Upper River Witham: Great Ponton Version 1.1 (14.02.14)
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River Habitat Enhancement Case Studies Upper River Witham: Great Ponton Version 1.1 (14.02.14) Location: Great Ponton, Lincolnshire (c3.5km south of Grantham) Upstream Grid Ref: SK929304 Length: 675m Completion Date: End February 2013 Cost: Fords: £11K, Fencing and willow layering £6.8K: Total £17.8K (this does not include the first phase undertaken in 2008) Partners: The scheme was implemented by the Environment Agency with the co-operation and agreement of the adjacent landowner (Stephen Jackson). Grantham Angling Association Fly Fishing Section (GAAFFS) assisted with site selection and landowner negotiations. © Steve Brayshaw © Steve Summary of Techniques: Channel narrowing and flow deflection using woody debris augmented by willow layering; ford refurbishment and riverside fencing to reduce sediment inputs. Location Map © Crown Copyright 2013. OS Licence number 100026380. Background The Upper River Witham rises west of South Witham and flows for more than 65 km northwards through Colsterworth, Great Ponton, Grantham, Long Bennington, Bassingham and North Hykeham towards Lincoln. More than 165 km of river and tributary streams drain the c573 km2 catchment. The landscape of the catchment is varied in character, ranging from the livestock-dominated limestone valleys upstream from Grantham, through the mixed farming terrain of the middle reaches, to the flat-lying arable farmlands downstream from Long Bennington. Over recent centuries, and particularly the last 100 years, the once naturally meandering river channels have been straightened, deepened, widened, impounded and embanked to reduce flood risk and improve land drainage. These modifications, together with catchment land management practices, have contributed to a decline in river corridor habitat quality. The Upper Witham and its tributaries are divided into 19 separate waterbodies for Water Framework Directive assessment and only 3 are assessed as having Good Ecological Status. The section of the Upper Witham which includes the Great Ponton reach is assessed as Moderate due to high phosphate levels, excessive algae (diatoms) and poor fish populations. The Great Ponton project seeks to address these issues and is the first phase of river enhancement to be undertaken as part of the wider Upper Witham River Corridor Habitat Plan. Pre-project Survey Work No specific pre-project survey work was undertaken, but brown trout and native white-clawed crayfish are known to be present through surveys conducted immediately above the restoration reach. Project Objectives Reduce the impact of sediment inputs as a result of erosion caused by livestock. Improve conveyance during higher flows. Enhance earlier channel narrowing work to further improve in-stream habitats. Provide refuges for fish and native white-clawed crayfish. A scheme based on these objectives was prepared by Environment Agency staff in consultation with Grantham Angling Association Fly Fishing Section (GAAFFS) and the landowner. Grantham Angling Association Fly Fishing Section (GAAFFS) Consultation and Consents An internal Environment Agency application for Flood Defence Consent to refurbish the existing fords was issued on 18th January 2013 (Internal Consent no. L/002626/12). The Enhancement Scheme The enhancement scheme was completed in February 2013. Prior to the enhancement works the channel was suffering from low flows and sedimentation as a result of eroding cattle crossings and bankside poaching, which was causing the loss of water-crowfoot (Ranunculus) and degradation of spawning gravels. The drawing in Annex 1 show the locations of all the elements of the completed scheme and the techniques used are described below. Channel Narrowing and Flow Deflectors During the initial phase of enhancement GAAFFS narrowed the section immediately below the downstream ford using logs to construct enclosures which projected into the channel. These enclosures created a significantly narrower and more sinuous watercourse with increased flow velocity which reduced sedimentation and improved the cleansing of the natural gravel bed. In addition the enclosures encouraged the development of an extended wetland margin by trapping sediments and still refuge pools on the margins of the channel. Immediately below the ford GAAFFS also installed a pair of upstream pointing log flow deflectors to encourage the development of a central scour pool. The initial works improved the condition of the watercourse. However, the enclosures and deflectors were constructed from recently cut willow which rapidly regenerated in to small trees, which, whilst providing beneficial shade, also increased channel roughness and potential flood risk. Tree Management The willow regeneration was addressed during the second phase of enhancement in 2013 using a layering technique. Trees were partially cut at the base, leaving a narrow bark and sapwood hinge, and then bent horizontally along the bank to create a tangle of twigs and branches at and just above the water level to provide important refuges for juvenile fish and invertebrates. Ash stakes and wire bindings were used to secure the layered trees in position. Occasional willows were retained as shade trees. © Steve Brayshaw © Steve © Steve Brayshaw © Steve Fig 1. Refuge pool contained by a log enclosure Fig 2. Flow deflector immediately below the ford © Matt Parr © Matt © Matt Parr © Matt Figs 3 and 4. Regeneration of the live willow logs used by GAAFFS to narrow the channel in 2008 © Steve Brayshaw © Steve © Steve Brayshaw © Steve Fig 5. Layered willow on channel narrowing enclosures Fig 6. Willow layering (detail) and retained “shade” willows Erosion Control Ford Refurbishment The river is crossed by two fords which also double as cattle drinkers. Prior to refurbishment they were in poor condition with bare, severely poached and eroded earth access ramps and nothing to prevent cattle access upstream and downstream. Refurbishment involved reprofiling the access ramps and consolidating the slopes and crossing point with crushed limestone to create a porous hard-standing. Post and rail fencing was erected to control access to the ford and electrified “scare-wires” across the river discouraged cattle from straying up or downstream. © Elizabeth Clements © Elizabeth © Steve Brayshaw © Steve Figs 7 and 8. The upstream cattle crossing before and after refurbishment Fencing Accumulation of sediments along the banks has naturally narrowed the channel upstream of the mill. As a result wide, vegetated, wet berms are developing along both banks. To prevent cattle from overgrazing and poaching these important wetland margins the banks have been fenced with post and 3 lines of barbed wire and a section of post and rail fencing in the paddock closest to the farm buildings. Post and wire fencing was also erected along the right bank either side of the refurbished ford. © Steve Brayshaw © Steve Brayshaw © Steve Figs 9 and10. Wide, wet, vegetated berms protected by post and wire and post and rail fencing Management Future management of the fencing and fords is now the responsibility of the landowner. GAAFFS will manage any further willow regeneration to maintain a mix of marginal woody habitat and shade trees. Monitoring Visual inspections will be undertaken, together with a photographic record, to monitor the integrity and performance of the in-stream enhancements and record any changes they are making to river morphology. Future Projects The large willow at the bottom of the restoration reach would benefit from repollarding to prevent future collapse. The resulting woody debris could be used to repair the erosion on the opposite bank. Selected alders which line the banks of the bypass channel immediately downstream of the sluice could be layered to allow more light to reach the river and diversify the instream habitat. The ash on the left bank immediately below the bridge at the top of the reach could be layered and secured to narrow the channel and provide a backwater refuge. Provision of fish and eel pass would be desirable to allow passage at the mill © Steve Brayshaw © Steve © Steve Brayshaw © Steve Fig 11. Pollard willow at the bottom of the reach Fig 12. Alders along the bypass channel © Steve Brayshaw © Steve Fig 13. Bypass channel sluice. Suppliers of Services and Materials Fencing and willow layering Woodland and Water Management Ltd: [email protected] or Tel. 01327 349073 Ford refurbishment P&R Plant Hire, Fleet, Spalding, Lincs. PE12 8NG. Tel 01406 422669. www.pandrplanthire.co.uk Further Information For further information about the scheme including arrangements for visiting, contact: Matt Parr Technical Officer (Fisheries) Environment Agency Waterside House Waterside North Lincoln. LN2 5HA E. [email protected] T. 01522 785859 © Steve Brayshaw © Steve Fig 14. A bed of water-crowfoot (Ranunculus) growing on clean gravels in the narrowed section The Water Framework Directive The Water Framework Directive (WFD) is a major area of work for the Environment Agency. The WFD aims to get all water bodies - lakes and groundwater aquifers as well as rivers - into ‘good ecological status’ - or better - by 2027, with a series of ‘landmarks’ (2015 and 2021) to check progress. The Water Framework Directive became UK law in December 2003. It provides an opportunity for the Environment Agency to plan and deliver a better water environment with the focus on ecology. The Water Framework Directive will help to protect and enhance the quality of: surface freshwater (including lakes, streams