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Hydrodynamics and sedimentary processes in the main drainage channel of a large open coast managed realignment site

Hydrodynamics and sedimentary processes in the main drainage channel of a large open coast managed realignment site
Hydrodynamics and sedimentary processes in the main drainage channel of a large open coast managed realignment site

Managed Realignment (MR) is becoming increasingly popular with many coastal managers and engineers. Monitoring of MR sites has provided growing evidence that many of the saltmarshes created in these environments have lower biodiversity than naturally formed intertidal marshes, and may not fully deliver the anticipated ecosystem services such as carbon sequestration and coastal flood defence. Despite the importance of the sedimentary environment in developing an intertidal morphology suitable for plant establishment and succession, the evolution of the sediment erosion, transportation, deposition and consolidation cycle in newly breached sites is rarely examined. This study evaluates the hydrodynamics and concentration of suspended sediment exported and imported along the main drainage channel within the Medmerry Managed Realignment Site, West Sussex, UK, the largest open coast realignment in Europe (at the time of breaching). Measurements were taken over a one year period (November 2015–October 2016) at the breach, at the landwards extremity where freshwater drains into the site, and in an excavated channel in the centre of the site. At the latter site, 1.7 cm of sediment accreted over the study period. Suspended sediment concentration (SSC) measurements indicate that, under ambient conditions, sediment is imported into and exported from the Medmerry site, although similar concentrations of sediment were recorded being internally redistributed around the site (typically 0.11 g/l measured in the breach area compared to 0.12 g/l measured in the centre of the site). Sediment is removed from the site following large (1–2 mm/hour) rainfall events, which take several tidal cycles to drain through the site. Peaks in SSC corresponding with lower intensity rainfall events, especially during periods when the intertidal mudflats have been exposed, have also been observed. Analysis of the hydrodynamics and patterns of sedimentation during and following storm occurrences (the 2015-16 Storms Eva, Imogen and Katie) however demonstrate the relative resilience (i.e. rapid recovery and minimal disturbance) of the site to extreme storm events.

Altimeter, Hydrodynamics, Managed realignment, Medmerry managed realignment site, Storms, Suspended sediment concentration, United Kingdom, West sussex
0272-7714
100-111
Dale, Jonathan
f998e92c-cd34-45c2-bc2c-d38ff72b6edc
Burgess, Heidi M.
96772c7e-ab57-463f-8979-b70dd5a360c3
Nash, David J.
a364e478-e641-48a9-ad56-93984f811c16
Cundy, Andrew B.
994fdc96-2dce-40f4-b74b-dc638286eb08
Dale, Jonathan
f998e92c-cd34-45c2-bc2c-d38ff72b6edc
Burgess, Heidi M.
96772c7e-ab57-463f-8979-b70dd5a360c3
Nash, David J.
a364e478-e641-48a9-ad56-93984f811c16
Cundy, Andrew B.
994fdc96-2dce-40f4-b74b-dc638286eb08

Dale, Jonathan, Burgess, Heidi M., Nash, David J. and Cundy, Andrew B. (2018) Hydrodynamics and sedimentary processes in the main drainage channel of a large open coast managed realignment site. Estuarine, Coastal and Shelf Science, 215, 100-111. (doi:10.1016/j.ecss.2018.10.007).

Record type: Article

Abstract

Managed Realignment (MR) is becoming increasingly popular with many coastal managers and engineers. Monitoring of MR sites has provided growing evidence that many of the saltmarshes created in these environments have lower biodiversity than naturally formed intertidal marshes, and may not fully deliver the anticipated ecosystem services such as carbon sequestration and coastal flood defence. Despite the importance of the sedimentary environment in developing an intertidal morphology suitable for plant establishment and succession, the evolution of the sediment erosion, transportation, deposition and consolidation cycle in newly breached sites is rarely examined. This study evaluates the hydrodynamics and concentration of suspended sediment exported and imported along the main drainage channel within the Medmerry Managed Realignment Site, West Sussex, UK, the largest open coast realignment in Europe (at the time of breaching). Measurements were taken over a one year period (November 2015–October 2016) at the breach, at the landwards extremity where freshwater drains into the site, and in an excavated channel in the centre of the site. At the latter site, 1.7 cm of sediment accreted over the study period. Suspended sediment concentration (SSC) measurements indicate that, under ambient conditions, sediment is imported into and exported from the Medmerry site, although similar concentrations of sediment were recorded being internally redistributed around the site (typically 0.11 g/l measured in the breach area compared to 0.12 g/l measured in the centre of the site). Sediment is removed from the site following large (1–2 mm/hour) rainfall events, which take several tidal cycles to drain through the site. Peaks in SSC corresponding with lower intensity rainfall events, especially during periods when the intertidal mudflats have been exposed, have also been observed. Analysis of the hydrodynamics and patterns of sedimentation during and following storm occurrences (the 2015-16 Storms Eva, Imogen and Katie) however demonstrate the relative resilience (i.e. rapid recovery and minimal disturbance) of the site to extreme storm events.

Text
Dale_et_al_2018_Medmerry_Hydrodynamics_and_Sedimentation_Processes_Main_Channel_preprint - Accepted Manuscript
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More information

Accepted/In Press date: 9 October 2018
e-pub ahead of print date: 16 October 2018
Published date: 31 December 2018
Keywords: Altimeter, Hydrodynamics, Managed realignment, Medmerry managed realignment site, Storms, Suspended sediment concentration, United Kingdom, West sussex

Identifiers

Local EPrints ID: 426206
URI: http://eprints.soton.ac.uk/id/eprint/426206
ISSN: 0272-7714
PURE UUID: 9edbac22-33c4-44f7-a208-3f6c97b1b002
ORCID for Andrew B. Cundy: ORCID iD orcid.org/0000-0003-4368-2569

Catalogue record

Date deposited: 16 Nov 2018 17:30
Last modified: 22 Nov 2021 06:57

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Contributors

Author: Jonathan Dale
Author: Heidi M. Burgess
Author: David J. Nash
Author: Andrew B. Cundy ORCID iD

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