Coastal Salinity and Water Management Practices in the Bengal Delta: A Critical Analysis to Inform Salinisation Risk Management Strategies in Asian Deltas

Abstract

Salinisation within delta environments is a dynamic process governed by the interaction between coastal, fluvial and geomorphological systems. Increasingly, these have been modified through human activity and management practices, which lead to unintended problems associated with waterlogging and salt accumulation in soils and water resources. As a result of these issues, over 100 million people in the Ganges–Brahmaputra and other Asian deltas are negatively affected by a lack of freshwater availability and decreased crop yields. Rising sea levels, climate change, and population increase are all likely to exacerbate these problems. Using an iterative approach of literature review, we analyse the evolution of water management practices and policy and how these have influenced salinity within the delta, with a conceptual framework of understanding developed to guide risk management strategies. We find that management of coastal flooding and salinisation is hampered by socio-economic conditions and the dynamic hydro-morphology of the delta, which has increasingly been altered through diversion and abstraction of upstream flow. Whilst engineering solutions protect large areas from inundation, interruption of natural flood-dynamics also increases the potential impact from storm-surge and fluvio-tidal flooding. To limit salinity, policies based on salinisation science, as well as the implementation of adequately financed, multi-layered, integrated risk management plans at the local, regional, and river basin levels, are required. The promotion of stakeholder engagement should be encouraged to ensure local co-operation and effective implementation of policies. The mitigation of the multiple and cascading hazards associated with salinisation caused by anthropogenic activity, climate change and socio-economic development is crucial for the populations of delta regions across Asia.

What drives changes in surface water salinity in coastal Bangladesh?

“…Previous research in low-lying Asian mega-deltas (Figure 1) has suggested a range of factors influencing the salinity of surface waters and groundwater (Yu et al, 2010;Salehin et al, 2018;Akter et al, 2019Akter et al, , 2020Sherin et al, 2020;Bricheno et al, 2021;Feist et al, 2023;Raff et al, 2023). These include: (i) changes in the magnitude and seasonality of upstream river discharge and sediment deposition; (ii) subsidence, sea-level rise (SLR) and seasonal tidal fluctuations; and (iii) the intensity and frequency of tropical cyclones and storm surges.…”

“…These include: (i) changes in the magnitude and seasonality of upstream river discharge and sediment deposition; (ii) subsidence, sea-level rise (SLR) and seasonal tidal fluctuations; and (iii) the intensity and frequency of tropical cyclones and storm surges. In the Bengal Basin of Bangladesh, surface water salinity regimes are also locally influenced by land-use change and human interventions such as coastal embankments known locally as "polders, " shrimp farming, and dry-season irrigation from surface waters and wells (Ayers et al, 2017;Islam et al, 2019;Shamsudduha et al, 2022;Feist et al, 2023). The complex interplay of these different factors makes it challenging to identify the primary drivers of saltwater intrusion over large, complex low-lying deltaic systems (Bricheno et al, 2021;Feist et al, 2023).…”

“…Previous research in the Bengal Basin drawing from observations and models has yielded insight into the drivers of spatiotemporal changes in salinity in the coastal region of Bangladesh. Reductions in the discharge of the transboundary River Ganges (Padma), especially during the dry season, have lowered flows from its main distributary (River Gorai) to the southwestern coastal region; these are thought to have, in turn, amplified the intrusion of salinity from the Bay of Bengal (Dasgupta et al, 2014;Sherin et al, 2020;Feist et al, 2023). Dry-season reductions in river discharge exacerbating the intrusion of salinity are also thought to result from freshwater withdrawals for irrigation either directly from surface water or as a consequence of groundwater use through freshwater capture (Sherin et al, 2020;Shamsudduha et al, 2022).…”

Salinisation of drinking water ponds and groundwater in coastal Bangladesh linked to tropical cyclones

“…This example demonstrates the need for rapid response to pond salinization (pond salinities with no remediation and remediations were compared in Fig. 4 d) in order to ensure low salinity pond drinking water in southern Bangladesh, and probably in other deltaic coasts in Asia 22 , 37 as well. The need for rapid responses to polder and pond management is likely to become even more critical in future years as climate change results in projected increases in tropical cyclone intensity and frequency 24 , 25 , 38 , as explored below.…”

Innovative soil fluoride estimation method: dual polarimetric saline-associated fluoride for agricultural patches

“…Use of Microwave radar data, exhibits accurate sensitivity to the dielectric constant for salt-affected soils and the ability to penetrate is independent of environmental factors. Numerous experimental studies (Hilhorst et al, 1998;Feist et al, 2023) have been carried out over the past using interfacial polarization mechanisms affecting dielectric soils behaviour at low to medium frequencies. Furthermore, several tools have been developed to demonstrate that the dielectric constant (DC) of a soil depends on its volumetric moisture content (Periasamy, 2020;Wang et al, 2016) in semi-arid regions.…”