Truro and Threemilestone
Development of a Sustainable Drainage, Biodiversity and Access Strategy
Stage 1 Scoping study and data collation
DRAFT 30 November 2007
Cornwall County Council
VOLUME 1 Main Text
This Stage 1 report is in 4 volumes:
Volume 1 Main Text Volume 2 Tables Volume 3 Figures Volume 4 Site data sheets
The report will remain in draft form until the end of December at which time it will be finalised. Any feedback on this draft can be incorporated into the final version.
Stage 2 of the work will report on the implications of the Stage 1 data analysis in terms of more specific proposals for SuDS. The Stage 2 report will also be finalised at the end of December.
CONTENTS CONTENTS ...... i 1 INTRODUCTION ...... 1 1.1 Background ...... 1 1.2 Objectives...... 2 1.3 Structure of this report...... 3 2 SUSTAINABLE DRAINAGE SYSTEMS (SuDS) ...... 4 2.1 Types of SuDS ...... 4 2.2 Guidance available for SuDS ...... 5 3. LEGISLATION/POLICY CONTEXT FOR BIODIVERSITY ...... 7 3.1 Biodiversity and Action Plans ...... 7 3.2 Legislation ...... 7 3.2.1 Biodiversity ...... 7 3.2.2 Statutorily Protected Sites ...... 7 3.2.3 European Protected Species...... 8 3.3 Carrick Local Development Framework Core Strategy ...... 8 3.4 Policy Guidance ...... 8 3.5 Green Infrastructure ...... 8 4 ACCESS ...... 10 5 DESCRIPTIONS OF THE SITES AND COLLATION OF DATA...... 11 5.1 Locations and extents ...... 11 5.2 Landscape Character ...... 11 5.2.1 Aerial photography ...... 11 5.2.2 Landscape character areas and description units ...... 11 5.3 Environmental Designations...... 12
i 5.4 Geology ...... 13 5.4.1 Solid ...... 13 5.4.2 Drift...... 13 5.5 Soils...... 13 5.6 Ecology...... 13 3.6.1 Broad Habitat...... 13 5.6.2 BAP Habitats ...... 14 3.6.3 BAP species ...... 15 5.6.4 Trees ...... 16 5.7 Biodiversity ...... 16 5.7.1 Trees and flowering plants ...... 17 5.7.2 Ferns and lower plants ...... 18 5.7.3 Insects ...... 18 5.7.3 Fish...... 19 5.7.4 Amphibians...... 19 5.7.5 Reptiles...... 19 5.7.6 Birds ...... 19 5.7.7 Mammals...... 19 5.8 Industrial...... 19 5.8.1 Mining...... 19 5.8.2 Fuel oil pipeline...... 19 5.8.3 Landfill ...... 20 5.9 Access...... 20 5.10 Topography ...... 21 5.11 Hydrology ...... 22 5.11.1 Watercourses ...... 22 5.11.2 Runoff analyses...... 23 5.11.3 Catchments ...... 24 5.12 Rainfall ...... 24 5.12.1 Average rainfall...... 24 5.12.2 Extreme rainfall events ...... 25 5.12.3 Flow gauging ...... 25 5.12.4 Extreme flow events ...... 25 5.12.5 Climate change impacts on rainfall...... 26 5.13 Flooding...... 27 5.13.1 PPS25 flood zones ...... 27 5.13.2 Flood warning ...... 27 5.13.3 Flood defence schemes ...... 28 5.13.4 Catchment Flood Management Plans ...... 28 5.13 Sewerage ...... 29 5.13.1 Problem drainage areas ...... 29 5.13.2 Sewerage network...... 29 5.13.3 Existing SuDS...... 30 6 DISCUSSION...... 31 6.1 Sustainable drainage systems ...... 31 6.3.1 Implications of the study...... 31 6.3.2 Data limitations...... 31 6.2 Biodiversity and ecology...... 31 6.3.1 Implications of the study...... 31 6.3.2 Data and survey limitations ...... 31 6.3 Access...... 32 6.3.1 Implications of the study...... 32 6.3.2 Data Limitations...... 32 7 REFERENCES ...... 33
ii 1 INTRODUCTION
1.1 Background Carrick District Council (CDC) is in the process of developing the Area Action Plan (AAP) for the Truro and Threemilestone area. The AAP identifies a number of sites for housing development within the AAP area.
Developments on greenfield sites will change the natural hydrology of the development site, as previously permeable and vegetated ground is replaced by impermeable surfaces such as roofs, hardstanding and roads. Development on brownfield and existing urbanised sites can provide opportunities to take action to reduce problems related to the control of rainwater runoff.
SuDS techniques are recommended through various guidance documents, such as Defra’s making space for water initiative and catchment flood management plans (ODPM 2003a, DEFRA 2004, EA 2004) for mitigating the hydrological impacts of development.
Truro and Threemilestone are in recognised problem drainage areas. The Environment Agency advice for such areas is to promote the use of sustainable drainage systems (SuDS) for controlling and managing surface water runoff from new development (EA 2004). Planning Policy Statement 25 on Development and Flood Risk (DCLG 2006) and its associated practice guide (DCLG 2007) also recommend the use of SuDS where applicable for reducing the downstream impact of urbanisation on flood risk. However, SuDS are not a universal panacea, as they may not be feasible in all circumstances, may be considered as alternative and unproven technology and may take up considerable space. However, SuDS can also provide innovative, environmentally and ecologically beneficial solutions.
CDC is committed to the principle of sustainable drainage and wishes to investigate the potential for the use of SUDS techniques within the proposed development areas. CDC also wishes to develop a biodiversity and access strategy linked to SuDS in order to maximise the potential benefits of such techniques for the wider ecological and community enhancements that they can potentially offer.
Each of the individual developers is responsible for designing and proposing their own surface water drainage systems dealing with their own sites. When considering SuDS on a piecemeal basis, however, the options for the use of SuDS may be considerably limited, particularly for the smaller site areas. There are also advantages in taking a strategic, more regional, view of the potential for SuDS within the wider development area than the individual site boundaries.
CDC commissioned Cornwall County Council (CCC) to undertake a scoping study on the potential for the use of SuDS within the proposed development areas in Truro and Threemilestone, including consideration of biodiversity and access issues.
This report presents the results of Stage 1 of the study and relates to the collation, analysis and interpretation of data. Stage 2 of the study will consider the implications of Stage 1 and provide proposals for the strategic implementation of SuDS within the AAP.
1 1.2 Objectives The main objective of the scoping study is to identify the potential for the use of SuDS in relation to the proposed development sites within the Truro and Threemilestone AAP area.
SuDS cannot be applied universally as the most appropriate system to use depends on many site-specific factors. The aim of this study is to identify these factors in order to consider the constraints that are present and also the opportunities that exist.
By taking a strategic approach, this study is independent of the constraints of individual developers dealing with single site areas.
The study also links SuDS with biodiversity and public access issues.
The study also informs masterplanning and landscaping aspects of the AAP, provides supplementary information for the Local Development Framework (LDF) and is relevant to the Strategic Flood Risk Assessment (SFRA) for the Carrick District.
The scope of the study is to assess the SuDS potential for the main development areas and the Truro Local Distributor Road (TLDR) that is also proposed in the area.
The study is GIS based and set out to assess: • Existing drainage problems • Existing sewerage infrastructure • Geological and hydrological influences • Physical and topographic constraints • Environmental, ecological, and amenity opportunities
The aims and objectives for biodiversity are: • To provide the ecological evidence base by collating the existing data relating to biodiversity in its widest sense. • To evaluate the existing value of the area and identify the most important sites. • To produce a green infrastructure that will maintain the biodiversity value of the area. • To provide guidance on how to enhance the biodiversity value of the area through SuDS and identify opportunities for other areas. • To identify data constraints and provide further recommendations for survey where there is insufficient data.
In terms of access, considering development proposals the following questions would be need to be considered:
• Is there adequate access from the proposed growth area into the surrounding countryside on foot, bike, horse etc? • What improvements could be reasonably made if resources were available • What connections to shops, schools, other services etc would be appropriate for the new development? • How will the areas in the growth area be interlinked by access to facilitate the use of local services and provide commuting opportunities? • What possibilities might exist to commute into the city centre, by means other than the car? • What recreation opportunities would people have access to that mean they don’t necessarily have to travel?
2 1.3 Structure of this report Section 2 of this report introduces SuDS and briefly describes the various types of systems that can be implemented.
Sections 3 and 4 introduce the framework with regards to biodiversity and access, respectively.
Section 5 contains the collation and analysis of the available data. It presents the GIS project and describes the data in regional terms.
Section 6 discusses the implications and limitations of the data with respect to drainage, biodiversity and access issues.
The Tables and Figures referred to in this report are provided as Volumes 2 and 3 respectively.
Volume 4 provides data sheets for each of the development sites. These contain the same information as described in Section 5, where relevant, but the information is presented at development site scale.
3 2 SUSTAINABLE DRAINAGE SYSTEMS (SuDS) Sustainable Drainage Systems (SuDS), or Sustainable Urban Drainage Systems (SUDS), are methods for managing rainwater runoff that do not involve direct disposal to piped sewers or watercourses. The SuDS philosophy is to mimic natural processes as far as possible. It is also desirable to dispose of rainwater as close to its point of source as possible.
2.1 Types of SuDS SuDS may be used to dispose of rainwater through infiltration to the ground, in which case the receiving water is groundwater, or by storage in detention or retention ponds with eventual, but considerably delayed, discharge to surface water courses, or as a combination of both.
They may be decentralised, whereby one property is served by a single system or centralised, whereby more than one property is served and maintenance and other responsibilities are shared or allocated to an individual body.
SuDS may be categorised as surface or sub-surface systems.
Sub-surface, below ground, systems are generally based on infiltration through the subsoil in the unsaturated zone above the groundwater level and include traditional, small-scale, decentralised soakaways serving individual properties. These are usually pits filled with stone that allow storage within the pores of the fill material and infiltration through the surface area of the pit, Figure 1(a).
Soakaways serving larger areas or as part of a centralised system, serving more than one property, may be constructed using pre-cast perforated concrete rings, Figure 1(b). These have the advantage of providing extra storage, as they do not need to contain fill material for stability.
Infiltration trenches, Figure 1(c), are similar to stone filled soakaways but may be fairly long and narrow. They may be placed close to a boundary strip or alongside a road or other linear structure. Infiltration trenches differ from compact soakaways in that they contain a higher ratio of surface area to volume and performance is biased toward infiltration rather than storage.
Permeable pavements, Figure 1(d), are plane infiltration devices relying more on vertical infiltration through the base of the structure. The surfaces may be open lattice concrete or porous tarmac to allow the entry of rainwater. The surface overlies a fill material that provides storage and allows infiltration to the sub-surface through the base. Permeable pavements are suitable for use in car parks or for other areas of hardstanding. Not all permeable pavements are infiltration based. Some may allow water to infiltrate into the fill material but are sealed from the sub-surface. Discharge of water is through pipes within the fill and to a connecting sewer or watercourse. The advantage here is in the time delay and attenuation of the flow from the system compared with that for impermeable surfaces, and they can be used where ground conditions are not favourable for the use of infiltration systems.
Not all infiltration-based systems are located below ground. Infiltration basins are landscaped depressions in the ground surface that are dedicated to storing water during and after rainstorm events, Figure 1(e). They are vegetated to keep the surface permeable and the stored water is allowed to soak away into the ground after the event.
4 Swales work in a similar fashion to infiltration basins but are linear features and are often used alongside a road, Figure 1(f). They normally have discrete sections separated by check dams to allow water to pond evenly along the swale length, but may also overflow from one section to another.
Other types of above ground systems rely on storage and attenuation of pulses of stormwater with relatively small losses to infiltration. These therefore require connection with outfalls, usually to a watercourse but can connect to a sewer or an infiltration based SuDS.
Detention ponds tend to be dry with surface vegetation during normal conditions. Following a storm event they will fill and store water, releasing it slowly into the hydrological environment after the main pulse has passed. They may be in-line, whereby the watercourse runs through the basin, or off-line, connecting to the watercourse through overflows at the upstream and downstream ends.
Retention ponds behave in a similar manner to detention ponds but are designed to retain water permanently (Figure 2a). Storage following rainstorm events is provided by freeboard capacity in the pond. Wetlands are a form of retention pond, but with a greater emphasis on ecological benefit in addition to its hydrological advantages.
There are no hard and fast rules for designing SuDS and combinations or hybrids of the schemes described above can be used and tailored to suit specific situations. The type of SuDS most applicable to a specific development will depend on specific circumstances and may be dictated by conditions encountered during detailed site investigations.
2.2 Guidance available for SuDS Source control techniques were identified by the Construction Industry Research and Information Association (CIRIA) as important factors in increasing the sustainability of urban drainage systems (CIRIA 1992). Source control refers to the fact that rainwater runoff is dealt with close to the location in which the rain fell. Since then the term SuDS has tended to replace the term source control.
In 1996 CIRIA published guidelines on the design of infiltration based SuDS (CIRIA 1996). This included procedures for the hydraulic design of such systems and set out a methodology to relate the results of percolation tests in the field to the required size of an infiltration system that will achieve a given performance.
CIRIA published general guidance on the use and selection of the different types of SuDS techniques in 2000 (CIRIA 2000). In a companion volume, CIRIA published a guide to best practice on the use of SuDS including examples and case studies (CIRIA 2001).
The EA produced two documents in 2003 providing an overview of SuDS (EA 2003a, 2003b) in order to encourage their use with developers.
In order to promote the use of SuDS, the National SUDS Working Group published a document in order to clarify the technical and legal framework relating to SuDS in England and Wales (ODPM 2003b). The purpose of this document was to remove some of the perceived barriers to the use of SuDS. This framework document provided a set of core standards and agreements between those public organisations with statutory or regulatory responsibilities relating to SuDS, leading to a Code of
5 Practice between the key organisations involved. It was designed to provide support for developers in promoting and implementing SuDS, to ensure their long-term viability and to promote consistent use.
The publication of the framework document led directly to the publication of an interim code of practice to facilitate the implementation of sustainable drainage in developments in England and Wales (ODPM 2004). The specific objectives of the document are to: • encourage the implementation of SUDS in new and existing developments • provide basic guidance for practitioners on the implementation of SUDS in new development • make the adoption and allocation of maintenance for SUDS more straightforward.
The interim code of practice lead to the publication of two supplementary reports: a technical guide and a guide on adoption and maintenance.
The technical guidance is provided by CIRIA (2004a). This report consolidates much of the design guidance previously published and aimed to fill some of the technical gaps in design.
The model agreements guide (CIRIA 2004b) provides basic advice on the use and development of maintenance agreements and provides an outline of how the long-term responsibilities for SuDS maintenance can be allocated.
In 2007 CIRIA produced a comprehensive design manual to consolidate much of the earlier guidance (CIRIA 2007a). This manual provides best practice guidance on the planning, design, construction, operation and maintenance of SUDS to facilitate their effective implementation within developments. The guidance supersedes previous general guidance on SUDS and addresses landscaping, biodiversity issues, public perception and community integration as well as water quality treatment and sustainable flood risk management. CIRIA also issued a separate site handbook to provide guidance on the construction of SUDS (CIRIA 2007b) to facilitate their effective implementation within developments. This handbook is aimed at site engineers and SUDS practitioners.
A web based resource for SuDS is available through SUDSnet, which can be accessed from the link below, and also provides links to other useful SuDS related resources: http://sudsnet.abertay.ac.uk/
This provides a UK-wide network for researchers, practitioners, agencies, developers and all those who are interested in Sustainable Drainage Systems. SUDSnet is funded by an Engineering and Physical Sciences Research Council (EPSRC) Network Grant and is held jointly by Coventry University and the Urban Water Technology Centre (UWTC) at the University of Abertay Dundee. SUDSnet also publishes a bi- annual newsletter.
6 3. LEGISLATION/POLICY CONTEXT FOR BIODIVERSITY
3.1 Biodiversity and Action Plans
Biodiversity is the range of organisms, plants and animals, in a particular ecological community or system.
The convention on biodiversity was signed by communities and member states in Rio de Janeiro in 1992. The aim is to halt the decline in biodiversity worldwide. The states are responsible for the conservation of their biodiversity and the sustainable use of their resources.
Following the Rio de Janeiro summit the UK government produced a UK Biodiversity Action Plan (BAP) which aims to reduce the current losses of species and habitats. There are also county, local, organisation and site BAPs which aim to reduce the losses in biodiversity.
3.2 Legislation
3.2.1 Biodiversity
The Countryside and Rights of Way Act 2000, section 74 details the need for the production of lists of species and habitats which are of principal importance for biodiversity. The Natural Environment and Rural Communities Act 2006 Section 41 list is the successor to this and has just been agreed in August 2007. The list has not yet been separated into countries but this work is planned for the end of the year. The latter Act also states that all Local Authorities in the exercise of their functions have regard to the purpose of conserving biodiversity.
These lists cannot protect our biodiversity without a comprehensive network of habitats that allow the survival and free movement of species between them. Compounded with existing threats to species and habitats is climate change. It is well recognised that a key approach is to reduce the isolation and fragmentation of our habitats. Without climate change this in itself will make species less vulnerable to extinction and given the predicted changes will at least allow animals and plants to try and adapt.
3.2.2 Statutorily Protected Sites
Sites of Special Scientific Interest (SSSI) are protected by the Wildlife and Countryside Act 1981 and are the best sites in the country for wildlife.
The Conservation (Natural habitats &.c) Regulations 1994 (as amended) detailed the necessity for protecting sites that are of European importance. This includes Special Areas of Conservation (SAC).
7 Where sites of European importance are affected by development an Appropriate Assessment is required. This could be a result of direct or indirect significant affects of development.
3.2.3 European Protected Species
In addition to the legislation providing guidance on the species essential for biodiversity, the Conservation (Natural habitats &.c) Regulations 1994 (as amended) details flora and fauna species which are of European importance. Where development affects these, such as proposed in the AAP, a European Protected Species (EPS) licence will be required. These have to meet three tests which include demonstrating how the species will be maintained at a favourable nature conservation status. This will include protecting more than the existing statutorily protected sites.
3.3 Carrick Local Development Framework Core Strategy
This Core Strategy has been submitted and is currently awaiting the Planning Inspector’s decision. The most relevant strategic objective is SO20 which aims to “Protect and enhance the biodiversity and geodiversity of the district”.
In addition spatial policy T4 details that it will “protect and enhance the biodiversity of the Truro River basin and in particular ensure that development has no adverse impact on the Special Area of Conservation (Fal and Helford SAC).
Spatial policy R4 Environment states the need to protect the countryside for its own sake and to protect and enhance the diversity of wildlife and distinctive landscape character from conflicting development proposals.
Core Policy 3 also states that the countryside will be protected by conserving and enhancing its …biodiversity,…..its nature conservation value. It also states that accessible local priority habitats will be protected and recreated in conjunction with new development.
3.4 Policy Guidance
Planning Policy Statement 9 (DCLG 2005) also details the need to protect biodiversity by following principles such as avoiding any adverse impact on ecology, the need to mitigate and compensate if the impacts are unavoidable and enhancing sites through the planning process. Most important of all is the recognition that adequate information (evidence base) is essential to complete this function effectively.
3.5 Green Infrastructure
Green infrastructure is the collective areas of green space which provide sites that are linked to protect the biodiversity of areas such as in the Truro and Threemilestone Area Action Plan. This green infrastructure will include all statutorily protected sites, sites of county importance (CWS/LS), BAP habitats from national to local importance, nature reserves, the additional habitat and links key to the survival of European Protected Species (EPS), open spaces offering buffering for protection of sites and
8 general open spaces. We anticipate that the latter will include the spaces required for the SuDS and Access land. As a principle we must seek to avoid, where possible, areas of existing high biodiversity value to enable SuDS and seek enhancement for biodiversity on low ecological value sites.
The green infrastructure must provide communities with accessible green space, functional habitat networks, valuable ecological services such as flood prevention and connections with nature through learning and experience.
At the masterplanning scale the aim is to provide guidance for a green infrastructure network for the Truro and Threemilestone Action Plan. It is essential that this links nature in the urban through suburban to the rural countryside.
There are key guidelines to the amount of space needed by people. The Woodland Trust recommend that no person should live more than 500m from at least one woodland of less than 2ha and at least one of +20ha within 4 km.
The NE (EN) greenspace standard determines; that no person should live more than 300m from their nearest natural green space of at least 2 ha in size; There should be provision of at least 2 ha of natural green space per 1,000 population; at least one accessible 20 ha within 2 km; one accessible 100ha site within 5km and one 500 ha within 10 km and that adjacent greenspaces are interconnected.
9 4 ACCESS Access is an important part of life for everyone, without it we are unable to meet our work, healthcare, educational, shopping and leisure needs.
Travel choices and the rurality in Cornwall inevitably lead to a high dependency on the car and other motorised vehicles to meet much of our travel needs. However much work is being carried out to try to improve the sustainability of communities to improve travel options and reduce the need to travel, whether within our own community or beyond.
There are many benefits that emerge from improved access, such as improved health, well-being, tackling congestion, the ability to access services, cost effectiveness and more recreation opportunities.
Cornwall County Council has recently approved the publishing of the Cornwall Countryside Access Strategy (Incorporating Cornwall’s Rights of Way Improvement Plan). This document has been produced as a requirement of the Countryside and Rights of Way Act 2000 (CRoW) and sets out Policies and Actions to improve the quality of countryside access over the coming few years.
The Strategy seeks to ensure that development proposals consider the needs of people to access the countryside and services and that proposals should not detrimentally affect the existing access network.
Should it be found that any development proposals affect a public right of way (which may include putative ways), it would be necessary to ‘stop up’ or ‘divert’ such a way before any permitted development can take place.
It may also be appropriate to consider the provision of additional public rights of way and arrangements for their long term maintenance in any development proposals as part of any sustainability measures to be included in the development.
The impact of incremental development on public rights of way should be considered in development proposals to ensure that increased pressure on such infrastructure is balanced with the increased maintenance resources to meet higher / heavier usage. This may be through surface maintenance agreements or other mechanisms.
10 5 DESCRIPTIONS OF THE SITES AND COLLATION OF DATA The GIS project has been set up to allow the sites to be analysed in terms of geographical characteristics, including physical and ecological nature and infrastructure.
This section provides an overview of the GIS datasets used and descriptions of the development area as a whole. The same approach is taken to each of the 12 development units, as listed in Table 1. For each individual development unit, the same data has been analysed and collated, where applicable. The results are presented as Site Data Sheets and these are provided in Volume 4 of this report.
5.1 Locations and extents CDC has provided CCC with the outlines of 11 development areas and CCC Highways has provided the proposed route of the TLDR. Three of the identified plots, Willow Green, Treliske and the Golf Course, are situated north of the present A390 and the other eight sites and the TLDR are located to the south. In addition it is believed that some areas of infill adjoining the sites may also be in various stages of planning for development.
The sites are listed in Table 1 and their locations are shown on Figure 3.
The TLDR cuts through a number of the southern sites. The areas listed in Table 1 include the areas taken up by the link road. Table 2 below provides a revised calculation of area taking into account that lost due to the presence of the TLDR. The area of the TLDR includes all roundabouts and areas of embankments and cuttings associated with the road.
Note that at the time of writing, the exact route of the TLDR, and in particular the spur roads linking with the development sites, has not been finalised.
5.2 Landscape Character
5.2.1 Aerial photography The latest aerial photography available was flown in 2005 and is held under licence by CCC, Figure 4.
The resolution of the aerial photography is 0.25 m.
5.2.2 Landscape character areas and description units These are defined by CCC, though should be considered as draft at the time of writing.
The county is divided into a series of Character Areas. The majority of the AAP area is located in the “Fal Ria, Truro and Falmouth” area, with the more industrialised area bordering the A390 being classified as “Redruth, Camborne and Gwennap”, Figure 5. Development on greenfield sites may result in areas transferring from the first category to the second.
11 The majority of the sites are within the “Fal Ria, Truro and Falmouth” area with just Cornwall County Council, the southwest part of the Golf Club, the western end of Goonvean and the southern part of Willow Green in the “Redruth, Camborne and Gwennap” area.
The landscape is further subdivided depending on its ecological, land use, physical and settlement characteristics, as shown in Figures 6, 7, 8 and 9.
The ecological description for all sites is “shallow brown soils on hard rock”, Figure 6.
Sites within the “Fal Ria, Truro and Falmouth” area have the physical description of “hard rock slopes and ridges”, whereas those in the “Redruth, Camborne and Gwennap” area are described as “hard rock plateau”, Figure 7.
In terms of land use description, the northern sites within the “Fal Ria, Truro and Falmouth” area are “secondary wooded pastures” and the southern sites are “ancient pastoral farmland”. Within the “Redruth, Camborne and Gwennap” area, the Cornwall County Council site and southwest part of the Golf Course are classed as “urban”, whilst the southern part of the Willow Green site and western part of Goonvean, are “settled pastures”, Figure 8.
In terms of settlement description, the “Fal Ria, Truro and Falmouth” area sites are “clustered with small farms” and within the “Redruth, Camborne and Gwennap” area, the Cornwall County Council site and southwest part of the Golf Course are classed as “urban”, whilst the southern part of the Willow Green site and western part of Goonvean, are “mining with small farms”, Figure 9.
These descriptions are summarised in Table 3.
5.3 Environmental Designations Figure 10 shows the locations of areas with international, national or county level environmental designations in the vicinity of the Truro and Threemilestone development sites.
None of the sites directly include any designated areas, though some may adjoin such areas.
The Fal and Helford estuary to the south and east of Higher Newham and Carrine Common to the south of, and opposite flank of the valley to, Goonvean, Newbridge Farm and Trethowan Estate are both designated as Special Areas of Conservation (SAC).
Carrine Common/Penweathers and the Malpas Estuary to the west of Higher Newham are also designated as Sites of Special Scientific Interest (SSSI).
County Wildlife Sites are designated at Treworder Woods to the north of Treliske, Halbullock Moor to the north of and adjoining Newbridge Farm, Nansavallon Wood to the south and on the other side of the River Tinney to Trethowan and Tregothnan Estates, Carrine Common and the Upper Truro River.
Halbullock Moor is also a Cornwall Wildlife Trust Reserve, as is Fox Corner located in the grounds of New County Hall between the Richard Lander and Tregothnan Estates sites.
12
5.4 Geology Figure 11 provides a solid and drift geological map of the area based upon the British Geological Survey (BGS) 1:50,000 series digital geological map.
5.4.1 Solid All but two of the sites lie on the Porthtowan Formation. This is made up of undifferentiated mudstones and sandstones from the mid to late Devonian period.
The Tregothnan Estates and Higher Newham sites are located on the Portscatho Formation, which is described as sandstone with interbedded argillaceous (muddy) rocks, also of the mid to late Devonian.
Some southwest-northeast trending dykes are present in the area, though only the Goonvean site is traversed by one. The dykes are felsite intrusions from the Permian period.
5.4.2 Drift The courses of the River Tinney and River Kenwyn contain alluvium that is confined to the narrow river valley bottoms.
The course of the stream that runs south from Gloweth to the River Tinney and Hallbullock Moor is characterised by Head deposits (highly weathered bedrock material).
5.5 Soils Figure 12 shows the soil associations according to the National Soil Classifications.
Although there are six soil units present in the area shown on Figure 12, only two of these, Denbigh1 and Denbigh2, are associated with the development sites. Willow Green, the western parts of Treliske and Goonvean, possibly part of the Golf Course and the western extremity of the TLDR are classified as Denbigh1 whilst the remaining sites are Denbigh2.
Table 4 lists the relevant properties of these soils. Figure 12 and Table 4 should only be considered as a guide to the actual distribution and properties of the soils present.
5.6 Ecology
3.6.1 Broad Habitat Habitat information is made available to CCC through the Environmental Records Centre for Cornwall and Isles of Scilly (ERCCIS). The habitat maps were digitised by ERCCIS from aerial photography dated 1995.
Broad habitat types do not completely mirror the BAP habitat definition. The following are the same categories: improved grassland, broadleaved, mixed and yew woodlands, neutral grassland and fen, marsh and swamp. Bracken and built up areas are not UK BAP habitats. Only arable field margins are BAP habitats for arable and horticulture, coniferous woodland (Scots Pine only native in Scotland) and open water
13 is subdivided from rivers and streams. Hedgerows are a BAP habitat which is present but not included within the data.
Table 5 details the broad habitat types for the development sites. Some of these are not BAP habitats but will have some value to wildlife.
The habitat map is provided as Figure 13 and the data for the development sites is summarised in Table 5. In Table 5, the TLDR is not included, as this overlaps with other sites (see Tables 1 and 2) and so leads to double-counting. The Site Data Sheets in Volume 4 provide an individual breakdown of this information for each site, including the TLDR.
Since the aerial photography of 1995 some of the improved grassland and hedgerows have been unmanaged and become of higher value as habitats and for faunal species. There are undoubtedly other changes which are as yet unidentified.
5.6.2 BAP Habitats Figure 14 shows the locations of Biodiversity Action Plan (BAP) habitats in the vicinity of the development area.
Special Areas of Conservation SAC (These sites are of International Importance and specially protected by the EU Habitats Directive)
The SAC’s are of vital importance for conserving biodiversity at an international/global level. Indirect impacts can affect their value. An Appropriate Assessment is required if a plan or project is likely to have a significant effect on the site.
There are two SAC’s within one kilometre of the proposed development. These are Carrine Common and the Fal and Helford SAC.
Carrine Common SAC is noted for its temperate Atlantic wet heath with some scrub and mesotrophic grassland. There are a number of fens that run along the course of a small stream that runs northwards through Carrine Common to the River Tinney.
The Fal and Helford SAC is primarily selected for its sandbanks, mudflats and sandflats, large shallow inlets and bays and Altantic salt meadows.
The River Tinney discharges to the Calenick Creek and the upper reaches of the creek are Coastal Saltmarsh.
Sites of Special Scientific Interest (SSSI’s) SSSI’s are wildlife sites of national importance for biodiversity. The two SAC’s are both SSSI’s as well. There are no other SSSI’s within a kilometre of the Area Plan.
County Wildlife Sites/Local Sites (CWS/LS) County Wildlife Sites are identified as of county importance for wildlife/biodiversity.
Halbullock Moor is a wildlife trust reserve and a County Wildlife Site, which is designated as wet woodland and drains toward Newbridge Farm and the Truro Tennis Club. The site is 4 hectares and is naturally regenerated from rough grassland.
Nansavallan Wood, on the south side of the River Tinney is a County Wildlife Site and ancient semi-natural woodland and is noted for its upland oakwood . Ancient semi-
14 natural woodland is not statutorily protected but is a habitat which cannot be recreated, and has a high biodiversity value and loss/damage should be avoided.
Other BAP Habitats Halbullock Moor, which drains toward Newbridge Farm and the Truro Tennis Club, is designated as Wet Woodland. The valley bottom part of the River Kenwyn running through Treworder Woods, to the north of the Treliske site, is also classified as Wet Woodland.
Much of the remainder of Treworder Wood is Upland Oakwood, as is Nansavallan Wood, on the south side of the River Tinney.
Carrine Common contains Lowland Heathland and also a number of fens are present along the course of a small stream that runs northwards through Carrine Common to the River Tinney.
Fens are also mapped on the River Tinney between the TLDR and the railway near the eastern end of the Trethowan Estate site. Fens are also present on the River Kenwyn in the flood storage area of New Mill Dam.
The River Tinney discharges to the Calenick Creek and the upper reaches of the creek are Coastal Saltmarsh.
There is a network of hedgerows on site of varying values. All types of hedgerow are now BAP habitats, whereas previously it was only ancient species rich ones. The hedgerows on site provide important green links for a wide range of species which are threatened by isolation and fragmentation.
Other Sites of wildlife value Fox Corner is a wildlife trust reserve and is noted for a wide range of species some of which are BAP species.
3.6.3 BAP species
European
Mammals Currently the following EPS are known to exist on site today: otter, hazel dormouse and bats.
The following bat species have been confirmed with recent survey work; Greater Horseshoe, Lesser Horseshoe, Brown Long-eared, Common Pipistrelle and Noctule. Previous records include Natterer’s, Whiskered, Brandts and Daubenton’s.
Records of the red squirrel have not been confirmed recently and are highly likely to be incorrect.
Grey seal, common dolphin.
Plants The shore dock is known from the Fal and Helford SAC.
National
15 The following species are known to occur from site surveys:
Mammals
Badger (recent confirmation), harvest mouse.
Amphibians and Reptiles
Common toad, common frog, palmate newt, slow worm, viviparous lizard.
All of the above, apart from common frog, are included on the new BAP list. There is also a recent record of grass snake.
Birds
With regard to the birds, the ERCCIS records (see Section 5.7 below) tell us little more than that people record waders etc. on the Fal and that there is some woodland, farmland and scrub in the area.
Plants The following BAP species have been recorded in the scoping area but have not been recorded in the last ten years but could still be found in the area including Chamaemelum nobile, Cicendia filiformis, Fumaria purpurea, Illecebrum verticillatum, Melittis melissophyllum, Pyrus cordata, Silene gallica and Viola lactea.
5.6.4 Trees Figure 15 shows the locations of tree preservation areas, tree preservation orders and areas of ancient woodland.
Part of Treworder Woods on the south side of the River Kenwyn to the north of the development areas is classified as replanted Ancient Woodland and Nansavallon Wood, to the south, as semi-natural Ancient Woodland.
A Tree Preservation Area extends from the northern boundary of the Newbridge Farm site, across Hallbullock Moor, through the development at Gloweth and Truro College to the north. Another extends southeast of Newbridge Farm to the railway and includes the Truro Tennis Club site and is crossed by the TLDR. A Tree Preservation Area also follows the course of the stream that flows southwards across the Trethowan Estate site to the River Tinney and is also traversed by the TLDR where it crosses the stream. The northern part of the Richard Lander site is a tree preservation area and is also the location of a roundabout on the TLDR. A small section on the east side of the Higher Newham site contains part of a Tree Preservation Area.
The only development site containing Tree Preservation Orders is the Cornwall County Council site, on the grounds of the old Richard Lander School. There are 26 TPO’s issued in 2006 on the site. These are shown in more detail on the site data sheet in the Appendix.
5.7 Biodiversity The notable species (as defined by the JNCC) database held by the Environmental Records Centre for Cornwall and the Isles of Scilly (ERCCIS) has been accessed to indicate the species that have been recorded in the area. The JNCC list is those
16 species which are globally vulnerable or threatened. Some of these species are relatively common in the UK.
An area of 45 km2, 9 km in an east-west direction (Easting 176,000 to 185,000) and 5 km in a north-south direction (Northing 42,000 to 47,000) was isolated from the full database to provide coverage of the region of Truro and Threemilestone. This resulted in a database of 10,167 records.
There is disparity in the degree of precision at which these records are recorded geographically. Some are recorded on a “tetrad” basis, which results in a precision of 2000 m. Others are given to a four figure grid reference (i.e. SW8145 = Easting 181,000; Northing 45,000) resulting in a precision of 1000 m, some to six figure grid reference with a precision of 100 m and the remainder to an eight figure grid reference with precision of 10 m. This means that the locations of the records sit on the nearest 10 m, 100 m, 1000 m or 2000 m grid point. The result is that many records overlie each other, obscuring those underneath when viewed on a map. Also, clearly, those with lower precision only indicate the approximate location of a record compared to those with higher precisions. Figure 17 shows the locations of the notable species records within the 45 km2 area in terms of their geographical precisions and Table 6 summarises the number of records with each precision.
The ERCCIS notable species database provides records dating back to 1900. Table 7 provides a breakdown of the numbers of species records by decade and also for the past five and ten years. Records of less than five years assume the species are still likely to be present. If the record is between five and ten years providing the habitat is still present the species is still likely to be present. Over ten years the record is seen as old and needs review but may still be a valid record. Table 7 shows that there is a paucity of data for the past five years compared to the period between five and ten years ago.
Table 8 provides a breakdown of the records by their taxon groups and also states the number of records within the past five or ten years.
Tables 9 to 20 list the records by taxon species for the ten year period 1997 – 2006. Similar tables were also compiled for the full chronological record and are provided as an Appendix as some records were clearly dated (i.e. records of Red Squirrel, that is no longer present). The Ap[pendix can be provided upon request.
The botanical records were also reviewed as key indicators of habitat type and status within Cornwall. For instance Armeria maritima is primarily a coastal species and is clearly not found in Gloweth but within the coastal influence of the estuary.
The mammals, amphibians and reptiles were also evaluated for status whether protected or BAP species.
5.7.1 Trees and flowering plants The list of species in table 10 includes species in the ERCCIS notable species database recorded within the last ten years in the scoping area. The majority of these have the IUCN category of being of Least Concern. The species of concern includes those that are Near Threatened, Vulnerable, Endangered or Critically Endangered. Additionally some species which are of Least Concern may still be Nationally Rare or Nationally Scarce and the list from the ERCCIS notable species database has been analysed to highlight these.
17
The species in the above categories within the scoping area seen in the last ten years excluding those of Least Concern but including Nationally Rare or Scarce includes Briza minor (Nationally Scarce), Erica ciliaris (Nationally Rare), Fumaria occidentalis (Nationally Scarce), Hypericum undulatum (Nationally Scarce), Misopates orontium (Vulnerable), Spergula arvensis (Vulnerable), Stachys arvensis (Near Threatened) and Viola tricolor (Near Threatened).
Other species falling into the categories above which have not been recorded in the scoping area in the last ten years but could well still be present include Allium ampeloprasum var. babingtonii (Nationally Scarce), Anagallis minima (Near Threatened), Anthemis arvenis (Enangered), Anthemis cotula (Vulnerable), Baldellia ranunculoides (Near Threatened), Brassica oleracea (Nationally Scarce), Bromus secalinus (Vulnerable), Chenopodium bonus-henricus (Vulnerable), Chenopodium murale (Vulnerable), Chrysanthemum segetum (Vulnerable), Cuscuta epithymum (Vulnerable), Cyperus longus (Near Threatened), Euphorbia exigua (Near Threatened), Filago vulgaris (Near Threatened), Gastridium ventricosum (Nationally Scarce), Hyoscyamus niger (Vulnerable), Puccinellia rupestris (Nationally Scarce), Radiola linoides (Near Threatened), Silene noctiflora (Vulnerable), Spiranthes spiralis (Near Threatened), Viola palustris subsp. juressi (Nationally Scarce),
Additionally the Botanical Cornwall Group and Botanical Society of the British Isles recorders for Cornwall have identified those species which are Rare, Scarce or Local in Cornwall even if they are of Least Concern nationally - highlighted with LC in the following list. Some of the above fall into these categories but additional ones include Alopecurus myosuroides (Cornwall Scarce LC), Bidens tripartita (Cornwall Scarce LC), Bromopsis erecta (Cornwall Scarce LC), Clinopodium vulgare (Cornwall Local LC), Dactylorhiza fuchsia (Cornwall Scarce LC), Draba muralis (Cornwall Rare LC), Epilobium roseum (Cornwall Local LC), Gentianella amarella (Cornwall Scarce LC), Hordeum secalinum (Cornwall Rare LC), Lathyrus nissolia (Cornwall Scarce LC), Lithospermum officinale (Cornwall Local LC), Myriophyllum spicatum (Cornwall Scarce LC), Papaver hybridum (Cornwall Local LC), Parapholis strigosa (Cornwall Scarce LC), Poa compressa (Cornwall Scarce LC), Potamogeton pusillus (Cornwall Scarce LC), Puccinellia distans (Cornwall Rare LC), Rhyncospora alba (Cornwall Local LC), Rosa micrantha (Cornwall Scarce LC), Rosa stylosa (Cornwall Scarce LC), Saxifraga tridactylites (Cornwall Local LC), Schoenoplectus lacustris (Cornwall Rare LC), Stellaria pallida (Cornwall Local LC), Torilis nodosa (Cornwall Local LC), Utricularia vulgaris (Cornwall Rare LC), Viscum album (Cornwall Scarce LC).
5.7.2 Ferns and lower plants Following the explanation of threat and rarity categories in 5.7.1, of ferns Asplenium obovatum is Near Threatened, Adiantum capillus-veneris Nationally Scarce and Ophioglossum vulgatum is Cornwall Scarce LC. These haven’t been recorded in the scoping area in the last ten years.
The records of notable lower plants are few in the scoping area but the recording of them and the identification to species level is notoriously difficult and usually undertaken by few people. The records here may not show the true picture as to what is present.
5.7.3 Insects There is clearly an under recording of butterfly species although the pearl bordered fritillary (not recorded in the past 10 years) is a UK BAP species.
18 5.7.3 Fish Only Bullhead and Brook Lamprey are recorded.
5.7.4 Amphibians The three commonest species of amphibians are noted and are likely to still be present. All require water bodies for breeding. These must be linked to other semi- natural habitats such as rough grass, hedgerows and woodland and ideally with no roads within 500m of the breeding pond. It is unlikely that smooth newts do occur here. This makes the water and areas of semi-natural habitat of Local Site (CWS) importance for biodiversity.
5.7.5 Reptiles Only slow worm (UK BAP species) and adder are recorded with the past 10 years
5.7.6 Birds Of the bird species recorded in Table 19, the Hose Martin is possibly in decline
5.7.7 Mammals There is clearly under-recording in this area as many common species are not listed.
The majority of the mammals recorded are of European status for conservation and fully protected by European and National Law. There are nine species of bat which makes the site of at least county importance as a local site. Evidence of otters is found throughout the stream/river network. They will also require other habitats for travel and breeding holts but these sites have not been identified.
The harvest mouse requires grassland/reed habitats for breeding.
The badger is a common mammal which normally requires a mix of grassland and woodland.
5.8 Industrial
5.8.1 Mining The southwest and northwest peripheries of the area contain features associated with mining, Figure 18. The only sites likely to be affected are Goonvean and Willow Green. These are considered further in the relevant data sheets in Volume 4.
An adit is present to the south of the sites but this appears to drain the southern side of the River Tinney catchment and so is not likely to impact on the hydrology of the development sites, these being on the northern side.
5.8.2 Fuel oil pipeline A fuel oil pipeline that runs from Falmouth Docks to Newquay Airport traverses through the development area, Figure 19.
The only sites likely to be affected by this are Goonvean and Treliske, which the pipeline runs directly through. Particular care will need to be taken if considering earthworks within a 30 metre buffer zone of this pipeline.
19 5.8.3 Landfill There are no landfill sites located directly within any of the designated development sites, Figure 20.
A small site containing inert waste is present to the northwest of Willow Green, on the River Kenwyn at Langarth. This site was licensed between 1990 and 1994. The site is upstream of any drainage related to the developments and therefore would not be affected.
Newham, southeast of the Higher Newham site, contains a major landfill that was active between 1943 to about 1975 receiving domestic, commercial and industrial wastes, sewage sludge and chemical wastes including acids and solvents, and also some inert wastes during the 1990s. It is unlikely that the development will have any impacts on this old landfill site.
One landfill site that is close to the development sites is located at the southern edges of Higher Newham and Tregothnan Estates, on the northern side of the River Tinney between the A39 and Calenick Village. This site received demolition wastes and inert material during 1991 to 1993.
5.9 Access Figure 21 shows the location of existing public rights of way (PROW). The Cornish Way cycle path is included on Figure 21.
Figure 22 shows the PROW in terms of their priority designations.
PROW are present on the south side of the railway, south of Trethowan Estates site at Penweathers (priority silver) and also through Carrine Common (priority gold). Also to the south is a PROW around Calenick (priority silver) and access to Calenick Creek (priority bronze), south of Tregothnan Estates and Higher Newham development sites.
There are PROWs (priorities gold and silver) to the north of the River Kenwyn, north of the Treliske site. PROWs (priorities gold and silver) exist to the east of the Golf Course, either side of the River Kenwyn, heading toward Truro.
A small PROW network is also present at Gloweth (priority gold), skirting the northern boundary of Halbullock Moor and linking to the A390 at the Treliske Hospital roundabout.
The Cornish Way cycle path leads from the southwest through Penweathers, skirting the northwest boundary of the Tregothnan Estates site before leading into the City of Truro. Another branch to the east connects with the old Newham railway branch line and follows the disused line along the southern boundary of the Higher Newham site and along the bank of the Truro River into the City.
Two areas of Open Access land exist to the south of Threemilestone. These are located at Carrine Common and near Cusveorth Coombe. These provide a right of access on foot.
20 5.10 Topography Topographic relief may be a major influence on the types of SuDS that are feasible, as well as influencing the hydrology and natural drainage patterns.
The main topographic dataset used for this part of the study was the NextMap Britain Digital Elevation Model (DEM) held under licence by CCC. This data comprises spot heights on a 5 m horizontal grid distance (sometimes referred to as post spacing). The elevation values are obtained from remote sensing by airborne radar - Interferometric Synthetic Aperture Radar (IFSAR ).
There are two versions of the DEM. The digital surface model (DSM) is the raw data and includes the elevations of the tops of buildings and tree canopies. The digital terrain model (DTM) is derived from the DSM but has had a filtering algorithm applied to it. The purpose of the filtering is to remove surface features from the DSM to produce a “bare earth” model. However, the filtering mechanism is never entirely accurate and some residual expressions of surface features tend to remain. The DTM also has the courses of rivers and streams slightly enhanced and bridges over rivers are incised so that when runoff analyses, such as that described in the next section, are conducted then the bridges do not act as dams obstructing the flow (See Figure 25).
Figures 23, 24 and 25 show the DTM as a contoured map, a raster image and as a hill-shaded image to highlight relief, respectively.
LIDAR (LIght Detection And Ranging) data held by the Environment Agency is a similar DEM dataset to the NextMap Britain data described above. The LIDAR data is more accurate in that it generally has a 1 m horizontal resolution and an improved vertical resolution, though it also suffers limitations due to the difficulties in converting the DSM to the DTM.
The LIDAR dataset was obtained from the EA but the coverage of the area is incomplete, Figure 26. Table 28 lists the areal coverage of each of the development sites by each of the DEM datasets.
LIDAR data was flown in May 1998 in a southwest-northeast swathe across Truro, Figures 27 and 28. The 1998 data has 2 m post spacing. This dataset provides 82% coverage of the Tregothnan Estates site though it may be possible to obtain complete coverage of this site if the data to the east of easting SW82 are available (Figures 26, 27 and 28 indicate that this should be the case – data up to easting SW84 was sought in the EA data request). No other sites are covered by this dataset.
The north-eastern part of the study area was flown in February 2005 at 1 m post spacing, Figures 29 and 30. This DEM provides full coverage of the Richard Lander, Cornwall County Council and Golf Course sites and partial coverage of Tregothnan Estates, Trethowan Estate and the TDLR.
Three separate areas were flown in March 2007 at 1 m post spacing, based upon the river valleys of the River Kenwyn, River Tinney and River Allen / Truro River, Figures 31 and 32. This DEM provides full coverage of Higher Newham, Trethowan Estate, Truro Tennis Club, Newbridge Farm and Goonvean. It also provides 95% coverage of Treliske, but only 5% of Willow Green.
Figures 33 and 34 provide composites of all of the LIDAR data. This provides full coverage of most of the sites, though some of the Tregothnan Estates site is only
21 covered by the 1998 dataset which is at 2 m post spacing and a small part is presently missing. A small part of the Treliske site is still missing data and almost the entire Willow Green site is not covered by any LIDAR dataset.
The NextMap DEM dataset has the advantage that complete and uninterrupted coverage is available but the disadvantage is the 5 m post spacing resolution, which is much coarser than the LIDAR data. The NextMap data can therefore be used for topographic analysis generally, but the LIDAR data can be used, on those sites for which it is available, to provide more detailed topographic analyses.
5.11 Hydrology
5.11.1 Watercourses The two main watercourses in the area are the River Kenwyn that drains the northern part of the development area and the River Tinney that drains the southern part. The hydrological divide, or watershed, between the two rivers lies close to the route of the A390.
Figure 35 highlights the watercourses present as taken from the Inland Water layer of the OS MasterMap digital map. This reflects the most accurate locations of water bodies, including ponds and man-made channels. Discontinuities in the stream paths reflect locations where there is no surface expression of a stream, such as where it goes beneath bridges or is culverted.
The definitive rivers map used for most flood studies is the Centre for Ecology and Hydrology (CEH) national rivers dataset. This is based on OS 1:50,000 scale mapping.
The River Kenwyn flows eastwards 200 to 300 m north of the northern boundaries of the northern development sites. It then flows into Truro, where it is heavily modified, channelled and culverted in places, before its confluence with the River Allen, flowing southwards, into the intertidal area at Garras Wharf, to form the Truro River.
The western side of the Willow Green site drains to a small stream that starts with springs near the centre of the site and flows northwards to the Langarth Stream, which is a tributary to the River Kenwyn. The eastern side of Willow Green drains to a stream that rises at ponds that are present adjacent to Willow Green Farm. It then flows north-eastwards, along a wooded corridor, through the Treliske site to the River Kenwyn just east of the “round” by Governs Wood. For the purposes of this report, this stream is referred to as Treliske Stream.
The Golf Course contains a small stream that rises at a pond by the Club House and flows eastwards. It is joined by a small northwards flowing stream draining Highertown before its confluence with the River Kenwyn.
The River Tinney, also known as the Calenick Stream, flows eastwards some 100 to 400 m south of the southern boundaries of the southern development sites and discharges to Calenick Creek at Calenick.
A small stream joins the River Tinney from the north and is referred to here as the Gloweth Stream. This stream contains the confluence of three streams at the southeast corner of Halbullock Moor. One of these streams drains the eastern side of Threemilestone and flows eastwards. Another drains the urbanised area of Gloweth
22 and flows south-easterly, through Halbullock Moor. Though the runoff analysis, below, shows this stream flowing through Halbullock Moor, it does not show as a surface feature on the OS MasterMap at this location, though it does both upstream and downstream. This may indicate that the stream flows underground or spreads to marsh/bog within Halbullock Moor. The other stream drains southwards from the A390 and along the boundary between the east side of Halbullock Moor and a parcel of land allocated to Persimmon Homes, though not on the list of development sites. After the confluence of the three streams, Gloweth Stream flows south-eastwards and crosses the unclassified road by the corner of the Newbridge Farm and Truro Tennis Club sites via a ford. It then flows southwards beneath the railway at Newbridge and into the River Tinney, just upstream of Penweathers.
Just upstream of the confluence with the Gloweth Stream, the River Tinney is joined by another tributary, referred to here as the Carrine Stream, flowing northwards from the south. This stream drains the eastern side of Carrine Common. It flows through a wooded corridor, woodland and is fed by a number of springs. As this stream is on the opposite bank of the River Tinney to the proposed developments, it is considered to be hydraulically isolated from the northern side of the River Tinney catchment and therefore should be hydrologically unaffected by drainage measures related to the developments.
A small stream appears to rise from springs on, or just to the northwest of, the Richard Lander site. This flows southeast for a short distance, also collecting runoff from the western side of New County Hall, runs beneath the railway and then south to the River Tinney at Treyew Mills. The location of the stream is predicted by the runoff model, below, but is shown as intermittent on the OS MasterMap data. This may indicate that the stream sinks below ground, through “spreads” or “sinks”, and re-emerges, through “issues”.
A drain is shown on the OS MasterMap flowing down the western side of the A39 at Arch Hill, the eastern border of the Tregothnan Estates site. The drain/stream disappears before re-emerging on the south side of the old Newham Branch Line disused railway embankment. It then enters the River Tinny just upstream of the A39 road crossing, just upstream of Calenick.
One more tributary enters the Calenick Stream from the south, about 100 m downstream of the A39 crossing. This drains from Kea and Killiow Park Golf Club. For the purposes of this report, this stream is referred to as Kea Stream.
5.11.2 Runoff analyses A runoff analysis has been conducted based on the topography from the NextMap DTM described in Section 5.10 above. Each spot height in the DTM represents a cell consisting of a 5 m by 5 m square (25 m2 area). The runoff algorithm used applies a unit of rainfall to each cell. The rainfall is then passed to the adjoining cell that is down-gradient of each cell. The runoff is allowed to accumulate so that the value in each cell represents the runoff from each cell that is up-gradient of it and this total runoff is then passed to each downstream cell, producing a cumulative runoff map. High runoff values represent the line of channels that receive the most runoff from surrounding cells. The values in the runoff map were then reclassified to produce a rivers map showing those cells accumulating greater than a given threshold value of runoff. The threshold value used was 400 units of runoff. This was chosen to identify all cells that receive runoff from 400 or more surrounding cells each of 25 m2 area, or 1 ha of drainage area. Finally, the raster image was converted to a vector line file representing the line of connection between each of the high runoff cells in order to
23 trace the routes of runoff. The result is a useful indicator of the flow paths for runoff, based on the topography, though it is dependent on the accuracy of the DTM and does not take account of small scale obstructions or man-made diversions of water courses.
The result is shown in Figure 36. The CEH rivers dataset and the OS MasterMap Inland Water dataset are included on Figure 36 for comparison. This is shown in more detail for each of the sites on the data sheets in Volume 4.
Further runoff analyses were conducted based on the LIDAR data, for comparison, though coverage is incomplete as discussed in Section 5.10 above. The results are shown in Figures 37, 38 and 39 for the 1998, 2005 and 2007 LIDAR datasets respectively. The NextMap runoff analysis and the inland water layer from OS MasterMap are included for comparison.
The LIDAR runoff analyses are not particularly useful as they are influenced by the boundaries of the coverages, especially for the 1998 and 2005 datasets. The 2005 data does, however, provide full runoff analyses for the Golf Course, Richard Lander and Cornwall County Council sites, and the 2007 data for Higher Newham, Trethowan Estate, Truro Tennis Club, Newbridge Farm, Goonvean and possibly the Treliske sites, at 1 m resolution post spacing.
The 2007 LIDAR data indicates an interesting feature alongside the railway embankment parallel to the River Tinney, Figure 39. It shows the embankment acting as a barrier to runoff flow, which does not show up on either the NextMap analysis or on the OS MasterMap Inland Water feature. Further evaluation of how runoff actually crosses the embankment to reach the River Tinney here needs to be investigated.
5.11.3 Catchments Figure 40 shows the river catchments for the area as defined by the EA for the purposes of the Water Framework Directive (WFD). The catchments have been defined from a similar runoff analysis as described in the above section, but using the CEH DEM, which is based on a 50 m post spacing, hence the blocky boundaries in Figure 40.
The northern development sites are in the defined River Kenwyn catchment (WFD ref GB108048002340) and the southern sites in the Calenick Stream (River Tinney) catchment (WFD ref GB108048001250) except for the eastern side of Higher Newham, which is in the Unnamed (Truro River) catchment (WFD ref 208048002520). The areas of the Kenwyn and Tinney catchments according to this dataset are 1977 ha and 1765 ha, respectively
Figure 41 shows the results of applying a similar catchment delineation algorithm to the results of the runoff analysis of the NextMap DTM described in the section above. The catchment areas of the Kenwyn to its confluence with the River Allen and the Tinney to the point where it meets Calenick Creek, according to this analysis, are 2000 ha and 1733 ha, respectively. The runoff pathways draining areas greater than 10 ha are included on Figure 41.
5.12 Rainfall
5.12.1 Average rainfall The 1941 – 1970 thirty year average rainfall is often accepted as a standard as it was used as a baseline characteristic in the Flood Studies Report (FSR) (NERC 1975) and
24 is referred to as the Standard Annual Average Rainfall (SAAR). The SAAR for Truro is 1100 mm.
More recently, the 1961 – 1990 thirty year average rainfall has been adopted as a baseline and is used by the United Kingdom Climate Impacts Programme (UKCIP) as a baseline for comparison with predicted rainfall trends. The reason that the 1971- 2000 thirty year average is not used is because the 1990’s are considered to be an unusual decade in meteorological terms, possibly due to the onset of observable climate change influences.
The 1961 – 1990 rainfall is available from UKCIP as monthly averages on a 5 km grid spacing. The River Kenwyn and River Tinney catchments fall between four of these grid points, Figure 42. The data for these four nearest points have therefore been averaged and the result is shown in Figure 43 as the monthly distribution of the 1961 – 1990 rainfall for Truro. The annual average rainfall according to this dataset is also 1100 mm.
5.12.2 Extreme rainfall events The Flood Estimation Handbook (FEH) (NERC 1999) has largely superseded the FSR. The methodology set out in the FEH for un-gauged catchments can be implemented using the FEH CD-ROM (CEH 2006) to provide the appropriate catchment descriptors and extreme rainfall statistics.
Figures 44 and 45 show the catchment areas for the River Kenwyn and River Tinney, respectively, as derived from the FEH CD-ROM.
The FEH catchment descriptors, for the full catchments, are provided in Table 22. Tables 23 and 24 provide the Depth-Duration-Frequency (DDF) statistics for the two catchments. These tables show the depth of rainfall that may be expected for a range of rainstorm durations and for given return periods, or statistical frequency, based on the FEH catchment descriptors.
5.12.3 Flow gauging There are no flow gauging stations present in the River Tinney catchment.
There is a flow gauging station present on the River Kenwyn at Truro. This is shown on Figures 44 and 45 and is National Rivers Flow Archive (NRFA) station (reference 48005). Details of this station can be accessed from the link below: http: //www.nwl.ac.uk/ih/nrfa/station_summaries/048/005.html [link no longer valid]
This station is also a “HiFlows-UK” station, which means that peak flow data is available in a statistical format that can be used in the FEH methodology for gauged catchments. Further details may be accessed from the link below: http://www.environment-agency.gov.uk/hiflowsuk/stations/48005/
5.12.4 Extreme flow events Although the River Kenwyn gauging station does provide historical data that can be used to estimate extreme flows using the FEH methodology for gauged catchments, CCC does not presently hold the software to implement these analyses. Instead, both the Tinney and Kenwyn catchments have been treated as un-gauged and a rainfall- runoff analysis has been applied using the revitalised methodology as described by Kjeldsen et al (2005) based on the FEH catchment descriptors, in order to provide some estimate of existing extreme peak flows.
25 According to the FSR/FEH methodology, the design critical event durations for the Kenwyn and Tinney catchments are 5.7 hours and 6.0 hours, respectively. Figure 46 shows the hyetograms for seasonally (winter) and areally adjusted rainfalls for the 100 year return period event and the net rainfall (that producing runoff) and also the corresponding hydrographs for runoff flow, baseflow and total flow, for the 5.7 hour duration event. Figure 47 shows the same data for the Tinney catchment, also for a 5.7 hour event. Table 25 lists the peak flows corresponding to the design duration events for a range of return periods for the two catchments.
The impacts of increased urbanised areas due to development in the catchments should not lead to increases in the peak flow rates listed in Table 25, if SUDS can be utilised effectively.
5.12.5 Climate change impacts on rainfall The UK Climate Impacts Programme (UKCIP) issued the results of their 2002 General Circulation Model (GCM) through the Meteorological Office’s Hadley Centre. The data is generally referred to as UKCIP02 scenarios.
Four scenarios are considered: High, medium-high, medium-low and low. These scenarios relate to greenhouse gas emissions and rest on assumptions regarding economic growth, technological developments and population growth.
There are three time-slices that the predictions refer to: 2020’s, 2050’s and 2080’s, with the climate change scenario results reported as an average for each: the 2020s represents the projected average climate for the period 2011-2040; the 2050s represents the projected average climate for the period 2041-2070; the 2080s represents the projected average climate for the period 2071-2100.
The baseline data with which these scenarios can be compared is the 30 year average for the period 1961-1990, Figure 43.
The GCM was run using a 50 km grid spacing. Many output datasets are available at this scale. However, for catchment scale analysis, 50 km is too coarse. The results have therefore been downscaled, by UKCIP, to a 5 km grid spacing, see Figure 42.
The average predicted monthly rainfalls for the three time-slices and for the high and low emissions scenarios, for the average of the four grid points in Figure 42 are compared with the 1961 – 1990 average in Figures 48 and 49. These are shown as relative changes from the 1961 – 1990 average in Figures 50 and 51. In keeping with general predictions from UKCIP, these show that winters are expected to become wetter, whilst summers are expected to become drier.
The current technological development of GCM’s does not allow timescales shorter than monthly to be simulated. However, critical design rainstorm durations for the two catchments are in the order of 5 to 6 hours, see Section 5.12.4 above, and for individual development or drainage areas may be even shorter.
General advice provided in Planning Policy Statement 25 on Development and Flood Risk (PPS25) (DCLG 2006) for allowing for climate change impacts is to increase design rainstorm intensities by 10% (2025-2055), by 20% (2055-2085) or by 30% (2085-2115), or to increase design peak river flow rates by 20% (2025-2115).
26 5.13 Flooding
5.13.1 PPS25 flood zones PPS25 utilises the concept of probabilistically-defined flood zones in order to test the acceptability of development close to river corridors.
Flood Zone 1 (low probability) comprises land assessed as having a less than 1 in 1000 annual probability of river or sea flooding in any year (<0.1%).
Flood Zone 2 (medium probability) comprises land assessed as having between a 1 in 100 and 1 in 1000 annual probability of river flooding (1% – 0.1%) or between a 1 in 200 and 1 in 1000 annual probability of sea flooding (0.5% – 0.1%) in any year.
Flood Zone 3 is sub-divided into two. Flood Zone 3a (high probability) comprises land assessed as having a 1 in 100 or greater annual probability of river flooding (>1%) or a 1 in 200 or greater annual probability of flooding from the sea (>0.5%) in any year. Flood Zone 3b (functional floodplain) comprises land where water has to flow or be stored in times of flood with an annual probability of 1 in 20 (5%) or greater in any year or is designed to flood in an extreme (0.1%) flood event.
The extent of Flood Zones 2 and 3 (3b is incorporated within 3a) as supplied by the EA are shown in Figure 52. Figure 53 presents the same information at a larger scale for the area around the village of Calenick, which historically suffers from flooding problems (see below).
These zones, as supplied by the EA, are indicative rather than definitive. More detailed modelling of the Flood Zone 2 and 3 areas is believed to be currently underway. The existing published zones for Zone 3 appear to be based on the Indicative Floodplain Map, which preceded the PPS25 flood zones, and is based on identifying the break in slope between relatively flat flood plain and relatively steep valley sides. The Flood Zone 2 area is based on coarse modelling and in many cases results in smaller extents than for Flood Zone 3. In these cases Flood Zone 2 has been extended to be coincident with the boundary of Flood Zone 3.
All of the development areas are within Flood Zone 1 though some, such as Higher Newham, Tregothnan Estates (Tolgarrick Farm) and Trethowan Estate have low- elevation (down-gradient) boundaries that are close to the flood zones / floodplain of the River Tinney and any plans for off-site SUDS could encroach into these zones.
5.13.2 Flood warning The Environment Agency runs a Flood Alert system to inform vulnerable residents and businesses of potential imminent flooding. The scheme is relatively new and is constrained by the presence of flow and water level monitoring stations. It has increased in density over the past few years and is currently expanding.
Both the River Kenwyn and the River Tinney are covered by Flood Warning systems.
The River Kenwyn is divided into two stretches. New Mill to Truro (Ref. 160007) has not been put on Flood Watch since its installation in November 2001, probably due to the presence of the Flood prevention scheme at New Mill, see below. The status of this station can be accessed from the link below: http://webarchive.nationalarchives.gov.uk/20140328084622/http://www.environment- agency.gov.uk/subjects/flood/floodwarning/1C0a
27 The Kenwyn at Truro (ref. 160006) includes St, George's Road, River Street, Victoria Square & Merryfield Close was similarly last put on Flood Watch on 27 November 2002 and again on 1 January 2003. The status of this station can be accessed from the link below: http://webarchive.nationalarchives.gov.uk/20140328084622/http://www.environment- agency.gov.uk/subjects/flood/floodwarning/1C0b The River Tinney at Calenick (ref. 160004) includes Bridge House, Corner House, End Cottage, Barton Croft, the A39 at Arch Hill and Calenick Lane. This station was similarly last put on Flood Watch on 27 November 2002 and again on 1 January 2003. The status of this station can be accessed from the link below: http://webarchive.nationalarchives.gov.uk/20140328084622/http://www.environment- agency.gov.uk/subjects/flood/floodwarning/1C3a 5.13.3 Flood defence schemes The River Kenwyn benefits from a flood defence scheme at New Mill. This consists of an embankment dam and flood storage area, as shown on Figure 54. This flood defence scheme was constructed in 1991 in response to the two catastrophic floods that impacted on Truro in 1988.
A flood defence scheme was installed on the River Tinney at Calenick. This was constructed in response to concerns by residents of Calenick Village to development taking place within the catchment at Gloweth. Responses to the proposed development framework from the residents of Calenick show a great deal of concern about the existing protection provided by the flood alleviation scheme and the need to upgrade it to cope with future flood pressures on the River Tinney.
5.13.4 Catchment Flood Management Plans The EA’s Catchment Flood Management Plan (CFMP) for West Cornwall, which is currently in draft, sets out the EA’s approach to flood management in the region over a timescale of the next 50 to 100 years.
Six policy options are available, as listed in Table 26. West Cornwall is divided into eight policy units for which three of these policy options: Policies 4, 5 and 6 are proposed. Figure 55 shows the distribution of these policy units and policy options for West Cornwall, as proposed by the draft CFMP. The Kenwyn and Tinney catchments, however, extend across two of the policy units: Upper Fal and Carnon Rivers (policy option 6) and Fal Estuary (policy option 5).
As the CFMP is catchment based, it would appear appropriate to align the policy unit boundaries with hydrological catchment boundaries. If the Kenwyn and Tinney catchments are allocated to the Fal Estuary policy unit then the Upper Fal and Carnon Rivers policy unit is dissected. It would therefore seem appropriate to allocate these catchments to the Fal Estuary policy unit and so policy option 5 would apply to these catchments, though the draft CFMP indicates that the area would be subject to policy option 6. This is a discrepancy that the EA will need to address when finalising the West Cornwall CFMP.
Figure 56 shows the West Cornwall CFMP policy units with the boundaries realigned to coincide with the WFD catchment boundaries, as shown in Figure 40 and Figures 57 and 58 show the same information as Figures 56 and 57 but at a larger scale, for the development areas.
28 5.13 Sewerage
5.13.1 Problem drainage areas The EA designate problem drainage areas (PDA) in order to advise local authorities on areas where the control of runoff from development areas is of the utmost importance (EA 2004).
Whilst the drainage advice has been partially superseded by the introduction of PPS25, the PDA’s are a useful indicator of areas with the most serious drainage issues. PDA’s are designated as either Red, the most serious, or Yellow. Red PDA’s are catchments where there are, or have been, severe flooding problems combined with significant development pressures that can cause even minor developments to contribute to increased flood risks. Yellow PDA’s do not have the same level of development pressures but for which flooding risks are still particularly sensitive to increases in runoff. There are only three Red designated PDA’s in Cornwall, one of which is the River Tinney catchment.
Figure 59 shows the PDA’s for the Truro area. All of the southern sites and the TLDR are within the Red PDA of the Tinney catchment. The northern sites are all within the Yellow PDA’s that make up parts of the Kenwyn catchment.
EA drainage advice (EA 2004) states that for development areas greater than 1 ha in area within Red PDA’s SUDS drainage should be designed to incorporate: (i) Infiltration drainage with capacity based on a 1 in 100 year annual probability design storm event (ii) Infiltration drainage to 1 in 30 year annual probability event with on-site detention of surface water up to the 100 year event (iii) Positive drainage restricted to the mean annual flood greenfield runoff rate and with storage provided for runoff in excess of this rate up to the 1 in 100 year return period storm.
For yellow PDA’s and development areas greater than 1 ha the criteria are: (i) Infiltration drainage to 1 in 30 year annual probability event with on-site detention of surface water up to the 50 year event (ii) Positive drainage with allowable discharge rates varying from greenfield runoff rates for the mean annual flood up to the 1 in 10 year return period flow and, for events exceeding this, for further storage on site up to the 1 in 100 year event.
5.13.2 Sewerage network Figure 60 shows the entire sewerage network that serves the Truro area and feeds into South West Water’s (SWW) sewage treatment plant at Newham. The network is made up of foul water sewers that do not contain surface water, surface water sewers that convey only rainwater runoff and combined sewers that carry a mixture of foul and surface water.
In addition to the Truro and Highertown areas the SWW network serves Shortlanesend, to the north, Malpas to the southeast, Feock to the south and Threemilestone to the west, all through combined sewers.
The combined sewer from Shorlanesend runs south and southeast, into the centre of Truro, where it is joined by foul and surface water sewers serving the city, and enters Newham sewage treatment works (STW) from the north, along the west side of the Truro River. The combined sewer from Malpas runs northwest along the east side of
29 the Truro River and crosses the river just south of Garras Wharf, joining the combined sewer from the city.
Threemilestone is served by separate foul and surface water sewers. The surface water drains to outfalls into two tributaries to the River Tinney. The foul water feeds into the main combined sewer spline that runs from west to east along the River Tinney valley to Newham STW.
Feock is served by a combined sewer that flows northwards and collects further discharges from Penelewey and Playing Place, from where some surface water sewers outfall to Cowlands Creek and into the Fal. The combined sewer continues northwards to join the main east-west combined sewer spline at Calenick, which then runs along the line of the Newham branch line, the southern boundary of the Higher Newham site, and enters the Newham STW from the west.
Figure 61 shows the sewerage network in more detail for the development area. It also includes the locations of surface water outfalls and combined sewer overflows (CSO). Maps showing the sewerage system adjoining each development site are included in the site data sheets in Volume 4 of this report.
5.13.3 Existing SuDS Also shown on Figure 61 are the locations of soakaways that are recorded on SWW’s database. This is, however, only a very small sample of the soakaways that are actually present in the area. SWW only started recording their locations in 2004 and many private soakaways will not have been registered with SWW.
It is also known that recent and currently being constructed sites will contain SuDS that do not appear yet on SWW’s sewerage database, and may never appear on any central database. For example, surface water drainage from the newly constructed Richard Lander School, at the western end of the TLDR, by the Goonvean sire, utilises a large soakaway combined with a detention pond. Also the new Park and Ride Scheme at Threemilestone will use a comprehensive system of SuDS involving infiltration, surface detention and swales.
30 6 DISCUSSION
6.1 Sustainable drainage systems
6.3.1 Implications of the study This Stage 1 report has collated information that is relevant to the application of SuDS within the Truro and Threemilestone area. General implications for each of the development sites and constraints that have been identified are listed at the end of each of the Site Data Sheets in Volume 4 of this report.
The Stage 2 report will address potential SuDS design at each of the sites in more detail.
The main constraints are: • Steep topography • The railway line and its embankments, including the Newham Branch Line Trail • Lack of space on some sites • The elongated shapes of some sites • The presence of the fuel on pipeline on the Goonvean and Treliske sites
6.3.2 Data limitations As discussed in Section 5.13.3 above, there is no database of existing SuDS. This would be useful information to have as it would indicate where, and which, systems are successful and add to the general knowledge base on SuDS.
Additionally, infiltration-based SuDS require percolation tests to be conducted in order to prove their suitability in specific ground conditions. Again, there is no central database of these results for sites in the locality that have been tested. Such a database would allow the variability of soil infiltration rates to be assessed and also may indicate geographical areas that have suitable, or less suitable, infiltration characteristics. Percolation tests conducted on behalf of the Local Authority (CDC or CCC) could be considered to be in the public domain and could be compiled and made available, but those conducted by developers may not be so accessible.
6.2 Biodiversity and ecology
6.3.1 Implications of the study The Stage 1 study has identified general areas of high ecological and biodiversity importance within the area. Species data in particular, however, is of limited use unless the results of site-specific surveys are made available (see below).
The Stage 2 report will identify biodiversity opportunities in relation to SuDS in more detail. The importance of hedgerows, tree lines and water courses as biodiversity corridors and linkages will be highlighted within the Stage 2 report.
6.3.2 Data and survey limitations Species records were mostly gathered by volunteers without a strict methodology. The broad habitat data is not directly parallel to the UK designations such as arable
31 field margins. There are habitats present such as hedgerows which are not included and yet are key for linking important wildlife sites.
The data used is of mixed ages and some is too old to be useful. This combined with the lack of detailed grid references means that it was not possible to produce meaningful maps.
The habitat data needs updating as it was collated in 1995 and there could have been substantial changes since then.
The species data is limited and needs review. This should establish the validity of the records. This includes identification of species, links to individual sites and date. Site surveys by local experts should identify what is present, especially invertebrates and lower plants.
The habitat data needs to be revised to include the new BAP Habitats.
New data for specific developments such as Richard Lander needs to be collated for species.
We need to identify the impacts to species and habitats off site so that we can consider how to reduce them/ compensate and enhance.
A hedge survey is essential for the whole area which follows nationally recognised systems. All hedgerows of a certain length are BAP habitat.
It is essential that up to date surveys are undertaken to supplement the existing species data. This will probably be on a site by site basis but ideally an 8 figure grid reference for notable species would be most useful.
There needs to be a clear decision between parties about what provides an adequate data base.
A walkover survey is necessary to identify the areas of opportunity for biodiversity which will both improve sites and link to other existing areas.
6.3 Access
6.3.1 Implications of the study The distribution and density of public rights of way in the area covered by this study indicates that there is poor connectivity between the existing public rights of way and the areas most likely to received additional residential development. Consultation with users groups, the existing residents and the Cornwall Countryside Access Forum
6.3.2 Data Limitations The Definitive Map and Statement should be consulted to obtain the legally recorded position of a recorded footpath, bridleway or byway (Cornwall currently has no restricted byways). There may be other public rights that exist that are not recorded at the current time.
32 7 REFERENCES
CDC (2007). Carrick Local Development Framework; Truro and Threemilestone Area Action Plan. Preferred options under Regulation 26. January 2007.
CEH (2006). FEH CD-ROM v.2.0. Centre for Ecology & Hydrology. Wallingford, UK.
CIRIA (1992). Scope for control of urban runoff. Report 123. Construction Industry Research and Information Association, London.
CIRIA (1996). Infiltration drainage: manual of good practice. Report 156. Construction Industry Research and Information Association, London.
CIRIA (2000). Sustainable urban drainage systems. Design manual for England and Wales. Report C522. Construction Industry Research and Information Association.
CIRIA (2001). Sustainable urban drainage systems. Best practice manual for England, Scotland, Wales and Northern Ireland. Report C522. Construction Industry Research and Information Association.
CIRIA (2004a). Sustainable drainage systems. Hydraulic, structural and water quality advice. Report C609. Construction Industry Research and Information Association.
CIRIA (2004b). Model agreements for sustainable water management systems Model agreements for SUDS. Report C625. Construction Industry Research and Information Association.
DCLG (2005). Planning Policy Statement 9: Biodiversity and Geological Conservation. Department for Communities and Local Government.
DCLG (2006). Planning Policy Statement 25: Development ad Flood Risk. Department for Communities and Local Government.
DCLG (2007). Development and Flood Risk: A Practice Guide Companion to PPS25. Department for Communities and Local Government.
DEFRA (2004). Making space for water – Developing a new Government Strategy for flood and coastal erosion management in England. Consultation document. Department for the Environment, Food and Rural Affairs.
EA (2003a). Sustainable Drainage Systems (SUDS). An introduction. Environment Agency.
EA (2003b). Sustainable Drainage Systems (SUDS). A guide for developers. Environment Agency.
EA (2004). Environment Agency Drainage Guidance for Cornwall. Environment Agency South Western Region.
EA (2007). Managing Flood Risk. West Cornwall Catchment Flood Management Plan. Consultation Draft Plan (February 2007). Environment Agency.
33 Kjeldsen, T. R., Stewart, E. J., Packman, J. C., Bayliss, A. C. and Folwell, S. (2005). Revitalisation of the FSR/FEH Rainfall-Runoff method. Final research report to Defra/EA, Centre for Ecology & Hydrology, Wallingford, UK.
NERC (1975). Flood Studies Report. Natural Environment Research Council.
NERC (1999). Flood Estimation Handbook. Natural Environment Research Council.
ODPM (2003a). Sustainable Communities; Delivering through planning. Office of the Deputy Prime Minister.
ODPM (2003b). Framework for Sustainable Drainage Systems (SUDS) in England and Wales. National SUDS Working Group. Office of the Deputy Prime Minister.
ODPM (2004). Interim Code of Practice for Sustainable Drainage Systems. National SUDS Working Group. Office of the Deputy Prime Minister.
34 01 Higher Newham
Site area = 53.36 ha
Fig. 01-1 Site boundary on OS MasterMap
Fig. 01-2 Site boundary on OS aerial photography (2005)
1
Fig. 01-3 Broad habitat (ERCCIS 1995)
Table 01-1 Broad habitat (ERCCIS 1995) Broad Habitat Area (ha) Area (%) Improved Grassland 49.815 93.35 Arable and Horticulture 1.377 2.58 Built-up areas and Gardens 1.167 2.19 Broadleaved, mixed and yew woodland 0.973 1.82 Coniferous woodland 0.032 0.06
2
Fig. 01-4 Tree preservation
Table 01-2 No of records from ERCCIS notable species database Records with 100 m precision within 50 m. 48 Records with 1000 m precision within 500 m. 274 Records with 2000 m precision within 1000 m. 3
Table 01-3 Taxon groups of notable species records within the Truro and Threemilestone region Taxon Group No. of records No. of species Conifer 2 1 Flowering plant 279 152 Fern 17 9 insect - butterfly 1 1 insect - hymenopteran 2 2 insect - true fly (Diptera) 4 4 Reptile 2 1 Bird 35 21 Terrestrial mammal 4 2
3
Fig. 01-5 Topographic relief as contours and hillshading, from DTM
Fig. 01-6 3D perspective view of DSM looking from the south east (Note: vertical exaggeration of times 2)
4
Fig. 01-7 3D perspective view of DSM looking from the south west (Note: vertical exaggeration of times 2)
Fig. 01-8 Drainage pathways from NextMap DTM
5
Fig. 01-8 Sewerage pathways
Implication for SuDS The site is predominantly improved grassland but with important hedgerows containing mature trees that provide valuable biodiversity linkages.
The site is dome-shaped, the highest elevation being northwest of the centre and sloping down to all sides.
The southern boundary of the site is marked by the Newham Trail. Though not marked as a Public Right of Way, as such, it is a designated cycle trail. It is the embankment of the old Newham Branch railway line. The embankment is very steep-sided and the land falls away sharply to the south toward Calenick Creek. This land is downstream of the village of Calenick and so there should be no implications for the village.
SuDS within the site area will need a buffer zone between them and the embankment to avoid excessive ponding of water against the embankment. SuDS off-site to the south could be accommodated between the embankment and the creek, though this land is outside of the present site ownership and is currently agricultural. Any water leaving the site through the site boundary would need to cross the embankment via a culvert or tunnel.
Drainage of the northern part of the site is generally in a northeast direction. Connection to the Truro River here would be constrained by the existing industrial area at Newham Quay.
6 Potential on-site SuDS solutions could include a series of southward running cascades with vegetated strips in an east-west direction, along the ground contours, to serve the southern part of the site. The northern part could be served with a lagoon / wetland in the northeast corner of the site. Drainage to the west should be avoided, as should connection to the combined sewer running along the western boundary of the site as this could create flooding and an increased pressure on the combined sewer overflow at Calenick.
7 02 Tregothnan Estates (Tolgarrick Farm)
Site area = 31.54 ha
Fig. 02-1 Site boundary on OS MasterMap
Fig. 02-2 Site boundary on OS aerial photography (2005)
8
Fig. 02-3 Broad habitat (ERCCIS 1995)
Table 02-1 Broad habitat (ERCCIS 1995) Broad Habitat ha % Improved Grassland 27.532 87.29 Built-up areas and Gardens 2.074 6.57 Broadleaved, mixed and yew woodland 1.911 6.06 Bracken 0.018 0.06 Coniferous woodland 0.006 0.02
Table 02-2 No of records from ERCCIS notable species database Records with 100 m precision within 50 m. 54 Records with 1000 m precision within 500 m. 486 Records with 2000 m precision within 1000 m. 3
9 Table 02-3 Taxon groups of notable species records within the Truro and Threemilestone region Taxon Group No. of records No. of species Conifer 2 1 Flowering plant 439 191 Fern 37 12 Lichen 1 1 Moss 1 1 insect - butterfly 1 1 insect - hymenopteran 2 2 insect - true fly (Diptera) 6 4 Amphibian 5 3 Reptile 2 1 Bird 35 21 Terrestrial mammal 3 3
Fig. 02-4 Topographic relief as contours and hillshading, from DTM
10
Fig. 02-5 3D perspective view of DSM looking from the south east (Note: vertical exaggeration of times 2)
Fig. 02-6 3D perspective view of DSM looking from the south west (Note: vertical exaggeration of times 2)
11
Fig. 02-7 Drainage pathways
Fig. 02-8 Sewerage pathways
12 Implication for SuDS This site is predominantly grassland, with some hedgerows and tree lines.
The southern boundary is the Newham trail along the old Newham railway branch line. This is on a steep embankment, and some cuttings, with a sheer, almost vertical, cliff face dropping down to the south in places.
A stream/drain runs along the southeast boundary, flowing down from Arch Hill. toward the River Tinney, upstream of Calenick village. Drainage is generally toward this and toward the southwest boundary, where the Newham train and embankment are.
There are two natural valleys on the site; the one with the stream by Arch Hill and one crossing the centre of the site. SuDs are likely to be centred around these features. Any water entering the stream by Arch Hill should be carefully controlled so as not to impact on Calenick village. Additionally, a relative flat area of ground appears to be present toward the western corner of the site that could be potentially used for SuDS serving that part of the site.
Care should be taken to avoid disturbance of the landfill area, just off-site near the southern corner, upstream of Calenick.
13 03 Richard Lander
Site area = 5.35 ha
Fig. 03-1 Site boundary on OS MasterMap
Fig. 03-2 Site boundary on OS aerial photography (2005)
14
Fig. 03-3 Broad habitat (ERCCIS 1995)
Table 03-1 Broad habitat (ERCCIS 1995) Broad Habitat ha % Improved Grassland 4.564 85.22 Broadleaved, mixed and yew woodland 0.406 7.58 Built-up areas and Gardens 0.342 6.38 Neutral Grassland 0.044 0.82
15
Fig. 03-4 Tree preservation
Table 03-2 No of records from ERCCIS notable species database Records with 100 m precision within 50 m. 0 Records with 1000 m precision within 500 m. 303 Records with 2000 m precision within 1000 m. 3
Table 03-3 Taxon groups of notable species records within the Richard Lander Site No of records from ERCCIS notable species database Taxon Group No. of records No. of species Flowering plant 252 130 Fern 24 11 Lichen 1 1 Moss 1 1 insect - true fly (Diptera) 2 1 Amphibian 3 3 Reptile 2 1 Bird 22 14 Terrestrial mammal 1 1
16
Fig. 03-5 Topographic relief as contours and hillshading, from DTM
Fig. 03-6 3D perspective view of DSM looking from thesout east (Note: vertical exaggeration of times 2)
17
Fig. 03-7 Drainage pathways
Fig. 03-8 Sewerage pathways
18 Implication for SuDS This is a highly scenic area with pasture and mature trees. There are believed to be a springs on site.
If the line of the TLDR remains as taken in this report then there will be little space for development.
The northern part of the site is a tree preservation area.
A valley crosses the centre of the site and there appear to be water issues along this valley, which is also wooded. The water appears to cross beneath the railway line opposite New County Hall before flowing south to the River Tinney. It is not presently clear how the watercourse crosses the railway, though it appears that it may be piped southward to the outflow, shown on Figure 03-7 above.
A combined sewer crosses the site just to the north of the streamline of the valley.
SuDS would be likely to be created either side of this valley centreline, serving the northern and southern parts of the site independently.
19 04 Cornwall County Council
Site area = 8.29 ha
Fig. 04-1 Site boundary on OS MasterMap
Fig. 04-2 Site boundary on OS aerial photography (2005)
20
Fig. 04-3 Broad habitat (ERCCIS 1995)
Table 04-1 Broad habitat (ERCCIS 1995) Broad Habitat ha % Improved Grassland 4.489 54.18 Built-up areas and Gardens 3.456 41.72 Coniferous woodland 0.206 2.49 Broadleaved, mixed and yew woodland 0.134 1.61
21
Fig. 04-4 Tree preservation
Table 04-2 Listing of Tree Preservation Order trees on site Species Number Ash 7 Two stemmed Ash 2 Birch 2 Cherry 1 Horse Chestnut 1 Oak 2 Pine 1 Purple Sycamore 1 Rowan 3 Sorbus 2 Sweet Chestnut 1 Sycamore 2 Willow 1
22 Table 04-3 No of records from ERCCIS notable species database Records with 100 m precision within 50 m. 3 Records with 1000 m precision within 500 m. 194 Records with 2000 m precision within 1000 m. 3
Table 04-4 Taxon groups of notable species records within the Truro and Threemilestone region Taxon Group No. of records No. of species Flowering plant 185 117 Fern 12 10 Moss 1 1
Fig. 04-5 Topographic relief as contours and hillshading, from DTM
23
Fig. 04-6 3D perspective view of DSM looking from the south east (Note: vertical exaggeration of times 2)
Fig. 04-7 3D perspective view of DSM looking from the north (Note: vertical exaggeration of times 2)
24
Fig. 04-8 Drainage pathways
Fig. 04-9 Sewerage pathways
25 Implication for SuDS This is the site of the old Richard Lander School. About half of the site is presently built up and the remainder is grassland with some woodland along the southern boundary. There are numerous tree preservation orders on the site.
The area is fairly flat and is close to the boundary of the River Tinney and River Kenwyn catchments. Drainage is generally outwards from the centre, though biased toward the southwest boundary and toward an unnamed tributary to the River Tinney that flows through the Trethowan Estate site.
There is little scope here for above ground SuDS and infiltration techniques may be the likely option.
26 05 Trethowan Estate
Site area = 25.07 ha
Fig. 05-1 Site boundary on OS MasterMap
Fig. 05-2 Site boundary on OS aerial photography (2005)
27
Fig. 05-3 Broad habitat (ERCCIS 1995)
Table 05-1 Broad habitat (ERCCIS 1995) Broad Habitat ha % Improved Grassland 21.765 87.13 Broadleaved, mixed and yew woodland 2.035 8.15 Neutral Grassland 0.749 3.00 Built-up areas and Gardens 0.430 1.72
28
Fig. 05-4 Tree preservation
Table 05-2 No of records from ERCCIS notable species database Records with 100 m precision within 50 m. 10 Records with 1000 m precision within 500 m. 384 Records with 2000 m precision within 1000 m. 3
Table 05-3 Taxon groups of notable species records within the Truro and Threemilestone region Taxon Group No. of records No. of species Flowering plant 358 168 Fern 28 12 Moss 1 1 Amphibian 1 1 Bird 8 7
29
Fig. 05-5 Topographic relief as contours and hillshading, from DTM
Fig. 05-6 3D perspective view of DSM looking from the south east (Note: vertical exaggeration of times 2)
30
Fig. 05-7 3D perspective view of DSM looking from the south west (Note: vertical exaggeration of times 2)
Fig. 05-8 Drainage pathways
31
Fig. 05-9 Sewerage pathways
Implication for SuDS This site is mainly improved grassland with a wooded valley, which is a tree preservation area, running through its centre. The stream appears to be fed via a spring located near the northern boundary of the site. This stream also receives surface water from the built up area of Highertown, south of the A390. The western boundary is also a wooded valley of the Gloweth Stream.
The line of the TLDR may make up the southern boundary of the site, running alongside the railway.
Drainage is generally in a southerly direction and toward the centre and western valleys.
SuDS are likely to be located adjacent to the two valleys. The railway line may form a constraint on the route of water to the River Tinney. Both streams crossing the site also cross the railway line before their confluences with the river.
SuDS schemes on this site need to take account of the drainage system for the TLDR and may need to work in conjunction with it.
32 06 Truro Tennis Club
Site area = 1.27 ha
Fig. 06-1 Site boundary on OS MasterMap
Fig. 06-2 Site boundary on OS aerial photography (2005)
33
Fig. 06-3 Broad habitat (ERCCIS 1995)
Table 06-1 Broad habitat (ERCCIS 1995) Broad Habitat ha % Built-up areas and Gardens 0.555 43.62 Broadleaved, mixed and yew woodland 0.370 29.08 Neutral Grassland 0.278 21.88 Improved Grassland 0.069 5.42
34
Fig. 06-4 Tree preservation
Table 06-2 No of records from ERCCIS notable species database Records with 100 m precision within 50 m. 5 Records with 1000 m precision within 500 m. 190 Records with 2000 m precision within 1000 m. 1
Table 06-3 Taxon groups of notable species records within the Truro and Threemilestone region Taxon Group No. of records No. of species Flowering plant 172 128 Fern 15 10 Amphibian 1 1 Bird 8 6
35
Fig. 06-5 Topographic relief as contours and hillshading, from DTM
Fig. 06-6 3D perspective view of DSM looking from the south east (Note: vertical exaggeration of times 2)
36
Fig. 06-7 Drainage pathways
Fig. 06-8 Sewerage pathways
37 Implication for SuDS This small and elongated site is presently about half urban (tennis courts and associated clubhouse) and the remainder is grassland with woodland boundaries. The whole site is within a tree preservation area.
It is bounded on the east by the Trethowan Estates site and to the west by the Gloweth Stream.
The natural drainage is westwards to the Gloweth Stream, which drains Gloweth and runs through Halbullock Moor Nature Reserve. At the northwest corner of the site the stream runs under the road and becomes a ford during times of high flow.
The possibilities for SuDS are extremely limited at this site due to its small size and its location in relation to the Gloweth Stream. On-site infiltration may be possible, but the close proximity to the stream may imply a high water table, which would limit infiltration drainage.
38 07 Newbridge Farm
Site area = 4.23 ha
Fig. 07-1 Site boundary on OS MasterMap
Fig. 07-2 Site boundary on OS aerial photography (2005)
39
Fig. 07-3 Broad habitat (ERCCIS 1995)
Table 07-1 Broad habitat (ERCCIS 1995) Broad Habitat ha % Neutral Grassland 1.925 45.50 Improved Grassland 1.863 44.04 Broadleaved, mixed and yew woodland 0.410 9.68 Built-up areas and Gardens 0.033 0.78
Table 07-2 No of records from ERCCIS notable species database Records with 100 m precision within 50 m. 0 Records with 1000 m precision within 500 m. 190 Records with 2000 m precision within 1000 m. 1
Table 07-3 Taxon groups of notable species records within the Truro and Threemilestone region Taxon Group No. of records No. of species Flowering plant 172 128 Fern 15 10 Bird 4 4
40
Fig. 07-4 Topographic relief as contours and hillshading, from DTM
Fig. 07-5 3D perspective view of DSM looking from the south east (Note: vertical exaggeration of times 2)
41
Fig. 07-6 3D perspective view of DSM looking from the north west (Note: vertical exaggeration of times 2)
Fig. 07-7 Drainage pathways
42
Fig. 07-8 Sewerage pathways
Implication for SuDS This site is mainly improved grassland and is bounded to the southwest by the unclassified road, to the west by a wooded hedgerow and to the north by Halbullock Moor and woodlands. The northern part of the site contains a wet meadow area that is likely to have a very high biodiversity value and it is important that this area is not allowed to dry out due to development.
The site slopes generally in a north-westerly direction, being on the southern side of the valley to the Gloweth Stream, toward the western corner of the site.
The natural drainage of this area is complex with the Gloweth stream running southward from Gloweth, through Halbullock Moor Nature Reserve, to the northern boundary of the site where it has its confluence with a tributary that runs eastwards along the northern boundary of the Goonvean site.
It is essential that the hydrology of Halbullock Moor is not adversely impacted by development in this area, or its associated drainage. This site is important from a hydrological and ecological perspective due to its proximity with Halbullock Moor and the generally high biodiversity value of the area.
On-site SuDS may take up a significant amount of space on this site in order to keep the existing wet meadow in a favourable condition, especially if the TLDR does dissect the site, as assumed in this report. This may leave little space for development. Drainage in this area is further complicated by the fact that land to the north has already been allocated for development. Plans for drainage of this site (Persimmon Homes) need to be taken into account.
43 08 Goonvean
Site area = 21.83 ha
Fig. 08-1 Site boundary on OS MasterMap
Fig. 08-2 Site boundary on OS aerial photography (2005)
44
Fig. 08-3 Broad habitat (ERCCIS 1995)
Table 08-1 Broad habitat (ERCCIS 1995) Broad Habitat ha % Improved Grassland 20.885 95.65 Broadleaved, mixed and yew woodland 0.709 3.25 Built-up areas and Gardens 0.218 1.00 Coniferous woodland 0.016 0.07 Arable and Horticulture 0.007 0.03
45
Fig. 08-4 Mining features with the 1880’s OS map as a backdrop
The areas shown in green to the south and on the western edge of the site are likely to contain mine waste. The mine to the south is North Jane.
This mine is thought to have commenced in 1707 as Besore Mine, operating as Wheal Evelyn in the 1850's (working on Lead Lode in the SE sector of the sett). The site became North Jane in 1861 and continued until 1875.
Main Lode was worked from Western Footway Shaft SW 7869 4392, Gossan Shaft at SW 7876 4393, New Shaft at SW 7883 4397, Kerrs Shaft at SW 7891 4400 and Kerrs Footway Shaft at SW 7899 4402.
There are three known adit portals. A cross cut adit from Western Footway Shaft extends 220m to its portal at SW 7883 4378. A parallel cross cut adit runs from Gossan Shaft to a portal at SW 7891 4378. Deep Adit portal is at SW 7956 4376.
The mine worked lead, arsenic (sulphides), silver and iron.
The trend of the mine workings is ENE, diverging from the approximately W to E flowing stream. At their closest point the main workings are 150m from this watercourse. The three adit portals are adjacent to this watercourse.
46
Fig. 08-5 Location of fuel oil pipeline and 30m buffer zone
Table 08-2 No of records from ERCCIS notable species database Records with 100 m precision within 50 m. 1 Records with 1000 m precision within 500 m. 194 Records with 2000 m precision within 1000 m. 1
Table 08-3 Taxon groups of notable species records within the Truro and Threemilestone region Taxon Group No. of records No. of species Conifer 2 1 Flowering plant 439 191 Fern 37 12 Lichen 1 1 Moss 1 1 insect - butterfly 1 1 insect - hymenopteran 2 2 insect - true fly (Diptera) 6 4 Amphibian 5 3 Reptile 2 1 Bird 35 21 Terrestrial mammal 3 3
47
Fig. 08-4 Topographic relief as contours and hillshading, from DTM
Fig. 08-5 3D perspective view of DSM looking from the north east (Note: vertical exaggeration of times 2)
48
Fig. 08-6 3D perspective view of DSM looking from the north west (Note: vertical exaggeration of times 2)
Fig. 08-7 Drainage pathways
49
Fig. 08-8 Sewerage pathways
Implication for SuDS This large site is presently improved grassland with hedgerows, some of which contain mature tree lines that may be important biodiversity links.
The TLDR runs slightly to the north of this site. The site slopes down to the north, being on the southern flank of a stream that flows eastwards to form a tributary to the Gloweth Stream, which itself is a tributary to the River Tinney.
Mining-related land may be present along the western boundary to the site, but this is unlikely to impact on the drainage as it is at the highest elevation of the site. The fuel oil pipeline runs across the western part of the site and both drainage and development should avoid this area, though it could be allocated as green space.
The likely location for SuDS is along the northern boundary of the site, probably toward the central area. The main constraints are the elongated shape of the site, the proximity of the stream and the presence of the pipeline.
50 09 Willow Green
Site area = 29.90 ha
Fig. 09-1 Site boundary on OS MasterMap
Fig. 09-2 Site boundary on OS aerial photography (2005)
51
Fig. 09-3 Broad habitat (ERCCIS 1995)
Table 09-1 Broad habitat (ERCCIS 1995) Broad Habitat ha % Improved Grassland 20.947 70.06 Arable and Horticulture 4.872 16.29 Broadleaved, mixed and yew woodland 2.245 7.51 Built-up areas and Gardens 1.441 4.82 Coniferous woodland 0.309 1.03 Openwater / Rivers and Streams 0.061 0.21 Fen, marsh and swamp 0.024 0.08
52
Fig. 09-4 Mining features with the 1880’s OS map as a backdrop
The areas shown in green are likely to contain mine waste. The mine at the west is South Penhaldarva and the one to the north is Penhaldarva. North Penhaldarva mine is slightly further to the north, see Figure 18 of main report.
Penhaldarva: Active 1855 - 1865. Being prospected in 1855. Suspended 1863 - 65.
Mined lead, copper (sulphide), silver.
Two of the three mine shafts in the valley bottom are within 30m of an ENE flowing watercourse. The third shaft is 70m S of this watercourse. The main area of associated land is 160m SSE of the above stream and 100m ESE of one of its tributaries.
South Penhaldarva Thought to have been active between 1857 and 1865, but was 'suspended' between 1863 and 1865.
Mined lead (sulphide).
The area of associated land 200m ESE of Willow Green is adjacent to a small ENE flowing watercourse.
53 Table 09-2 No of records from ERCCIS notable species database Records with 100 m precision within 50 m. 54 Records with 1000 m precision within 500 m. 145 Records with 2000 m precision within 1000 m. 2
Table 09-3 Taxon groups of notable species records within the Truro and Threemilestone region Taxon Group No. of records No. of species Flowering plant 159 82 Fern 4 2 insect - butterfly 2 1 Amphibian 5 2 Bird 30 13 Terrestrial mammal 1 1
Fig. 09-4 Topographic relief as contours and hillshading, from DTM
54
Fig. 09-5 3D perspective view of DSM looking from the north (Note: vertical exaggeration of times 2)
Fig. 09-6 3D perspective view of DSM looking from the north east (Note: vertical exaggeration of times 2)
55
Fig. 09-7 Drainage pathways
Fig. 09-8 Sewerage pathways
56 Implication for SuDS This site is generally rolling pasture with hedgerows, some of which contain mature trees.
There may be some mining-related land in the central-northern and the eastern areas of the site that could indicate potential contaminated land issues.
The land slopes generally north and east, and is in the River Kenwyn catchment. The western and central areas contain a valley with a northward flowing stream that is a tributary to the Langarth Stream. The eastern site drains to a stream that flows eastwards, directly to the River Kenwyn.
The eastward flowing stream contains ponds at its source, within the site.
Mains drainage in the area is constricted to the southern side of the River Kenwyn / River Tinney catchment divide. Positive drainage associated with this site would need to be pumped across the catchment boundary or else a new sewerage spline would need to be constructed within the River Kenwyn valley.
There do not appear to be any particular constraints to the use of SuDS on this site. The site is likely to be separated into two for drainage purposes, each section centred on each of the two streams.
57 10 Treliske
Site area = 18.72 ha
Fig. 10-1 Site boundary on OS MasterMap
Fig. 10-2 Site boundary on OS aerial photography (2005)
58
Fig. 10-3 Broad habitat (ERCCIS 1995)
Table 10-1 Broad habitat (ERCCIS 1995) Broad Habitat ha % Improved Grassland 17.498 93.47 Broadleaved, mixed and yew woodland 0.981 5.24 Built-up areas and Gardens 0.169 0.90 Broadleaved, mixed and yew woodland 0.066 0.35 Arable and Horticulture 0.003 0.02 Fen, marsh and swamp 0.003 0.01
59
Fig. 10-4 Location of fuel oil pipeline and 30m buffer zone
Table 10-2 No of records from ERCCIS notable species database Records with 100 m precision within 50 m. 1 Records with 1000 m precision within 500 m. 236 Records with 2000 m precision within 1000 m. 1
Table 10-3 Taxon groups of notable species records within the Truro and Threemilestone region Taxon Group No. of records No. of species Flowering plant 190 120 Fern 9 6 Lichen 2 2 insect - butterfly 2 1 Amphibian 5 2 Bird 28 13 Terrestrial mammal 3 1
60
Fig. 10-4 Topographic relief as contours and hillshading, from DTM
Fig. 10-5 3D perspective view of DSM looking from the north east (Note: vertical exaggeration of times 2)
61
Fig. 10-6 3D perspective view of DSM looking from the west (Note: vertical exaggeration of times 2)
Fig. 10-7 Drainage pathways
62
Fig. 10-8 Sewerage pathways
Implication for SuDS This site is very elongated – it is believed that the shape is constrained by the possible route of a northern distributor road.
The site is improved grassland with a wooded stream, originating from the eastern end of the Willow green site, running across the centre.
The fuel oil pipeline runs across the western part of this site and both development and drainage should be avoided in this area.
Drainage is to the central valley and at the eastern extreme to a smaller valley to the east.
A surface water drain flows north across the eastern side of the site. This is a private sewer that conveys water from Treliske Hospital.
There is potential for SuDS along the course of the stream with the woodland providing a buffer strip between the SuDS and the stream. The main constraint with on-site SuDS is the elongated shape of the site.
63 11 Golf Course
Site area = 44.99 ha
Fig. 11-1 Site boundary on OS MasterMap
Fig. 11-2 Site boundary on OS aerial photography (2005)
64
Fig. 11-3 Broad habitat (ERCCIS 1995)
Table 11-1 Broad habitat (ERCCIS 1995) Broad Habitat ha % Improved Grassland 36.418 80.95 Broadleaved, mixed and yew woodland 4.420 9.83 Coniferous woodland 2.483 5.52 Built-up areas and Gardens 0.924 2.05 Unmapped 0.744 1.65
Table 11-2 No of records from ERCCIS notable species database Records with 100 m precision within 50 m. 28 Records with 1000 m precision within 500 m. 276 Records with 2000 m precision within 1000 m. 4
65
Table 11-3 Taxon groups of notable species records within the Golf Course site region Taxon Group No. of records No. of species Conifer 0 0 Flowering plant 195 126 Fern 16 9 Lichen 2 2 Moss 1 1 Reptile 1 1 Bird 91 9 Terrestrial mammal 2 1
Fig. 11-4 Topographic relief as contours and hillshading, from DTM
66
Fig. 11-5 3D perspective view of DSM looking from the east (Note: vertical exaggeration of times 2)
Fig. 11-6 3D perspective view of DSM looking from the north (Note: vertical exaggeration of times 2)
67
Fig. 11-7 Drainage pathways
Fig. 11-8 Sewerage pathways
68 Implications for SuDS This site is presently used as a golf course and the land use is classed as improved grassland with strips of coniferous and broadleaved woodland, forming valuable biodiversity and habitat linkages.
Treliske Preparatory School is enclosed by the site. There does not appear to be any mains drainage associated with the school.
The western side of the site slopes eastwards and northwards. The centre of the site is a high point and slopes down to the north, east and south. The northern part of the site drains northwards to the River Kenwyn, just upstream of the New Mill Dam flood storage area. There is no surface expression of this drainage route (on the OS map) and so rainfall here probably dissipates through infiltration. The southwest limb of the site drains eastwards to join an eastward flowing tributary to the River Kenwyn, downstream of New Mill Dam. This stream rises at a pond on the site of the school.
The stream has steeply sloping valley sides. The right bank (south side) of the sream is wooded, providing a buffer between the stream and the existing urban area at Highertown. The stream provides a high value biodiversity corridor.
The steeply sloping valley sides of the stream are a constraint on SuDS in the south- eastern part of the site. The valley in the northern part of the site could provide a focus for SuDS with ponds that outfall to infiltration.
69 12 Truro Local Distributor Road (TLDR)
Site area = 14.34 ha
Fig. 12-1 Site boundary on OS MasterMap, west side
Fig. 12-2 Site boundary on OS MasterMap, east side
70
Fig. 12-3 Site boundary on OS aerial photography (2005), west side
Fig. 12-4 Site boundary on OS aerial photography (2005), east side
71
Fig. 12-5 Broad habitat (ERCCIS 1995), west side
Fig. 12-6 Broad habitat (ERCCIS 1995), east side
72 Table 12-1 Broad habitat (ERCCIS 1995) Broad Habitat ha % Improved Grassland 11.273 78.59 Broadleaved, mixed and yew woodland 1.389 9.68 Neutral Grassland 0.812 5.66 Built-up areas and Gardens 0.768 5.36 Coniferous woodland 0.072 0.50 Fen, marsh and swamp 0.030 0.21
Fig. 12-7 Tree preservation, west side
73
Fig. 12-8 Tree preservation, east side
Table 12-2 No of records from ERCCIS notable species database Records with 100 m precision within 50 m. 19 Records with 1000 m precision within 500 m. 497 Records with 2000 m precision within 1000 m. 4
Table 12-3 Taxon groups of notable species records within the Truro and Threemilestone region Taxon Group No. of records No. of species Flowering plant 439 184 Fern 41 13 Lichen 2 2 Moss 1 1 insect - true fly (Diptera) 1 1 Amphibian 5 3 Bird 31 19 Terrestrial mammal 2 2
74
Fig. 12-9 Topographic relief as contours and hillshading, from DTM, west side
Fig. 12-10 Topographic relief as contours and hillshading, from DTM, east side
75
Fig. 12-11 3D perspective view of DSM, west side, looking from the east (Note: vertical exaggeration of times 2)
Fig. 12-12 3D perspective view of DSM, west side, looking from the south (Note: vertical exaggeration of times 2)
76
Fig. 12-13 3D perspective view of DSM, east side, looking from the west (Note: vertical exaggeration of times 2)
Fig. 12-14 3D perspective view of DSM, east side, looking from the south (Note: vertical exaggeration of times 2)
77
Fig. 12-15 Drainage pathways, west side
Fig. 12-16 Drainage pathways, east side
78
Fig. 12-17 Sewerage pathways, west side
Fig. 12-18 Sewerage pathways, east side
79 Implications for SuDS The route of the TLDR as assumed for this report is not necessarily the finalised route and, in particular, the spur roads and the roundabouts may not be as shown here. However, planning for the TLDR is at a more advanced stage than for the development sites.
The main route of the TLDR follows the valley of the eastward flowing tributary of the Gloweth Stream, north of the River Tinney and the Goonvean site (08). It then continues southwards along the lower reach of the Gloweth Stream, through the Newbridge Farm site (07) and west of the Tennis Club site (06) before continuing eastwards along the northern flank of the River Tinney valley, skirting the southern boundary of the Trethowan Estates site (05), alongside the railway line. The road then crosses the railway line at the Richard Lander site (03) as it continues east, passing south of New County Hall and onto the Tregothnan Estates site (02).
There is scope for shared SuDS systems between the TLDR and the development sites that it runs through or adjacent to.
The main constraint on SuDS in relation to the TLDR is the presence of the railway line and the lack of space between the route of the road and the railway, in places. The steep topography of the River Tinney valley is also a feature that constrains the use of SuDS.
Key areas of hydrological concern along the route of the TLDR, where SuDS need to be considered particularly carefully, are the region to the south of Halbullock Moor by Newbridge Farm and the region around the Richard Lander site and New County Hall.
80 13 Kenwyn
Site area = 49.14 ha
Fig. 13-1 Site boundary on OS MasterMap
Fig. 13-2 Site boundary on OS aerial photography (2005)
14
Fig. 13-3 Broad habitat (ERCCIS 1995)
Table 03-1 Broad habitat (ERCCIS 1995) Broad Habitat ha % Improved Grassland 43.670 88.93 Built-up areas and Gardens 2.955 6.02 Broadleaved, mixed and yew woodland 1.736 3.53 Coniferous woodland 0.422 0.86 Arable and Horticulture 0.325 0.66
15
Fig. 13-4 Tree preservation
Table 13-2 No of records from ERCCIS notable species database Records with 100 m precision within 50 m. 11 Records with 1000 m precision within 500 m. 148 Records with 2000 m precision within 1000 m. 3
Table 13-3 Taxon groups of notable species records within the Kenwyn Site No of records from ERCCIS notable species database Taxon Group No. of records No. of species Flowering plant 122 77 Fern 8 6 Lichen 0 0 Moss 2 1 insect - true fly (Diptera) 3 3 Amphibian 3 2 Reptile 1 1 Bird 19 10 Terrestrial mammal 2 1
16
Fig. 13-5 location of landfill sites
Fig. 13-6 Topographic relief as contours and hillshading, from DTM
17
Fig. 13-7 3D perspective view of DSM looking from the south (Note: vertical exaggeration of times 2)
Fig. 13-8 3D perspective view of DSM looking from the east (Note: vertical exaggeration of times 2)
18
Fig. 13-9 Drainage pathways
Fig. 13-10 Sewerage pathways
19 Implication for SuDS The site is predominantly improved grassland but also contains the present rugby ground. Kenwyn Caravan Park is located in the centre of the site and the future of this is presently uncertain, so it could potentially be incorporated into the site.
The area is generally dome-shaped with a well defined valley running eastward to the River Allen. To the west and south the land slopes down steeply into the Kenwyn Valley.
This site straddles two river catchments: the Kenwyn to the west and the Allen to the east. Both the Kenwyn and the Allen have detention dams and associated flood storage areas but these are both upstream of the site and so the site is between the flood defences and the city of Truro which means that no protection is afforded to Truro from surface runoff generated from this site.
The existing urban area adjoining the site to the south is generally drained to combined sewer systems.
The eastern part of the site is potentially an area containing inert landfill waste, which may create a restriction on SuDS, pending detailed site investigation.
The site would need to contain two separate strategic SuDS. One to the east in the Allen catchment could be focussed on the eastward trending valley. To the west, in the Kenwyn catchment the steep topography may restrict the potential for strategic SuDS and a diffuse system, such as individual soakaways, may be required.
20