How to improve Gorai and other distributaries?
Whenever the flow in a river decreases it becomes sluggish which causes sediment to get deposited raising the bed and forming chars and shoals. This makes the rivers ineffective and inoperable for navigation, irrigation and agriculture. When the withdrawal upstream becomes severe, only a limited amount of water can flow into the main Ganges channel and the distributaries. For this water levels fell sharply in distributaries, and even some became dry. The dredging of the Gorai river can provide short-term remedy.

As a result of low flow salinity intrusion from the sea through the moribund channels took place. This affected agriculture, drinking water, fishery, forestry, ground water (depletion of ground water levels), land and environment. Some short-term remedial measures for improvement of the deplorable conditions in the area are suggested below. Long term solution is costly and time-consuming, but must also be taken urgently. Though there is agreement on sharing of water of the Ganges, for some reasons may be for inadequate monitoring, low flow condition became severe of late than it was before.

Some suggested short-term solutions
Bangladesh including southwestern region has innumerable small dry streams, swamps, land depressions scattered all over the country. During dry season small earthen dams (2 to 3m high) may be constructed on lands with favourable topography, though such topography is not easily available. Swamps may be excavated and deepened to hold rain water, thus creating small reservoirs. Abandoned dry rivers may be excavated to create mini reservoirs. Even ponds/tanks may be excavated for one or two family holdings. (In India millions of tanks are used for drinking water and small irrigation).

We may have to sink shallow tubewells for drinking water and minor irrigation. Bangladesh with copiously high rainfall is adequate to recharge the ground water aquifers to regain its full capacity for use in the next dry season. Wells in the rural areas are sparsely located while pumping of water by closely sited deep tubewells in the city of Dhaka or elsewhere depletes the ground water levels to such an extent that it cannot be fully recharged. The phenomenon of ground water mining occurs when annual recharge is less than withdrawal. Serious depletion may occur for long-term mining which may cause lowering of the level of the earth surface, as it happened in California, USA and elsewhere.

There is no short-cut and easy-solution for repelling salinity in the absence of fresh water during low flow in the Ganges in the dry period. Salinity can be pushed downstream only if there is enough fresh water flow in the river. For improving low flow situation we may have to wait for the proposed Ganges Barrage.

The proposed Ganges Barrage
Long-term solution is improving flow in the Ganges channel and its distributaries during the critical dry season. As it is not possible to flush the channels for lack of fresh water due to withdrawal of waters upstream, we may think of some water augmentation scheme on the Ganges at a suitable site, to be determined only after comprehensive relevant surveys and data analysis.

Only flushing of nearly dry distributaries including Gorai will not justify the construction of a structure of such gigantic magnitude and dimensions. Perhaps, Ganges Kobadak Project constructed in the fifties and sixties, is facing water problem due to withdrawal at Farakka and low water level near the pump house so water from the barrage will be used for revamping the GK Project.

Definitely, some new irrigation projects have been envisaged on both banks of the Ganges. Also, perhaps the postponed or nearly abandoned GK Project Jessore phase may be revived by using water from the Barrage. Water will also flow through other rivers and channels downstream through Kushtia, Faridpur, Jessore and Khulna and flush saline and polluted water and repel intrusion of saline water from the sea. Soils and agriculture damaged over the last 50 years or so in the greater Khulna and the lower part of Jessore and even Kushtia may be rejuvenated in a few years.

Some areas around Satkhira and elsewhere, where nearly irreversible damage might have occurred, may take longer time to recover. BWDB had one experimental agricultural station at Benerpota near Satkhira for conducting research to grow salinity resistant rice crops in late fifties and early sixties. The writer worked in that project with FAO experts in its design and construction. If this farm still exists it might have important and valuable data on intrusion of salinity through the adjoining rivers, soil fertility and productivity of rice showing a comparison from the sixties to date. This may show gradual deterioration of the land, agriculture and fishery over the last 50 years.

The Ganges Barrage is an awesomely massive and a gigantic project. It will be staggeringly costly. But economic benefit should out weight the cost, in order to make the project financially viable. Internal rate of return/benefit-cost ratio should be positive and acceptable. Surely, designers and financial analysts will look into it. The writer as a dam and barrage designer (including design and supervision of construction of some dams in Nigeria) is of the opinion that to save the nearly hydrologically dead, water-starved, salinity affected south-western region; to reclaim the moribund, dead and drying rivers to revamp the famous GK Project and its further expansion southwards up to Jessore and other possible new irrigation projects; to revitalise the degraded and polluted environment and deteriorated ecological settings (including fishery and forestry), the construction of the barrage should be considered seriously and decision taken in right earnest.

The barrage for its regulated ecological flow during the dry season will keep the main Ganges channel and distributaries flowing upstream and downstream, the barrage will maintain the rivers hydrologically living with adequate fresh water and transform the SW part into economically vibrant, ecologically healthy region and turn the environment congenial and pleasing.

For controlled flow from the barrage there will be further relief and benefit from floods which are a regular annual recurring. Floods on both banks of the Ganges, particularly in south Pabna, Kushtia and Faridpur will be controlled. Also flooding in the distributaries like the Gorai and other rivers will be mitigated; ground water condition will improve which will help agriculture and drinking water supply. Sundarbans will be rejuvenated with fresh water diluting the salinity. And there will be healthy development of fishery in the whole Ganges basin including the larger southwestern region of Bangladesh.

Repelling saline water intrusion
There is no short-cut solution for repelling saline water from the sea. Short-term solution suggested is introducing salinity-resistant crops. Only long-term and perhaps permanent solution is flushing the deteriorated, silted up channels by fresh water from the Ganges barrage. Salinity was highest in Satkhira area, the salinity contour of which gradually sloped down towards southeast and became salinity free near the Barisal river border. The writer had the experience of salinity intrusion survey and study with FAO team in the area.

Salinity survey in the river channels in SW region was conducted by FAO/UNSF Hydrological survey Programme in collaboration with the BWDB/EPWAPDA in the sixties for nearly a decade. It was a highly capital-intensive, instrumentation/equipment-intensive and qualified and experienced man-power-intensive project.

Monthly contour lines of salinity were drawn on the map in the SW region to see variation with respect to Ganges low discharge in the dry months. The worst affected period was April when the discharge was the lowest in the Ganges. In the worst condition at that time an area of about 10-12,000 Km2 was found to be affected by harmful salinity of 1000 micromhos (700 mg/I or 700 PPM).

It may be mentioned that the situation and coverage of area by harmful salinity might have increased over the 50 years since then due to much lower discharge of the Ganges now. For low discharge all the rivers in the area silted up, some even dried up, creating desert like condition during the dry months.

Due to very low flow of the Ganges in dry months, the whole Padma and the lower Meghna channels have been affected, which might have affected the river banks and beds. This must have affected easy and smooth navigation, and might also fishery. And how far flood hazards have increased in the Padma and lower Meghna basins is now a matter of serious concern.

Summary of short-term and long-term measures
Short-term: Construction of small reservoirs may be undertaken by excavation of derelict and abandoned channels, depressions, swamps, dry rivers, ponds. To have the mini reservoirs filled up by rain water during the monsoon for use in the next dry season as drinking water and minor irrigation. Suitable topography should be found to build small earthen dams for holding 5,000 to 50,000 m3 water shallow tubewells of 30 to 50m deep may be sunk for drinking water and minor irrigation. Farmers should go for salinity and drought resistant crops. Rice Research Institute and other agricultural institutes may be of help in sorting out the types of crops and methods of cultivation. Some dry and silted up distributaries and rivers may be dredged to store water during the monsoon for use in the dry season.

Long-term: Long-term and perhaps permanent solution is construction of Ganges Barrage. It should be built as early as possible.

Since the measures suggested are of multi-faceted and multi-dimensional in nature, their planning, design and execution will need involvement of experienced professionals of some major organisations under the Ministries of Water Resources, LGRD, Agriculture and Environment. The suggestion is that a committee will manage small projects in SW region and BWDB will execute the Ganges Barrage Project.

The writer is a Professor of Civil Engineering at the World University of Bangladesh, and a water specialist.