Chapter 9: Water, Hydrology and Drainage Land West of Uttoxeter

Transcription

1 Chapter 9: Water, Hydrology and Drainage Land West of Uttoxeter ENVIRONMENTAL STATEMENT: VOLUME 1

2 9.1 INTRODUCTION This Chapter considers the effects of the Project on surface water and groundwater resources, flood risk and local drainage infrastructure. The assessment also considers the potential for flood risk associated with alterations in the surface water regime and from adjacent watercourses. Potential effects during the construction period are also identified and assessed The Chapter describes the policy context and methods used to assess the impacts of the Project. It reviews the Site s hydrology, hydrogeology, flood risk and drainage prior to development of the Project and the baseline conditions currently existing at the Site. The potential effects of the Project are assessed, taking into account the measures which have been adopted to prevent, reduce, mitigate or offset the impacts. The significance of the residual effects is also presented Potential impacts to ground and surface water quality are assessed in Chapter 8: Ground Conditions, whilst potential effects on aquatic flora, fauna and protected sites are addressed in Chapter 6: Ecological Resources (including Arboriculture). This Chapter has been written by Waterman Transport and Development Ltd and draws on the findings of a Flood Risk Assessment and Drainage Strategy prepared by Waterman Transport and Development (WTD) (presented in Volume 4 of this Environmental Statement). 9.2 METHODOLOGY Baseline conditions relating to hydrology, hydrogeology, flood risk and drainage at the Site have been established using a combination of published information and site surveys. A full list of information sources is presented within the Flood Risk Assessment and Drainage Strategy in Volume 4, however, main sources of information include: Site visits and walkover surveys; Consultation with the Environment Agency (EA); Consultation with Severn Trent Water Consultation with East Staffordshire Borough Council Consultation with Staffordshire County Council Consultation with the Highways Agency Consultation with Connect Roads (A50 maintenance contractor) British Geological Survey (BGS) Information; The Flood Risk Assessment and Drainage Strategy in Volume 4, which forms the basis of this Chapter, followed the approach set out in National Planning Policy Framework, the Technical Guidance to the National Planning Policy Framework, EA Flood Risk Assessment Guidance Note 1 and the East Staffordshire Borough Council Level 1 Strategic Flood Risk Assessment and examined: Site hydrology, hydrogeology and drainage; Potential sources of flooding; 1

3 Impact of the Development on flood risk; Mitigation measures required to reduce flood risk to the Development and elsewhere and; The management of surface and foul water so as not to increase and if possible decrease flood risk elsewhere This assessment determines the relative significance of water, hydrology and drainage issues and impacts. The assessment of potential and residual impacts / risks has therefore used the following seven-point scale of significance, which has been based upon professional judgement and experience: Substantial Beneficial: Significant local-scale / moderate to significant regional scale improvement to the quantity of potable groundwater, surface water resources, drainage infrastructure or reduction in flood risk. Moderate Beneficial: Moderate local-scale / minor regional improvement to the quantity of potable groundwater, surface water resources, drainage infrastructure or reduction in flood risk. Minor Beneficial: Minor local-scale improvement to the quantity of potable groundwater, surface water resources, drainage infrastructure or reduction in flood risk. Negligible: No appreciable impact on groundwater, surface water resources, drainage infrastructure or flood risk. Minor Adverse: Minor local-scale reduction in the quantity of potable groundwater, or surface water resources, reversible with time, minor reduction in the capacity of drainage infrastructure or minor local-scale increase in flood risk. Moderate Adverse: Moderate local-scale / minor regional increase in flood risk, severe temporary or permanent reduction in the quantity of a potable groundwater or surface water resources or severe temporary or permanent reduction in capacity of drainage infrastructure. Substantial Adverse: Significant local-scale / moderate to significant regional scale increase in flood risk, permanent reduction in the quantity of a potable groundwater or surface water resources or permanent reduction in capacity of drainage infrastructure. 9.3 PLANNING POLICY CONTEXT National National Planning Policy Framework (March 2012) 10. Meeting the challenge of climate change, flooding and coastal change The National Planning Policy Framework sets out Government policy on development and flood risk. It aims are to ensure that flood risk is taken into account at all stages of the planning process, to avoid inappropriate development in areas at risk of flooding by directing development 2

4 away from areas at highest risk, but where development is necessary, making it safe without increasing flood risk elsewhere. The National Planning Policy Framework advocates the use of the risk-based Sequential Test, to steer new development to areas with the lowest probability of flooding. The National Planning Policy Framework states that Development should not be allocated or permitted if there are reasonably available sites appropriate for the proposed development in areas with a lower probability of flooding. The National Planning Policy Framework also recommends that within any Development, the most vulnerable development is located in areas of lowest flood risk unless there are overriding reasons to prefer a different location, the development is appropriately flood resilient and resistant, including safe access and escape routes where required, any residual risk can be safely managed, including by emergency planning and it gives priority to the use of sustainable drainage systems. Local East Staffordshire Borough Council Green Infrastructure Study (March 2008) The overall purpose of this study is to provide a long term vision for green infrastructure within East Staffordshire to ensure that the current strategic growth of the Borough is fully integrated with and informed by its green infrastructure and to ensure that no net loss of green infrastructure value or provision occurs This study recommends that all developments should be served by Sustainable Drainage Systems (SuDs) where feasible and that the component features of these systems should be designed and managed to deliver additional green infrastructure benefits, such as wildlife habitat improvement and provision, landscape enhancement and informal recreation. East Staffordshire Borough Level 1 Strategic Flood Risk Assessment (Feb 2008) The East Staffordshire Borough Council Level 1 Strategic Flood Risk Assessment (SFRA) provides a robust assessment of the extent and nature of the risk of flooding and its implications for land use planning. In addition, the SFRA sets the criteria for the submission of planning applications in the future and for guiding subsequent development control decisions The SFRA recommends that no development should take place in the Functional Floodplain (Flood Zone 3b), all proposals in Flood Zones 2 and 3 should be subjected to the Sequential Test and the Exception Test (if required), the surface water drainage arrangements for any development site should be such that the volumes and peak flow rates of surface water leaving a developed site are no greater than the rates prior to the proposed development, unless specific off-site arrangements are made and result in the same net effect, Developers are encouraged to promote the use of SUDS for the management of run-off, Developments which include areas likely to flood will need to provide appropriate flood warning and formulate appropriate emergency plans to ensure their safe occupancy in the future and Developers should always consider residual flood risk issues relating to a development. 3

5 9.4 BASELINE CONDITIONS Topography A topographical survey shows that the Site generally falls to the northeast from a high point of approximately 112 meters Above Ordnance Datum (m AOD) in the southwest of the Site to approximately 90m AOD in the north of the Site. Hydrology A number of unnamed ordinary watercourse s are present across the Site which drain the surrounding fields. All of these unnamed ordinary watercourse s drain via a number of culverts beneath the A50 to the River Tean located approximately 250m north of the Site There are four licensed discharges to surface water within the 2km of the Site which are summarised in the table below. Operator Discharge Type Receiving watercourse Distance from the Site Trust Inns Limited Sewage Tributary of the River Tean 51m NE Severn Trent Water Sewage Local ditch 102m E Severn Trent Water Sewage Park Brook (River Tean) 122m E J A Hemingway Sewage Not defined 556m N There is one licensed surface water abstraction within the 2km of the Site which is summarised in the table below. Operator Abstraction Purpose Water Feature Distance from the Site East Staffordshire Municipal Grounds: Bramshall Recreation 927m S Borough Council Lake And Pond Ground - Picknall Brook Throughflow Geology Ground conditions beneath the Site are summarised below and have been established from the British Geological Survey Map 140 Burton Upon Trent Solid & Drift Edition 1:50,000 scale and exploratory holes from the British Geological Survey website. 4

6 Stratum Area Covered Thickness of stratum Typical Description Surfacing Whole Site Up to 0.6m Topsoil Buried structures Park Farm Up to 1.2m Foundations, services and former basements Made Ground Park Farm Unknown Maybe present around current buildings and former gravel pits Glacial Till Whole Site 2m to 3m Brown sandy CLAY with gravel Glaciofluvial Deposits North west of the Site 2m to 3m Loose to very dense fine to coarse sub rounded to sub angular GRAVEL with silty sand layers Groundwater Groundwater is not anticipated in the low permeability Glacial Till. Groundwater is likely to be present in the Glaciofluvial Deposits and the more permeable horizons in the Mercia Mudstone Group. Groundwater is recorded in the majority of the exploratory hole records obtained from the British Geological Survey, within the Glaciofluvial Deposits, at between 0.5mbgl and 2.7mbgl There are two licensed discharges to groundwater within the 2km of the Site which are summarised in the table below. Operator Discharge Type Distance from the Site Giltan Homes Limited Sewage 186m N Steven Russell Sewage 290m E There are six licensed groundwater abstractions within the 2km of the Site which are summarised in the table below. Operator Abstraction Purpose Distance from the Site Mr T Tideswell General Farming and Domestic 673m NW Mr T R Statham General Agriculture 714m S Mr T R Statham General Farming and Domestic 714m S Mr R C Meakin General Farming and Domestic 1572m S Mr A C Ede General Farming and Domestic 1695m N JW Brandwick & Son General Farming and Domestic 1781m W 5

7 Drainage Surface water at the Site is currently drained via a number of unnamed ordinary watercourses which are tributaries of the River Tean approximately 250m north of the Site. No positive foul water drainage features are present at the Site Severn Trent Water maps in Appendix E of the Flood Risk Assessment and Drainage Strategy in Volume 4, show a network of 150mm to 225mm diameter public sewers draining to a pumping station off Torrance Grove, approximately 160m east of the Site, which serves the residential area to the east of the Site A private pumping station associated with the JCB World Parts Centre is located approximately 125m north of the Site. A private rising main from this pumping station flows east along the A522 until it becomes a public rising main approximately 550m east of the Site. Flood Risk The information below is based upon the findings of the Flood Risk Assessment and Drainage Strategy in Volume 4, which should be referred to for further information The Site is considered to be at low risk of flooding from tidal, groundwater, reservoir, canal and artificial sources The risk of fluvial flooding from the River Tean is considered to be low. Proposed hydraulic modelling of the unnamed ordinary watercourses at the Site is required to assess the risk of fluvial flooding from these watercourses at the Site. It was agreed at a meeting with the Environment Agency on 21 st May 2013 that this modelling will be undertaken during the planning application determination period. On completion of this modelling the Flood Risk Assessment and Drainage Strategy in Volume 4 and this Chapter will be updated Environment Agency Areas Susceptible to Surface Water Flooding Map and Surface Water Flood Maps in Appendix D of the Flood Risk Assessment and Drainage Strategy in Volume 4 suggest that there are areas of the Site that are more susceptible to surface water flooding. These areas are either unnamed ordinary watercourses or low spots at the Site A topographical survey and OS mapping show that any pluvial flows originating to the west of the Site would be routed towards the Site. Hence, there is considered to be a risk of pluvial flooding occurring at the Site. 9.5 POTENTIAL EFFECTS Parts of the Project are shown crossing the unnamed ordinary watercourses at the Site. If no consideration is given to peak flows, proposed crossings of the unnamed ordinary watercourses at the Site could have a long term moderate adverse effect on flood risk at the Site. Temporary crossings may also be required during construction. If no consideration is given to peak flows, such crossings could have a potential short term moderate effect on the risk of flooding at the Site Depending on groundwater levels present in the Glaciofluvial deposits in the northwest of the Site dewatering activities may be required during construction. Any dewatering could temporally affect 6

8 groundwater levels at the Site and elsewhere and could potentially affect flows in the unnamed ordinary watercourses at the Site. Dewatering during construction could have a short term minor adverse effect on the quantity of potable groundwater at the Site and elsewhere and on surface water resources at the Site The increase in impermeable area with the Project could reduce the rate of groundwater recharge to the underlying Glaciofluvial Deposits which could affect groundwater flows and consequently groundwater available for extraction from nearby licensed boreholes Construction earthworks, dewatering and temporary site drainage associated with construction traffic routes and temporary car parks could increase surface water runoff into the unnamed ordinary watercourses at the Site which could have a short term substantial adverse affect on flood risk at the Site and downstream The Project would result in an increase in impermeable area and could increase surface water runoff into the unnamed ordinary watercourses at the Site which could have a long term moderate adverse effect on the quantity of potable groundwater elsewhere and a long term substantial effect impact on flood risk at the Site and elsewhere Discharging foul water from the Project to the existing public sewer network is likely to cause surcharging and/or flooding of the existing public sewer network, which could have a long term substantial adverse impact on flood risk and the capacity of drainage infrastructure elsewhere. 9.6 PROJECT DESIGN Any existing culverts on the Site should be abandoned as part of the Project. To reduce the number and length of crossings it is proposed to divert the unnamed ordinary watercourses in accordance the Manual for River Restoration Techniques Where crossing are required to allow essential access over the Ordinary Watercourses, these could be spanning bridges or culverts. Any culverts would need to be designed in accordance with CIRIA Report C689 Culvert Design and Operation Guide Appropriate water discharges rates and volumes will be agreed with the EA prior to any dewatering taking place SuDs such as infiltration devices, pervious surfaces, swales, filter drains, infiltration basins or ponds would to be incorporated into the Project. Where applicable these features would be unlined to allow infiltration in the northwest of the Site and partial infiltration in the rest of the Site to allow the recharge of groundwater During construction a temporary drainage system would be provided to ensure surface water runoff to unnamed ordinary watercourses at the Site is restricted to a greenfield rate The Project would have a sustainable drainage system which restricts surface water runoff from the Site to unnamed ordinary watercourses to a greenfield rate of 5l/s/ha The Project would not connect to the existing public sewer network until any required upgrading works have been undertaken. 7

9 9.6.8 To reduce the risk of surface water flooding, surface water attenuation will be provided at the Site for up to the 1 in 100 year (+30% for climate change) storm event Land drainage from the land to the west of the Site would be catered for in the proposed sustainable drainage system Although hydraulic modelling is required to assess the risk of fluvial flooding from unnamed ordinary watercourses at the Site. If required, to manage the risk of fluvial flooding at the Site and ensure flood risk is not increased at the Site or elsewhere, the following mitigation measures could be utilised: setting building finished floor levels 600mm above the 1 in 100 year (+20% for climate change) flood level flood compensation works if the Project encroached into the floodplain establishment of a safe dry access/egress route from the Site during a 1 in 100 year (+20% for climate change) flood event. 9.7 ASSESSMENT OF EFFECTS Demolition and Construction Effects Temporary crossing over the unnamed ordinary watercourses at the Site would be designed in accordance with CIRIA Report C689 Culvert Design and Operation Guide. The temporary crossings over the unnamed ordinary watercourses at the Site could have a short term minor beneficial effect on flood risk at the Site As appropriate water discharges rates and volumes will be agreed with the EA prior to any dewatering taking place, dewatering at the Site during construction could have a short term negligible effect on the quantity of potable groundwater at the Site and elsewhere and surface water resources at the Site By restricting runoff surface water runoff to unnamed ordinary watercourses at the Site to a greenfield rate during construction there should be a short term negligible effect on flood risk at the Site and elsewhere. 9.8 RESIDUAL EFFECTS Operational Effects As existing culverts on the Site should be abandoned as part of the Project, the length and number of crossings would be reduced by diversion of unnamed ordinary watercourses and any proposed diversions of ordinary watercourse or culverting should be designed in accordance with the Manual for River Restoration Techniques and CIRIA Report C689 Culvert Design and Operation Guide. The proposed crossings over the unnamed ordinary watercourses at the Site could have a long term minor beneficial effect on flood risk at the Site. 8

10 9.8.2 Unlined SuDs such as infiltration devices, pervious surfaces, swales, filter drains, infiltration basins or ponds could mean that the Development has a long term negligible effect on the quantity of potable groundwater at the Site and elsewhere As the Project should have a sustainable drainage system which restricts surface water runoff from the Site to unnamed ordinary watercourses to a greenfield rate of 5l/s/ha there should be a long term negligible effect on flood risk at the Site and elsewhere As the Project should not connect to the existing public sewer network until any required upgrading works have been undertaken there should be a long term negligible effect on flood risk and the capacity of drainage infrastructure elsewhere As surface water attenuation should be provided at the Site for up to the 1 in 100 year (+30% for climate change) storm event there should be a long term moderate beneficial effect on the risk of surface water flooding at the Site As land drainage from the land to the west of the Site would be catered for in the proposed sustainable drainage system there should be a long term moderate beneficial effect on the risk of pluvial flooding at the Site Although hydraulic modelling is required to assess the risk of fluvial flooding from unnamed ordinary watercourses at the Site. If required, to manage the risk of fluvial flooding at the Site and ensure flood risk is not increased at the Site or elsewhere, the following mitigation measures could be utilised: setting building finished floor levels 600mm above the 1 in 100 year (+20% for climate change) flood level flood compensation works if the Development encroached into the floodplain establishing a safe dry access/egress route from the Site during a 1 in 100 year (+20% for climate change) flood event would be established As a minimum this would ensure there was a long term negligible effect on fluvial flooding at the Site and elsewhere. 9.9 CUMULATIVE EFFECTS This section assesses the likely significant effects of this Project when considered in the context of other future projects During construction, following implementation of the mitigation measures outlined above there would be a short term minor beneficial impact on flood risk at the Site and a short term negligible impact on flood risk elsewhere, the quantity of potable groundwater at the Site and elsewhere and surface water resources at the Site During operation of the Project, following implementation of the mitigation measures outlined above there would be a long term moderate beneficial impact on the risk of surface water and pluvial flooding at the Site, a long term minor beneficial impact on flood risk at the Site and a long term negligible impact on flood risk elsewhere, the quantity of potable groundwater at the Site and elsewhere and drainage infrastructure elsewhere. 9

11 9.9.4 No future projects allocated within development plans (current adopted or emerging), having planning permission or awaiting consent have been identified during the preparation of this ES that would increase the likely significant effects of this Project 9.10 STATEMENT OF EFFECTS During construction by ensuring temporary crossings are designed and constructed correctly, agreeing dewatering rates with the Environment Agency and restricting surface water runoff to unnamed ordinary watercourses at the Site to a greenfield rate, there would be a short term minor beneficial effect on flood risk at the Site and a short term negligible effect on flood risk elsewhere, the quantity of potable groundwater at the Site and elsewhere and surface water resources at the Site During operation of the Project the following design and mitigation measures would be implemented: Abandoning existing culverts; Limiting the number of crossing required over the unnamed ordinary watercourses at the Site; Ensuring crossings and watercourse diversions are designed and constructed correctly, Utilising unlined SuDs; Restricting surface water runoff from the Site to unnamed ordinary watercourses to a greenfield rate of 5l/s/ha; Not connecting the Development to the existing public sewer network until any required upgrading works have been undertaken; Providing surface water attenuation for up to the 1 in 100 year (+30% for climate change) storm event at the Site; Catering for land drainage from the land to the west of the Site in the proposed sustainable drainage system; Ensuring building finished floor levels are set 600mm above the 1 in 100 year (+20% for climate change) flood level; Utilising flood compensation works if the Development encroaches into the floodplain and; Establishing a safe dry access/egress route is available from the Site during a 1 in 100 year (+20% for climate change) storm Hence, there would be a long term moderate beneficial effect on the risk of surface water and pluvial flooding at the Site, a long term minor beneficial effect on flood risk at the Site and a long term negligible effect on flood risk elsewhere, the quantity of potable groundwater at the Site and elsewhere and drainage infrastructure elsewhere. 10