In the southern part of the region, the tidal flows dominate the rivers and saline water penetrates deep inland especially in the central and western parts of the southwest region. There is clear evidence that dry season flows in the Ganges have been seriously depleted due to upstream abstraction. Gorai River is the only source of freshwater flow to the southwest in the dry season. It has been observed that wet season flows have also started to reduce, indicating that a complete cutoff of Gorai from the Ganges is imminent. The Government of Bangladesh implemented the Gorai River Re-excavation Project in 1997, and then took up the Gorai River Restoration Project (GRRP) in 1998.

In 1996, the historic Ganges Water Sharing Treaty (GWT) between Bangladesh and India was signed. The GWT assures Bangladesh with a defined quantum of flow release at the Farakka Barrage in India for the next 30 years. GoB now has the opportunity to plan a more sustainable development of the Ganges with increased confidence. With the availability of increased dry season flows in the Ganges consequent to the GWT, more water could be diverted towards the GDA. It is necessary to assess the likely future water needs in the GDA, estimate the local resources and examine options for diverting and distribution of the dry season Ganges flows to meet any deficits in different part of the area. In view of this, a special study on Options for the Ganges Dependent Area (OGDA) started in 1999 under the National Water Management Plan Project (NWMPP). SWMC, under a subcontract with Sir William Halcrow and Partners, has been engaged to carry out mathematical modelling for the Options for Ganges Dependent Area (OGDA) Studies. SWMC is involved in data collection for the modelling studies, development and application of hydrodynamic and salinity models for the GDA.

Hydrodynamic model has been used to study a large number of options for various combinations of diversion and distribution works. The options for the diversion of water from the Ganges included pumping or construction of a barrage or a combination of dredging of the Gorai offtake and river training works. The set of options for the distribution of the diverted water were studied to assess how the watercourses within the GDA could be augmented using natural and rehabilitated channels. The salinity model was used to study movement of the salinity front with various options of diversion and distribution of Ganges flow in the GDA. In total, 8 options were studied. The study shows that with the limited flow available during dry months, it is a better option to distribute the flow more widely through various rivers in the GDA in terms of area to be benefited from pushing the salinity front further south.

The GDA models were also used to assess the impact of global climate changes in the GDA. Increase in sea water levels and changes in evaporation and rainfall represented the climate changes.