TROWSE NEW PRIMARY SCHOOL FLOOD RISK ASSESSMENT And
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TROWSE NEW PRIMARY SCHOOL TROWSE NEWTON FLOOD RISK ASSESSMENT and DRAINAGE STRATEGY On behalf of Norfolk 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, Norwich, 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 South Norfolk 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 River Yare and River Tas are approximately 285m north west Ground Separate report undertaken by HBS, Ground Investigation Investigation Report 22-24-17-1-1036 GIR1 The site is not considered to be at risk of fluvial or pluvial flooding The site is not considered to be at risk of groundwater flooding The proposed development is appropriate for the site. The drainage scheme proposed is in compliance with the National Planning Policy Framework and Associated Planning Policy Guidance and the Non-Statutory Technical Standards for Sustainable Drainage Systems The proposed drainage for the Primary School site is appropriate and safe without increasing flood risk elsewhere The Primary School site is encompassed in a larger Norfolk Homes residential area development site which has planning permission from South Norfolk Council. Conclusions The proposed drainage for the Primary School will connect into both the foul and surface water drainage systems of the larger Norfolk Homes residential area development site. CONCLUSIONS CONCLUSIONS The surface water greenfield runoff rate connection from the Primary School has been restricted to a 5l/s discharge rate. Ground conditions preclude the use of soakaways for the surface water disposal but the greenfield runoff rate can be achieved with a positive outfall into the Norfolk Homes drainage system. There is a higher contributing area of agricultural land to the east of the Primary School site, which is proposed as part of the Arminghall Estate residential site. The greenfield overland flows are currently intercepted by a substantial tree belt, but an allowance has been made within the calculations for this anticipated flow from upstream The proposed Primary School and Nursery Development is appropriate for the site and the proposed drainage systems are Recommendations satisfactory for the development and are safe without increasing flood risk elsewhere. 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 Report 17-1-1095/FRA Trowse New Primary School August 2018 4 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 Report 17-1-1095/FRA Trowse New Primary School August 2018 5 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.