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WATER RESOURCES, DRAINABLE AND FLOOD RISK
INTRODUCTION
An assessment of the potential effects on the water environment, to comprise surface water
(hydrology), groundwater (hydrogeology) and flood risk, within the vicinity of the application site will be carried out.
Key Issues
The site slopes and naturally drains from east to west towards Silverstone Brook. 1.3
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Silverstone Brook is a right bank tributary of the River Tove (which flows in an easterly direction on the northern side of Towcester). Silverstone Brook flows in a north-easterly direction approximately 100 m from the application site’s north-western boundary.
According to the EA Flood Map the site is located in Flood Zone 1 (low probability). However, significant areas of Towcester are in Flood Zones 2 and 3 (moderate to significant probability respectively).
Silverstone Brook is included in the Water Framework Directive (WFD) Anglian River Basin
Management Plan (RBMP). The ecological status of Silverstone Brook has been assessed by the
Environment Agency (EA) as Moderate (and expected to remain Moderate by 2015).
The Upper Ouse and Bedford Ouse Catchment Abstraction Management Strategy (March 2005) indicates the River Tove is used for public water supply within the catchment.
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According to the EA Groundwater Vulnerability Map the site is partly underlain by a Secondary A
Superficial Aquifer, and by a Principal, Secondary A and B Bedrock Aquifer. These aquifers are referred to in the Anglian RBMP as the Upper Bedford Ouse Oolite Principal 1 and Upper Bedford
Ouse Oolite Secondary.
According to the RBMP, the quantitative status of both groundwater bodies underlying the site is assessed as Good. The chemical status for the Upper Bedford Ouse Oolite Principal 1 and the
Upper Bedford Ouse Oolite Secondary is assessed as Poor and Good respectively.
1.10 According to the British Geological Survey (BGS) Groundwater Flooding Hazard Map the susceptibility to groundwater flooding varies across the site generally from not susceptible to significant susceptibility.
1.11 POTENTIAL SIGNIFICANT ENVIRONMENTAL EFFECTS
Significance Criteria
1.12 Surface and sub-surface receptors potentially susceptible to environmental impact from flooding and drainage issues associated with the proposed development have been provisionally identified. This includes the assessment of construction and operational impacts. These are subject to confirmation as the EIA is undertaken and baseline conditions assessed.

1.13 The ‘importance’ of each receptor will be designated using professional judgment and by reference to relevant guidance criteria, taking into account the quality and rarity of each receptor.
1.14 In order to assess the impact significance of the proposed development on the identified receptors, the characteristics of each identified impact at the construction and operational stages have been considered.
1.15 Identified impacts may be significant at the level of importance defined for the receptor, or at a lesser geographical scale. For example, limited impacts on a watercourse of County value might be assessed as being significant at a District level.
1.16 Thus, the significance of effects will be determined from the importance of the receptor, the magnitude of the impact and, where appropriate, the likelihood of the effect occurring.
Receptors
1.17 The likely receptors and their importance/scale to be assessed are listed in Table 1 below. All receptors and receptor importance will be confirmed as the EIA is undertaken.
1.18 Table 1: Development Receptors – Preliminary Identification and Importance
Receptor Nature of Impact Receptor Importance
Local to District Silverstone Brook
Agricultural drains
Water quality (Construction and
Operational Phase)
Water quality/flood risk (Construction and Operational Phase)
Aquifers Water quality (Construction and
Operational Phase)
Development residents and visitors
(north-west of the site)
Flood risk (Operational Phase)
Towcester residents and property
Flood risk (Construction and
Operational Phase)
Local
Regional
Very high
Very high
Note: To be confirmed during the EIA
Potential Effects
1.19 The potential unmitigated water environment effects considered significant to the application site include:
Construction Phase
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A reduction in surface and ground water quality due to contamination of runoff and/or changes to surface water drainage patterns and pathways from the surface to the underlying aquifer; and

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Increased risk of flooding to people and plant due to: o Increase in volume of construction related traffic using the A43 to the north-west of the site, o Increase in runoff due to soil compaction.
Operational Phase
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An increase in surface water runoff (volume and rate) due to an increase in impermeable areas; leading to o An increase in risk of flooding due to increase in volume of water in the minor spring sourced agricultural drains, which run along the southern and northern boundaries, and within the centre area of the site; o A reduction in surface water runoff quality due to an increase in impermeable areas and in traffic volumes. Contaminated surface runoff could enter local water bodies; and
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Foul water from the developed site could pollute receptor water bodies.
Cumulative Impacts
1.20 The ES chapter will include a consideration of the cumulative impacts arising from the development of sites at:
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Towcester Vale
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Land off Belle Baulk, Towcester
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Moat Lane, Towcester
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Wood Burcote Court
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Silverstone Circuit, Silverstone
1.21 These sites are within close proximity to the application site and/or are located within the
Silverstone Brook/River Tove catchment, and could potentially impact on part/all of the same environmental receptors as those identified for the application site.
1.22 We do not propose including the Brackley urban extension site in the cumulative assessment due to its distance from the application site (approximately 14 km) and the fact that the site is located within the upper River Great Ouse catchment.
1.23 SCOPE OF THE WATER RESOURCES, DRAINABLE AND FLOOD RISK ASSESSMENT
1.24 The assessment will consider the potential effects on the water environment (both surface and sub-surface) and local hydrology. It will consider the capability of available water resources and supply networks to service the proposed development, in addition to an assessment of the location and capacity of the existing sewerage infrastructure including wastewater treatment works.

1.25 The assessment will be informed by a Flood Risk Assessment (FRA) based on the requirements of the National Planning Policy Framework and its Technical Guidance. The FRA will include:
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Details of historic flooding events;
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Identification of potential sources of flooding;
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An appraisal of the scope of possible measures to reduce the risk of flooding to and from the proposed development;
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An assessment of pre and post development runoff rates, including the identification of the most appropriate method of surface water disposal;
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Calculations for indicative storage volumes, including consideration of climate change; and
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A surface water drainage scheme based on sustainable drainage principles highlighting how sustainable drainage measures can be utilised to mitigate the impact of the proposed development on the water environment.
Methodology of the Assessment
1.26 Baseline information considering water quality, flooding and drainage, ground conditions, and topography, will be based on a desktop study, site visits, stakeholder consultations, and relevant guidance and legislation.
1.27 The methodology for carrying out baseline research includes the following:
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Review currently available data and information, including information on water resources
(abstractions, designations etc) and on surface and sub-surface water quality, at and within the vicinity of the application site;
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Review international and national legislation and regulations relevant to the assessment of potential impacts to hydrology and drainage. In addition, review guidance and policy documents including, yet not exclusively, those published by the Department of Communities and Local Government, DEFRA, the EA, CIRIA and by relevant regional and local authorities including Strategic Flood Risk Assessments and Catchment Management Plans;
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Consult with the EA and Northampton County Council (NCC) (the Local Lead Flood Authority) regarding flood risk and drainage issues;
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Consult with NCC and South Northamptonshire Council regarding highways flooding and flooding of ordinary watercourses;
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Consult with Anglian Water regarding the potential impact of the proposed development on the existing sewerage infrastructure and on the availability of potable water to service the site and surrounding area; and
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Review the risk of groundwater flooding and the potential impact of the development on the quality of groundwater and amount of groundwater recharge with reference to soil types, the
British Geological Survey groundwater flooding maps, and the impact of the proposed

development and associated SuDS scheme on the quality and quantity of surface water infiltration.
1.28 MITIGATION M EASURES
1.29 It is envisaged that the potential impacts on the water environment from the proposed development will be mitigated through a series of measures during both the construction and operational phases of the proposed development.
Construction Phase
1.30 These may include:
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Implementation of a Construction Environmental Management Plan;
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Best construction practices; and
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Sealed storage vessels to contain foul water from temporary staff welfare facilities and disposed of off-site.
Operational Phase
1.31 These may include:
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Implement a surface water drainage scheme based on sustainable drainage principles;
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Implement a maintenance and management regime to prevent build up of debris and/or rubbish in water bodies on site; and
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Develop a foul water drainage strategy through consultation with Anglian Water and the EA to ensure foul water from the proposed development is sustainably managed.