The impact of rain events on the supply and movement of fine sediment in engineered intertidal systems

Burgess, H. M., Dale, J. ORCID: https://orcid.org/0000-0002-5242-8071 and Smith, M. P. (2026) The impact of rain events on the supply and movement of fine sediment in engineered intertidal systems. Continental Shelf Research, 299. 105674. ISSN 0278-4343 doi: 10.1016/j.csr.2026.105674

Abstract/Summary

Low-tide rainfall events can strongly influence sediment dynamics in intertidal systems, but their role remains understudied, especially in engineered environments such as Managed Realignment (MR) sites. This research investigates how natural precipitation influences suspended sediment concentrations (SSC), bed elevation, and sediment fate at Pagham Harbour, a historic unManaged Realignment (uMR) site on the south coast of the UK. The presence of tidal flaps controlling freshwater input at this site enabled the separation of terrestrial runoff from low-tide pluvial eroded sediment. Nine years of high-frequency monitoring captured water depth, SSC, and bed elevation along with rainfall data. From 6581 hours of rainfall, 142 discrete rain events containing one or more hours of heavy rain (≥4 mm/h) were identified, with 13 coinciding with low-tide and complete datasets. Results show that heavy rainfall during low-tide triggers immediate increases in SSC and measurable changes in bed elevation. We demonstrate that pluvial erosion influences subsequent tidal SSC peaks, with flood-tide peaks rising by up to 400% and ebb-tide peaks by 280%. Bed responses varied: most events showed initial erosion followed by rapid recovery, while sustained lowering was occasionally observed during neap tide periods. Recovery rates were influenced by tidal range, antecedent conditions, and sediment availability. Tidal flaps induced tide locking, delaying freshwater inflow and increasing low-tide water levels within the low-tide creeks. Consequently, sediment laden terrestrial runoff, along with any associated pollutants, was able to bypass the intertidal system and discharge directly into the nearshore waters. A conceptual algorithm was developed to predict sediment retention or loss as a function of rainfall timing, creek velocity, and tidal harmonics. These findings demonstrate the complexity of interactions between rainfall and tides, and their wider implications for sediment budgets, pollutant transport, and coastal management. They highlight the need for whole-catchment sediment and pollutant management together with long-term, high-frequency monitoring to strengthen resilience modelling and inform adaptive strategies under changing climate and sea level conditions.

Item Type	Article
URI	https://centaur.reading.ac.uk/id/eprint/129242
Identification Number/DOI	10.1016/j.csr.2026.105674
Refereed	Yes
Divisions	Science > School of Archaeology, Geography and Environmental Science > Department of Geography and Environmental Science
Publisher	Elsevier
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