Case study:Glaisdale Beck diversion scheme - Revision history

Alexrrc at 09:59, 3 January 2019

2019-01-03T09:59:54Z

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	{{Case study status		{{Case study status
	\|Approval status=~~Draft~~		\|Approval status=Approved
	}}		}}
	{{Location		{{Location

Alexrrc at 09:58, 3 January 2019

2019-01-03T09:58:58Z

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	\|Contact organisation=Newcastle University		\|Contact organisation=Newcastle University
	\|Multi-site=No		\|Multi-site=No
			\|Project picture=Newcastle-University-logo.jpg
	\|Project summary=The Esk is a river of both ecological and economic importance at a national scale. It is the principle river in Yorkshire for Atlantic salmon and sea trout and is one of only two rivers on the east coast of England to have known populations of the freshwater pearl mussel, one of the most critically endangered bi-valves in the world. However, siltation and excessive suspended sediment concentrations (SSCs) have been attributed to causing their		\|Project summary=The Esk is a river of both ecological and economic importance at a national scale. It is the principle river in Yorkshire for Atlantic salmon and sea trout and is one of only two rivers on the east coast of England to have known populations of the freshwater pearl mussel, one of the most critically endangered bi-valves in the world. However, siltation and excessive suspended sediment concentrations (SSCs) have been attributed to causing their
	decline. This has led to local conservation and restoration efforts being driven by the National Park over the last 20 years.Previous research has highlighted the Glaisdale subcatchment as a key contributor to fine sediment fluxes in the Esk catchment. Through local surveys, a critical source area of fine sediment supply to the beck was identified. This was a section of exposed, near-vertical, ∼ 3 m high channel banks ∼ 100 m in length consisting of unconsolidated sediments and overlain by shallow surface vegetation, which is regularly accessed by livestock. The availability of accessible material is also exacerbated by progressive movement of a large hillslope failure complex which supplies large quantities of easily eroded sediment directly to the river channel. Such failures are well documented in the North York Moors. It was deemed that this combination of factors limited the potential for success of traditional channel margin stabilization approaches. Following consultation and the presentation of available options, the competent agencies decided the most appropriate course of action was to divert the existing channel away from the toe of the large hillslope landslide,		decline. This has led to local conservation and restoration efforts being driven by the National Park over the last 20 years.Previous research has highlighted the Glaisdale subcatchment as a key contributor to fine sediment fluxes in the Esk catchment. Through local surveys, a critical source area of fine sediment supply to the beck was identified. This was a section of exposed, near-vertical, ∼ 3 m high channel banks ∼ 100 m in length consisting of unconsolidated sediments and overlain by shallow surface vegetation, which is regularly accessed by livestock. The availability of accessible material is also exacerbated by progressive movement of a large hillslope failure complex which supplies large quantities of easily eroded sediment directly to the river channel. Such failures are well documented in the North York Moors. It was deemed that this combination of factors limited the potential for success of traditional channel margin stabilization approaches. Following consultation and the presentation of available options, the competent agencies decided the most appropriate course of action was to divert the existing channel away from the toe of the large hillslope landslide,

Alexrrc at 09:51, 5 June 2017

2017-06-05T09:51:02Z

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	and re-establish the stream course further to the north. The impact of this management was considered from a biotic and geomorphic viewpoint through the collection of data between 2007 and 2014.		and re-establish the stream course further to the north. The impact of this management was considered from a biotic and geomorphic viewpoint through the collection of data between 2007 and 2014.

			Works included: Diversion of the existing channel away from the toe of the large hillslope landslide.
	\|Monitoring surveys and results=From the analysis of over 2 years of river flow and in-stream sediment concentration data prior to, and following the diversion of Glaisdale Beck, it is clear that the sediment transfer regime has become more restrictive. This is evidenced by		\|Monitoring surveys and results=From the analysis of over 2 years of river flow and in-stream sediment concentration data prior to, and following the diversion of Glaisdale Beck, it is clear that the sediment transfer regime has become more restrictive. This is evidenced by
	- Reductions in median suspended sediment concentrations from 35.19 to 18.98 mg/L,		- Reductions in median suspended sediment concentrations from 35.19 to 18.98 mg/L,
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	Although direct monitoring of the hydrology and sediment dynamics at Glaisdale beck was concluded in 2009, 2 years after the channel diversion, the longer term development of the site was observed through site visits up until 2014. During this period, continued erosion in the form of a headward migrating knick point (visible as a step in the river bed) has resulted in a progressive wave of channel instability that has migrated upstream. This is the response to over-steepening of the channel gradient in the vicinity of the original channel diversion.		Although direct monitoring of the hydrology and sediment dynamics at Glaisdale beck was concluded in 2009, 2 years after the channel diversion, the longer term development of the site was observed through site visits up until 2014. During this period, continued erosion in the form of a headward migrating knick point (visible as a step in the river bed) has resulted in a progressive wave of channel instability that has migrated upstream. This is the response to over-steepening of the channel gradient in the vicinity of the original channel diversion.

	Due to a lack of appropriately engineered grade control (drop) structures in the engineered reach this has resulted in channel bed lowering, bank undercutting and lateral bank failures upstream. During this time extensive bank erosion and channel widening occurred. At this particular site, erosion was evident only 2 weeks after the initial diversion with the knickpoint migrating through the reach, lowering the bed elevation. In response, the banks started to slump. However, due to increased channel width the final phase of bank collapse resulted in a soil wedge at the base of the bank which appears to have protected the toe of the bank preventing further lateral expansion.		Due to a lack of appropriately engineered grade control (drop) structures in the engineered reach this has resulted in channel bed lowering, bank undercutting and lateral bank failures upstream. During this time extensive bank erosion and channel widening occurred. At this particular site, erosion was evident only 2 weeks after the initial diversion with the knickpoint migrating through the reach, lowering the bed elevation. In response, the banks started to slump. However, due to increased channel width the final phase of bank collapse resulted in a soil wedge at the base of the bank which appears to have protected the toe of the bank preventing further lateral expansion.

	\|Lessons learn=Channel reconfiguration can be effective in mitigating fine sediment flux in headwater streams but the full value of this may take many years to achieve whilst the fluvial system slowly readjusts.		\|Lessons learn=Channel reconfiguration can be effective in mitigating fine sediment flux in headwater streams but the full value of this may take many years to achieve whilst the fluvial system slowly readjusts.

Alexrrc at 09:50, 5 June 2017

2017-06-05T09:50:33Z

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	}}		}}
	{{Measures		{{Measures
	\|Floodplain / River corridor=~~Diversion of the existing~~ channel ~~away from the toe of the large hillslope landslide~~		\|Floodplain / River corridor=River channel diversion,
	}}		}}
	{{Hydromorphological quality elements header}}		{{Hydromorphological quality elements header}}

Alexrrc at 13:08, 3 January 2017

2017-01-03T13:08:32Z

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	\|Specific mitigation=Excessive fine sediment threatening aquatic habitats		\|Specific mitigation=Excessive fine sediment threatening aquatic habitats
	}}		}}
	{{Measures}}		{{Measures
			\|Floodplain / River corridor=Diversion of the existing channel away from the toe of the large hillslope landslide
			}}
	{{Hydromorphological quality elements header}}		{{Hydromorphological quality elements header}}
	{{Hydromorphological quality element table row		{{Hydromorphological quality element table row

Perksieuk at 20:17, 30 August 2016

2016-08-30T20:17:31Z

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	{{Additional Documents end}}		{{Additional Documents end}}
	{{Additional links and references header}}		{{Additional links and references header}}
			{{Additional links and references
			\|Link=doi.pangaea.de/10.1594/PANGAEA.864201
			\|Description=Monitoring datasets
			}}
	{{Additional links and references footer}}		{{Additional links and references footer}}
	{{Supplementary Information}}		{{Supplementary Information}}
	{{Toggle content end}}		{{Toggle content end}}

Perksieuk at 20:15, 30 August 2016

2016-08-30T20:15:56Z

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	}}		}}
	{{Site}}		{{Site}}
	{{Project background}}		{{Project background
			\|Reach length directly affected=400
			\|Project started=2007/09/21
			\|Works started=2007/10/10
			\|Works completed=2007/10/10
			\|Project completed=2014/10/01
			\|Monitoring Lead organisation=Durham University
			}}
	{{Motivations		{{Motivations
	\|Specific mitigation=Excessive fine sediment threatening aquatic habitats		\|Specific mitigation=Excessive fine sediment threatening aquatic habitats

Perksieuk at 20:13, 30 August 2016

2016-08-30T20:13:44Z

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	{{Site}}		{{Site}}
	{{Project background}}		{{Project background}}
	{{Motivations}}		{{Motivations
			\|Specific mitigation=Excessive fine sediment threatening aquatic habitats
			}}
	{{Measures}}		{{Measures}}
	{{Hydromorphological quality elements header}}		{{Hydromorphological quality elements header}}

Perksieuk at 20:11, 30 August 2016

2016-08-30T20:11:59Z

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	\|Result=Improvement		\|Result=Improvement
	}}		}}
	~~{{Hydromorphological quality element table row~~
	~~\|Monitored before=No~~
	~~\|Monitored after=No~~
	~~\|Qualitative monitoring=No~~
	~~\|Quantitative monitoring=No~~
	~~\|Control site used=No~~
	}}
	{{End table}}		{{End table}}
	{{Biological quality elements header}}		{{Biological quality elements header}}

Perksieuk at 20:11, 30 August 2016

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