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FLOOD RISK ASSESSMENT

FOR PROPOSED

HARLEY WAY QUARRY

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14th December 2011

Harley Way Quarry, Oundle - Flood Risk Assessment 1

Contents Page 1.0 Introduction 2 2.0 Planning Policy & Methodology 2 3.0 Development Location & Description 2 4.0 Development Proposals 3 5.0 Sequential Test 3 6.0 Potential Sources of Flooding 4 7.0 Appraisal of Sources of Flooding 4 8.0 Probability 5 9.0 Climate Change 5 10.0 Flood Risk Management Measure 5 11.0 Off Site Impacts and Proposed Mitigation Measures 6 12.0 Management of Residual Risks 6 13.0 Conclusions 6 Appendix 1 Drawings Appendix 2 Calculations

Harley Way Quarry, Oundle - Flood Risk Assessment 2

1.0 Introduction 1.1 This Flood Risk Assessment has been produced in support of the planning application for the proposed quarry and agricultural restoration scheme at Harley Way, Oundle. 2.0 Planning Policy & Methodology 2.1 Planning policy for flood risk is set out in Planning Policy Statement (PPS) 25 ‘Development and Flood Risk’ published in March 2010. The policy document sets out key planning objectives in relation to land usage and flood risk management. The development proposals are designed to be compliant with the requirements of PPS25. 2.2 The Flood Risk Assessment has been carried out to assess the effects of the development in respect of surface water run-off, risk from fluvial flooding and risk from other sources of flooding such as groundwater, man made structures and sewers. 3.0 Development Location & Description 3.1 The site is located just west of Oundle in Northamptonshire in the grounds of Chruchfield Farm and is currently used as an agricultural field. To the north of the site is a country lane called Harley Way. To the south is Lyvedon Brook which is a tributary to the River Nene. On the east side of the site is a quarry and to the west is agricultural land. A location plan of the site is shown below.

Site Location Plan

Harley Way Quarry, Oundle - Flood Risk Assessment 3

3.2 Lyvedon Brook is the primary conveyor of surface water run-off from the site and upstream of the site. The topography of the site has a gradient of approximately 1 in 20 falling towards Lyvedon Brook. The site area measures approximately 6.4 hectares. 4.0 Development Proposals 4.1 The proposal is for the site to be quarried for stone. Upon completion of the quarrying, the site will be restored to existing ground levels using inert waste and finished off with topsoil. It is proposed that the western side of the site will be used as a horse paddock and the eastern side will be used as a camping facility. 5.0 Sequential Test 5.1 In accordance with Table D.2 in Annex D of PPS25, the end use facility should be classified as ‘Highly Vulnerable’. 5.2 The Environment Agency’s detailed flood plain map is shown below. It shows the development site falls within flood Zone 1 ‘low probability’ area as defined in Table D.1 Annex D of PPS25.

Environment Agency Flood Plain Map

5.3 Using the Sequential Test set out in PPS25, the proposed development use defined in Table D.2 is permitted in Zone 1 (refer to Table D.3 shown below) and therefore passes the Sequential Test.

Harley Way Quarry, Oundle - Flood Risk Assessment 4

6.0 Potential Sources of Flooding 6.1 The following sources have been identified as having potential to cause flooding:

Fluvial flooding from the Lyvedon Brook. Surface water run-off from the development. Surface water run-off from land uphill of the development. Possible elevated groundwater levels.

6.2 There are no public surface water sewers, reservoirs, canals or other artificial sources of flooding identified in the immediate vicinity of site which might cause a risk of flooding. 7.0 Appraisal of Sources of Flooding 7.1 The extent of fluvial flooding has been examined using the Environment Agency’s detailed flood map. This has been superimposed onto the topographical survey and quarry layout with the resulting drawing entitled ‘Fluvial Flood Risk’ located in Appendix 1. It can be seen that the development proposals lie outside of the 1000 year flood limit and therefore the proposed development is not at risk from fluvial flooding. 7.2 During the course of the quarrying operation, worked areas will be lower than existing ground levels and therefore be prone to flooding from rainwater collecting in the excavation. These areas will therefore not yield any run-off. Instead, water will be pumped out into a settlement lagoon and then into the Brook at a rate agreed with the Environment Agency in the Discharge Consent which will be applied for prior to any discharge taking place. 7.3 Upon completion of each phase of the quarrying work, the void will be filled with overburden, waste stone and inert waste. The exact composition of the waste is unknown and therefore, for the purposes of assessing the worst case for run-off, it has been assumed that the material will be relatively impermeable. As a result, run-off from the restored site will be increased and this will need to be controlled to ensure flooding does not occur in the Lyvedon Brook.

Harley Way Quarry, Oundle - Flood Risk Assessment 5

7.4 Land to the north of the site is elevated higher than the proposed quarry site. Between this elevated land and the site is the road known as ‘Harley Way’ which has a ditch running alongside. The ditch collects run-off from the higher ground and discharges it into the Brook, thereby eliminating much of the risk of flooding from run-off upstream of the site. 7.5 The topography of the site has a significant gradient and the existing geology is relatively permeable. Therefore groundwater levels will be low and this has been confirmed by the recent boreholes which showed groundwater at approximately five metres below existing ground level. Quarry excavations will occasionally go below the water table and therefore some dewatering will be necessary to prevent flooding when groundwater levels are high. However, dewatering will be infrequent as the quarry will only be worked seasonally. When the site is restored, the groundwater levels will remain well below finished ground levels and will consequently not be a risk to flooding of the development. 8.0 Probability 8.1 The flood mapping shows the site is outside the 1000 year flood area and therefore it is deemed to be at low risk of flooding, typically less than 1 in 1000 annual probability. 9.0 Climate Change 9.1 Table B.2 of Annex B of PPS25 suggests that a 20% increase in peak rainfall would be applicable to take account of climate change for a development with a lifespan up to 75 years. Calculations for the proposed attenuation pond are based upon a 100 year rainfall event plus a 20% climate change allowance. 10.0 Flood Risk Management Measures 10.1 Prior to commencing quarrying work, two settlement lagoons will be excavated in the south east corner of the site. Perimeter swales will be constructed to capture run-off from the site and these will feed into the settlement lagoons. Any dewatering necessary from the excavations will be pumped into the lagoons which will serve as retention ponds and also allow sedement to settle prior to discharging to the adjacent watercourse which discharges to Lyvedon Brook. The rate of discharge will be agreed with the Environment Agency at the time when the Discharge Consent is applied for. Refer to drawing entitled ‘Quarry Scheme Drainage’ in Appendix 1 for the proposed drainage layout. 10.2 Upon completion of the quarrying works and prior to the completion of the restoration works, the settlement lagoons will be modified to become a balancing pond. The feeder swales will be retained and this will allow the capture of the increased run-off from the fill which is expected to be much more impermeable than the original geology. Refer to drawing entitled ‘Restoration Scheme Drainage’ in Appendix 1 for the proposed drainage layout. 10.3 Discharge from the balancing pond will be limited to the green-field run-off rate prior to development which has been calculated as 24.1 l/s using the Ministry of Agriculture, Fisheries and Food’s ADAS Report 345 ‘The Design of Field Drainage Pipe Systems’. The volume of attenuation is based on a 100 year return period plus a 20% allowance for climate change in accordance with Table B.2 of Annex B of PPS25. The volume of the pond has been calculated as 1457m3 using Microdrainage. Calculation details are located in Appendix 2.

Harley Way Quarry, Oundle - Flood Risk Assessment 6

11.0 Off Site Impacts and Proposed Mitigation Measures 11.1 There will be no off site impact due to the following mitigation measures:

The development site will be remote from the flood plain. There will be no increased run-off from the site. The settlement lagoons will ensure that mobilised sediment will not be discharged into the

Brook. 12.0 Management of Residual Risks 12.1 The drainage system should be routinely inspected and maintained to ensure that it functions adequately. All drainage shall be inspected annually for blockages, silting and functionality, and the appropriate remedial works undertaken after the inspection. Inspections shall involve examination of all ditches, pumps, ponds and flow control chambers. 13.0 Conclusions 13.1 The site has been found to pass the Sequential Test. 13.2 The site does not impact on the existing Lyvedon Brook flood plain. 13.3 The proposed drainage will ensure that there is no increase in discharge rates to the Brook.

……………………………………………….. 14th December 2011 Ian Brazier BEng (Hons) CEng MICE On Behalf of Abington Consulting Engineers Limited

APPENDIX 1 – Drawings

APPENDIX 2 – Calculations

HARLEY WAY QUARRY – DRAINAGE CALCULATIONS Greenfield Run-off Calculations for Development Site using ADAS A = 3.01ha L = 126m S = (53.5 – 48.7)/126 = 0.038 C = 0.0001 x 126/0.038 = 0.33 Crop = Arable AAR = 574mm ST = 1.0 (clay) F = 8.0 QO = 1.0 x 8.0 x 3.01 = 24.1 l/s Surface Water Limited Discharge Limited discharge rate Q = 24.1 l/s Surface Water Storage Design Impermeable Area from Restored Site = 3.01ha Return Period = 100 years Limited Discharge Rate = 24.1 l/s Climate change allowance (PPS25 Annex B, Table B.2) for peak rainfall intensity = 20% For storage volume refer to Microdrainage calculations

Summary of Results for 100 year Return Period (+20%)

Storm

Event

Max

Level

(m)

Max

Depth

(m)

Max

Control

(l/s)

Max

Volume

(m³)

Status

15 min Summer 100.441 0.441 21.9 617.4 O K30 min Summer 100.574 0.574 21.9 803.2 O K60 min Summer 100.705 0.705 21.9 986.4 O K120 min Summer 100.822 0.822 22.5 1151.4 O K180 min Summer 100.875 0.875 22.9 1225.6 O K240 min Summer 100.900 0.900 23.1 1260.5 O K360 min Summer 100.911 0.911 23.2 1275.1 O K480 min Summer 100.905 0.905 23.2 1267.1 O K600 min Summer 100.897 0.897 23.1 1255.5 O K720 min Summer 100.886 0.886 23.0 1240.7 O K15 min Winter 100.495 0.495 21.9 692.7 O K30 min Winter 100.645 0.645 21.9 902.3 O K60 min Winter 100.793 0.793 22.3 1109.7 O K120 min Winter 100.927 0.927 23.4 1298.2 O K180 min Winter 100.990 0.990 23.9 1385.8 O K240 min Winter 101.021 1.021 24.2 1429.8 O K360 min Winter 101.040 1.040 24.4 1456.6 O K480 min Winter 101.037 1.037 24.4 1452.0 O K600 min Winter 101.021 1.021 24.2 1430.0 O K

Storm

Event

Rain

(mm/hr)

Time-Peak

(mins)

15 min Summer 111.940 1930 min Summer 73.565 3360 min Summer 46.096 64120 min Summer 27.939 122180 min Summer 20.582 182240 min Summer 16.478 242360 min Summer 11.961 360480 min Summer 9.535 418600 min Summer 7.993 478720 min Summer 6.916 54215 min Winter 111.940 1930 min Winter 73.565 3360 min Winter 46.096 62120 min Winter 27.939 120180 min Winter 20.582 178240 min Winter 16.478 236360 min Winter 11.961 348480 min Winter 9.535 456600 min Winter 7.993 548

Date 08/06/2011 08:18 File Pond.srcx Micro Drainage

Harley Way Oundle 100 yr +20%

Designed By mvirdee Checked By Source Control W.12.4

Page 1

©1982-2010 Micro Drainage Ltd

Summary of Results for 100 year Return Period (+20%)

Storm

Event

Max

Level

(m)

Max

Depth

(m)

Max

Control

(l/s)

Max

Volume

(m³)

Status

720 min Winter 101.007 1.007 24.1 1409.1 O K

Storm

Event

Rain

(mm/hr)

Time-Peak

(mins)

720 min Winter 6.916 572

Date 08/06/2011 08:18 File Pond.srcx Micro Drainage

Harley Way Oundle 100 yr +20%

Designed By mvirdee Checked By Source Control W.12.4

Page 2

©1982-2010 Micro Drainage Ltd

Rainfall Details

Rainfall Model FSR Winter Storms YesReturn Period (years) 100 Cv (Summer) 0.750

Region England and Wales Cv (Winter) 0.840M5-60 (mm) 19.000 Shortest Storm (mins) 15

Ratio R 0.400 Longest Storm (mins) 720Summer Storms Yes Climate Change % +20

Time / Area Diagram

Total Area (ha) 3.010

Time

(mins)

Area

(ha)

0-4 3.010

Date 08/06/2011 08:18 File Pond.srcx Micro Drainage

Harley Way Oundle 100 yr +20%

Designed By mvirdee Checked By Source Control W.12.4

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©1982-2010 Micro Drainage Ltd

Model Details

Storage is Online Cover Level (m) 102.000

Tank or Pond Structure

Invert Level (m) 100.000

Depth (m) Area (m²) Depth (m) Area (m²) Depth (m) Area (m²) Depth (m) Area (m²)

0.000 1400.0 1.400 1400.0 2.800 1400.0 4.200 1400.00.200 1400.0 1.600 1400.0 3.000 1400.0 4.400 1400.00.400 1400.0 1.800 1400.0 3.200 1400.0 4.600 1400.00.600 1400.0 2.000 1400.0 3.400 1400.0 4.800 1400.00.800 1400.0 2.200 1400.0 3.600 1400.0 5.000 1400.01.000 1400.0 2.400 1400.0 3.800 1400.01.200 1400.0 2.600 1400.0 4.000 1400.0

Hydro-Brake® Outflow Control

Design Head (m) 1.000 Diameter (mm) 198Design Flow (l/s) 24.1 Invert Level (m) 100.000Hydro-Brake® Type Md5 SW Only

Depth (m) Flow (l/s) Depth (m) Flow (l/s) Depth (m) Flow (l/s) Depth (m) Flow (l/s)

0.100 7.0 1.200 26.1 3.000 41.0 7.000 62.60.200 16.1 1.400 28.0 3.500 44.3 7.500 64.80.300 20.7 1.600 29.9 4.000 47.3 8.000 66.90.400 21.9 1.800 31.7 4.500 50.2 8.500 69.00.500 21.8 2.000 33.5 5.000 52.9 9.000 71.00.600 21.7 2.200 35.1 5.500 55.5 9.500 72.90.800 22.4 2.400 36.7 6.000 58.01.000 24.1 2.600 38.1 6.500 60.3

Date 08/06/2011 08:18 File Pond.srcx Micro Drainage

Harley Way Oundle 100 yr +20%

Designed By mvirdee Checked By Source Control W.12.4

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©1982-2010 Micro Drainage Ltd