TROWSE NEW PRIMARY SCHOOL NEWTON

FLOOD RISK ASSESSMENT

and DRAINAGE STRATEGY

On behalf of County Council Children’s Services

Report 17-1-1095/FRA Rev B August 2018

Contents

1 Introduction 1 1.1 Context 1 1.2 Development Site and Location 1 1.3 Development Proposals 5 1.4 Sequential Test 6 1.5 Exception Test 6 1.6 Climate Change 7 2 Sources of Flood Risk 8 2.1 Flood Risk Assessment 8 2.2 Location Of Main Rivers and watercourses 9 2.3 Fluvial Flooding 10 2.4 Surface Water Flooding 11 2.5 Topography 12 2.6 Site Ground Investigation 12 2.7 Existing Public Sewers 14 3 Surface Water Flood Risk Management 15 3.1 Catchment Area 15 3.2 Sustainable Drainage 15 3.3 Surface Water Drainage Strategy 17 3.4 Disposal of Foul Water 20 3.5 Occupants and Users Of The Development 20 3.6 Maintenance and Management 20 3.7 Residual Flood Risk 20 4 Conclusions and Recommendations 22

APPENDICES A Site Location Plan Norfolk Homes Foul and Surface Water Plan – 5903756 School Site Layout Topography B Environment Agency Maps British Geological Survey Maps Anglian Water Sewers C Micro Drainage Calculations HR Wallingford Greenfield Runoff D Drainage Strategy; Drainage Maintenance Plan

Executive Summary

Client Director of Children’s Services, Norfolk County Council Site Trowse New Primary School

Off White Horse Lane, Trowse Newton, , Site Location NR14 8GD (nearest).

National Grid 624662, 306406 Reference Approximate Site 1 ha Area Elevations range from approximately Topography 15m OD in the south east to 10m OD in the north west Current Land and Undeveloped Agricultural land to present day Historic Site Use INFORMATION Proposed New Primary School and Nursery

SITE SITE Development Planning Authority Norfolk County Council Local Authority Council

The site lies within the Environment Agency Flood Zone 1 (FZ1) Flood Zone Defined as being at low risk of river or sea flooding.

No Groundwater encountered in testing. Groundwater inflows Groundwater are likely to be negligible. Based upon Environment Agency Flood Risk Map from Surface Surface Water Water, the site is designated to be at Low Risk of Flooding from Surface Water. The underlying geology of medium dense locally clayey slightly gravelly sand over weathered chalk bedrock with a medium high Soakaways risk of dissolution features has been identified, therefore soakaways are not considered to be a feasible option for surface

GENERAL INFORMATIONGENERAL water drainage on this site. Foul Drainage Anglian Water Geology Lowestoft Formation (Diamicton) over White Chalk Group Bedrock: Principal Aquifer Hydrogeology Lowestoft Formation: Unproductive. The site lies within an Outer Zone 2 of a Source Protection Zone Hydrology and River Tas are approximately 285m north west Ground Separate report undertaken by HBS, Ground Investigation Investigation Report 22-24-17-1-1036 GIR1 .

CONCLUSIONS Recommendations Conclusions

flood risk elsewhere. flood satisfactory for the development and are safe witho Development Nursery proposedthedrainagesite andthe appropriatefor and School Primary proposed The The site is not considered to be at risk of fluvial loac hs en ae ihn h cluain for calculations the within anticipated made from flow upstream bel been tree substantial has a allowance by intercepted currently are pa as proposed Arminghall Estate residential site. The greenfield is which site, School Primary the of There is a higher contributing area of agricultural system. ra runoff for achieved with a positive outfall the into Norfolk greenfield H soakaways the but of disposal water use surface the preclude conditions Ground PrimarySchoolbeen restrictedhas to 5l/s discha a connection rate runoff greenfield water surface The Homes residential Norfolk area site.development of systems drainage water surface and foul the both willc PrimarySchool the drainage proposedfor The permission NorfolkSouth from Council. p has which site development larger area residential a i Homes in encompassed is site site School Primary School The Primary the for safe appropriate and drainage without increasing risk flood proposed The DrainageSustainable Systems with Policy Guidance and the Non-Statutory Technical Sta compliance P in Associated and Framework is Policy Planning National proposed scheme drainage The proposed The isdevelopment appropriate the for sit site is consideredThe not torisk at be ofgroundw or pluvial flooding land to the east omes drainage overland flows

elsewhere elsewhere ater flooding ater ut ut increasing rge rate. systemsare e. e. onnect into onnect the larger the e a be can te ndards ndards for rm the from , u an but t, rt of the the of rt lanning lanning Norfolk this the the the is s

1 Introduction

1.1 Context

Defra EA Guidance for Flood risk assessment for planning applications has been followed for the production of this Flood Risk Assessment report for the construction of a new Primary School to meet the requirements of the National Planning Policy Framework.

This report describes the work undertaken and presents the data obtained together with an evaluation of their significance in relation to the proposed works. It assesses the impact that the site will have on surrounding areas and recommends the drainage design for the proposed new Primary School and Nursery. The report demonstrates that the flood risk to the site is very low and that there is no increase in flood risk to others.

1.2 Development Site and Location The Ordnance Survey National Grid Reference (NGR) for the centre of the site is 624662, 306406. The site location is shown below:

SITE

Report 17-1-1095/FRA Trowse New Primary School August 2018 1

The Trowse New Primary School Site, coloured red on the Site Location Plan, is currently an agricultural field that extends to 1.0ha and lies to the east of White Horse Lane in Trowse Newton, north of the A146, approximately 2.5 kilometre to the south east of Norwich.

The new Primary School Development is within a larger development, included in the South Norfolk Council (SNC) ‘Site Specific and Allocations Development Plan Document’, which is inclusive of the development sites called ‘Land on White Horse Lane’ and ‘Land to the rear of Charolais Close and Devon Way’

Report 17-1-1095/FRA Trowse New Primary School August 2018 2

The site is bounded: to the west and north by an agricultural field which is the Norfolk Homes Ltd proposed residential housing development site ‘Land off White Horse Lane’, to the east by an agricultural field which is the Arminghall Estate proposed residential housing development site ‘Land to the rear of Charolais Close and Devon Way’, to the south is the A146. Access to the Primary School will be from the Norfolk Homes development site.

South Norfolk Council Planning Application 2013/0463/O Land off White Horse Lane, Trowse - Outline Planning Permission was granted by SNC.

Subsequent Planning Applications with Condition stating that prior to the commencement of work on site full details of the means of surface water drainage shall be submitted to and agreed with the local planning authority.

Norfolk Homes Ltd as the developer for the overall site had to make provision for the 1.0-hectare site reserved for the new Primary School and associated playing fields. The Lead Local Flood Authority agreed the discharge of the Surface Water Drainage Condition for the development site.

The Norfolk Homes Ltd development site surface water drainage system has the provision of storage on site with an approved restricted discharge to the nearby Trowse Newton Drain watercourse. This watercourse is designated as a Main River in the Norfolk Rivers Internal Drainage Board area who have confirmed the discharge from the development site can be accommodated.

An agreed discharge rate of 5l/s has been made for the New Primary School surface water drainage to be connected to the Norfolk Homes Ltd development.

The connection point is at the south west corner of the school site into Surface Water manhole S18 indicated on South Norfolk Council Planning Application 2017/0962 –C6 Foul and Surface Water Schedules and Plan-5903756 ASD Engineering drawing number 1031/DRA/050 as shown below .

Report 17-1-1095/FRA Trowse New Primary School August 2018 3

South Norfolk Council Planning Application 2017/0962 –C6 Foul and Surface Water Schedules and Plan-5903756 ASD Engineering drawing number 1031/DRA/050

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1.3 Development Proposals

The development proposal is for the construction of a new Primary School, 1 Form of Entry, with a future allowance for an additional 0.5 FE at a later date, plus a 26 place Nursery on the greenfield site. The new provision includes 1 class base for each of the Key Stages 1 and 2, in accordance with the Norfolk Standard School Model in relation to teaching provision plus a detached Nursery building comprising 2 class bases. The external works includes hard play and parking and drainage as shown on the Site Layout Plan below

This gives a change of use for the site from an agricultural field to a primary school. The vulnerability to flooding classification is changing from ‘Less Vulnerable land used for agriculture to ‘More Vulnerable’ for Non – residential use for educational establishments is appropriate for this site and the estimated lifetime of the proposed development thought likely to be 100 years

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1.4 Sequential Test

In accordance with Planning Practice Guidance (PPG) relating to Flood Risk and Coastal Change, the Sequential Test does not need to be applied as;

• The development site is within the South Norfolk Council Site Specific and Allocations Development Plan Document and

• is wholly within flood zone 1 as defined in PPG Table 1 , and

• the flood risk vulnerability classification as defined in PPG Table 2 is ‘More Vulnerable’ for non-residential uses for educational establishments which is appropriate use for Flood Zone 1.

The Sequential Test is satisfied.

The development is appropriate in accordance with PPG Table 3 the Flood Risk Vulnerability and Flood Zone Compatibility

1.5 Exception Test

The flood risk vulnerability classification shows the development is appropriate and therefore no exception test is required.

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1.6 Climate Change

The influence of Climate Change on rivers and watercourses is likely to increase the frequency of flood events and the overall volume of water that passes the site. The Primary School surface water drainage strategy is designed so that the peak rate of surface water runoff is no greater than the greenfield runoff rate and an additional 40% allowance to take into account the potential impact of climate change on future weather patterns during the design life of the building.

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