IAP-24-083

Investigating how well coastal protection strategies trap and keep sediment for mangrove rehabilitation in the Guiana Shield

This novel, multi-disciplinary and timely research will explore the feasibility and benefits of nature-based solutions (NBS) and hybrid approaches for coastal protection in line with mangrove rehabilitation, along the South American Guiana Shield coastline.

You will use physical (lab-based), physics-informed machine-learning (AI) and numerical (computational) models to understand the change in conditions that NBS or hybrid solutions (e.g. sediment trapping units (STUs), dykes (mud, rock or textile) or groynes) have on ocean current strength and direction, and on sediment transport and deposition along the Guyana and Suriname coastlines to guide local coastal protection strategies, including mangrove rehabilitation techniques.

Models will be based upon existing and planned real-world structures at various scales in Suriname and Guyana, and will be informed by recent observations, including ocean, meteorological and geomorphological data collected with in-situ instrumentation, satellite imagery and drones, alongside local observations of structure behaviour and environmental impact. Field work with local partner, Anton de Kom University of Suriname (AdeKUS), will involve additional data collection. There may be opportunities for AdeKUS to implement and trial solutions derived from this research.

This research is needed urgently and will help fill a gap in understanding, providing much-needed numerical verification of impacts and processes, and guiding future interventions and mangrove rehabilitation strategies.

The local coastal system is very dynamic with huge sediment migration, strong waves and currents, often preventing establishment of new mangrove seedlings or destroying young trees. Processes happen quickly, have large impacts and are very visible, facilitating process identification and model verification.

Mangroves provide multiple ecosystem services to coastal communities, including protecting against erosion and flooding. They reduce hazard intensity on landward margins by attenuating waves through their root system, capturing sediments and building soils (IPCC 2022). Guyana and Suriname are amongst the most vulnerable globally to coastal flooding and erosion (Dasgupta et al 2009) with coastlines mostly below mean sea level and >85% of the populations living along narrow coastal plains. Coastal areas have suffered severe land losses due to mangrove removal and erosion with flooding >2km landward of the shore observed during episodes of moderate surge coinciding with high tide. Sea walls provide alternative coastal protection but are expensive to build and maintain, may be undermined by erosion leading to catastrophic failure, and disrupt other coastal systems, such as mangroves.

To explore long-term, cheaper NBS, AdeKUS have been trialling STUs in the region for over 10 years (Figures 1,2,3). These trap sediment, giving seedlings a stable environment to establish themselves. Similarly, the Guyana Government is installing groyne defences along areas defended by sea walls to encourage sediment accumulation and mangrove growth to help protect sea walls. However, these interventions may fail under extreme conditions, and the evidence of efficacy of these interventions at local scale has not been explored. Evidence is needed to support policy and strategy, and promote best practice and action locally.

Outputs: The project aims to model how well structures capture and retain sediment to enable mangrove growth under a range of environmental conditions along the Suriname and Guyana Coastlines.

Novelty: Studies are needed that examine a range of factors (e.g. wind direction, wave height, current strength, sediment transport) and their interaction with STUs affecting mangrove response, as these are highly dependent on site-specific variations (Wilson 2017) and drivers of change have not been well quantified in many places due to data constraints (Osland et al 2016). This research will enhance understanding of local processes acting on coastal systems and address knowledge gaps by developing robust new evidence and knowledge to inform local and international coastal protection strategies.

Modelling: Tailored to student interests, modelling of structures can take various forms.
(i) Scaled experiments: Experimental work will include hydraulic lab experiments conducted in controlled conditions to validate models for a variety of sediment trap designs and materials using experiments at (1) Newcastle University (1m width, 12m length flume; flow rate 10-450l/s), and (2) AdeKUS (larger flume, option to include local materials).
(ii) Computational Modelling: A variety of approaches will be investigated to capture sediment trap behaviour including:
1. Physically-based hydrodynamic models of structures.
2. Physics-informed machine learning (PIML) models.
3. Semi-empirical models developed using standard statistical techniques.
Successful designs may be built and implemented in the field, allowing verification of the modelling results.

Datasets: The research will utilise empirical evidence from currently operating schemes. Publicly available historical remote sensing and recently collected drone imagery will be used to pinpoint climatic events that have caused major environmental change. Model parameters will be informed by field-observations (collected 2024-26) collected under DEFRA-sponsored GCBC Enhances project, including near and off-shore currents and wave heights, wind and other meteorological data, water parameters (including turbidity, temperature, conductivity and pH), sediment accumulation measurements.

Field work: New data informed by modelling needs will be collected during 1-2 field campaigns, supported by AdeKUS.

Year 1

Comprehensive literature review of the latest developments in sediment trapping structures (e.g. groynes, leaky barriers), methods for modelling such structures and the rapidly developing area of physics-informed machine learning (PIML) to inform the research direction. Evidence gathering about impacts of existing structures at field sites. Planning experiments and modelling approaches. Field visit to Suriname to set up data-gathering (e.g. small-scale STUs each side of physical structures) and refine modelling parameters. Journal paper: review of state-of-the-art.

Year 2

Work with AdeKUS to collect data to inform modelling. Build, refine, and run scaled and physical models to gather results. Calibrate and validate models. Present results at European conference. Journal paper on one aspect of modelling.

Year 3

Second field visit to Suriname to disseminate results and finalise data collection. Showcase best designs for AdeKUS to build structures. Gather data on structure behaviour. Present results at international conference. Journal paper on results.

Year 3.5

Complete thesis, submission and viva.

The candidate will gain valuable skills in the context of (a) developing analytical, empirical physical and hydrodynamic models, experimental design, data integration and analysis; (b) knowledge of hydrological processes and functioning of tropical coastal systems; (c) nature based and hybrid coastal protection methods. The student will benefit from one-to-one coaching by project team and training facilities offered by supervising universities. Training will include attendance at national/international training events and conferences.