Case study:Afon Merin Natural Process Restoration

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Location: 52° 23' 56.58" N, 3° 46' 27.57" W

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Project overview

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Status	Complete
Project web site	http://westwalesriverstrust.org/the-human-beaver/
Themes	Environmental flows and water resources, Fisheries, Flood risk management, Habitat and biodiversity, Hydromorphology, Land use management - forestry, Monitoring, Water quality
Country	Wales
Main contact forename	Ieuan
Main contact surname	Davies
Main contact user ID	User:Ieuan
Contact organisation	Natural Resources Wales
Contact organisation web site	http://naturalresources.wales/?lang=en
Partner organisations
This is a parent project encompassing the following projects

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Project summary

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The Afon Merin is one of the principal tributaries of the Rheidol system, flowing from its upland SSSI catchment, through NRW managed Welsh Government estate Myherin woodland and onwards into the Rheidol Valley. A 3km section provided landscape scale intervention opportunities to "kick-start" natural processes to benefit biodiversity, water quality and quantity, and carbon sequestration.

The site offered the potential to undertake a pilot study of low cost high nature value interventions on Welsh Government Woodland Estate. While seemingly in a natural state, the rivers was incised and disconnected from the wider flood plain, with a lack of suitable gravels for the resident native Brown Trout population. Felling commenced in 2018 and some of the timber was used to begin ditch blocking and creating leaky dams within the main channel. Early observations showed that the results had been positive with the hydrological systems soon renaturalising within the valley floor, wet areas were developing and the main channel began to take on a more braided characteristic by occupying historic channels. In channel flow diversity increased markedly allowing a more complex sediment matrix to appear.

Monitoring surveys and results

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Water immediately started to spill out of bank picking up a network of relict channels within the floodplain. Subsequent high flow events have seen gravel depositing instream and as shoals, more dynamic flow patterns and a complex of side channels, permanent and temporary pond features.

Prework aerial studies of the area and fixed point photography at key areas through the valley have allowed a gross study of early geomorphological changes within the system, including stream number and width, and changes within the network of wet areas across the valley floor.

Aberystwyth University are undertaking flow measurements and will continue to do so over an extended time period. Ecological studies will be undertaken across this and a control site on the same water body to monitor changes.

Lessons learnt

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The implementation of this scheme on Welsh Government Woodland Estate has shown that there are high value gains possible at low cost inputs which can be imnplemented alongside current Forest management techniques. These can yield multiple benefits and studying these allows us to put forward a case for spreading this work and ethos across the wider Woodland Estate with potential for large scale projects. The multiple benefits are closely aligned with NRW's wider Corporate and Business plans and better ways of working which look to generate positive outcomes through nature based solutions giving positive benefits across a broad spectrum of habitats, species and communities.

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Catchment and subcatchment Select a catchment/subcatchment Edit the catchment and subcatchment details (affects all case studies in this subcatchment) Catchment River basin district Western Wales River basin South West Wales Subcatchment River name Mynach - headwaters to confluence with Rheidol Area category 10 - 100 km² Area (km2) Maximum altitude category 500 - 1000 m Maximum altitude (m) 609609 m <br />0.609 km <br />60,900 cm <br /> Dominant geology Siliceous Ecoregion Great Britain Dominant land cover Coniferous Woodland Waterbody ID GB110063041560 Site Edit 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 Edit project background Reach length directly affected (m) 3,0003,000 m <br />3 km <br />300,000 cm <br /> Project started 2018/02/01 Works started Works completed Project completed Total cost category 10 - 50 k€ Total cost (k€) 30,00030,000 k€ <br />30,000,000 € <br /> 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 Supplementary funding information Total project cost including felling and installation of dams and scrapes was approximately £30,000 Reasons for river restoration Edit reasons for restoration Mitigation of a pressure Hydromorphology Biology Physico-chemical Other reasons for the project Measures Edit Measures Structural measures Bank/bed modifications 15 leaky dams and scrapes. Floodplain / River corridor Planform / Channel pattern Other Non-structural measures Management interventions Social measures (incl. engagement) Other Monitoring Hydromorphological quality elements Edit Hydromorphological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Biological quality elements Edit biological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Physico-chemical quality elements Edit 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 Edit Other responses Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Monitoring documents Upload monitoring documents Additional documents and videos Upload additional documents Additional links and references Edit links and references Link Description http://youtu.be/9T55beo efc UK riverprize finalist video Supplementary Information Edit Supplementary Information Historical maps showed a more dynamic river system prior to agriculture, conifer afforestation and land drainage in the catchment. The river had cut down into its bed, severing it from its floodplain on all but extreme events. Gravels had been scoured out of large areas of the watercourse leaving a cobble substrate sub-optimal for spawning salmonids. Significant lengths of the river were also dry during the extended dry spell in summer of 2018. The project commenced in early 2018 with felling of conifer, ditch blocking and instream structures to wet up the site and re-link the river to the floodplain and then the installation of 15 leaky dams and scrapes.