The sedimentology of gravel beds in groundwater-dominated chalk streams: Implications for sediment modelling and management

A - Papers appearing in refereed journals

Mondon, B., Sear, D. A., Collins, A. L., Shaw, P. J. and Sykes, T. 2024. The sedimentology of gravel beds in groundwater-dominated chalk streams: Implications for sediment modelling and management. River Research and Applications. https://doi.org/10.1002/rra.4250

AuthorsMondon, B., Sear, D. A., Collins, A. L., Shaw, P. J. and Sykes, T.
Abstract

Elevated fine sediment accumulation in a river system's gravel bed is known to cause detrimental ecological impacts. Current sediment targets and approaches to mitigation have failed due to the oversimplification of geomorphological processes controlling fine sediment accumulation and the lack of relevant scientific knowledge underpinning them. This is particularly apparent in chalk streams (groundwater-dominated systems) which regularly exhibit high rates of sediment accumulation despite low suspended sediment yields. A necessary first step is to better characterise their sedimentology; thus, the novelty of this study was to determine the sedimentological characteristics of chalk stream gravel beds, specifically the quantity and distribution of fine sediment with depth. We collated published and unpublished freeze-core data, encompassing 90 sites across 11 UK chalk streams. Results showed average quantities of fine sediment (<2 mm) in chalk stream gravel beds were 25% by weight, with >75% of beds exceeding thresholds for ecological degradation. Quantities of fine sediment increased with increasing depth into the bed, with an average increase between surface and subsurface layers of 54%, and 89% of the gravel bed over-saturated with fine sediment. Regional differences were attributed to differences in stream power and local sediment sources, including surficial geology and catchment land use. Additionally, a major contrast was identified between experimental conditions in flume studies used to establish models describing interactions/mechanisms of fine sediment infiltration into immobile gravel beds and the natural conditions observed in chalk streams. As such, the use of such models as a basis to explore sediment management scenarios is unlikely to predict the outcome of such management techniques correctly in a real-world situation.

KeywordsColmation ; Fine sediment targets ; River restoration ; Riverbed substrate ; Sediment budget
Year of Publication2024
JournalRiver Research and Applications
Digital Object Identifier (DOI)https://doi.org/10.1002/rra.4250
Web address (URL)https://onlinelibrary.wiley.com/doi/10.1002/rra.4250
Open accessPublished as ‘gold’ (paid) open access
FunderBiotechnology and Biological Sciences Research Council
Funder project or codeS2N - Soil to Nutrition - Work package 3 (WP3) - Sustainable intensification - optimisation at multiple scales
Environment Agency PhD Studentship
Publisher's version
Output statusPublished
Publication dates
Online08 Feb 2024
Publication process dates
Accepted18 Jan 2024
PublisherWiley
ISSN1535-1459

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