Flood Risk Assessment for Planning November 2019

V3.0 251119 Flood Risk Assessment for Planning

Prepared for: Mr and Mrs Coppen-Gardner

Location: Halls Farm November 2019 Ash Lane Silchester

Reading Our reference: Berkshire 88068-CoppenGardner-HallsFarm v3.0 RG7 2NH

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Document Issue Record

Project: Flood Risk Assessment for Planning

Client: Mr and Mrs Coppen-Gardner

Location: Halls Farm, Ash Lane, Silchester, Reading, Berkshire RG7 2NH

Application: Replacement of stables and other ancillary buildings with the erection of a four bed dwelling house and car port with associated parking, landscaping and private amenity space

Our reference: 88068-CoppenGardner-HallsFarm

Version: v3.0 051119

Lead Consultant: Mr Edward Bouët, Ms Jackie Stone

Amended: Mr Edward Bouët

Authorisation: Mrs Emma Jeffery

This report (including any enclosures and attachments) has been prepared for the exclusive use and benefit of the commissioning party and solely for the purpose for which it is provided. Unless we provide express prior written consent, no part of this report should be reproduced, distributed or communicated to any third party. We do not accept any liability if this report is used for an alternative purpose from which it is intended, nor to any third party in respect of this report. Any data and information provided by third parties and referred to herein has not been checked or verified by us unless otherwise expressly stated within this report. This report was checked and approved on the date it was issued and is therefore valid on this date. Understanding, circumstances, regulations and professional standards do change, which could subsequently affect the validity of this report.

Southpoint, Old Brighton Road, Gatwick, West Sussex, RH11 0PR

+44 (0) 1293 214 444

www.unda.co.uk

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Key Facts

Flood Risk Posed:

 Site is within Flood Zones 3a, 2 and 1.  Fluvial risk from the Silchester Brook.  Product 4 data has been provided by the EA (Ref: THM_151597).  Comparison of the modelled 1:100 year flood level with allowance for climate change (66.11mAOD) with topographic site levels (65.17m AOD – 68.28m AOD) confirms that the site is partially below the design flood level.  Records of historical flooding in the area September 1992.  Risk of pluvial flooding would appear to be “Very Low” to “Low”.  The site is not located upstream or within a designated Critical Drainage Area.  Risk of groundwater and sewer surcharge flooding would appear to be low.

Flood Risk Management:

 Development will not take place within 8m of a main river. A Flood Risk Activity Permit will therefore not be required.  All proposed new buildings are located outside of Flood Zone 3, and on land above the modelled 1:100 year flood level with allowance for climate change (+70%).  There will be no loss of fluvial flood storage within Flood Zone 3, or below the 1:100 year (+70%) allowance for climate change flood level.  The site is not located within an EA flood warning area.  Flood proofing of the buildings will be incorporated as appropriate.  Dry, safe escape can be provided from the site to an area entirely outside of Flood Zones 2 and 3, as per the technical requirements of the NPPF.

Assuming accordance with these flood risk management measures, Unda Consulting Limited consider the proposed application to be suitable in flood risk terms.

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Introduction

Unda Consulting Limited have been appointed by Mr and Mrs Coppen-Gardner (hereinafter referred to as “the applicant”) to undertake a Site Specific Flood Risk Assessment (FRA) for Planning at Halls Farm, Ash Lane, Silchester, Reading, Berkshire RG7 2NH (hereinafter referred to as “the site”). The FRA has been undertaken in accordance with the National Planning Policy Framework (NPPF) July 2018 and the associated technical guidance.

The site appears to be located within Flood Zones 1, 2 and 3a as defined by the Environment Agency (EA) on their Flood Map for Planning. Under the National Planning Policy Framework (NPPF), a FRA is required if a proposed development:

 includes building or engineering works in Flood Zone 2 or 3;  includes building or engineering works on land classified by the Environment Agency as having critical drainage problem;  changes the use of land or buildings in a location at risk of flooding from rivers or the sea, or with critical drainage problems;  changes the use of land or buildings in a way that increases the flood vulnerability of the development where it may be subject to other sources of flooding;  is larger than 1 hectare.

Given that the proposed application site is located partially within Flood Zones 1, 2 and 3a (Low, Medium and High Risk of flooding from rivers or the sea respectively), and includes building works, the applicant is required to submit a FRA under the NPPF. The assessment should demonstrate to the Local Planning Authority (LPA) and EA how flood risk will be managed now and over the development’s lifetime, taking climate change into account, and with regard to the vulnerability of its potential users.

The objectives of a FRA to support a planning application are to establish:

 whether the proposed development is likely to be affected by current or future flooding from any source;  whether it will increase flood risk elsewhere;  whether the measures proposed to deal with these effects and risks are appropriate.

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Existing Situation

Site Usage:

The site is currently occupied by stables and other ancillary agricultural and equine buildings. The property is located at Halls Farm, Ash Lane, Silchester, Reading, Berkshire RG7 2NH.

Detailed existing site plans are provided in the report Appendix.

An image showing site location is presented below in Figure 1.

Figure 1: Aerial view of the site and immediate surrounding area (Source: Google Earth)

Topography:

A topographic survey has been undertaken for the site by 360Geomatics in January 2018 (drawing number: 360G/1002T/100).

Recorded ground topographic levels on site indicate there is a slight downward gradient on the site from south 65.95m AOD to north 68.28mAOD.

A copy of the topographic survey is provided in the report Appendix.

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Geology and Soil:

The British Geological Survey (BGS) Map indicates that the bedrock underlying the site is London Clay Formation - Clay, Silt and Sand. Sedimentary Bedrock formed approximately 48 to 56 million years ago in the Palaeogene Period. There is no record of any superficial geology underlying the site.

Figure 2: Bedrock geology (Source: BGS)

The soil type on site, is taken from the UKSO data, is deep river riverine clay, sands and gravels with a clay to sandy loam soil texture with a neutral soil pH.

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Figure 3: Local soil types (Source: UKSO)

Hydrology:

The nearest watercourse Silchester Brook is located 13m from the northern boundary of the site.

The Greenfield Runoff Rate has been calculated using Micro Drainage (ICP SUDS); this can be found in the report Appendix. Please note that a minimum flow of 5 l/s applies to any site.

As per the newly published climate change allowances (February 2016) for anticipated changes in extreme rainfall intensity in small and urban catchments, the upper end (40% increase) peak rainfall intensity allowances should be assessed to understand the impact of climate change.

Riparian Ownership:

A riparian owner is someone who owns land or property alongside a river or other watercourses. A watercourse is any natural or artificial channel through which water flows including flow through a culvert, ditch, drain, cut, dyke, sluice or private sewer.

Riparian owners have statutory responsibilities, including:

 Maintaining river beds and banks;  Allowing the flow of water to pass without obstruction;  Controlling invasive alien species

Further guidance for riverside property owners can be found in the Environment Agency’s helpful booklet ‘Living on the Edge, 5th Edition’ published in June 2014.

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Environmental Permit for Flood Risk Activity:

Under the Environmental Permitting (England and Wales) Regulations 2010 any activity within 8m of the bank of a main river, or 16m if it is a tidal main river, or any activity within 8m of any flood defence structure or culvert on a main river, or 16m on a tidal river or any activity within 16m of a sea defence structure may require a permit. Some activities may be excluded or exempt. Further details and guidance are available on the GOV.UK website: https://www.gov.uk/guidance/flood-risk-activities-environmental-permits.

For more information and to apply please contact the Partnerships and Strategic Overview team at:

 National Customer Contact Centre on 03708 506 506 or  [email protected]

Please be aware that Environment Agency permits, consents and licences are separate from the planning process and are not guaranteed.

The applicant has confirmed that development will not take place within 8m of a main river. A Flood Risk Activity Permit will therefore not be required.

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Proposed Development

The proposed planning application is for the replacement of stables and other ancillary buildings with the erection of a four bed dwelling house and car port with associated parking, landscaping and private amenity space.

Detailed proposed site plans are provided in the report Appendix.

Figure 5: Proposed block plan (Source: Morse Webb)

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Assessment of Flood Risk

Flood Zones:

Within planning, Flood Zones refer to the probability of river and sea flooding, ignoring the presence of defences. They are shown on the Environment Agency’s Flood Map for Planning (Rivers and Sea), available on the Environment Agency’s web site.

Flood Zone Definition Zone 1 Land having a less than 1 in 1,000 annual probability of river or sea flooding. (Shown as Low ‘clear’ on the Flood Map – all land outside Zones 2 and 3) Probability Zone 2 Land having between a 1 in 100 and 1 in 1,000 annual probability of river flooding; or Land Medium having between a 1 in 200 and 1 in 1,000 annual probability of sea flooding. (Land shown Probability in light blue on the Flood Map) Zone 3a Land having a 1 in 100 or greater annual probability of river flooding; or Land having a 1 in High 200 or greater annual probability of sea flooding. (Land shown in dark blue on the Flood Probability Map) Zone 3b This zone comprises land where water has to flow or be stored in times of flood. Local The planning authorities should identify in their Strategic Flood Risk Assessments areas of Functional functional floodplain and its boundaries accordingly, in agreement with the Environment Floodplain Agency. (Not separately distinguished from Zone 3a on the Flood Map)

Table 1: Flood Zones

The Flood Zones shown on the Environment Agency’s Flood Map for Planning (Rivers and Sea) do not take account of the possible impacts of climate change and consequent changes in the future probability of flooding.

Figure 6: Environment Agency Flood Map for Planning (Rivers and Sea) (Source: EA)

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The site is located partially within Flood Zone 1 (Low Probability), which means it is defined as land having a less than 1 in 1,000 annual probability of river and sea flooding, Flood Zone 2 (Medium Probability), which means it is defined as land having between a 1 in 200 and 1 in 1,000 annual probability of river and sea flooding and Flood Zone 3a (Medium Probability), which means it is defined as land having between a 1:100 and 1 in 1000 annual probability of fluvial flooding.

The risk would appear to be fluvial, and originate from the Silchester Brook 13m from the northern boundary of the site.

Fluvial (Silchester Brook):

The Silchester Brook is 11.06 km in length and has a catchment area of 2,315 ha. It is classified as a main river by the Environment Agency and is not designated artificial or heavily modified. It flows in a west to east direction and falls within the Kennet catchment.

Modelled flood levels and events:

Site-specific modelled flood levels and flood extents had been requested from the EA as part of a Product 4 data request (Ref: THM_151597). The EA Product 4 data is provided within the report Appendix. The EA has provided modelled in channel undefended flood levels and flows from the Foundry Brook (Sicester to M4) Flood Mapping Study completed in 2004. The study was carried out using 1D modelling software (ISIS). This model has been partially superseded by the M4 2D model in Isis-Tuflow called Kennet (Tyle Mill to Thames Confluence) 2007. The fluvial levels for these node points are shown in Figure 7.

Figure 7: Node Locations Map centred on RG7 2NH (Source Ref: THM_151597)

Node point 06122_MN_02.081 is positioned upstream of the property, and is considered to provide the most suitable conservative level for use within this assessment. As part of this information, an in-channel 1:100 year flood level of 65.50m AOD has been provided.

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The data provided by the EA does not include an allowance for climate change as required under the NPPF. In line with the climate change guidance published in February 2016, a 70% increase in river flows is required to allow for climate change (More Vulnerable development in Flood Zone 3 uses the Upper End 70% allowance for the Thames Basin District).

No modelled flood levels with a 70% increase in flows was available from the EA. As such, in line with EA guidance the Intermediate Approach is applied, where a Stage-Discharge relationship is derived from the modelled flood levels and flows provided, and then interpolated / extrapolated to estimate a flood level for a 70% increase in flows.

Stage-Discharge relationship for node 06122_MN_02.081

30 y = 28.814x - 1861.9 25 20 15 10

Flow (cumecs) 5 0 64.9 65 65.1 65.2 65.3 65.4 65.5 65.6 Level (mAOD)

Figure 8: Stage-Discharge for Node 06122_MN_02.081 (Source Ref: THM_151597)

A 1:100 year flow of 25.29m3/s has been provided by the EA. Increasing this by 70% gives a flow of 42.99m3/s. As such, the stage-discharge relationship is extrapolated to give a 1:100 year climate change (+70%) flood level of 66.11mAOD.

Comparison of the modelled 1:100 year flood level with allowance for climate change (66.11mAOD) with topographic site levels (65.17m AOD – 68.29m AOD) confirms that the site is partially below the design flood level.

Flood defences:

The EA has confirmed that there are no formal flood defences in this location and they do not currently have any flood alleviation works planned for the area.

Historical flood records:

The EA have confirmed that examination of their records of historic flooding show that the general area has previously flooded in September 1992 which was caused by the channel exceeding capacity. The records show flooding to the land and do not necessarily indicate that properties within the historic flood events were flooded internally. It is also possible that the pattern of flooding in this area has changed and that this area would now flood under different circumstances.

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Figure 9: EA Historic Flood Map centred on RG7 2NH (Source Ref: THM_151597)

Pluvial (Surface Water):

Pluvial (surface water) flooding happens when rainwater does not drain away through the normal drainage systems or soak into the ground, but lies on or flows over the ground instead.

In 2013 the EA, working with Lead Local Flood Authorities (LLFAs), produced an updated Flood Map for Surface Water. It is considered to represent a significant improvement on the previous surface water flood maps available, both in terms of method and representation of the risk of flooding. The modelling techniques and data used and considerably improved, and also incorporated locally produced mapping where this is available to represent features best modelled at a local scale.

The Flood Map for Surface Water assesses flooding scenarios as a result of rainfall with the following chance of occurring in any given year (annual probability of flooding is shown in brackets):

 1:30 (3.3%)  1:100 (1%)  1:1000 (0.1%)

The mapping below shows the Risk of Flooding from Surface Water centred on the site. Please note that the EA to not consider this information suitable to be used to identify the risk to individual properties or sites. It is useful to raise awareness in areas which may be at risk and may require additional investigation.

The EA Surface Water Flood Map suggests that the site is located within an area at “Very Low” to “Low” risk of flooding from surface water.

According to the Basingstoke and Deane Strategic Flood Risk Assessment, 2010 the site is not located upstream or within a designated Critical Drainage Area.

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Figure 10: Extract from Environment Agency Surface Water Flood Map (Source: EA)

Groundwater:

Groundwater flooding occurs as a result of water rising up from the underlying rocks or from water flowing from abnormal springs. This tends to occur after much longer periods of sustained high rainfall. Higher rainfall means more water will infiltrate into the ground and cause the water table to rise above normal levels. Groundwater tends to flow from areas where the ground level is high, to areas where the ground level is low. In low-lying areas the water table is usually at shallower depths anyway, but during very wet periods, with all the additional groundwater flowing towards these areas, the water table can rise up to the surface causing groundwater flooding.

Groundwater flooding is most likely to occur in low-lying areas underlain by permeable rocks (aquifers). These may be extensive, regional aquifers, such as chalk or sandstone, or may be localised sands or river gravels in valley bottoms underlain by less permeable rocks. Groundwater flooding takes longer to dissipate because groundwater moves much more slowly than surface water and will take time to flow away underground.

According to the Basingstoke and Deane Strategic Flood Risk Assessment, 2010 there are no records of groundwater flooding at the site or surrounding area.

The EA Groundwater Source Protection mapping confirms that the site is not located within a source protection zone.

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Sewer Surcharge:

Sewer flooding occurs when the sewer network cannot cope with the volume of water that is entering it. It is often experienced during times of heavy rainfall when large amounts of surface water overwhelm the sewer network causing flooding. Temporary problems such as blockages, siltation, collapses and equipment or operational failures can also result in sewer flooding.

All Water Companies have a statutory obligation to maintain a register of properties/areas which have reported records of flooding from the public sewerage system, and this is shown on the DG5 Flood Register. This includes records of flooding from foul sewers, combined sewers and surface water sewers which are deemed to be public and therefore maintained by the Water Company. The DG5 register records of flood incidents resulting in both internal property flooding and external flooding incidents. Once a property is identified on the DG5 register, water companies can typically put funding in place to address the issues and hence enable the property to be removed from the register. It should be noted that flooding from land drainage, highway drainage, rivers/watercourses and private sewers is not recorded within the register.

There are no records of sewer flooding at the site.

Other Sources:

Reservoirs with an impounded volume in excess of 25,000 cubic metres (measured above natural ground level) are governed by the Reservoirs Act and are listed on a register held by the Environment Agency. The site is outside the maximum inundation extent on the EA Reservoir Inundation Map. The EA also advise on their website that reservoir flooding is extremely unlikely. There has been no loss of life in the UK from reservoir flooding since 1925. All major reservoirs have to be inspected by specialist dam and reservoir Engineers. In accordance with the Reservoirs Act 1975 in England, these inspections are monitored and enforced by the EA themselves. The risk to the site from reservoir flooding is therefore minimal and is far lower than that relating to the potential for fluvial / tidal flooding to occur. The Environment Agency Reservoir Flood Map illustrated below, illustrates the largest area that might be flooded if the storage area were to fail and release the water it is designed to hold during a flood event.

Records of flooding from reservoirs and canals are erratic as there is no requirement for the Environment Agency to provide information on historic flooding from canals and raised reservoirs on plans. In particular, the NPPF does not require flood risk from canals and raised reservoirs to be shown on the Environment Agency flood zones.

Overflows from canals can be common as they are often fed by land drainage, and often do not have controlled overflow spillways. Occasionally, major bank breaches also occur, leading to rapid and deep flooding of adjacent land.

There are no known Internal Drainage Boards covering the site area.

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Figure 11: Extract from Environment Agency Reservoir Inundation Map (Source: EA)

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Flood Risk Management Measures

Vulnerability to flooding:

The NPPF classifies property usage by vulnerability to flooding. The existing site usage is “less vulnerable” as the site is occupied by stables and other ancillary agricultural and equine buildings.

Post development, the site will become “more vulnerable” throughout, as the proposed application is for the replacement of stables and other ancillary buildings with the erection of a four bed dwelling house and car port with associated parking, landscaping and private amenity space.

As such, there will be an increase in vulnerability post development.

EA Standing Advice:

The EA Standing Advice guidance is for domestic extensions and non-domestic extensions where the additional footprint created by the development does not exceed 250m2. It should not be applied if an additional dwelling is being created, e.g. a self-contained annex or additional commercial unit.

The application is for the redevelopment to form a new residential dwelling.

Physical Design Measures:

All proposed new buildings are located outside of Flood Zone 3, and on land above the modelled 1:100 year flood level with allowance for climate change (+70%).

The NPPF requires new residential floor levels to be set at least 300mm above suitable modelled 1:100 year plus allowance for climate change flood levels. As such, all finished ground floor levels will be set at least 66.41mAOD – 300mm above the modelled 1:100 year flood level with allowance for climate change (+70%).

To help protect against flooding during extreme events, the applicant has agreed to implement flood resistant design measures into the proposed new buildings. These measures may include the following:

 Waterproof screed used on floors;  Closed-cell foam used in wall cavities;  Waterproof ground floor internal render;  External walls rendered resistant to flooding to first floor level;  Exterior ventilation outlets, utility points and air bricks fitted with removable waterproof covers;  Boilers, control and water storage / immersion installed at first floor level or above;  Gas meter installed at first floor level or above;  Plumbing insulation of closed-cell design;  Non-return valves fitted to all drain and sewer outlets;  Manhole covers secured;  Anti-syphon fitted to all toilets;  New kitchen units of solid, water resistant material.

The applicant should also consider the use of demountable flood defence barriers to defend ground level doorways and low windows.

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Safe Escape:

The NPPF requires a route of safe escape for all residents and users to be provided from new residential properties in Flood Zone 3. Safe escape is usually defined as being through slow moving flood water no deeper than 25cm.

The site is situated within Flood Zones 2 and 3 when using the Environment Agency Flood Map for Planning (Rivers and Sea).

The proposed escape route is to leave the property to the south and head down the track towards the ménage.

Undefended modelled flood levels provided by the EA have been compared with topographic ground levels along the escape route (where available obtained from a site-specific topographic survey undertaken by 360Geomatics on behalf of the applicant).

All proposed new buildings are located outside of Flood Zone 3, and on land above the modelled 1:100 year flood level with allowance for climate change (+70%).

Accordingly, dry “safe escape” can be provided from the site to an area entirely within Flood Zone 1 as per the technical requirements of the NPPF.

Flood Warning:

The EA is responsible for issuing flood warnings. Flood warnings are issued to the emergency services and local authorities. Both private individuals and organisations can sign-up to receive warnings via phone, text or email. This system of receiving warnings is currently voluntary.

Advice regarding severe flood warnings will generally be given during weather forecasts on local radio and TV. In the case of extreme events, warnings can also be disseminated via door to door visits by the police or locally appointed flood wardens. The EA issue flood warnings/alerts to specific areas when flooding is expected.

The site is not located within a Flood Warning area.

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The flood warning service has three types of warnings that will help you prepare for flooding and take action:

Flood Flood Alert Flood Warning Severe Flood Warning Warning

What it Flooding is possible. Flooding is expected. Severe flooding. means? Be prepared. Immediate action required. Danger to life. Two hours to two days in Half an hour to one day in When flooding poses a When it's advance of flooding. advance of flooding. significant threat to life. used?

Be prepared to act on your Move family, pets and Stay in a safe place with a flood plan. valuables to a safe place. means of escape.

Prepare a flood kit of Turn off gas, electricity and Be ready should you need to essential items. water supplies if safe to do evacuate from your home. What to so. do? Monitor local water levels Co-operate with the and the flood forecast on Put flood protection emergency services. our website. equipment in place. Call 999 if you are in immediate danger.

Table 2: Flood Warnings

Flood Plan:

It is recommended that the applicant and future owners, occupiers and Landlords of the proposed property prepare a flood plan to protect life and property during a flood event:

Before a flood:

 Find out if you are at risk of flooding.  Find out if you can receive flood warnings.  Prepare and keep a list of all your important contacts to hand or save them on your mobile phone.  Think about what items you can move now and what you would want to move to safety during a flood such as pets, cars, furniture, and electrical equipment.  Know how to turn off gas, electricity and water supplies.  Prepare a flood kit of essential items and keep it handy. It can include copies of important documents, a torch, a battery-powered or wind-up radio, blankets and warm clothing, waterproofs, rubber gloves and a first aid kit including all essential medication.  Consider buying flood protection products such as flood boards and airbrick covers to help reduce flood water getting into your property.

During a flood:

 Tune into your local radio station on a battery or wind-up radio.  Fill jugs and saucepans with water.  Grab your flood kit - if you have prepared one.  Collect blankets, torch, first aid kit, medication and food.

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 Move important documents, personal items, valuables, and lightweight belongings upstairs or to high shelves.  Raise large items of furniture, or put them in large bags if you have them.  Move people, outdoor belongings, cars and pets to higher ground.  Switch off water, gas and electricity at mains when water is about to enter your home. Do not touch sources of electricity when standing in water.  Fit flood protection products, if you have them, for example flood boards, airbrick covers, sandbags.  Put plugs in sinks and baths. Weigh them down with a pillowcase or plastic bag filled with soil.  If you do not have non-return valves fitted, plug water inlet pipes with towels or cloths.  Move your family and pets upstairs or to a high place with a means of escape.  Listen to the advice of the emergency service and evacuate if told to do so.  Avoid walking or driving through flood water. Six inches of fast-flowing water can knock over an adult and two feet of water can move a car.

After a flood:

 If you have flooded, contact your insurance company as soon as possible.  Take photographs and videos of your damaged property as a record for your insurance company.  If you don't have insurance, contact your local authority for information on grants and charities that may help you.  Flood water can contain sewage, chemicals and animal waste. Always wear waterproof outerwear, including gloves, wellington boots and a face mask.  Have your electrics, central heating and water checked by qualified engineers before switching them back on.

Off-Site Impacts:

Fluvial floodplain storage:

The NPPF requires that where development is proposed in undefended areas of floodplain, which lie outside of the functional floodplain, the implications of ground raising operations for flood risk elsewhere needs to be considered. Raising existing ground levels may reduce the capacity of the floodplain to accommodate floodwater and increase the risk of flooding by either increasing the depth of flooding to existing properties at risk or by extending the floodplain to cover properties normally outside of the floodplain. Flood storage capacity can be maintained by lowering ground levels either within the curtilage of the development or elsewhere in the floodplain, in order to maintain at least the same volume of flood storage capacity within the floodplain.

In undefended tidal areas, raising ground levels is unlikely to impact on maximum tidal levels so the provision of compensatory storage should not be necessary.

For development in a defended flood risk area, the impact on residual flood risk to other properties needs to be considered. New development behind flood defences can increase the residual risk of flooding if the flood defences are breached or overtopped by changing the conveyance of the flow paths or by displacing flood water elsewhere. If the potential impact on residual risk is unacceptable then mitigation should be provided.

All proposed new buildings are located outside of Flood Zone 3, and on land above the modelled 1:100 year flood level with allowance for climate change (+70%).

Post development, there will be no unacceptable loss of floodplain storage or increase in run-off from the site.

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Surface Water Drainage Strategy:

The development will utilise Sustainable Drainage Systems (SuDS) design in accordance with the NPPF for Planning Applications as follows:

1. Store rainwater for later use; 2. Infiltration techniques; 3. Attenuate rainwater by storing in tanks for gradual release; 4. Discharge rainwater direct into watercourse; 5. Discharge rainwater into surface water sewer; 6. Discharge rainwater into a combined sewer; 7. Attenuation of rainwater in ponds or open water features with controlled discharge into the local watercourse.

All surface water runoff generated by the proposed development up to 1:100 year rainfall event (plus climate change) will be stored on site, prior to being discharged.

Due to the scale of the development, a full Surface Water Drainage Strategy has not been undertaken at this stage of planning. The proposed application will utilise the existing drainage arrangements on site.

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Sequential and Exception Test

The Sequential Test aims to ensure that development does not take place in areas at high risk of flooding when appropriate areas of lower risk are reasonably available.

The site is situated partially within Flood Zones 1, 2 and 3a when using the Environment Agency Flood Map for Planning (Rivers and Sea). Post development, the site will become “more vulnerable” throughout, as the application is for the replacement of stables and other ancillary buildings with the erection of a four bed dwelling house and car port with associated parking, landscaping and private amenity space. Accordingly, it is considered that the vulnerability of the site will increase post development.

Flood Zones Flood Risk Vulnerability Classification Essential Highly vulnerable More vulnerable Less Water

infrastructure vulnerable compatible

Zone 1 ✓ ✓ ✓ ✓ ✓

Zone 2 ✓ Exception Test ✓ ✓ ✓

required

Zone 3a Exception Test ✗ Exception Test ✓ ✓

required required

Zone 3b Exception Test ✗ ✗ ✗ ✓

required

Table 3: Flood risk vulnerability and flood zone ‘compatibility’

Using the table above, the proposed application is considered to be suitable within Flood Zones 1, 2 and 3a, further to implementation of the Exception Test.

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Conclusion

Unda Consulting Limited have been appointed by Mr and Mrs Coppen-Gardner to undertake a Site Specific Flood Risk Assessment (FRA) for Planning for Halls Farm, Ash Lane, Silchester, Reading, Berkshire RG7 2NH. The FRA has been undertaken in accordance with the National Planning Policy Framework (NPPF) July 2018 and the associated technical guidance.

The applicant has confirmed that development will not take place within 8m of a main river. A Flood Risk Activity Permit will therefore not be required.

The existing site usage is “less vulnerable” as the site is occupied by stables and other ancillary agricultural and equine buildings. Post development, the site will become “more vulnerable” throughout, as the proposed application is for the replacement of stables and other ancillary buildings with the erection of a four bed dwelling house and car port with associated parking, landscaping and private amenity space. As such, there will be an increase in vulnerability post development.

The site is situated within Flood Zones 1, 2 and 3a when using the Environment Agency Flood Map for Planning (Rivers and Sea). The risk would appear to be fluvial, and originate from the Silchester Brook 13m from the northern boundary of the site.

Site-specific modelled flood levels and flood extents had been requested from the EA as part of a Product 4 data request (Ref: THM_151597). The EA has provided modelled in channel undefended flood levels and flows from the Foundry Brook (Sicester to M4) Flood Mapping Study completed in 2004. The study was carried out using 1D modelling software (ISIS). This model has been partially superseded by the M4 2D model in Isis- Tuflow called Kennet (Tyle Mill to Thames confluence) 2007.

The EA has confirmed that there are no formal flood defences in this location and they do not currently have any flood alleviation works planned for the area.

The EA have confirmed that examination of their records of historic flooding show that the general area has previously flooded in September 1992 which was caused by the channel exceeding capacity.

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The EA Risk of Flooding from Surface Water Map suggests that the site lies within an area of “Very Low” to “Low” risk of flooding from surface water.

According to the Basingstoke and Deane Strategic Flood Risk Assessment, 2010 the site is not located upstream or within a designated Critical Drainage Area.

Additionally, the risk of flooding posed to the site by groundwater and sewer surcharge flooding would appear to be low.

All proposed new buildings are located outside of Flood Zone 3, and on land above the modelled 1:100 year flood level with allowance for climate change (+70%).

To help protect against flooding during extreme events, the applicant has agreed to implement flood resistant design measures into the property, in consultation with the Local Authority building control department.

A route of dry, safe escape can be provided from the site to an area entirely within Flood Zone 1 as per the technical requirements of the NPPF.

The applicant has confirmed that:

Assuming accordance with these flood risk management measures, Unda Consulting Limited consider the proposed application to be suitable in flood risk terms.

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Appendix

 Site location plan;  Topographic survey;  Existing and proposed plans;  Greenfield runoff rates;  Environment Agency Product 4 Data.

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Coordinate Table

Station Eastings Northings Level Description

Scale bar 0 2 4 6 8 10 12 14 16 18 20m 1:200 0

8 Note 10

20m 1:200

Abbreviations (Where Applicable)

Fence Types

Legend

Rev Suffix Revision Details Initial Date

Surveyed by

10 Salters Heath Road Monk Sherborne, Tadley Hampshire RG26 5HY Tel: 01256 851672 Mob: 07734 233459 Email: [email protected] Website: www.360g.co.uk

Client: MIKE COPPEN-GARDNER HALLS FARM ASH LANE SILCHESTER RG7 2NH

Job Title: SURVEY OF LAND BESIDE HALLS FARM ASH LANE SILCHESTER RG7 2NH

Drawing Title: TOPOGRAPHICAL SURVEY

Drawing No: Rev Suffix: 360G/1002T/100

Drawn: Checked: Scale: Date: PB DR 1:200 JAN 2018

Job No: Sheet: Sheet Size: 360G/1002T 1 of 1 A1

Unda Consulting Ltd Page 1 Southpoint Halls Farm Old Brighton Road Ash Lane Gatwick RH11 0PR RG7 2NH Date 24/08/2018 Designed by JCS File Checked by EB XP Solutions Source Control 2017.1

ICP SUDS Mean Annual Flood

Input

Return Period (years) 100 Soil 0.450 Area (ha) 0.018 Urban 0.000 SAAR (mm) 700 Region Number Region 6

Results l/s

QBAR Rural 0.1 QBAR Urban 0.1

Q100 years 0.3

Q1 year 0.1 Q30 years 0.2 Q100 years 0.3

Product 4 is designed for developers where Flood Risk Standing Advice FRA (Flood Risk Assessment) Guidance Note 3 Applies. This is: i) "all applications in Flood Zone 3, other than non-domestic extensions less than 250 sq metres; and all domestic extensions", and ii) "all applications with a site area greater than 1 ha" in Flood Zone 2.

Product 4 includes the following information: Please note:

Ordnance Survey 1:25k colour raster base mapping; If you will be carrying out computer modelling as part of your Flood Risk Flood Zone 2 and Flood Zone 3; Assessment, please request our guidance which sets out the requirements Relevant model node locations and unique identifiers (for cross referencing to the water and best practice for computer river modelling. levels, depths and flows table); Model extents showing defended scenarios; This information is based on that currently available as of the date of this FRA site boundary (where a suitable GIS layer is supplied); letter. You may feel it is appropriate to contact our office at regular intervals, Flood defence locations (where available/relevant) and unique identifiers; (supplied to check whether any amendments/ improvements have been made. Should separately) you re-contact us after a period of time, please quote the above reference in Flood Map areas benefiting from defences (where available/relevant); order to help us deal with your query. Flood Map flood storage areas (where available/relevant); Historic flood events outlines (where available/relevant, not the Historic Flood Map) and This information is provided subject to the enclosed notice which you should unique identifiers; read. Statutory (Sealed) Main River (where available within map extents); This letter is not a Flood Risk Assessment. The information supplied can be used to form part of your Flood Risk Assessment. Further advice and guidance regarding Flood Risk Assessments can be found on our website at: A table showing: i) Model node X/Y coordinate locations, unique identifiers, and levels and flows for https://www.gov.uk/guidance/flood-risk-assessment-local-planning-authorities defended scenarios. ii) Flood defence locations unique identifiers and attributes; (supplied seperately) If you would like advice from us regarding your development proposals you iii) Historic flood events outlines unique identifiers and attributes; and can complete our pre application enquiry form which can be found at: iv) Local flood history data (where available/relevant). https://www.gov.uk/government/publications/pre-planning-application-enquiry- form-preliminary-opinion

Red Kite House, Howbery Park, Wallingford, Oxon OX10 8BD Customer services line: 08708 506 506 Email: [email protected] www.environment-agency.gov.uk Flood Map for Planning centred on Halls Farm Ash Lane Silchester Created on 22/11/19 REF: THM_151597

Kilometres 0 0.25 0.5

Legend

Main River Flooding from rivers or sea (FZ3) Extent of extreme flood (FZ2)

Flooding from rivers or sea without defences (Flood Zone 3) shows the area that could be affected by flooding: - from the sea with a 1 in 200 or greater chance of happening each year - or from a river with a 1 in 100 or greater chance of happening each year.

The Extent of an extreme flood (Flood Zone 2) shows the extent of an extreme flood from rivers or the sea with up to a 1 in 1000 chance of occurring each year.

© Environment Agency copyright and / or database rights 2019. All rights reserved. © Crown Copyright and database right. All rights reserved. Environment Agency, 100024198, 2019. Contact Us: National Customer Contact Centre, PO Box 544, Rotherham, S60 1BY. Tel: 03708 506 506 (Mon-Fri 8-6). Email: [email protected] Defence information THM_151597

Defence Location: No defences on Main River

Description: This location is not currently protected by any formal defences and we do not currently have any flood alleviation works planned for the area. However we continue to maintain certain watercourses and the schedule of these can be found on our internet pages.

Model: Foudry Brook (Sicester to Grazeley) 2004

Description: The information provided is taken from the Foundry Brook (Sicester to Grazeley) Flood Mapping Study completed in 2004. The study was carried out using 1D modelling software (ISIS). This model has been partially superceeded from Grazeley to upstream of the M4 by the Foudry Brook (Grazeley to upstream of M4) 2017 model and from there to the confluence of the Thames by the Kennet (Tyle Mill to Thames Confuence) 2018 model.

Model design runs: 1 in 5 / 20% Annual Exceedance Probability (AEP); 1 in 20 / 5% AEP; 1 in 100 / 1% AEP; 1 in 100+20% / 1% AEP plus 20% increase in flows and 1 in 1000 / 0.1% AEP

Mapped Outputs: 1 in 5 / 20% AEP; 1 in 20 / 5% AEP and 1 in 100 / 1% AEP

Model accuracy: Levels ± 250mm

Kilometres 0 0.25 0.5

06122_MN_02.080

06122_MN_02.081 Legend 06122_MN_02.078 (! Foudry Brook Model Node Data 06122_MN_02.076 Main River (! 20% AEP flood extent (! (! (! (! (! 5% AEP flood extent 1% AEP flood extent 06122_MN_02.083 1%+20% AEP flood extent

AEP = Annual Exceedance Probability The probability of a flood of a particular magnitude, or greater, occuring in any given year

Where available climate change extents have been calculated with an additional flow added to an AEP event. An example of how this is written is 1%+20% AEP.

The modelled flood levels and flows for the closest most appropriate model node points for your site that are within the river channel are provided below:

Flood Levels (mAOD)

1% AEP (+20% Node label Model Easting Northing 20% AEP 5% AEP 1% AEP 0.1% AEP increase in flows)

06122_MN_02.077 Foudry Brook (Sicester to Grazeley) 2004 463656 160706 64.73 64.95 65.33 0.00 65.91 06122_MN_02.078 Foudry Brook (Sicester to Grazeley) 2004 463554 160694 64.83 65.04 65.40 0.00 65.99 06122_MN_02.080 Foudry Brook (Sicester to Grazeley) 2004 463465 160685 64.91 65.11 65.44 0.00 66.03 06122_MN_02.081 Foudry Brook (Sicester to Grazeley) 2004 463370 160685 65.02 65.19 65.50 0.00 66.06 06122_MN_02.083 Foudry Brook (Sicester to Grazeley) 2004 463277 160692 65.15 65.32 65.61 0.00 66.17

Flood Flows (m3/s)

1% AEP (+20% Node label Model Easting Northing 20% AEP 5% AEP 1% AEP 0.1% AEP increase in flows)

06122_MN_02.077 Foudry Brook (Sicester to Grazeley) 2004 463656 160706 11.31 16.59 25.12 30.10 46.67 06122_MN_02.078 Foudry Brook (Sicester to Grazeley) 2004 463554 160694 11.33 16.60 25.14 30.11 46.69 06122_MN_02.080 Foudry Brook (Sicester to Grazeley) 2004 463465 160685 11.36 16.64 25.19 30.14 46.73 06122_MN_02.081 Foudry Brook (Sicester to Grazeley) 2004 463370 160685 11.39 16.68 25.29 30.21 46.83 06122_MN_02.083 Foudry Brook (Sicester to Grazeley) 2004 463277 160692 5.25 6.14 7.24 8.04 12.03

Note: Due to changes in guidance on the allowances for climate change, the 20% increase in river flows should no longer to be used for development design purposes. The data included in this Product can be used for interpolation of levels as part of an intermediate level assessment.

For further advice on the new allowances please visit https://www.gov.uk/guidance/flood-risk-assessments-climate-change-allowances

Kilometres 0 0.25 0.5

Legend

Main River NAME 06SeptemberAutumn1992

Our records show that the area of your site has been affected by flooding. Information on the floods that have affected your site is provided in the table below:

Source of Flood Event Name Start Date End Date Cause of Flooding Flooding 06SeptemberAutumn1992 01/01/1992 12/12/1992 main river channel capacity exceeded