Tiverton
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 6).
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 Cottey Brook, is one of those prioritised micro catchments.
The micro-catchment for Cottey Brook is 163 ha and highlights 5 properties potentially at risk fromsurface water flooding, many of these are in Tiverton. 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 FrameworkDirective (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. There is therefore little or limited opportunity to effect localised flood improvement, although the ability to mitigate part of a larger flood riskdownstream (less localised) should not be discounted. Additionally, the walkover presented some opportunity to deliver or contribute towards WFD (Water FrameworkDirective) improvements in the wider catchment.
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 Exe catchment that would ultimately benefit the local community. The NFM opportunities identified in this report include riparianwoodland planting and other habitat creation surrounding existing habitats across the catchment to slow surface water flow into watercourses and enhance habitat networks. More areas of land entering into an agri environment scheme agreement could also contribute to improved soil health and biodiversity in the absence of significant habitats. The flatter, downstream, part of the catchment could be considered for attenuation, but the proximity to the urban environment will need to be carefully considered when designing NFM measures and this could present a major opportunity for community engagement to facilitate delivery.
This documentisa study for causesof flooding,priorityconsiderations,and opportunitiesforNFMin the micro-catchmentfor CotteyBrook, covering some of the Tivertonurban 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 24preparatoryinvestigationsonprioritised micro 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 the CotteyBrookwhich is shown in red.
Themicro-catchment was selectedin theGISmodelling step becauseit contains alarge numberof properties in Tiverton that are potentiallyat flood risk.
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 5 buildingspotentiallyatriskout of 40 in the catchment, approximately12.5%of them.
The catchment’ssize of 1.63km2 givesanarea of 0.33km2 perbuilding atrisk.
The waterframeworkdirective (WFD)statusinthe widerExe (Barle to Culm) catchmentis Moderate.
If property ownersare willing to workwithland owners and vice versa, then small scale NFMmeasuresupstream in the catchmentcould have the potential to benefita small numberof propertiesand improve waterquality.
The micro catchment covers the west urban area of the town of Tiverton as well as several farms. The micro catchment forms the watershed for the Cottey Brook that flows east northeast through Tiverton where it joins the river Exe. The total river length present in the catchment is approximately 4.2km. The micro catchment falls within the Mid Devon District Council and is administered by Tiverton Town Council.
The map on the right shows the steepness of slopes. The town of Tiverton has a significantly flatter topography than the rest of the catchment. The micro catchment has steep sides to the north of the river while the south bank has large, flat surfaced, sloped fields that drain into the main stream and its tributaries. As the stream reaches the town the slope of the north bank becomes lessened and a flatter plain emerges. The town is the flattest partof the micro catchment.
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 improved grassland, accounting for 56% of the catchment, followed by woodland that covers another 30.5%. Most of the woodland is broadleaved, with Hensleigh Wood being the largest woodland in the west of the catchment. There is a singular patch of coniferous woodland in the northwest.
Tiverton makes up the majority of the remaining area, covering 10% of the micro catchment. One large field of arable and horticultural land is identified south of the stream.
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 arable land use marked on the map appears to have been changed to grassland for the 2022 season.
The catchment area funneling down to Tiverton is relatively small, but it is very steep and therefore could have a very ‘flashy’ response to heavy rainfall.
There is a reasonable amount of broadleaved woodland in the catchment area which should help intercept rainfall and promote infiltration where soils allow.
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.
Roughly half of the Tiverton buildings in the catchment are classed as “Relatively high” in the Neighbourhood Flood Vulnerability Index (NFVI), meaning that they are slightly more vulnerable to losses in wellbeing from a flood event than the UK average. The center and south of the catchment is classed as “Average”, meaning they are no more or less vulnerable than the UK average. The rest of the catchment is classed as “Relatively low” and are therefore slightly less vulnerable.
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, half of the Tiverton buildings are classed as “Moderate” in the SFRI for river and coastal flooding. This increases to “High” in a 2 degree temperature increase by the 2050s scenario, and increases further to “Very High” in a 4 degree increase scenario. The centre and south of the catchment is classed as “Low” in all scenarios. The rest of the catchment is classed as “Exposed” in all scenarios but the NFVI remains below the UK mean.
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.
There are no recorded flood outlines in the catchment, but this doesn't mean it has never flooded. It is possible that flood waters have receded before a flood outline could be recorded. News articles from Devon Live describe flood events in Tiverton in March 2022 due to flash rains, and July 2020 which resulted in Chapel Street flooding (outside of the catchment). There are currently some short lengths of natural high grounds either side of the Cottey Brook in Tiverton that act as flood defences. These are owned by private individuals, were last inspected in May 2021, and are next due to be inspected in September 2022.
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. This extends the whole length of the Cottey Brook to its source in Hensleigh Wood.
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 nearest water 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. This identifies several depressions in the west of the catchment adjacent to the Brook’s tributaries.
The flood riskdoesn’t appear to match the modelled flood risk discussed in previous pages and there appears to be less flood risk than anticipated. During the walkover residents couldn’t recall any flood events.
That is not to say that the modelling is incorrect when including climate change scenarios, but the present conditions appear to be lower probability.
Tiverton certainly suffers some flood risk from the main River Exe and the community appears to be proactive in managing the riskand supporting any higher risk areas.
Tiverton Town Council have an active Flood and Snow Warden who posts warnings and updates about flood risk on social media since February 2020. There are no mentions of risk in the Cottey Brook area to date.
Sustainable Tiverton is a local group with aims to encourage local projects that combat global warming and environmental damage; by supporting community groups to set up, run activities and events, get publicity, and work with others nearby. Their focus is on biodiversity, reducing carbon dioxide emissions, building climate resilience.
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, priority wetlands, or aquatic habitats in the catchment. However, it overlaps slightly in the northeast with the Mid Devon Nitrate Vulnerable Zone (NVZ) for Ground Water.
The catchment falls within a wider Drinking Water Safeguard Zone for Surface Water, identified as being at risk of failing the drinking water protection objectives due to contamination by pesticides.
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 with restricted water for licensed water abstraction (left map) but is bordered to the west by an area is not available for licensed abstraction
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 bottom half of the catchment scores relatively low ay 0.466 on the VHI (right map), indicating slightly low risk to plant life from drought stress, but the north of the catchment scores higher at 0.586 inferring above average risk.
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.
However, there are no designated sites or habitats present within the Tiverton micro catchment.
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 Tiverton area and areas proximal to the A361 have a relatively high concentration of air particulate matter of 6.79PM2.5 from emissions, but this falls to 6.39PM2.5 towards the east of the catchment where there are comparatively fewer roads.
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.
The catchment borders a small greenspace in its northeastern corner at the catchment outlet, located within Tiverton. The greenspace is Westexe Recreation Ground and hosts a bowling green, gazebo, playing field and playground. Another greenspace nearby and just outside of the catchment boundary features a playing field and a children’s play space.
No Public Rights of Way (PRoW) or Countryside Right of Way (CRoW)
Lands are present within the catchment.
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.
Multiple patches of broadleaved and coniferous woodland are present in the centre and west of the catchment, with Hensleigh Wood being the most prominent. Much of these patches are deciduous woodland priority habitats, and coniferous woodlands are interspersed amongst these. Many of these woodlands are adjacent to the Cottey Brook or its tributaries.
A central section of Hensleigh Wood is also designated as an ancient deciduous woodland.
There is also a small patch of mixed mainly conifer woodland in the very north of the catchment.
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 and on the edge of the larger Exe (Barle to Culm) WFD river waterbody catchment, accounting for 2% of it’s area.
The river Exe (Barle to Culm) is overall classed as Moderate meaning it is failing WFD regulations. It is currently failing on both ecological and chemical status. 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 Exe (Barle to Culm) is not assessed for Fish but is classed as Good for Phosphate and either Good or High for most other biological quality elements. However, it is only classed as Moderate for Macrophytes and Phytobenthos. The overall ecological status is therefore Moderate, and the waterbody is consequently failing WFD regulations on ecological grounds.
It is failing for Macrophytes and Phytobenthos because of poor soil, pesticide, and nutrient management, riparian and in river activities (including bankside erosion), domestic septic tanks, farm infrastructure and sewage discharges by South West Water.
The waterbody is classed as Good for nearly all chemical classifications, except for mercury and its compounds, and PBDEs, where it is classed as Failing. The waterbody’s overall chemical status is consequently Failing and is 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/WaterBody/GB108045015050
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 town of Tiverton and smaller dwellings as non vegetated with the majority of the catchment classed as grassland and clusters of trees. The map shows maize is grown in a field in the centre and on the north western corner of the catchment. However, the maize in the centre appears to have been changed to grass in 2022.
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 Hallsworth 2, followed by Neath in the north. Hallsworth 2, Manod, and Conway can all be found on the eastern edge of the catchment around Tiverton.
Soil health in the catchment appeared adequate through general observation and further investigation would be needed to conclusively determine if the fertility was correctly calculated or if there is underlying issues with compaction.
The initial walkover was not carried out by a soil expert, but there was some fine clay content in the soil. Clays can be of benefit in soils but can also introduce extra riskas the finer sediment can be highly mobile and susceptible to erosion. It would be advantageous to look closer at soil health for the benefit of food production as well as natural function and water quality in this catchment.
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 majority of the catchment is comprised of claystone and mudstone, with a small area of Breccia in the northeast corner.
The walkover didn’t uncover any initial suspicion of groundwater 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 are no recorded pollution incidences in the catchment but there is one source of consented discharges. Located west of Tiverton but proximal is a sewage discharge attributed to St. Pauls Vicarage and Pentlands. The type of discharge is recorded as final/treated effluent and is discharged into a soakaway with the aim of infiltration into the soil. Another consented discharge site is located just outside of the catchment outlet. This is for the paddling pool at West Exe Recreation Ground discharging the pool water into the Cottey Brook.
Licensed water abstraction points may serve as sources of risk to ground water quantity and availability. There is a water abstraction point located within Tiverton on the Cottey Brook at the catchment outlet. This abstraction site is located within the flood risk zone. The licensed abstraction is for Mid Devon District Council for industrial, commercial, and public services.
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 skews the modelling process and the 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.
A strip grazing layout was noted during the survey.
If this practice were to take place in a wet February on such a steep slope then the field may be susceptible to compaction, erosion and rapid run off of poor water quality.
No animals were present at the time.
Bare soil and stubble was noted in a neighbouring catchment which shows standing water, run off and lack of infiltration.
This wasn’t observed in the Cottey Brook, but the similar soil means that a closer look at soil health could be advantageous to water quality and infiltration.
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. The greatest opportunity identified by these WWNP datasets for the catchment is tree planting, both throughout the wider catchment and directly along the stream’s banks. Areas that have been excluded from tree planting are where trees are already present which are explained on page 40. The tree planting opportunities spread over the rest of the catchment, including some areas within Tiverton.
In addition, there are opportunities to construct smaller scale runoff attenuation features upstream in the existing woodlands 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 small areas of floodplains upstream in the catchment in Hensleigh Wood.
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).
Much of the agricultural area is classed as 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.” The exceptions within the Network Enhancement Zone 2 area woodland areas or within the Tiverton town boundary.
There is already a significant amount of woodland in the catchment, and creation of other types of habitats, such as meadows, could contribute considerably to ecological diversity.
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 land parcels under an agri environment scheme currently in the catchment. However, WRT may be able to give guidance and facilitate applications to schemes if land owners are interested.
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.
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 the central woodlands and the Tiiverton urban area. 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. The areas around the woodlands on the catchment edge and adjacent to Tiverton have few to no constraints and would be ideal for tree planting and other habitat creation.
The agricultural land grade is Grade 3 across the catchment which is considered average and there is therefore no high grade land present. 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.
Given current land use, there is also a reasonable amount of cross slope boundaries with hedges, and trees along the river. There could be more benefit if greater margins and buffers to the watercourse were created, and one or two fields on the southern slopes could see benefit from being made smaller with contour boundaries added.
Due to the reduced flood risk perceived during ground truthing, identifying multiple opportunities for NFM interventions was not done in great detail.
Opportunities do exist in the catchment, but the greatest changes could come from a change of land use when dealing with such a steep sided valley.
There is already a reasonable percentage of woodland in the catchment, but more woodland would be of benefit.
benefit
attenuation
water and climate
rapid surface water run off and
infiltration will provide better
resilience at the same time
risk throughout the catchment
may be
Cottey
the opportunities are limited in this catchment
to the steep sides and lack of floodplain in this v shaped
but where multiple smaller interventions are possible to give a cumulatively significant benefit, it is worth exploring further.
There are 11 landowners in the Cottey Brook catchment. WRT has engaged with farmers managing 4.65% of the total farm area under Upstream Thinking 3. WRT has not engaged the catchment community in other projects.
The local community appears to already have measures to increase the climate resilience of the catchment name. Details of the village’s flooding groups can be found on slide 18. There is also a community response group called Sustainable Tiverton. This is for residents of Tiverton to communicate about local solutions to face the climate emergency. They mainly focus on the areas of biodiversity, reducing carbon dioxide emissions, and building climate resilience.
More information on Upstream Thinking activities on the Exe catchment can be found in regular newsletters on the WRT website.
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 are no active CSI sampling sites in the catchment. However, there may be the potential for new sampling sites along the main Cottey Brook in Tiverton and further up the catchment in 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 reasonsforthe possible causesand remediesforflooding inthe micro catchmentforthe TivertonCottey Brookhave been mapped in this study, as have otherfactorsthat are key to considerwhen making NFM decisions.
It islikelythat a combinationof causesare at playhere contributing to there being propertiesatflood risk,including the topography,land use and absence of habitatsincertainareasof the catchment, howeverthe flood riskmay not be as highas modelled incurrentcircumstances. Thatis not to saythat flood risk won’t rise in the future, and that interventionswill help future proof againstdroughtand waterqualityaswell as flooding,butinvestmentmayneed to be justified further.
Benefitsarising from thiscatchmentmay also be realized ina largercumulative contextelsewhere downstream.
Giventhe low perceived riskthat has come to lightasa result of the survey and alternative areaswhichhave shown higher risk factors,it is recommended thatno further actionbe taken in this catchmentatthis time unless more informationissupplied thatcauses re evaluationand increased concern.
The nextsteps could then be to engage and empowerthe community inthe catchment to discuss and worktowardsbuilding climate change resilience throughsome of the opportunitiesidentifiedinthe previouspages.It is imperative thatpropertyownersand landownersshare perspectivesand worktogether to find solutions agreeable to all sides.Opportunitieswillprovidesecondarybenefitstowardsimproving the catchment’s WFD ecologicalstatusbutmust be proportional to the risk.
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 databse right 2022.
Drinking Water Safeguard Zones (Ground Water)
EnvironmentAgency © EnvironmentAgency and/ordatabase rights. Derivedfrom BGSdigital data under licence from British Geological Surveycopyright NERC.
Drinking Water Safeguard Zones (Surface Water) EnvironmentAgency
© EnvironmentAgency copyrightand/or database right.All rights reserved. Derived fromBGS digitaldata underlicence fromBritish Geological Survey ©NERC. Derived fromCentre
Flood
Flood
Historic
by
in part from data
SPAs
