Tidal river management: Indigenous technology for saving coastal ecosystems
The Southwestern coastal region of Bangladesh has been marked as a critical disaster hotspot. This region includes four districts—Khulna, Satkhira, Bagerhat and Jessore—which have high concentrations of rivers and canals, forming a dynamic coastal ecosystem. The coastal ecological system is changing more rapidly than before due to different cross-cutting social, political and natural factors. Prolonged and recurring water-logging due to inappropriate and poorly-managed engineering interventions, semi-intensive aquaculture, and diversion of river flow in the upstream have all dramatically altered human livelihoods. On top of that, climate change effects have exacerbated the crisis in recent years.
This region is a concrete example of how multifaceted natural, political and social factors create a complex socio-ecological system. The southwest of Bangladesh is part of the greater Ganges floodplain, an extraordinarily complex and sensitive ecosystem. This ecosystem relies on a delicate balance between water flows from two directions: downward flow from the source river and drainage tributaries, and upward flows of sediment-laden estuarine rivers from the Bay of Bengal (that causes riverbed siltation). Riverbed siltation and brackish water effect due to sea-level rise and high tide have led to prolonged and recurring water-logging in southwest Bangladesh in the last two to three decades.
In the coastal areas of Bangladesh, 139 polders have been constructed since 1960 to control the unstable environment and support agricultural growth. Such large-scale intervention initially resulted in increased agricultural yield until the 1980s. However, the delta floodplain got disconnected from the dense river channel network, and the siltation rate accelerated in the river beds, culminating in the emergence of a water-logging problem. Water-logging causes extreme economic, social and cultural damage to these areas. Since all of the affected districts are majorly agriculture-dependent, water-logging will more adversely affect farmers' income and daily labour. Most of the dwellers of this region depend on shrimp farming, weaving, poultry, cultivating lands to produce paddy, lentils, and seasonal crops for their living.
From the early 1980s, local people started cutting dykes based on a practice from the past built on local knowledge to address the worsening impacts. After years of modelling and systematic experiments, a large body of experts, researchers and institutions now support the community approach called "tidal river management" (TRM). TRM is an environment-friendly, cost-effective, technically feasible, participatory and highly socially acceptable method that provides a unique solution to the water-logging problem. TRM has been implemented in Salta, Betna, Kapothakkha and Hari-Mukteshwari rivers as an indigenous solution for river management. It has had an extended effect on enhancing river navigation and creating better sediment management.
Tidal River Management is considered the most effective method to save rivers and the ecosystem. To put it simply, TRM controls the sediment of the rivers as high tide brings muddy water flow with a dense concentration of sediment. Local people cut the embankment to a certain point where the tidal water can get into the floodplain, deposit a part of the sediment into the floodplain, and go back to the ocean. Over time, the disposition of residue raises the land level and enriches the soil. Hence, the process does not let the sediment settle on the river bed and so the depth of the river increases and makes the river accessible.
According to research and community consultation, TRM can be scaled up and replicated on river basins throughout the southwest coastal region, making it the most effective method to increase cultivable lands, mitigate water-logging crises, and increase rivers' navigability. This sediment management technique has been practiced for years as an indigenous solution by the locals, as they have discovered it to be the best method of climate change adaptation to protect the region from sea level rise. According to a very recent study based on sophisticated modelling techniques, 106 beels in the coastal area are suitable for use in TRM. The same research suggests that TRM can reduce flood susceptible areas by 35 percent in suitable beels and enhance agricultural production in the long term. As sedimentation is a necessary coastal ecological process, TRM will also potentially contribute to land reclamation.
Arguably, Tidal River Management also comes with a few challenges. First, planners and engineers often neglect this system as it is an entirely indigenous invention. Second, the implementation of TRM requires a large volume of land that local people do not want to give up for several reasons. Land owned by the government (Khas land) often remains under the control of influential local people as well, and they have no incentives for giving up that land. Third, many people are dependent on the land for agricultural production, and they have limited capacity to embrace a new livelihood method for survival at the advent of land acquisition. So arises the need for timely and appropriate compensation for locals, which is a critical issue in the TRM implementation process.
Fourth, TRM requires a great deal of synchronisation between stakeholders for successful implementation and desired outcomes, including local government, resource management agencies, the community and non-governmental organisations. For instance, in Khuksia beel, an unplanned implementation of TRM, without sufficient cooperation between stakeholders and government agencies, resulted in several disruptions during operation, and the water-logging problem remained. Last but not least, to bring holistic change in coastal governance, relevant stakeholders must accept the value of local knowledge. In the Bangladeshi context, engineers, government representatives and bureaucrats are deemed the "social supreme class" and their inputs dictate the decision-making process at the grassroots level.
For a healthy coastal ecosystem in the southwest of Bangladesh, a scientific understanding of sediment and fluid dynamics needs to be adequately developed. There is a higher degree of consensus that proper sedimentation management by keeping the canals and creeks connected to the rivers will end the water-logging crisis in the coastal region. In this regard, indigenous practices by local people must be utilised for a more appropriate solution to the water-logging problem. We must also reiterate the need for political goodwill for adaptive ecosystem management by ensuring participatory governance. Uses of Tidal River Management (TRM) should be considered and given more emphasis for facing the aforementioned challenges.
Taslima Akter Shikha is the District Manager of Ovibashi Karmi Unnayan Program (OKUP). Md. Ekhtekharul Islam is a Senior Lecturer in the Department of Environmental Science and Management at Independent University, Bangladesh (IUB).