The flow in the Ganges is low during dry season and it has been a fact for decades that the Gorai does not always remain open, but some years dry out during the dry season. The lack of dry season flow in the Gorai has adverse effects on agriculture, fisheries, and it increases salinity intrusion etc. Conditions have deteriorated, particularly during the last decade with the Gorai drying out for entire dry season every year. Sedimentation at the Gorai offtake has increased considerably and the Gorai is nearly isolated from the Ganges flow. This isolation has been enhanced by the decreasing dry season flows of the Ganges in the last decade. This has resulted in nearly catastrophic effect to the agro-socio-ecology of the Southwest region extending even to the northern area of the Sundarbans.

The objective of the project is to restore the Gorai River, i.e., to ensure fresh water flow in the wet season and augment this flow during the dry season. A number of alternative options have been suggested by the Feasibility Consultant for testing of their functionality in the mathematical model. Options are combinations of dredging and different engineering measures in the Ganges and the Gorai including the offtake. The proposed engineering measures are as follows: (i) 9 groynes along the right bank of the Ganges between Hardinge bridge and Talbaria (A), (ii) a flow divider at the Gorai offtake (B), (iii) a guiding dike in the Ganges left bank down-stream of Hardinge bridge (C), (iv) a cross-bund in the Ganges left bank opposite of Talbaria (D), (v) a shore revetment in the Gorai offtake (E) and (vi) a series of groynes along the left bank and an advanced revetment along the right bank in the Gorai river 8h2 (see figure).

Mathematical morphological model of the Ganges-Gorai river has been developed in association with DHI to support the feasibility consultant for full project preparation in 1998. Hydraulic and morphological impact of different engineering measures proposed by the Main Consultant have been assessed quantitatively for both short to medium to long term where applicable. Model simulations for the options were given under boundary conditions (discharge hydrograph at the upstream boundary and water level hydrograph at the downstream boundaries) and initial conditions (bathymetry). 1999 hydrograph as average monsoon, and 1998 hydrograph, as extreme monsoon, have been chosen to use as boundary conditions for design event. All the options are simulated with the 1999 hydrologic event; but only selected options have been screened out as found better from 1999 hydrologic event and have been tested with 1998 hydrologic event. This has saved time, as the options have to perform in both a normal and a strong monsoon. In both hydrologic events, the simulation period is from June to October. On the selected options, dry season simulation (November to March ) was carried out for both hydrologic events. For each hydrograph, prior to the simulation of engineering measures, a base line was simulated, which is a prediction without any measures of improvement implemented and with the same flow conditions.

The objective of the project is to restore the Gorai River, i.e., to ensure fresh water flow in the wet season and augment this flow during the dry season. A number of alternative options have been suggested by the Feasibility Consultant for testing of their functionality in the mathematical model. Options are combinations of dredging and different engineering measures in the Ganges and the Gorai including the offtake. The proposed engineering measures are as follows: (i) 9 groynes along the right bank of the Ganges between Hardinge bridge and Talbaria (A), (ii) a flow divider at the Gorai offtake (B), (iii) a guiding dike in the Ganges left bank down-stream of Hardinge bridge (C), (iv) a cross-bund in the Ganges left bank opposite of Talbaria (D), (v) a shore revetment in the Gorai offtake (E) and (vi) a series of groynes along the left bank and an advanced revetment along the right bank in the Gorai river 8h2 (see figure).