This document is an output from the Devon and Cornwall Soils Alliance, delivered by Westcountry Rivers Trust.
Flood risk is a major issue for numerous communities across the South West and with the expected future impacts of climate change, as well as compounding factors such as population growth and development, it is a problem that is becoming all the more urgent. A number of projects are currently underway to understand the causes of flooding and investigate potential solutions. This includes the Upstream Thinking - Rapid Response Catchments project and Devon and CornwallSoils Alliance (more info on page 5).
A mapping exercise was carried out to identify all the micro catchments (5km2 or 10km2)above flood risk properties in Devon and Cornwall. The idea being that Natural Flood Management (NFM) measures and engagement with the local community weremost likely to be effective at this scale. These micro catchments were then prioritised according to a number of factors. The catchment described in this report, the Woodbury Salterton Stream, is one of those prioritised micro catchments.
The Woodbury Salterton micro-catchment for the Grindle Brook flowing into the River Clyst is 145ha and highlights 29 properties potentially at riskfrom surface water flooding, many of these are in Woodbury Salterton. There are multiple possible contributing causes of this, including the topography, land use, and scarcity of habitats such as woodland. The catchment is failing Water Framework Directive (WFD) regulations on chemical status and is within a Drinking Water Safeguard Zone at riskof contamination by pesticides.
A rapid walkover survey wascarried out by an experienced surveyor from the Westcountry RiversTrust (WRT) to further inform potential issues and opportunities for flood riskmitigation. During the walkover, the micro catchment, did not display much localised flood risk, but the village does actively manage the stream through it. There doesn’t appear to be much opportunity to effect localised flood improvement at present, although the ability to mitigate for increased risk due to climate change or to mitigate part of a larger flood risk downstream (less localised) should not be discounted. The walkover survey did present opportunity to deliver or contribute towards WFD (Water FrameworkDirective) improvement.
Implementation of Natural Flood Management (NFM) measures may have the potential to mitigate some of the flood risk and simultaneously make progress towards reaching “good” WFD status for the wider River Clyst catchment that would ultimately benefit the local community. The NFM opportunities identified in this report include changing land use and habitat creation surrounding existing habitats across the catchment to slow surface water flow into watercourses and enhance habitat networks. Areas of land entering into an agri-environment scheme agreement would also contribute to improved soil health and biodiversity in the absence of significant habitats. In addition, there are opportunities for runoff attenuation which may present an opportunity for community engagement to facilitate their delivery.
This documentisa study for causesof flooding,priorityconsiderations,and opportunitiesforNFMin the micro-catchmentforthe Balland Stream, covering some of the Ashburton urban area in South Devon.
The study is builton multiple layersof mapped environmentalinformationand the results of the walkoversurvey. This informationhasbeenused to explore the current state of the catchmentand its environment, and then map areasfor further investigationand actionsto make improvements.
This micro-catchment scaleassessmentwillbe usedto guide efforts incommunityengagement andNFM.
The study has 5 key chapters,based on the current status of the micro catchmentand whatopportunitiesthere mightbe.
1. Micro-catchmentOverview
2. PriorityAreasand Drivers
• Flooding
• WaterQuality
• WaterQuantity
• Designated Sites
• Tourism and Recreation
3. Existing Natural Assetsand Their Condition
• Habitats
• Soils
• Crops
4. Issues
• Abstraction,Discharges,Pollution,and Runoff
• HydrologicalConnectivity
• Issues identified during Walkovers
5. Opportunities
• Existing Opportunities
• OpportunitiesIdentified during Walkovers
It isnot possible to map all aspectsof the status of the micro catchmentwithexisting datasets,and the true state of the catchmentmay not be fully reflected inthe datasetsforvariousreasons including the age of the data,the resolution, and the level of local knowledge takeninto consideration when the data has beencollected and mapped.
Assessing the qualityand conditionof natural assetsin particularischallenging due to the level of detail required.Nonetheless,the availabledata has beenreviewed and the bestdata currently availablehasbeenused. A full set of referencescan be found on pages53 56.
Flooding isa problem thatis experienced widelyacrossDevonand Cornwall,witha large portionof caseslinked to rivers(fluvial flooding as opposed to surface wateror sea).Riverwaterqualityisalso a key issue in the region,withall 381assessed rivers failing to achieve “good” statusin 2019.One importantreasonfor waterqualityfailure islinked to soil erosion.Soil erosioncan also contribute to increased fluvial flood riskdue to reduced channel capacitiesand blockages.Therefore,waterqualityand floodriskdriversare often interlinked and the solutionsto alleviate these pressures are often multifunctional.Two projectscurrentlyunderwayare aiming to tackle these issues by working withlocal communitiesto deliver small scale,land basedmeasures(“nature basedsolutions”).These projectsare Devonand Cornwall SoilsAlliance (DCSA) and Upstream Thinking
Afteritwas found that over 40%of soilsacrossDevonand Cornwall are degraded,the collaborativeprojectof the DCSA waslaunched inJune 2019. This aimsto build the capacityand capabilityinsoilsadvice forthe projectpartnersacrossthe 2 counties to work towards restoring degraded soils. One significantbenefitof improving soil healthisgreatersurface waterinfiltrationinto the ground before itreachesand overwhelmswatercourses, thereby reducing flood riskand preventing potential pollutantsfrom entering the water.Thisalso has the potential to make considerable Water FrameworkDirective (WFD) improvementsto waterquality.
AcrossDevonand Cornwall there are hundreds of Rapid Response Catchmentsthat are characterised byquicklydraining catchmentareasunder 10km2 (and under 5km2) , where during high rainfall eventssurface flowsand overland run off overwhelm small communities(1 50propertiesin flood zone 1).Flood eventshave increased inthese types of catchmentdue to degraded soilsthatno longerhave the infiltrationcapacity,simplified drainage patternsand more variable and extreme weatherpatternsassociated witha changing climate.UST RRCwill focusonworking withsmall communitiesinthese rapid response catchments to help them develop and delivertheirown climate resilience plansbyrestoring some of the hydrological functionalitywithinthe landscape.
The DCSA isworking in partnership with the UST RRCprojectacrossDevonto develop 24preparatoryinvestigationsonprioritisedmicro catchmentsto identifylikelyareasfornature based solutionsand NFM (Natural Flood Management) interventionswhere land ownership showsa willingnessand waterqualitycanbe improved.Communityengagementwill be criticalwhenimplementing NFMasmeasures need to be numerous and spread out across the catchmentto provide the greatestbenefits.If propertyowners and landownerscan work togetherand share perspectives, then measures canbe designed thatare agreeable to all stakeholdersinvolved.Thisalso helpsto fostera sense of community stewardship overtheir catchmentand NFM measuresthat would enhance theirlongevityand resilience.
OverviewThere may be opportunitieseverywhere forNFM measures and other nature-based solutionsatlow cost that also bring additional benefits to human health,biodiversity,and the aestheticsof the landscape. However,the scattered and fragmented locationsof propertiesat flood riskand the limited accessible fundsrequiresidentifying only the largestclustersof flood riskpropertieswiththe smallestupstream micro catchmentsto deliverthe mostimpactwiththe resources available.
The processof identifying priorityareasforopportunitiesto deliver improved waterqualityand quantityforclimate change resilience wasundertaken in four steps.
1. The South Westareasof Devonand Cornwall were modelled using GIS (Geographic InformationSystems) to identifywhere opportunityareaswere located.
2. The modelled opportunityareaswere ground-truthed in theory using desk based studies
3. The top prioritised opportunityareaswhere ground-truthed physicallyusing rapid walkoversurveys
4. Internal evidence reviews,external evidence reviews,and 2pagers summary documentswill be writtenfor24 trial investigationareas where physical interventionscan take place.
For more informationonthe first 3steps please see the appendix.
The final 24micro catchments,including WoodburySaltertonwhichis shown in red.
Themicro-catchment was selectedin theGISmodelling step becauseit contains alarge numberof properties in Woodbury Salterton that are potentiallyat floodrisk.
The map below showswhichbuildingsoverlap withthe EA’s modelled “Flood Zone 2” area,specificallyareasatriskof flooding from rivers,as identified during the micro catchmentmapping process.
There are 29buildingspotentiallyatriskout of 61 in the catchment, approximately47.5%of them.Most of the propertiesin the catchmentsare residential.
The catchment’ssize of 1.45km2givesan area of 0.05km2 perbuilding atrisk
The waterframeworkdirective (WFD)statusinthe widerGrindle Brook catchmentis Poor
If property ownersare willing to workwithlandownersand vice versa, then small scale NFMmeasuresupstream in the catchmenthave the potential to benefita large numberof propertiesand improve water quality.
The urban area of Woodbury Salterton lies in the north of the catchment with the rest of the catchment largely consisting of fields and scattered residential buildings. There are no major roads running through the catchment which is connected by a series of small lanes. The micro catchment forms the watershed for an unnamed tributary of the Grindle Brook that this report will call the Woodbury Salterton Stream, that branches off in to several smaller tributary’s to the south east. The main tributary flows northwest through the catchment and through the urban area of Woodbury Salterton where it joins the main Grindle Brook outside the northern boundary. The micro catchment falls within the Woodbury Civil Parish and is administered by Woodbury Parish Council.
The map on the right shows the steepness of slopes. The majority of the catchment has fairly uniform slopes with higher slopes along the length of the tributary, possibly indicating that the stream is incised.
The way the land is used has significant impacts on flood management. Land use has been mapped here using the Centre for Ecology and Hydrology’s (CEH) Land Cover Map 2019. This is a model derived from satellite imagery at 25m resolution.
The land use here is primarily arable and horticulture, accounting for 61% of the catchment, followed by the suburban area of Woodbury Salterton that covers another 23%. Patches of improved grassland and broadleaved woodland are scattered throughout the micro catchment, accounting for 10% and 5% respectively .
It should be noted that this land cover map model is not a perfect representation of land use as it simplifies UK land cover into very broad classes.
Land use observed during the catchment walkover mostly matched the land use mapped here using the Centre for Ecology and Hydrology’s (CEH) Land Cover Map 2019 above.
The suburban element is slightly overstated in the CEH data and more improved grassland (grazing), arable and horticulture is present.
The predominant land use at the time of survey was pasture and maize whole crop silage in the rural upstream catchment. The late harvesting of maize can be detrimental to water quality due to the timing of cropping and can be detrimental to groundwater infiltration if heavy machinery is used on wet ground causing compaction.
Flooding hasthe potential to negativelyaffectpeople and communities. Byconsidering boththe vulnerabilityof communitiesand the opportunitiesforland managementinterventions,actionscanbe targeted to have a positive impactoncommunitiesmostatrisk.
Flooding isone of a number of natural hazardswhichcan cause harm to people,the environmentand the economy.The primarydriverfor targeting thiscatchment isflooding.However,there are otherpriorityareasand driverswhich will be affected byNFMand candetermine the mostappropriate type of NFM forthe catchment. These are mapped inthe following pages.
The Neighbourhood Flood Vulnerability Index (NFVI) characterises vulnerability as communities likely to experience losses in wellbeing during flood events. This is based on their susceptibility, preparedness, responsiveness, and ability to recover, all without significant support from emergency services.
Most of the buildings in the catchment are classed as “Relatively Low” in the Neighbourhood Flood Vulnerability Index (NFVI), meaning that they are slightly less vulnerable to losses in wellbeing from a flood event than the UK average. The rest of the catchment is classed as “very low”, meaning they are much less vulnerable than the UK average
The Social Flood Risk Index (SFRI) is a geographic measure of flood disadvantage. It identifies communities who are both exposed to flood risk by living on a flood plain and who are more vulnerable to the effects of flooding, due to factors such as health, preparedness and the availability of community support. Higher numbers of people living in a flood plain coinciding with high social vulnerability result in higher index values. The map highlights neighbourhoods identified as at riskof fluvial flooding higher than the national average. Please note that this is based on flood risk from rivers and the sea, so coastal areas may not be affected by changes in land management upstream.
At present, the entire catchment is classed as “Exposed” in the SFRI for river and coastal flooding, though the NFVI remains below the UK mean. This doesn’t increase in future projected scenarios of 2 and 4 degree temperature increases by the 2050s..
When considering flooding, it is necessary to investigate records of previous flood events and combine this with modelled scenarios of what could happen, particularly in the face of the uncertainty of climate change affecting weather patterns.
The catchment has recorded flood outlines from both the Grindle Brook north of the catchment outlet and the Woodbury Salterton Stream. The latter has previously flooded in December 1965 and July 1972 where channel capacity was exceeded with no raised defences. It flooded in the north of the catchment at the outlet on both these occasions, and also more recently in October 2008 due to an obstruction in a culvert. There are not currently any flood defences in the catchment.
The EA’s modelled fluvial Flood Zone 2 dataset show areas predicted to flood from rivers in a storm event so severe it is likely to occur only once every 1000 years. This is also known as a 0.1% Annual Exceedance Probability. Flood Zone 2 was used to identify buildings potentially at flood risk as shown previously on page 8. Here, this occurs along the whole length of the Woodbury Salterton Stream and its tributaries.
The EA’s Risk of Flooding from Surface Water (RoFSW) dataset shows the extent of flooding caused by rainwater flowing across the ground towards the nearestwater course in a 1 in 1000 year storm event. This overlaps frequently with Flood Zone 2, but also shows depressions in the ground where surface water will accumulate.
There has been at least one flood event in Woodbury Salterton in the past. The flood riskappears to match the modelled outputs above, but in asking a member of public, the flood riskhails from blocked infrastructure in the village which is now actively managed by the community. Therefore the problem may be limited.
The watercourse is channelised through Woodbury Salterton, although the extent of historic flooding wasn’t determined at the time of survey.
The flooding pinch points in the village appears to be culverted road crossings. If these become blocked the risk of surface water flooding increases.
Key infrastructure such as the primary school, village hall and sewage works could be specifically asked if flooding is a problem, or if it is perceived to be a problem in the future with more extreme weather events.
The roads leading to the village from the upstream catchment appear to be a rapid route for water to travel with verges/gutters being reinforced against erosion by concrete.
Picture of the road running to the village (past village hall) with scour protection against verge.
A sign of rapid run off of surface water.
Community stakeholder groups are active in Woodbury Salterton.
There is a Woodbury Salterton Resilience Group that work to combat climate change impacts in their area.
The parish council doesn’t have a flooding plan available online.
To prevent flooding, the community have semi regular clearances of debris from the stream and removal of vegetation from the stream banks.
There is a Neighbourhood Plan which aims to increase connectivity of nature and promote biodiversity through habitat corridors.
Some involvement with the Woodland Trust. Tree planting by WT in the Parish protects areas from development
Clean and plentiful water is vital for a huge variety of our activities, and for supporting healthy ecosystems. Good water quality supports an efficient water supply, healthy natural habitats and cultural ecosystem services. A plentiful water supply is important for drinking water and household use, irrigation, industrial use and for maintaining habitats. Water quality is a key underpinning for the Water Framework Directive.
There are no Water Framework Directive monitoring sites, Drinking Water Safeguard Zones, priority wetlands, or aquatic habitats in the catchment. However, the entire micro catchment falls within the Mid Devon Nitrate Vulnerable Zone (NVZ) for ground water.
For more information on water quality go to slide 26.
The amount of water available for abstraction is an indicator of how much drinking water is available for people. The catchment sits within an area available for licensed water abstraction (left map).
In the context of NFM, it is also necessary to consider water availability for plants and wildlife. Drought can cause vegetation to die back, leaving bare soil exposed and more vulnerable to erosion and runoff when it eventually rains. The Vegetation Health Index (VHI) uses satellite data to combine temperature and vegetation condition to characterise vegetation health. Areas are scored between 0 and 1 with lower values indicating low drought risk to plant health and higher values indicating higher risk. The catchment is scored significantly low at 0.187on the VHI (right map), indicating very low risk to plant life from drought stress.
Designated habitat sites, from small local nature reserves all the way up to large national parks, need to be protected for the wealth of benefits they provide to people and the environment, including already providing some degree of NFM. A site being designated can be an indicator of habitat health.
There are no designated sites within the boundary of this micro catchment and it doesn’t fall within any larger designated areas. Just beyond the southwest boundary of the catchment however is the East Devon AONB.
Clean air is important for people’s health and for healthy ecosystems. Air quality is the term used to describe the levels of pollution in the air. When air quality is poor, pollutants in the air may be hazardous to people, particularly those with lung or heart conditions. In the past, the main air pollution problem was smoke and sulphur dioxide from fossil fuels such as coal. Now, the major threat to clean air is from traffic emissions. Petrol and diesel motor vehicles emit a variety of pollutants, principally carbon monoxide (CO), oxides of nitrogen (NOx), volatile organic compounds (VOCs) and particulate matter (PMx).
A growing body of researchsuggested that smaller particles, in particular PM less than 2.5μm in diameter (PM2.5), is a metric for air pollution which is closely associated with the adverse health effects of poor air quality. Therefore, this section will use data relating to PM2.5 where relevant.
Improvements to the soil and surrounding environment have the potential to also deliver improvements to air quality through natural filtering processes.
The entire catchment has relatively low concentrations of background particulate matter. The northern, urban area of Woodbury Salterton has slightly higher concentrations of 7.11PM2.5 than the rest of the catchment, whilst the southeast measures the lowest at 6.77PM2.5
Areas and features important for tourism and recreation may also be at flood risk and it is necessary to protect them for a healthy society and environment.
There are two greenspaces within the micro catchment, both of which lie within the urban area of Woodbury Salterton. One is a small area of allotments and the other is a children’s play area.
There is a Public Right of Way (PRoW) running from Toby Lane, southwestward through fields and out of the southern boundary of the micro catchment towards the urban area of Woodbury.
Biodiversity,the varietyof life of earth,is valuable initsown right. Italso supports recreation,food,flood protection and climateregulation. This sectionwill predominantlyexplore whathabitatsand othernatural assetsare presentin the catchmentthat will already be contributing to NFM and could be improved withfurther NFM measures.Water, soilsand crops are natural assets in themselvesand will also be investigated.
The natural assets mapped below are habitats which have the potential to support thriving plants and wildlife. Thriving vegetation is very valuable for NFM as it roughens the ground, thereby slowing down surface water flow, meaning water courses are less likely to be overwhelmed in a storm. In addition, plant roots provide structural support for the soil and prevent surface water washing soil into water courses.
Where the assets are present the landscape is likely to be contributing to the provision of habitats, biodiversity and even NFM. Where assets are absent there may be a lack of habitats which contribute to or support thriving plants and wildlife. Assets may still be present however in the form of crops and soils which are mapped in the following pages.
There are two traditional orchards in the area, the larger of the two is to the west of Woodbury Salterton and the other is in the east of the catchment. There is a patch of broadleaved, deciduous woodland priority habitat in the catchment’s centre where Village Road, Whitecross Road, and Toby Lane meet. There is also a patch of mixed mainly broadleaved woodland in the southeast of the catchment.
Aside from these, the restof the catchment is comparatively habitat sparse.
It is important to determine the current condition of water quality. Poor water quality can be detrimental to people, wildlife, and may cause other negative effects during a flood event. Good water quality should always be protected. A key set of evidence used to assess the water quality in a catchment is the Water Framework Directive (WFD). The status of a waterbody is measured using a series of parameters and is recorded on the scale: high; good; moderate; poor; bad (with moderate and worse being regarded as a failure).
There are no assessed WFD river waterbodies present. However, the micro catchment sits within the larger Grindle Brook WFD river waterbody catchment, accounting for 7.2% of it’s area.
The Grindle Brook is overall classed as Poor meaning it is failing WFD regulations. It is currently failing on chemical status and ranked poor for ecological class. In 2019, 100% of waterbodies in the UK failed on chemical status after the EA included monitoring “mercury and its compounds” and “Polybrominated diphenyl ethers (PBDE)” into its water quality monitoring methodology.
The Grindle Brook has been classed as Poor for Fish, Phosphate, Macrophytes, and Phytobenthos. Despite scoring Good or High on other ecological elements, its ecological status is overall Poor and therefore failing WFD regulations on ecological grounds.
It is failing for fish due to poor soil management and barriers causing ecological discontinuity. It is failing for Phosphate, Macrophytes, and Phytobenthos due to poor livestock management.
The Grindle Brook waterbody has been assessed as Failing for Mercury and its Compounds as well as PBDEs, but is classed as Good for all other chemical elements. Despite this, its overall chemical status is Bad and therefore failing WFD regulations on chemical grounds as well as ecological.
The are over 60 metrics that the EA can use to monitor waterbody catchment statuses. For more information and a breakdown of this catchment’s status go to https://environment.data.gov.uk/catchment planning/v/c3 draft plan/WaterBody/GB108045008710
Crops can be a natural assetin themselves, providing the food we eat and storing carbon. Some crops however, could be considered natural liabilities. One such crop is maize which is planted in wide rows, leaving bare soil exposed and without structural supportfrom roots. Furthermore, it is often harvested in late Autumn when the weather becomes wetter, meaning little to no vegetation can regrow to protect it over Winter. This leaves the soil much more susceptible to being carried away by surface water runoff. Despite this, maize can be successfully managed to grow and harvest while minimising runoff.
The Crop Map of England (CROME) dataset is derived from satellite data and generalised to hexagons. It identifies the urban area of Woodbury Salterton and a caravan storage unit in the southeast of the catchment as non vegetated. The majority of the catchment is classed as grassland with some large areas of maize being grown in the centre by Woodbury Salterton as around much of the catchment boundary. There are various scattered clusters of trees and perennial crops as well as some wheat being grown.
The nature of the soil can determine how much surface water infiltrates into the ground, as well as what plants will growand where. Understanding soils is vital to providing effective NFM and improving water quality. The aim with water quality improvements is to keep the soil on the land and improve groundwater infiltration and recharge, therefore allowing a slower and more naturally filtered water route to the river.
Degraded soil structure, where the soil profile is compacted at shallow depths or capped at the surface and impermeable can lead to excessive unnatural run off of surface water instead of percolation and infiltration. More than 60% of soils in Devon and Cornwall are naturally well drained and should rarely become saturated.
The Farming Rules for Water (FRFW) were introduced at the start of 2018 as legislation to help protect surface water quality. The regulations are designed to help manage cultivated agricultural land well, without over management, nutrient run off, or waste affecting surface water.
The diagram above shows good soil structure on the left and compacted soil structure on the right. In compacted soil, little surface water can infiltrate into the soil subsoil due to surface capping or compacted layers, while vegetation can be deprived of oxygen due to compression of pores that normally transport air and water (sourced from SEPA NFM Handbook).
The NATMAP soils dataset from Cranfield University shows that the catchment is primarily composed of the soil series WHIMPLE 3 – deep red loam to clay. To the northwest of Woodbury Salterton, the soil is composed of Newnham loam over gravel.
Geological conditions impacts groundwater and soil type. When rocks are sufficiently permeable it can lead to groundwater flooding. If local flooding is caused be groundwater levels then it is unlikely that changes to land management and NFM will improve flood resilience.
The geology of the micro catchment is mainly comprised of claystone and mudstone. Along the length of the Grindle Brook tributary, and in the south east of the catchment, the underlying geology is made up of colluvium. There are also areas of sandstone in the northwest of the catchment around Woodbury Salterton
The walkover didn’t uncover any suspicion of groundwater influenced flooding and the perception is that any flood risk would originate from surface flow.
Multiple issues have already been mentioned and mapped that could be contributing to flood risk and WFD failures. However, there are further potential issues that may be influential which will be explored in the following pages.
Pollution incidences themselves will directly affect water quality, but consented discharges into watercourses and chemical runoff from roads exacerbated by rainwater may also be sources of pollution.
There have been no pollution incidences in the catchment itself, but there has been a Category 2 Significant water pollution incident in a Grindle Brook tributary in February 2016 just north of the catchment outlet.
Another pollution incident occurred just to the west of this in June 2014, though this was considered Category 2 Significant to air and Category 4 (No Impact) to water.
There is one source of consented discharge for South West Water (SWW) for sewage from a storm tank overflow into the Woodbury Salterton Stream, just outside the catchment boundary north of the catchment outlet.
Licensed water abstraction points may serve as sources of risk to ground water quantity and availability. There is an abstraction point just outside of the catchment in the southeast for Castle Brake Holiday Park for general agricultural and commercial use.
Surface flow pathways are the routes rainwater accumulates and follows when it lands to the nearest depression or watercourse. As it flows, surface water can pick up any number of chemicals, soil, and debris and carry them into the watercourse with it. This serves to demonstrate why community engagement and working with land owners is so important, as the effects of practices upstream in the catchment cascade down via these routes. Pathways have been modelled in 2 different ways here.
The first are modelled using topographic data and software called SCIMAP (left). Only the routes with above average wetness are shown. The flat topography of floodplains can skew the modelling process and any pathways in these areas should be considered unreliable.
The second method uses SCALGO Live (right). Flow routes with at least 1km2 upstream area are shown. Areas that would be flooded if 15cm of rain were to fall during a storm event are also mapped. Flooded areas are coloured by their water volume from light to dark.
During the walkover surveys, experienced surveyors at WRT recorded points of interest and concern, as well as potential natural flood management opportunities. The results are mapped (right) but it should be noted that the map is by no means exhaustive.
Some soil in the catchment may be compacted which can increase surface water run off. This would need further investigation with a trial pit. This gradually sloping field has little vegetation cover and the lowest point is a gate leading out onto the road.
There is potential risk of rapid runoff down the road to the village from this location.
There is a lot of maize grown in this catchment which can present a higher risk of soil runoff and water quality degradation if the cropping timings are late, if the soils are compacted, and if the land is left without vegetation cover over winter.
This map of issues was generated after one walkover survey, reflecting the situation at the time of survey. It is not exhaustive and doesn’t reflect all issues present in the catchment which will take much more effort to determine. A greater range of all the issues is present within the previous section. Any projects delivering in the catchment should undertake their own walkovers for confirmation and addition to the list.
There are many options to reduce flood and coastal erosion risk across the country which involve implementing measures that help to protect, restore and emulate the natural functions. These options are known as Working With Natural Processes (WWNP) or Natural Flood Management (NFM). These measures increase flood resilience by slowing the flow of water and disperse energy to keep the water at the top of the catchment or to improve groundwater infiltration and recharge, therefore allowing a slower and more naturally filtered water route to the river.
Where rapid surface water run off has been noted there may be opportunities for WWNP to mitigate both water quality and to regulate flow. An example of some NFM interventions are given below. They are intended to slow water, store water, increase infiltration and intercept rainfall.
The illustration above shows various natural flood management techniques (sourced from CIRIA).
The Environment Agency have mapped potential opportunities for WWNP to reduce flood and coastal erosion risk across the country. These include opportunities for different types of woodland planting, floodplain reconnection features like restored riverside wetlands and meadows, and runoff attenuation features which aim to slow pathways of water across the land, like storage ponds or leaky barriers. Anumber of areas are also excluded from the woodland maps such as urban areas and existing woodland. These are mapped separately on page 40.
The greatest opportunity identified by these WWNP datasets for the catchment is riparian tree planting along the length of the Woodbury Salterton Stream and its tributaries. There are combined opportunities for floodplain woodland planting in some of these areas immediately upstream of Woodbury Salterton.
In addition, there are opportunities to construct smaller scale runoff attenuation and gully blocking features near the streams and roads that are strategically placed to slow the flow of surface water before it reaches the water course, allowing excess water to dissipate rather than flood during a storm event.
Furthermore, it may be possible to reconnect some narrow areas of floodplains along the lengths of the tributary.
There may be current habitat creation and river restoration projects where opportunities exist to work together with organisations to provide simultaneous benefits to habitats, rivers, and flood resilience.
Natural England have also identified opportunities to expand on existing habitats to create habitat networks across the landscape.
While there are no recorded habitat creation or river restoration projects in the catchment, there are significant opportunities for expanding habitat networks around existing priority habitats (see page 24).
In the northwest of the catchment, surrounding the traditional orchard priority habitat is Network Enhancement Zone 1, defined as “Land within close proximity to the existing habitat components that are unlikely to be suitable for habitat re creation but where other types of habitat may be created or land management may be enhanced including delivery of suitable Green Infrastructure.”
In the southeast of the catchment is the Network Expansion Zone, defined as “Land within relatively close proximity to the Network Enhancement Zones that are more likely to be suitable for habitat creation for the particular habitat and identifying possible locations for connecting and linking up networks across a landscape.”
Just outside the northern boundary is Network Enhancement Zone 2, “Land within close proximity to the existing habitat components that are unlikely to be suitable for habitat re creation but where other types of habitat may be created or land management may be enhanced including delivery of suitable Green Infrastructure.”
Agri environment schemes are government initiatives that aim to financially compensate farmers for providing benefits to wildlife on their land. Areas under agri environment scheme agreements may provide opportunities simultaneously for the landowner to meet the agreement’s objectives and deliver NFM to benefit the catchment community.
There are currently no agri environment schemes in place within this catchment, however there may be opportunities for land owners to enter into these. Habitat creation in the southeast and northwest in particular may be facilitated in the Habitat Enhancement and Expansion Zones as identified on page 38 if land owners were to enter into an agri environment scheme.
A further consideration for the targeting of NFM via soil improvement, habitat enhancements, restoration or creation is existing areas which may not be suitable for changes in land use or land management. This may be because they are already valuable sites for wildlife (e.g. designated wildlife sites), because the land use is difficult to change (e.g. urban land) or because the land is highly valuable for farming (high grade agricultural land). There may be further historic or natural heritage designations to consider.
There are no designated sites within this catchment that would provide administrative challenges, however the traditional orchard and deciduous woodland priority habitats may. There is still the opportunity to improve these habitats further by getting more partner organisations involved in the process and even access additional sources of funding.
The WWNP woodland constraints dataset highlights any urban areas and existing woodlands (including woodlands not listed as priority habitats not shown here) where additional tree planting may be difficult. This excludes some of the urban areas of the catchment including along many of the roads. This does not mean urban tree planting is impossible, and would also provide another avenue to get the community involved the closer the planting is. Much of the rural areas of the catchments have no constraints.
The agricultural land grade is grade 3 across most of the catchment which is considered average. However, an area in the northwest of the catchment left of Woodbury Salterton is considered grade 1 which is very high quality. Creating habitats in this area and changing the land use from agriculture may therefore prove difficult.
There are also no scheduled monuments present.
During the walkover surveys, experienced surveyors at WRT identified opportunities for NFM measures and improvements to other key considerations mentioned. The results are mapped (right) but it should be noted that the map is by no means exhaustive.
A few mixed trees have been planted on a steep slope in the headwaters.
If there was opportunity from landowners then more tree breaks and tree cover along the watercourse, giving wider stream margins, could be beneficial to surface water.
Some channel management of the stream through the village may be beneficial and complementary to the ‘active management’ undertaken by the local community.
It may be beneficial to crown lift or open branches to help protect the bank from erosion and to let more sunlight to the banks for vegetation and biodiversity.
This map of opportunities was generated after one walkover survey, reflecting the situation at the time of survey. It is not exhaustive and doesn’t reflect all opportunities present in the catchment which will take much more effort to determine. A greater range of all the opportunities is present within the following section. Engagement with landowners and stakeholders is required for a more comprehensive list of opportunities and ascertain if suggestions can be implemented in conjunction with current land use, future land use and business plans.
of
that dominates the mid to upper
be considered for change
were willing to growless risky crops for the
benefit of
the upstream areas of the catchment where runoff has rapid routes down tracks and roads, improving soil health and water acceptance would be highly desirable to reduce the amount of runoff in the first place, but also to accept runoff if it were diverted away from the road system back in to fields.
There are limited opportunities to improve flood resilience in the Woodbury Salterton Stream through increasing channel and floodplain roughness to slow the flow.
Given the shortness of the catchment, the gradient, and the perceived limited benefit to flooding in the village (i.e. local community doesn’t think it’s a big issue), there is limited opportunity for in channel improvements that will make a significant difference although complementary ecosystem benefits should not be discounted.
It is possible that the village community could look at in channel improvements in the stream running through the village. There is possibility to allow more sunlight to vegetate and stabilise banks, and a more detailed survey could help determine if flood riskcould be further reduced by allowing more space for the watercourse.
NaturalFlood Management (NFM) or
withNaturalProcesses (WWNP)
benefit in catchment
provider identified
of opportunity matches
maps
Channel restoration,sinuosity
Large/coarse woodeddebris introduction
Floodplainreconnection (paleochannel reconnection)
Riparianbufferstripsor woodland (sloped)
Floodplainwoodland orwet woodland
flow leakybarriers
Bed renaturalisation armour/ gravel augmentation
There are 13 landowners in the catchment. Woodbury Salterton RRC is not within a UST catchment but is close to the UST Otter catchment. Through this WRT has engaged with farmers managing 21.5% of the total farm area. The 3 largestlandowners own 40.21% of the catchment.
WRT has also engaged the catchment community through citizen science investigations.
The local community appears to already have measures to increase the climate resilience of Woodbury Salterton. Details of the village’s resilience group and neighborhood plan can be found on slide 18. The Woodbury Salterton Resilience Group is a Facebook group for local residence to get involved and help tackle the impacts of climate change in their area.
There is an initial indication of a willingness to work from local land managers, but the case would need to made to align with their business plans.
It is noted that there is very little or no uptake of environmental schemes in the catchment and so with the changing incentives at present; this may be opportunity to look at more environmental benefits from the land use.
As well as the opportunities identified in the previous section, there may be opportunities for you to get involved as an individual.
WRT runs a Citizen Science Investigation (CSI) team of volunteers across the south west, whereby volunteers receive a testing kit and training to procure water samples from a watercourse. Westcountry CSI aims to engage people with their local environment, and produce water monitoring data that can identify pollution events quickly and target improvement work.
There three active CSI sampling sites in the urban area of Woodbury Salterton. There may be the potential for more sampling sites further upstream on any of the tributaries if there is suitable access to the water.
For more information about Westcountry CSI, including instructions on what’s involved and how to sign up, visit our website at wrt.org.uk/westcountry csi
Another opportunity for you to get involved in is the Riverfly Partnership’s Anglers’ Riverfly Monitoring Initiative (ARMI). This recognises that anglers are very well placed to monitor river water quality and facilitates communication between them and their local Environment Agency contact.
There are no riverfly survey sites within the micro catchment, but, as with CSI sites, it may be possible to start a new site if there is suitable access to the water and with communication with the Environment Agency.
For more information on ARMI, visit their website at riverflies.org/anglers riverfly monitoring initiative armi
Multiple reasons for the possible causes and remedies for flooding in the micro-catchment for the Woodbury Salterton Stream have been mapped in this study, as have other factors that are key to consider when making NFM decisions.
It is likely that channel infrastructure causing pinch-points is the main cause of flood risk, and since the flood event in 2008 there is community led active management to reduce this risk.
The next steps would be to investigate realistic flood risk further under future extreme weather scenarios. This would be required to justify the extent of the problem and to justify investment in interventions in this catchment.
If investigations concluded higher risk than perceived by the local community then following steps would be to engage and empower the community in the catchment to discuss and work towards building flood resilience through some of the opportunities mapped in the previous pages. It is imperative that property owners and land owners share perspectives and work together to find solutions agreeable to all sides. Some opportunities may provide secondary benefits towards improving the catchment’s WFD chemical status.
The processforidentifying the highest impacting locationsof NFMmeasures acrossDevonand Cornwall involved several stepsin a Geographic InformationSystem (GIS).The first step was to identifywatercourseswithan upstream watershed less than 10km2 and less than 5km2 in size,then to identifypropertiesadjacentto these watercoursesthat overlapped withthe EnvironmentAgency’s (EA) fluvial “Flood Zone 2”dataset.Next,pour pointswere placed onthe watercoursesin front of the furthest downstream flood riskproperties.These pourpoints were thenused to delineate the upstream micro catchmentboundaries.A total of 1270micro catchmentswithpropertiespotentiallyatriskwere identified across the 2counties.
For every micro catchmentidentified,itsarea wasdividedbythe number of flood risk propertieswithinitto calculate the area perproperty atrisk foreach micro catchment.Those withthe lowestarea perpropertyindicated higherpotential forsmall scaleNFMmeasuresto benefitthe greatest number of flood riskproperties.
Lastly,additional factors,suchas WFD classificationsand previousWRT engagementwithfarmers,were considered alongsidethe area perproperty atflood risk toprioritise a small numberof micro-catchmentsto targetcommunityengagementand NFM delivery.
➢
Due to the large geographic extent(Devonand Cornwall)and the manual elementof the mapping (bothcausing the mapping processto be time consuming),the resolution/accuracyof some datasetsmaybe compromised.
➢ The buildingsdataset(OS VectorMap Buildings) isnotasaccurate as OS MasterMap some propertiesare amalgamatedinto a single polygon and very small buildingsare notshown. Therefore propertiesatriskof flooding maybe underestimated.
➢ Potential flood riskisidentifiedbyselecting building polygonsthatintersectthe flood zones;no detailed local information (e.g.drainage or defences) ormodelling hasbeenused.
➢
The spatial resolutionof the topographydata iscoarse (50m).Thisisused to calculate the upstream catchmentarea foreach communityat-risk. Therefore,some errors mayoccur (additionsoromissions) whenidentifying micro-catchments.
➢ The mapping method involvesanelementof manual validation,whichhasthe potential to be subjective and/orpossible errors.
Once catchmentswere modelled and the informationtabulated to show theoretical flood risk in conjunctionwithWFD failures, a systematic approach to ground truthing was adopted.
Catchmentsthat were perceived to have elevated water quality and water quantity risks were discussed with local land management advisors and regulators to determine if the modelled risk was likely to be correct.
Upon a theoretical, or desk based ground truthing,the catchmentswere then surveyed using a rapid walkover survey to observe run off pathways and confirm if useful managed interventions could be implemented to reduce flood risk locallyand improvewater quality in the process.
A further modelling process using SCIMAP was undertaken to identify high risk run off pathways of the specific micro catchmentbeingsurveyed to assist the surveyor in locating issues within a <10km2 area.
Where possible, surveyors reacted to high rainfall predictions and went out to observe the catchmentwhen the conditions were right.
Walkover surveys were undertaken noting observations about surface water run offand taking photographs of key areas and issues. All walkovers aimed to provide:
Dry or Wet weather photos,
Identify stakeholder PROVIDERS where NFM can be instigated,
Identify stakeholder BENEFICIARIES by property and number people,
Establish opportunities in each catchmentand feasibility of action.
Georeferenced photos were taken to provide a visualoverview of issues, opportunities, and as general reference notes.
Where issues and opportunities existed, further investigation was made or attempted to establish the realistic chances of further action. This was achieved by either speaking withthe localcommunityor contacting communitygroupsor key landowners.
All 1270 micro catchments with properties potentially at risk were identified across the 2 counties.
CIRIA (Slide 43)
The Construction Industry Research and Information Association’s (CIRIA) Natural Flood Management Manual (C802) (PDF)
FRFW (Slide 32)
Statutory guidance for Farming Rules for Water (FRFW) (Webpages)
https://www.ciria.org/Books/Free_publications/C802F.aspx
https://www.gov.uk/government/publications/applying the farming-rules-for-water/applying-the-farming-rules-for-water
SEPA NFM Handbook (Slide 32)
Handbook describing various natural flood management interventions and case studies (PDF)
https://www.sepa.org.uk/media/163560/sepa-natural-floodmanagement-handbook1.pdf
Dataset Source AttributionStatement
Agricultural Land Classification Natural England © Natural England copyright. Contains Ordnance Survey data © Crowncopyright anddatabase right2022.
Air Quality Management Areas UKAIR
© Crown copyright and database rights licensed under Defra's PublicSectorMapping Agreementwith Ordnance Survey(licence No. 100022861) and the Land andProperty Services Department(Northern Ireland) MOU206.
Ancient Woodland Natural England © Natural England copyright. Contains Ordnance Survey data © Crowncopyright anddatabase right2022.
AONB Natural England © Natural England copyright. Contains Ordnance Survey data © Crowncopyright anddatabase right2022.
Areas Benefitting fromFlood Defences EnvironmentAgency
© EnvironmentAgency copyrightand/or database right 2018. Allrights reserved.Some features of this mapare based on digital spatial data from the Centre for Ecology & Hydrology,© NERC (CEH) © Crowncopyright anddatabase rights 2018Ordnance Survey 100024198
Bathing Water Monitoring Locations EnvironmentAgency © EnvironmentAgency copyrightand/or database right 2015. All rights reserved.
Country Parks NaturalEngland © Natural England copyright. Contains Ordnance Survey data © Crowncopyright anddatabase right2022.
Countryside StewardshipScheme Agreements
Natural England © Natural England copyright. Contains Ordnance Survey data © Crowncopyright anddatabase right2022.
Crop Map of England Rural Payments Agency © Rural Payments Agency
CRoW Access Land NaturalEngland © Natural England copyright. Contains Ordnance Survey data © Crowncopyright anddatabase right2022.
CRoW RegisteredCommonLand NaturalEngland © Natural England copyright. Contains Ordnance Survey data © Crowncopyright anddatabase right2022.
DetailedRiver Network EnvironmentAgency © EnvironmentAgency Crown copyrightand databseright 2022.
Drinking Water Safeguard Zones (Ground Water)
Drinking Water Safeguard Zones (Surface Water)
EnvironmentAgency © EnvironmentAgency and/ordatabase rights. Derivedfrom BGSdigital data under licence from British Geological Surveycopyright NERC.
EnvironmentAgency
© EnvironmentAgency copyrightand/or database right.All rights reserved. Derived fromBGS digitaldata under licence fromBritish Geological Survey ©NERC. Derived fromCentre of Ecology andHydrology data
Flood
Hillshade
Historic
by
in part from data
SPAs
