Mangrove forests can be an effective coastal defence in the Pearl River Delta, China

Abstract

Coastal vegetation can reduce extreme water levels during storm events, but the controlling factors and processes in complex estuary or delta systems are still unclear. This limits an effective implementation of nature-based coastal defences in delta mega-cities in low-lying coastal areas. Here we have numerically modelled how mangroves can offer coastal protection to the large coastal cities located in the Pearl River Delta (China), such as Guangzhou and Shenzhen, during strong typhoons, like Hato (2017). Water level attenuation by mangroves is effective during extreme water level conditions and differences in mangrove forests’ properties drive their coastal protection function. The local (within-wetland) attenuation of extreme water levels is more effective with wide vegetation patches and higher vegetation drag. Narrower vegetation patches can still provide non-local (upstream) water level attenuation if located in the upper estuary channels, but their design needs to avoid amplification of water levels in other delta areas.

Mangrove ecosystem properties regulate high water levels in a river delta

“…Stark et al, 2016;Smolders et al, 2015;Lawler et al, 2016;Sheng et al, 2021;Harrison et al, 2022) or in developed tropical countries (e.g. Zhang et al, 2012;Li et al, 2012;Liu et al, 2013;Dominicis et al, 2023). Here, we demonstrate how freely available data can contribute to filling this gap in geographical coverage of deltaic high water level modelling.…”

“…Chen et al, 2021;Zhang et al, 2012). The latter typically consider flood propagation through a continuous belt of mangroves or along a single estuarine channel fringed by mangroves (Chen et al, 2021;Deb and Ferreira, 2017;Dominicis et al, 2023;Smolders et al, 2015;Willemsen et al, 2016). To our knowledge, no studies exist that consider large-scale (order of 100 km 2 ) river deltas, accounting for the effects of the complex geometry formed by networks of branching channels, varying in size from wide (order of 10 3 m) to small (order of 10 m), and intertwined with vegetated and unvegetated intertidal areas.…”

Coastal futures: New framings, many questions, some ways forward

“…On developed coasts, physical and ecological processes clearly impact human communities; the very processes that create and maintain coastal environments, including sea-level rise, storms, and ecological change, often represent hazards for people, structures and infrastructure. On the other hand, human decisions and actions have resulted in the removal, degradation and fragmentation of coastal environments and have lessened the ability of these systems to adapt to climate change and act as natural protective barriers for coastal populations (Simkin et al, 2022;De Dominicis et al, 2023). These impacts are not new; there have been centuries of modification, degradation and loss from the anthropogenic activities of land conversion (for agriculture, aquaculture, industry, housing and infrastructure) and misuse (dredging and canalisation, waste disposal and pollution) although one might argue that the scale of human impactand its consequenceshas greatly increased in the last 100 years.…”

Mangroves as nature-based mitigation for ENSO-driven compound flood risks in a large river delta

“…The landscape setting and network of channels and intertwining wetlands strongly affect the effectiveness of wetlands to attenuate extreme sea levels (Temmerman et al, 2023). Numerical hydrodynamic models explicitly consider the geometry of wetlands and channels (Smolders et al, 2015;Dominicis et al, 2023;Temmerman et al, 2023) in contrast to analytical approaches which typically describe wetlands as uniform un-channelized zones with increased friction (Montgomery et al, 2019) or a single channel (Van Rijn, 2011). Research on the capacity of mangroves to attenuate ESLs typically does not consider the interaction with increased river discharge.…”