RAMESES: The resilience and sustainability of the Mekong delta to changes in water and sediment fluxes

The world's 33 largest deltas are being drowned by relative sea level rise and are, as a result, rapidly losing land. This process is also driving an exacerbation of flood risk in these environments, which is placing many large cities, key infrastructure and over 0.5 billion people at risk globally. These issues are most acute for deltas across Southern and Southeast Asia, where an estimated 20% of land will be lost by 2100. These risks are significant. For example, floods during the 2011 Asian monsoon killed an estimated 2000 people and caused ~US$45 billion in economic damage across SE Asia. Moreover, these deltas, and their ecosystem services, underpin regional food security for rapidly growing populations. There is therefore an urgent need to evolve an improved generic understanding of the processes behind the relative sea level rise and flood risk dynamics in these deltaic environments into the future. Significant recent advances have been made in our understanding of many aspects of delta morphodynamics and evolution. This has included work on distributary channel flow processes, bifurcation stability and bar dynamics, and the profound influence of tidal backwater effects on longer-term channel hydro- and sediment dynamics. However, despite this progress there are significant uncertainties around the influence of: i) upstream migrating backwater effects, forced by sea-level rise, on delta bifurcation stability; ii) declining sediment delivery and increased hydrological variability on distributary channel stability; iii) connectivity between the channels and the delta surface on the routing, dispersal and trapping of sediment. Each of these uncertainties are key knowledge gaps that must be addressed for effective delta management, flood risk mitigation and maintenance of ecosystem services. Our project will investigate flow and sediment routing through the Mekong delta across the annual monsoon flood and develop a new generic understanding of the impact of relative sea-level rise and sediment routing processes through distributary channels and key bifurcation sites on the delta. This will be achieved through collection of new state-of-the-art field datasets, development and application of morphodynamic numerical modelling and utilization of system dynamics modelling to guide aquaculture and agriculture adaptations to changes. We will leverage a range of existing links we have to engage with, and communicate the outcomes of the work, to agencies and policy makers in the region and inform water resource planning and mitigation/adaptation strategies in the context of climate change.