Newton Fund: Salt intrusion: Understanding the Pearl River Estuary by Modelling and field Experiments (SUPREME)

Saltwater intrusion in deltas and estuaries results from the complex interaction between water and salt dynamics, and is affected by climate change and human intervention. In the Pearl River Estuary (PRE) in China, these changes endanger freshwater availability affecting over 40 million people. PRE's complex shape (geometry and bathymetry) makes salt intrusion processes inherently three-dimensional. However, as previous research was mainly restricted to longitudinal variability, current knowledge is insufficient to unravel the interwoven longitudinal and lateral salt transport mechanisms.

The overall aim of the SUPREME project is to understand these three-dimensional salt transport mechanisms, and their sensitivity to variations in external forcing and local geographic shape. The knowledge and tools developed/applied in this project will help assess the effectiveness of possible measures to alleviate undesired changes in salt intrusion.

We adopt an integrated approach, involving both idealized and numerical modelling, as well as field measurements and data analysis. Idealized models include the essential physics and large-scale geometrical/bathymetrical features in a schematised way. Thus, they are specifically geared to clarify the interactions between governing physical mechanisms. Complex numerical models extend these results to transient forcing conditions and provide site-specific information. The combination of these two approaches provides insight, motivated and validated by new field measurements and existing data.

This joint project between the Netherlands, China and the UK presents a new integrated framework to understand salt dynamics in the PRE and other estuaries. It further provides a more solid scientific basis for estuarine management to prevent damaging saltwater intrusion in these regions. In order to provide more generic and global outlook and applicability to our work, we will compare salt intrusion in the PRE to salt intrusion in two other estuaries: the Mersey (UK) and the Ems (Netherlands/Germany).

The UK contribution of the project will be delivered by the National Oceanography Centre. The main focus of the UK research effort will be to develop and implement a state-of-the-art unstructured grid, numerical model of the PRE and other study areas. This numerical model will be used to conduct prognostic and diagnostic investigations. We will review a range of scenarios of future climate change and human interventions (e.g., sea level rise, river runoff, dredging, and freshwater abstraction). The UK contribution will also include long-term observations for the Mersey estuary, which will act as a pilot study for low-cost, long-term monitoring of salt intrusion in an estuary, thus providing proof-of-concept for a framework, which will be broadly applicable to other estuarine and deltaic systems in the world, including the PRE.

To enhance proper management of freshwater resources in the fast growing (both with respect to population and economic activity) deltaic regions, it is essential to better understand the dominant salt transport processes. Our integrated modelling approach allows for a novel assessment strategy to optimize possible mitigation measures. After rapidly assessing the efficiency of a large number of; or combinations of; measures using the idealized model approach, the most promising options can be preselected and further tested using a complex numerical model. This paradigm shift allows for a coarse quick, wide exploration of possible measures and an in-depth assessment of only the most promising options, instead of a more traditional in-depth study of a limited number of mitigation scenarios, often chosen subjectively and arbitrarily.

Direct beneficiaries of this paradigm shift will be the public and governmental bodies that regulate water resources in estuaries. For our primary study site in the Pearl River Estuary, possible mitigation scenarios will be chosen in close collaboration with our partners from Guangdong Provincial Research Institute of Water Resources and Hydropower and the Shenzhen Marine Management Bureau at the Urban Planning and Land Resources Commission of Shenzhen Municipality. Operators of (desalination) water plants will also benefit from the results of the project following which they will be able to optimise location and operations of desalination plants, thus improving water accessibility and quality.

We will synthesise our results with the specific aim to address estuarine management and planning issues pertaining to alleviating salt intrusion while balancing interests from navigation, pollution control, protection from river floods and storm surges. As such, the project's results will be beneficial to all users of estuarine ecosystem services by informing future planning of human interventions. These users include the coastal and marine planners, actors of planned interventions (e.g., dredging companies, coastal engineering contractors), waterbodies regulators, port and other estuarine infrastructure operators.