast morphological changes are the principal characteristics of this system, which presents exceptional challenges for river engineering. Distributary rivers from the major rivers in Bangladesh are a key element in providing fresh water to the SouthWest and Central regions of the country. With the arrival of the dry season and the drop of water levels in the rivers, some of the distributaries become disconnected during several months from their parent rivers because of aggradation at the offtake during the monsoon season. Acquisition of all the field data required for a detailed morphodynamic study of those offtakes is very often not possible, specially for preliminary designs or during the initial stages of a project. For the rivers of Bangladesh, bed topography data are even outdated in a matter of months because of the extremely dynamic nature of those rivers. In order to overcome this lack of data, the approach of this MSc thesis is to use a physicsbased morphodynamic numerical model based only on the most significant characteristics of the offtake system to be analysed. If this model correctly reproduces the most important characteristics and evolution of the river and offtake system, it is then possible to use it for an initial assessment of remedial measures to prevent offtake closure. An analysis of the offtake systems is made before setting up the numerical model. The focus of this analysis is on the relevant physical processes for the evolution of offtakes, with the conclusion that processes such as helical flow, transverse bed-slope effects on sediment transport or retarded scour need to be taken into account in the numerical model to reproduce the morphodynamics of the system. Furthermore, the causes of offtake closure occurring at the main distributaries of Bangladesh are identified and possible remedial measures are proposed to prevent them. The setup of the model is based on the findings from these previous analyses. The choice is for a 2-D depth average numerical model using the software package Delft3D. A schematised geometry roughly based on the Ganges and Gorai rivers and offtake is used, with a total length of 100 km for the parent river and 20 km for the distributary channel. The |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://repository.tudelft.nl/islandora/object/uuid:691dbc0b-a713-4f29-9354-202c713cc4bc/datastream/OBJ/download |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
