Development of Operation Rule of Proposed Ganges Barrage Using Mathematical Model

Abstract

The main objective of the proposed Ganges Barrage is to divert the dry season flow to meet the overall water demand of Ganges dependent area (GDA). The proposed barrage over the Ganges needs to be operated in such way that can pass additional flow during monsoon saving inundation and store flow during dry period diverting flow through the distributaries of the Ganges. The successful performance of barrage mainly depends on proper regulation system. Prior to the implementation of the project, such barrage regulation system can only be assessed and developed through the application of mathematical models. Primary gate operation plan of the Ganges Barrage has been prepared in this study with the aid of mathematical models by dividing the Ganges flow in selected flow bands. The flow bands are consisting of lower to higher discharge. One dimensional hydrodynamic model MIKE 11 has been used for the development of the operation rules. Morphological consequences at barrage site due to gate operation have also been assessed using two-dimensional morphological model MIKE 21C. It is found that for the flow up to 45000 m3/s, barrage gate operation is necessary to create required design water level at 12.5 mPWD at upstream to meet the maximum demand for GDA. Two methods of barrage operation system such as still pond system and Semi open pond system have been investigated in this study. It reveals that Semi open pond system of barrage operation has been found appropriate for the operation of Ganges Barrage. Emphasis has been given for preparing the operation plan of barrage in case of different discharge ranges. A system of rule curves, which define stage-discharge relation, have been prepared for various gate opennings to suggest a guideline for the barrage gate operation.. Gate openning up to 1.0 m height for undersluice portion is found to be sufficient to create required pond level for dry weather discharge ranges i.e. 0 to 1000 m3/s. Regulation of water through the barrage has always been resulted morphological changes in the river at immediate upstream and downstream locations of barrage. While preparing the operation plan, such morphological changes and sedimentation pattern of the proposed barrage for both semi open operation system and still pond operation system have been investigated. It is found that developed operation plan would maintain a flow channel towards undersluice at barrage upstream. The net sedimentation rate at barrage upstream has been assessed for semi open operation system. It is found that for the low discharges, the net sedimentation rate at barrage upstream is 1.25 mm/day/m length for proposed operation system and is less compared to that of the other method of operation