The sedimentology of gravel beds in groundwater‐dominated chalk streams: Implications for sediment modelling and management
The sedimentology of gravel beds in groundwater‐dominated chalk streams: Implications for sediment modelling and management
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 We collated published and unpublished freeze-core data, encompassing 90 sites across 11 UK chalk streams.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.
colmation, fine sediment targets, river restoration, riverbed substrate, sediment budget
508-528
Mondon, Beth
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Sear, David A.
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Collins, Adrian L.
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Shaw, Peter J.
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Sykes, Tim
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May 2024
Mondon, Beth
af15d99f-67c6-49f3-93fe-05a9844bd914
Sear, David A.
ccd892ab-a93d-4073-a11c-b8bca42ecfd3
Collins, Adrian L.
700e5f6a-4de3-4406-ad7a-d9d8ec0a5069
Shaw, Peter J.
dcb6c9af-bf38-4dfe-8395-8aeac2ad5cc7
Sykes, Tim
e622a522-7490-4fc8-9869-0f376f73561c
Mondon, Beth, Sear, David A., Collins, Adrian L., Shaw, Peter J. and Sykes, Tim
(2024)
The sedimentology of gravel beds in groundwater‐dominated chalk streams: Implications for sediment modelling and management.
River Research and Applications, 40 (4), .
(doi:10.1002/rra.4250).
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.
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River Research Apps - 2024 - Mondon - The sedimentology of gravel beds in groundwater‐dominated chalk streams
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Accepted/In Press date: 2024
e-pub ahead of print date: 8 February 2024
Published date: May 2024
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© 2024 The Authors. River Research and Applications published by John Wiley & Sons Ltd.
Keywords:
colmation, fine sediment targets, river restoration, riverbed substrate, sediment budget
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Local EPrints ID: 488310
URI: http://eprints.soton.ac.uk/id/eprint/488310
ISSN: 1535-1459
PURE UUID: 368f8732-653d-4d27-af0d-bcdb866a610b
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Date deposited: 19 Mar 2024 18:26
Last modified: 06 Jun 2024 02:07
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Author:
Adrian L. Collins
Author:
Peter J. Shaw
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