Delta Plan 2100
Fresh water conservation for irrigation
Under 'Delta Plan 2100' the major goals for 'fresh water conservation' is related with hot spot entitled 'Brand and drought prone area'. The major strategies for 'fresh water conservation' are: abstraction of surface water through barrages and reservoirs, restoration of beels and water bodies, regional cooperation for trans-boundary water management and efficiency of water usages etc.
Demand for fresh water will be increasing. During dry season, water scarcity is a constrain, mainly in 'Barind and Drought Prone Areas' due to low rainfall, adverse effects of Farrakka and due to effect of climate change. Due to lack of dry season flow in coastal rivers- salinity causes deterioration of fresh water - it causes lower crop productivity.
'Delta Plan 2100' should give us guidelines; how to maintain flow of rivers and how to preserve river water. A hydro-dynamic modeling research conducted in major rivers (data on flow and depth) and adjacent flood plains (depth, duration of flooding)--could be useful for selecting best locations for reservoirs.
Under intensive agriculture, water table is lowering due to over sinking of underground water, especially in northern districts. We have to pay attention on surface water development projects rather than tube wall water. Excavation of silted rivers and canals are essential- irrigation pump could be installed in river sites to utilize large scale river water.
The barrage and reservoirs are main source for river water conservation. Construction of barrages on the Padma near Kushtia and on the Jamuna near Jamalpur has been proposed. The flood water could be diverted and conserved in river and in reservoir (water storage) by 'constructing barrage across the river. Through construction of barrage (concrete structure)- monsoon river water could be diverted to a nearby reservoir through canal.
However, there is a challenge towards construction of the Padma barrage in the face of environmental issues, as well withdrawal of water at Farrakka. 'Delta plan 2100' might provide an approach for effective regional cooperation- regarding barrage construction. Regional cooperation is needed for fruitful solutions on water sharing of the Padma, Teesta and all other trans-boundary rivers.
We can accept more water from India, but it is uncertain. We have to plan in our way to use ooue water resources. The huge amount of our river water remains unused into sea, which could be stored for irrigation. There is no alternate but conservation of water in all rivers, estuaries, haor, beels, and canals.
An 'alternative water conservation' approach found feasible in USA, Singapore and China over traditional dam. Construction of 'reservoir' in haor or beel areas adjacent to the river without diverting river flow- is an innovation. The reservoir areas are separated by building a surrounding dam. No barrage is constructed and no lands are submerged- it will not create major social and environmental problems, as like Barrage.
The haors and beesl are not reservoirs. They contain huge amount of water in wet season, but water is passing out unused --they become almost dry in winter. Only a lower part of haor/beel contains a less amount of water during dry season. An innovative idea is to 'construct reservoir in haor or beel areas'- so that water is available in reservoir for navigation and fish cultivation during both wet and dry months.
There is plenty of water in haors and beels in wet season- surrounded by villages (act as natural walls) and raised water level of rivers. At the end of wet season, major parts of water are drained through natural outlet /rivers/canals. However, dry season draining of water could be blocked from a part of haor areas- through surrounding those areas by a long artificial dam (wall of reservoir).
A fresh water reservoir could be formed in haor areas with a series of sluices. At the end of wet season, when sluices are closed--water couldn't pass from the reservoir. Fresh water from reservoir could be released into networks of canals for irrigation in low-lying adjacent haor areas. Irrigation will be possible without any pumps.
The low-lying 'Chalan Beel' is connected with the Padma River having huge water discharge- seems to be best for construction of wall/dam of reservoir. A reservoir could be formed at a portion of 'Chalan Beel' by surrounding a long dam without any barrage in the Padma.
Proposed dam (wall of reservoir) could be constructed during dry season- when there is no water in Beel areas. The concrete foundation of dam will be built first and then surrounding long dam (7-8 meters height) will be filled with earths and covering with rocks. A series of sluice gates will be installed facing to waterway.
After construction- monsoon flow will enter into reservoir through sluices. During dry season, water from reservoir could be released into networks of canals for irrigation. Irrigation will be possible without pumps, as beels are at lower topography than reservoir's water level. It is assumed that without construction of barrages in a river - monsoon rain water could be preserved in reservoir in beel areas.
Feasibility studies could be done on 2 major rivers (the Padma and Jamuna) flood plains for selecting the best reservoir sites. Four sites has been proposed: a. Chalan Beel near Rajshahi, b. Bahadurabad ghat near Jamalpur , c. Two rivers connection point, Goalanda, Rajbari, d. Near the Padma, Madaripur.
Further, Sylhet region has plenty of rainfall adjacent to Meghalaya, India. During wet season, there is a huge water resource in Hakaluki and Tangura haors, as well in rivers (Surma- Kushiyara) and canals. It is assumed that without construction of barrages (blocking flow) across the rivers- monsoon water could be preserved through converting a portion low-lying haor area into a reservoir.
However, Sylhet basin's eco-system has been changing. In future, hydroelectric dam of India at Tipaimukh will divert flow of the Surma- Kushiyara and would have adverse effects on haor eco- systems (Hakaluki and Tanguar haor). The connected upper and lower Meghna Rivers in south-eastern regions (Cumilla, Chandpur, Noakhali and Bhola) may also be affected.
We must be well prepared for storage of water in 'low-lying haor area' in the face of adverse 'effect of Indian Tipaimukh dam'. Thus, five large reservoirs on the Surma-Kasiyara-Meghna river systems have been proposed: a) Part of Hakaluki haor, Fenchuganj, Sylhet b) Part of Tanguar haor, Tahirpur, Sunamgonj , c) Low-lying areas at Surma-Kasiyara junction, Habiganj. d) Part of haor, near the Meghna, Kishorganj, e) Low lying areas, near Upper Meghna, Chandpur.
There are huge water resources in our river systems with large Himalayan discharges. A series of reservoirs on low-lying sides/haor/beels of 'the Padma, Jamuna, Kushiara, Surma, upper and lower Meghna and river estuaries' has been proposed. This is in response of dry season drastic river flow deterioration- accelerated by withdrawal of water at Farakka and Teesta, as well as due to climate change.
The reservoirs could serve as a source of irrigation water; as well as community based large scale fish culture involving public and private sector stakeholders could be initiated- by whom both farmers and business entrepreneurs will be benefitted. The land owners/farmers of reservoir areas will be benefited based on income from leasing of their lands.
'Delta Plan 2100' has emphasized 'fresh water conservation' through barrages and reservoirs. An environmental friendly "low lying area management" policy could build- emphasizing crop diversification, varietal development, water conservation etc. A large investment in fisheries sector has high possibilities with emphasizing export oriented processed fish culture and agro industries.
With dynamic leadership of Honourable Prime Minister Sheikh Hasina- Bangladesh will achieve the goal in 'water conservation sectors' and will eliminate poverty from the country by 2030.
The writer is a Chief Scientific Officer, Bangladesh Rice Research Institute, Gazipur