Case study:Glaisdale Beck diversion scheme

From RESTORE
Jump to: navigation, search
0.00
(0 votes)


To discuss or comment on this case study, please use the discussion page.


Location: 54° 25' 32", -0° 49' 31"
Edit location
Loading map...
Left click to look around in the map, and use the wheel of your mouse to zoom in and out.


Project overview

Edit project overview
Status Complete
Project web site
Themes Environmental flows and water resources, Fisheries, Habitat and biodiversity, Hydromorphology, Land use management - agriculture, Monitoring, Water quality
Country England
Main contact forename Matthew
Main contact surname Perks
Main contact user ID User:Perksieuk
Contact organisation Newcastle University
Contact organisation web site
Partner organisations
Parent multi-site project
This is a parent project
encompassing the following
projects
No
Project picture

Project summary

Edit project overview to modify the 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, 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

Edit project overview to modify the Monitoring survey 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, – 5 % reduction in flow-weighted mean sediment concentrations. – Negative trend in sediment concentrations. - Dampened response of sediment concentration during periods of high flow.

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.

Lessons learnt

Edit project overview to modify the lessons learnt.


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.

The channel is continuing to adjust to the diversion with evidence of continuing local instability. It is therefore recommended that this approach to reducing the fine sediment flux of upland rivers should not be adopted as standard practice.

However, where significant modifications to upland channels are made, comprehensive in-stream monitoring and geomorphological assessments should be regularly conducted to evaluate the response of the river to the new conditions.

This research has highlighted the importance of ensuring appropriate controls on sediment release during in-stream works and effective installation and maintenance of grade control (drop) structures. If these measures had been rigorously applied the overall goal of reducing fine sediment flux through the fluvial system could have been achieved in a more timely fashion.


Image gallery


ShowHideAdditionalImage.png


Catchment and subcatchment

Catchment

River basin district Humber
River basin Esk and Coast

Subcatchment

River name Glaisdale Beck catchment (trib of Esk)
Area category 10 - 100 km²
Area (km2) 15.6
15.6 km²
1,560 ha
Maximum altitude category 200 - 500 m
Maximum altitude (m) 401
401 m
0.401 km
40,100 cm
Dominant geology Calcareous
Ecoregion Great Britain
Dominant land cover Heather
Waterbody ID GB104027068070



Site

Name
WFD water body codes
WFD (national) typology
WFD water body name
Pre-project morphology
Reference morphology
Desired post project morphology
Heavily modified water body
National/international site designation
Local/regional site designations
Protected species present
Invasive species present
Species of interest
Dominant hydrology
Dominant substrate
River corridor land use
Average bankfull channel width category
Average bankfull channel width (m)
Average bankfull channel depth category
Average bankfull channel depth (m)
Mean discharge category
Mean annual discharge (m3/s)
Average channel gradient category
Average channel gradient
Average unit stream power (W/m2)


Project background

Reach length directly affected (m) 400
400 m
0.4 km
40,000 cm
Project started 2007/09/21
Works started 2007/10/10
Works completed 2007/10/10
Project completed 2014/10/01
Total cost category
Total cost (k€)
Benefit to cost ratio
Funding sources

Cost for project phases

Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname
Investigation and design
Stakeholder engagement and communication
Works and works supervision
Post-project management and maintenance
Monitoring Durham University



Reasons for river restoration

Mitigation of a pressure Excessive fine sediment threatening aquatic habitats
Hydromorphology
Biology
Physico-chemical
Other reasons for the project


Measures

Structural measures
Bank/bed modifications
Floodplain / River corridor River channel diversion
Planform / Channel pattern
Other
Non-structural measures
Management interventions
Social measures (incl. engagement)
Other


Monitoring

Hydromorphological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative
Channel pattern/planform Yes Yes No Yes No
Continuity of sediment transport Yes Yes No Yes No Improvement


Biological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Physico-chemical quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Any other monitoring, e.g. social, economic

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative


Monitoring documents



Additional documents and videos


Additional links and references

Link Description
http://doi.pangaea.de/10.1594/PANGAEA.864201 Monitoring datasets

Supplementary Information

Edit Supplementary Information