Author(s): Pintu Kanungoe; A. K. M Ashrafuzzaman
Linked Author(s):
Keywords: Barrage; Bankfull discharge; Design discharge; Sediment transport; Calibration and T head groyne
Abstract: A barrage across the Ganges River at Pangsha has been envisaged as an essential structural intervention to store water and augment dry season flow into the distributaries of the Ganges particularly the Gorai. Physical model investigation has been conducted to support Feasibility Study in relation to appropriate barrage location, planning and layout of the proposed barrage. A comprehensive distorted morphological model covering an extent of about 53km of the Ganges has been constructed that includes alternative barrage locations. An extent of about 13km of the Gorai has also been reproduced. The length and depth scale is selected 600 and 80 respectively. The scale of different basic and derived parameters including the depth scale has been determined from calibration of the model for bankfull discharge. After due assessment of model limitations and capabilities model runs have been conducted over calibrated bathymetry for four distinct return period discharges including design discharge to establish baseline hydraulic and morphological conditions. Performance of preliminary layout of barrage and guide bund at two alternative barrage locations (Tagorebari and Pangsha) has then been tested for design discharge. Comparison between alternative barrage locations is made in terms of hydraulic and morphological parameters in with and without barrage conditions. Pangsha site is considered to be suitable for barrage construction taking relevant issues into consideration. The preliminary barrage layout at the selected site has been tested for an exceptionally high discharge. The test results indicate that the clear waterway should be increased reasonably to allow for safe passage of an extreme event. The modified barrage layout is tested with and without upstream river training works. All the tests with structures in place have been conducted for bankfull discharge followed by higher discharges. It is observed from the rest results that two upstream T head groynes will be required in order to have favourable river approach to the barrage, prevent very high flow concentration and consequent formation of large scour depth at undersluice location and avoid likely shoal formation along the left guide bund. It is also inferred from the test results that since the guide bunds will function together with upstream gyones the adopted shape of the upstream termination of the guide bunds may be reviewed for optimization.
Year: 2012