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 Alren Stream, is one of those prioritised micro catchments.
The micro-catchment for the catchment name is 898ha and highlights 5 properties potentially at riskfrom surface water flooding, many of these are in the downstream area with further flooding known below the study area. 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, was found to have localised flood risk during heavy rain events although further investigation is needed to ascertain if more properties are actually at risk. There are definite opportunities to effect localised flood improvement and the ability to mitigate part of a larger flood risk downstream (less localised) will also be beneficial. Additionally, the walkover presented opportunity to deliver or contribute towards WFD (Water FrameworkDirective) elemental 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 Tamar 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 may also contribute to improved soil health and biodiversity in the absence of significant habitats. In addition, there are major opportunities for floodplain reconnection and runoff attenuation on large and small scale 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 pages36 38.
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 theAlrenStream whichis shown in red.
Themicro-catchment was selectedin theGISmodelling step becauseit contains alarge numberof properties in Old Mill 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 201 in the catchment, approximately2.5%of them.
The catchment’ssize of 8.98km2 givesanarea of 1.8km2 perbuilding atrisk.
The waterframeworkdirective (WFD)statusinwidercatchmentis Moderate
If property ownersare willing to workwithland owners and vice versa, then small scale NFMmeasuresupstream in the catchmenthave the potential to benefita large numberof propertiesand improve water quality.
The micro catchment covers the villages of Stoke Climsland, Old Mill, Venterdon, Downgate and Kelly Bray. The micro catchment forms the watershed for the Alren stream that flows west to east to the south of Stoke Climsland through Old Mill. There are several tributary’s originating in the north and south, the longest of which flows northward from Kelly Bray and joins the Alren Stream just before Old Mill. The A388 main road runs north to south near the western boundary of the catchment. Overall, the micro catchment falls within the Stoke Climsland Civil Parish
The map on the right shows the steepness of slopes. There is a steep valley following the length of the Alren stream where it passes through Old Mill as well as along the length of the tributary which flows south towards the village of Kelly Bray.
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 58% of the catchment, followed by woodland which covers another 17%. Patches of broadleaved woodland and fields of arable and horticultural land are scattered throughout the catchment. There is a significant area of coniferous woodland along the Alren Stream east of Old Mill and a large area of heather in the southeast corner of the catchment. There are several small urban/suburban areas scattered throughout the catchment indicating the villages mentioned in slide 11.
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.
Any discrepancy is very minor or probably due to seasonal change between grass and arable.
The catchment is very agricultural in nature, rearing mostly beef, sheep and dairy, and is home to one of the only agricultural colleges in the region as well as the ‘Future Farm’ of West Coombeshead
The majority of fields are given to grassland and arable, with interspersed treelines more in the south of the catchment. Some valley floor areas appeared to be wet in places and of lower agricultural value which may present future opportunities for working with natural processes.
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.
All of the buildings in the catchment are classed as “Relatively low” in the NFVI, meaning that they are slightly less vulnerable to losses in wellbeing from a flood event 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 land around the village of Kelly Bray is classed as “Low” in the SFRI for river and coastal flooding, though this reduces in future projected scenarios of 2 and 4 degree temperature increases by the 2050s to “Exposed” but the NVFI remains below the UK mean. The rest of the catchment are classed as “Exposed” but below the UK mean for NFVI in all scenarios.
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 Alren Stream has previously flooded in November 2000 where channel capacity was exceeded with no raised defences. 3 of the 5 buildings identified as potentially at flood risk on page 8 fall within this recorded flood outline. There are currently a series of linear natural high grounds, an engineered high ground, and a demountable defence that all act as flood defences along the Alren Stream, though they are not completely contiguous. These are owned by a mix of private individuals and the Environment Agency, were last inspected in May 2021, and are next due to be inspected in August 2023.
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 covers the main Alren Stream, a large area in the catchment’s centre, and the length of it’s northern tributary from Venterdon.
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. It is the only modelled risk of flooding along the tributaries that feed into the Alren Stream.
The survey confirmed that the modelled flood risk appears to be accurate although there was more localised flood risk noted near water pathways that weren’t watercourses such as on roads or as a result of rapid run off.
There is a pinch point adjacent to the Stoke Climsland to Kelly Bray road which may have been influenced by historic channel management. Other pinch points in the watercourse exist from historic infrastructure such as millponds or mining ponds.
There is known flood riskdirectly downstream of this catchment which any measures taken up will help alleviate.
Community Stakeholder groups exist in the area and could be important in helping shape any projector interventions within the catchment.
Stoke Climsland Climate Change Action Group ‘SCCCAG is a community based group which has been set up following the Parish Council declaration of Climate Emergency. It is intended to provide opportunities for parishioners to assist in the goal of achieving carbon neutrality by 2030. SCCCAG has a role to play in providing advice for parishioners, developing projects to reduce the carbon footprint of the parish, sourcing funding streams for climate related projects and providing manpower in the form of volunteers.’
Local events around flooding that have happened in the last year or planned for the future:
• Workshop on being Flood Resilient Stoke Climsland 09 10 2021, with Calstock Parish Council
Other projects that may be able to help with flood alleviation that have been active or are active in the area include:
• Tamara Landscape Partnership is operating here and in the wider Tamar catchment.
• Cow to Catchment Project with Duchy College.
• Upstream Thinking project focusing on improving water quality in the Tamar catchment.
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. It also does not fall within a Nitrate Vulnerable Zone (NVZ).
However, the catchment falls within a wider Drinking Water Safeguard Zone for Surface Water, identified as being at riskof failing the drinking water protection objectives due to contamination by pesticides.
It is also important to note that there is a historic landfill site in the east of the catchment close to the Stream. 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 that is currently 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 majority of the catchment (area below the village of Stoke Climsland) is scored very high at 0.803 in the VHI (right map), indicating significantly high risk to plant life from drought stress. The area surrounding Stoke Climsland scores relatively lower at 0.575, but is still at 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.
The eastern edge of the catchment falls with the Tamar valley Area of Outstanding Natural Beauty. Kit Hill Local Nature Reserve is located in the south eastern corner of the catchment, within the Tamar AONB boundary.
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 concentration of air particulate matter from emissions. The area surrounding the A388 main road in the east of the catchment has slightly higher concentrations of 6.41PM2.5.
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.
The catchment boasts a large greenspace in its southeast corner at Kit Hill. This area is also a country park and Countryside Right of Way (CRoW) Access Land.
There are several other smaller greenspaces located within the villages of Stoke Climsland, Venterdon and Kelly Bray. The Stoke Climsland and Venterdon greenspaces comprise two playing fields, two sets of religious grounds, a children’s play space, and some allotments. The Kelly Bray greenspaces feature a playing field, a children’s play space, and a cemetery.
There are a number of public rights of way (PRoW) throughout the catchment, particularly around Stoke Climsland, Venterdon, Holmbush, and Old Mill.
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 woodland are scattered throughout the catchment. All off these patches are also deciduous woodland priority habitats. There are several large areas of coniferous woodland, particularly around Old Mill either side of the Alren Stream, and in the southwest of the catchment.
There is a large area of lowland heathland in the southeast corner at Kit Hill Country Park. There are also several traditional orchards dispersed throughout. A small strip of calaminarian grassland is present in a residential garden north of Kelly Bray.
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).
The catchment sits on the western edge of the larger Lower River Tamar waterbody catchment, accounting for 13.5% of it’s area.
The Lower River Tamar 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.
It should be noted that there are two Environment Agency (EA) Water Quality Monitoring (WIMS) sites in the catchment; one on the tributary south of Stoke Climsland, and the other on the Alren Stream at Old Mill.
The Lower River Tamar is classed as Good for Phosphate, and Good or High for most other ecological quality elements. However, it is only classed as Moderate for Copper and Macrophytes and Phytobenthos. The overall ecological status is therefore Moderate and thereby failing WFD regulations on ecological grounds.
It is failing for Copper due to an abandoned mine. It is failing for Macrophytes and Phytobenthos because of poor livestock, nutrient, and soil management, as well as riparian/in river activities (including bankside erosion) and continuous sewage discharge by South West Water.
The waterbody is classed as Good for most chemical classification items, except for the previously mentioned Mercury and its compounds and PBDEs, with the addition of Perfluorooctane Sulphonate (PFOS). It is classed as Failing for all 3. The waterbody’s overall chemical status is consequently Failing and is therefore failing WFD regulations on chemical grounds as well as ecological.
The reason for failure for PFOS is currently pending investigation.
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/GB108047007860
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 villages mentioned in slide 10 as non vegetated with the majority of the catchment classed as grassland with various clusters of trees.
Maize and wheat are grown in the catchment’s centre and in various fields on the northern boundary. Barley is grown in multiple fields along all boundaries, except for the southeast. A few fields of winter oats are present north of Kelly Bray, and various fields of spring peas are in the catchment’s centre and southwest of Stoke Climsland.
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 Denbigh 1 with areas of Trusham in the north around Stoke Climsland and Venterdon, and Sportsmans on the southern boundary. The area around Kit Hill is composed of Moor Gate, and Manod can be found in the southwest.
The initial walkover was not carried out by a soil expert, but the soil type throughout the catchment appeared rich and loamy, possibly with a little more diversity in the wetter valley bottoms. Soil health in the catchment wasn’t determined and further investigation will be required into the structure and composition.
The majority of land use was livestock oriented or arable associated with livestock. This could mean that soil health is worth investigating to help determine and possibly improve both the natural function of the soil and the fertility for production.
Anecdotal evidence would suggest there could be some soil issues as some coloured water was observed washing down the road during light rain during the survey.
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 northwest of the catchment is comprised of weakly metamorphic rocks and sandstone, whilst the south and east are largely argillite slate. Along the Alren stream and its tributary is riverine clay and floodplain sands and gravel with a band of sandstone and mudstone surrounding the main river channel. There is a small area comprised of tuff to the southeast of Stoke Climsland, and both tuff and basalt northeast of it. The south east corner at Kit Hill is mostly granite. There is also an area with basalt rock geology on the western boundary of the catchment.
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 two reported pollution incidents within the catchment. There was a Category 1 Major incident in the Alren Stream’s southern tributary just north of Kelly Bray in September 2009 from crude sewage. This was also classed as a Category 3 Minor pollution incident to air and land, as opposed to Category 4 (No Impact).
There was a Category 2 Significant incident in a small tributary just north of Old Mill in October 2010 from slurry. This was also classed as a Category 3 (Minor) incident to air and land.
There are six sources of consented discharges in the catchment. At the furthest downstream site at Old Mill, South West Water (SWW) have consented discharges for sewage from both a pumping station and a sewer storm overflow tank into the Alren Stream. SWW’s site further upstream is for a waste water treatment works discharging treated effluent and sewer storm overflows into the tributary. The western consented discharge is for domestic properties discharging treated effluent into a soakaway. The southern discharge site is for council houses run by Cornwall Council also for discharging treated effluent into a soakaway. Licensed water abstraction points may serve as sources of risk to ground water quantity and availability. However, there are no water abstraction points present in this catchment.
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 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 crop timing in the catchment can result in stubble or bare soils as the wetter seasons begin.
If soil compaction is an issue then rapid run off of surface water and soil may occur.
Some maize is yet to be harvested (end Sept.).
Downstream, the channel is heavily incised and disconnected from the floodplain.
The downward erosion of the channel has stripped the river bedload down to smooth bedrock which may increase the water speed to areas already vulnerable to flooding.
Steep valley sides create rapid runoff.
The river passes through an established wooded floodplain which may present opportunities to deal with reconnection of the river to slow the flow.
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 46.
The greatest opportunity identified by these WWNP datasets for the catchment is floodplain reconnection in the centre of the catchment at the confluence of the tributaries, as well as further up the tributaries in the north by Stoke Climsland, and along the main Alren Stream to the catchment outlet.
In addition, there are opportunities to construct smaller scale runoff attenuation features in or near the streams and the 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, there are opportunities for riparian woodland planting along all of the tributaries where there is none currently. This includes a wide area between Old Mill and the largest floodplain reconnection opportunity.
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 priority habitats to create habitat networks across the landscape.
Habitat restoration and creation is known to occur in some areas at Kit Hill.
Immediately north of them is Restorable Habitat defined as “Areas of land, predominantly composed of existing semi natural habitat where the primary habitat is present in a degraded or fragmented form, and which are likely to be suitable for restoration.”
Just outside this and elsewhere in the catchment’s centre surrounding the patches of deciduous woodland and traditional orchards 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.”
Elsewhere in the south and east 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.”
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. Some of the land parcels in the southeast at Kit Hill are under either Environmental or Countryside Stewardship Scheme Agreements, or both.
There may be opportunities for land owners in the restof the catchment to enter agri environment schemes. Habitat creation in the centre and south in particular may be facilitated in the Habitat Enhancement and Expansion Zones as identified on page 32.
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 Tamar Valley AONB designation (see page 23) in the east may provide administrative challenges, as will the woodlands, heathlands, and traditional orchard priority habitats. However, there is still the opportunity to improve these habitats and designated sites 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 much of the southwest, the area surrounding the Alren Stream at the catchment outlet, and Kelly Bray. 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 north and western areas of the catchment on the other hand have few to no constraints.
The agricultural land grade is grade 3 across mostthe of catchment which is considered average. This falls to grade 4 in the south and west, and grade 5 at Kit Hill which are considered poor and very poor respectively. There is therefore no high grade land present.
There are two scheduled monuments present, both north of Kelly Bray. The larger left hand monument is “Holmbush Mine: Hitchen’s Shaft Complex” and the smaller right hand monument is “Holmbush Mine: Windsor Lane rotative engine house with adjacent boiler house, loadings and platform”. The latter is approximately 50m away from the small strip of calaminarian grassland priority habitat.
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.
There are two larger coniferous woodlands in the catchment with some mixed age trees.
If the opportunity existed, some native and mixed species trees could be integrated to provide buffer, attenuation, or even bioremediation (for mining legacy pollution) features.
Floodplain reconnection and biodiversity enhancement could take place downstream to attenuate water and pollution.
There are multiple opportunities in the catchment to reconnect the floodplain or create/restore new/existing ponds for the benefit of water storage, water quality and biodiversity.
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.
to
both new and
of existing. These features can have huge
quality, as well as extra freeboard
flow
and swales in permanent pastures are possible, and
coupled with a few trees, can provide multiple benefits to
be examined closely and could
many attenuation features which will particularly benefit the northern side of the catchment.
There are 27 landowners in the Alren Stream catchment. The 3 largest landowners own 43.09% of the catchment. WRT has engaged with farmers managing 19.55% of the total farm area under UST.
WRT has also engaged the catchment community in other projects such as through citizen science investigations.
The local community appears to already have measures to increase the climate resilience of the Alren Stream. There is also a community climate action group on Facebook called Stoke Climsland Climate Action Group (see page 18). This is for residents of the parish to communicate about local solutions to face the climate emergency.
There may be further opportunity to engage just downstream where additional benefits may be realized.
The Alren Stream catchment lies within the Tamara Landscape Partnership Scheme Area. WRT is also a partner in this is a 5 year projectthat aims to create a brighter future for the Tamar Valley and its communities.
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 is an active CSI sampling site as well as an available site on the Alren stream at Old Mill . There may be the potential for more sampling sites along the main Alren Stream as well as along its tributaries in the rest of the catchment 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 AlrenStream have beenmapped inthis study, as have other factorsthat 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. Asthe issues are likelyto be complex and arise from manysmallerpointsources providing a compounded orexaggeratedeffect;itisrecommended thatthe solutionsbe multiple and cumulative aswell.
It has beenestablished thatthere iswaterqualityissues through WFD failuresand problemswithsurface waterflooding,althoughthe full extent will need further investigation. Ithas also beenconfirmed thata solutionexists withinthe community,through a willingnessfrom the rural communityto make adjustmentsto the waythe land is managed.
There are a couple of large opportunitiesto reconnectthe floodplainand possiblyenhance the reconnectionwithfurther attenuationfeatures. This would need to be done in conjunctionwith the landowner’sagreementand fitwiththeir business planbut maybring many environmental benefitsincluding bioremediationfrom historic mining improving waterqualityaswell aswaterattenuation.
The nextsteps are to engage and empowerthe communityin the catchmentto discuss and work towardsbuilding flood resilience throughsome of the opportunitiesmapped inthe previouspages.It is imperative thatpropertyownersand landownersshare perspectivesand worktogetherto find solutionsagreeable to all sides.Some opportunitieswillprovide secondarybenefitstowardsimproving the catchment’sWFD 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 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
