manor farm, drayton hopkins homes ltd...manor farm, drayton, bird hazard risk assessment 2020 page 1...

Manor Farm, Drayton

Hopkins Homes Ltd

Bird Hazard Risk Assessment;

Addendum Report

March 2020

Manor Farm, Drayton, Bird Hazard Risk Assessment 2020

Control Sheet

Job Number/ Name: Manor Farm, Drayton

Client: Hopkins Homes Ltd

Prepared by: Jade Relf (Ecologist)

Checked by: Sean Carter (Director / Environmental Consultant)

Date of Issue: 04/03/2020

Revision 1

Status Final

This report has been produced by Carter Sustainability Ltd for the sole and exclusive use of Hopkins Homes Ltd to their particular instruction. No liability is accepted for any costs or losses arising from the use of this report or any part thereof for any purpose other than that for which it was specifically prepared for or by use of any other party other than Hopkins Homes Ltd. The report has been prepared by an ecological specialist and does not purport to provide legal advice. Legal advice must be sought independently. The information which has been prepared and provided is true, and is in accordance with the BS42020:2013 and the Chartered Institute of Ecology and Environmental Management’s Code of Professional Conduct.

Signed (Author)

Signed (QA)


Contents

1. Introduction ....................................................................................................................................................... 1

2. 2017 Assessment Summary .......................................................................................................................... 1

3. 2020 Addendum Assessment ........................................................................................................................ 2

4. Conclusions and Recommendations ............................................................................................................ 3

5. References ........................................................................................................................................................ 4

Appendix A – Site Location and Wider Landscape Plan ................................................................................... 5

Appendix B – Offsite Basins Drainage Design .................................................................................................... 6

Appendix C – Surface Water Drainage Network Key Plan ............................................................................... 7

Appendix D – Filtration Rates ................................................................................................................................ 8

Appendix E – Maintenance of Infiltration Basins ................................................................................................. 9


Page 1

1. Introduction

1.1 Carter Sustainability Ltd was commissioned by Hopkins Homes Ltd to undertake an update bird hazard risk assessment of the proposed site at Manor Farm, Drayton (TG 18205 14067). Outline planning permission has been granted on 17 Feb 2020 for the development of 250 homes, with associated infrastructure. Reserved matters are to be submitted to confirm final development detail.

1.2 Concerns were previously raised towards the initial planning application by Norwich Airport specifically with regards to the proposed offsite filtration basin on the south eastern site boundary. This was due to the location of the development, and resultant basin, being within the safeguarding zone of the airport; typically recognised to be within 13 km of the aerodrome reference point1. The site itself lies approximately 2.4 km west from the airport boundary. In line with these concerns an initial bird hazard risk assessment (BHRA), and subsequent Bird Hazard Management Plan (BHMP), was completed by Airfield Wildlife Management Ltd in Feb 2017. The assessment evaluated any likely or possible change in numbers, distribution and movements of birds as a result of the development and how these changes may impact upon the bird strike hazard to aircraft at or within the vicinity of Norwich Airport.

1.3 The assessment within this report re-evaluates the potential risk of increased bird presence (of species hazardous to bird strikes) in line with updated development plans. A newly proposed site design includes an increase to 267 homes within a moderately increased development footprint of 16.2 ha (previously 13 ha). In line with these changes an update flood risk assessment (FRA) and drainage statement has been undertaken by MLM Consulting Engineers Limited in Feb 20202. The resulting drainage design incorporates two offsite basins on the north eastern and south eastern boundary of the site, in addition to three smaller onsite basins within the western area of the site. In line with the previous concerns raised by Norwich Airport, this update assessment is based principally on the two offsite infiltration basins which present the highest potential for use by wildfowl.

1.4 As outlined within the planning application, the drainage design is to accommodate both existing flooding of the site, whereby water sheds from the northern and eastern fields westwards towards Drayton village, as well as capture anticipated runoff from within the development. Both the 2017 assessment and this update assessment takes into account this existing flooding issue when evaluating whether the proposed management for offsite and onsite flooding would increase the risk of bird presence.

1.5 This report has been written as an addendum to the initial bird risk assessment undertaken in 2017. The assessment is based solely on the adjustments within the updated drainage design to accommodate the new development details. As such this report should be read in conjunction with the 2017 report.

1.6 The assessment has been undertaken by Jade Relf MSc, BSc (Hons) and includes a desk-based study utilising existing data available online (including open aerial mapping software such as MAGIC map) in addition to reports and designs provided by the client.

2. 2017 Assessment Summary

2.1 The previous assessment was based on an initial basin design of one large offsite infiltration basin on the south eastern boundary of the site. The basin was of a capacity of 20,000m³ designed to capture runoff from a one in 100 year flood, with an additional 30% capacity for climate change. The basin had a maximum depth of 2 m, with half of this volume discharging within 15 hours, and the remaining within one to one and a half days. For average rainfall the concluded results were that the majority of rainfall would infiltrate at the point of falling, with any flows reaching the basin infiltrating quickly resulting in minor depths of water, typically less than 50 mm.

1 CAA CAP 772 Wildlife Hazard Management at Aerodromes Revision 2 dated Oct 2017 2 6600556-MLM-ZZ-XX-RP-C-0001 Flood Risk Assessment and Drainage Statement Revision 00 dated 14 Feb 2020


Page 2

2.2 The main species considered to be of concern for bird strikes at this site location are larger wildfowl such as swans, geese and larger duck species. The previous assessment included the presence of existing bird populations and habitats/landscape features currently supporting populations within proximity to the site. Of note were the following findings:

• Current populations of wildfowl within: Taverham lake and Costessey Pits 2km SW of proposed basin; River Wensum running along the south western boundary of Drayton and Taverham villages; Dobbs’ Beck Lake and the Springs 3.7 km east of development; and, Norfolk Broads to east of airport (closest points approximately 6 km north east and south east).

• Existing bird risk within the ‘pre-development’ agricultural land including:

o significant numbers of feeding gulls and corvids within the fields which will reduce proportionately to the development footprint;

o no risk from waterfowl species such as herons and cormorants due to lack of food resources within the basin;

o no measurable change in roosting/ nesting birds subject to landscaping proposals being comparable to existing features;

o existing risk from the wildfowl supported within the existing habitats outlined above.

2.3 Significant conclusions from the assessment include:

• Highest risk from bird movements would be from the basin eastwards in the direction of the airport (and vice versa), however existing features supporting wildfowl near the development already pose this risk. Any movements from the basin are also more likely to be towards closer alternative opportunities to the west of the development (away from the airport);

• Drainage time would not allow for colonisation of floral and faunal food resources within the basin;

• Steep sides limit foraging opportunities in comparison to alternative options nearby;

• Water depth below 30 mm increases predation risk so has negligible potential for wildfowl use;

• Any limited use is likely to be opportunistic mallard ducks which pose negligible risk to aircraft;

• Current areas of flooding provide greater areas of open water than the infiltration basin would provide at full capacity.

3. 2020 Addendum Assessment

3.1 The proposed design outlined in the updated FRA incorporates two individual offsite drainage basins in comparison to the single large basin previously proposed. Appendix B outlines the design of the basins, Appendix C illustrated the drainage networks to feed into each basin and Appendix D provides the calculated filtrations rates.

3.2 The detail of each offsite basin is provided below. Both basins include side slopes of 1:3 gradient with a 5 m maintenance strip.

Offsite Northern Infiltration Basin (ONIB)

3.3 The ONIB is the larger of the two basins with a depth of 2.55 m and base area of 4300m³. The basin is designed to collect runoff from both Network 1 (northern area of the development) and Network 5 (overland flow from north and north eastern fields). Subject to a 1 in 100 year storm, the half drain time for the respective network drainage inputs are 2.6 days (water depth of 1.028 m) and 1.95 days (1.87 m depth). Consequently, a full basin would drain completely within approximately 5 – 6 days.

3.4 Flooding anticipated to be experienced more frequently, such as a 1 in 1 year storm, would drain in 0.3 and 0.67 days (depths of 0.21 m and 0.37 m), respectively.


Page 3

Offsite Southern Infiltration Basin (OSIB)

3.5 The smaller OSIB is 1.45 m deep with a base area of 1690m³. The basin design collects from Network 6 only (overland flow from the eastern field), with no catchment from the development itself. Subject to a 1 in 100 year storm the half drain time for the basin would be 13.4 hrs with a water depth of 0.885 m. Consequently, a full basin would drain in just over one day.

3.6 Flooding anticipated to be experienced more frequently, such as 1 in 1 year storm, would drain in 3.5 hours (depth 0.171 m).

Comparison of Basin Designs

3.7 The principle differences between the basin designs include: direct change from one very large basin to two much smaller basins; ONIB with slightly increased overall depth and consequently slightly longer drainage time; OSIB with shallower depth and quicker drainage time; increased gradient of banks from 1:4 to 1:3 slopes.

Existing Open Water Habitats within the Wider Landscape

3.8 Aerial imagery, as shown within Appendix A, illustrates the location of existing features within the local environment which already support, or have the potential to support, large numbers of bird species hazardous to aircraft strikes, some of these have already been outlined within point 2.2 above. Additional features shown include the River Tud and Shallow Brook Lakes to the south of the River Wensum and numerous balancing ponds associated with the A1270 road network construction which extends around the northern airport boundary. The imagery demonstrates the extensive opportunities already available for bird species around the vicinity of the development as well between the development and the airport. Should the basins be utilised at any time by large numbers of birds, or larger species, then movements between the basins and these features could be considered to increase risk of bird strike. However, the majority of movements, if any, from the basin are considered more likely to be towards the closest suitable, and more optimal, habitats to support birds which include the River Wensum floodplain to the south and numerous pits and lakes to the west; all of which are in the opposite direction of the airport.

4. Conclusions and Recommendations

4.1 Although the drainage time for the ONIB is shown to be slightly longer, the newly proposed basins are not considered to increase the risk of supporting bird populations and subsequently the risk of bird strikes to aircraft operating within or around Norwich airport. The accompanying designs for the smaller basins are considered to equate to, and for some elements be lower than, the risk concluded within the 2017 assessment, this is due to:

• Less open space to accommodate large numbers of birds due to smaller basin sizes as well as narrower designs which are less comparable to natural open water habitats such as ponds and lakes;

• Comparative drainage times restricting colonisation of floral and faunal food sources;

• Less favourable areas of potential foraging, roost and nest sites due to steeper slopes, more enclosed spaces and lack of in-basin features such as islands;

• Higher risk of predation for bird species from predation due to steeper sides, low water volumes and enclosed spaces (aided by additional landscaping);

• Availability of more suitable alternative habitats within the local area (see point 2.2 and 3.9 above and Appendix A);

• The overarching purpose of the design to alleviate existing flooding experienced by Drayton village from the area both within and adjacent to the development footprint, and therefore remove the existing standing water available for exploitation by risk bird species at times of flood.


Page 4

4.2 Control measures have been identified within the 2017 BHMP. These controls are considered to still be suitable and acceptable for the newly proposed design. The management and mitigation principles to be implemented are inclusive of, but not limited to:

• Implementation of the basin design inclusive of specified depths and side gradients;

• Seeding of grassland areas with seed mix less palatable to bird species;

• Mowing of grassland to maintain an appropriate height with a dense grass dominated sward, eliminating the potential for foraging by wildfowl on broadleaf ‘weeds’ (‘Long Grass Policy’3);

• Soft landscaping to deter ingress of birds, i.e. reducing flight lines and predator visibility, such as bunded sides or planting of trees/ tree belts (and scrub where appropriate);

• Production of a well-informed and detailed maintenance plan to ensure basin drainage times remain achievable (outline maintenance plan has been provided in the Surface Water Maintenance Plan4 within the FRA; an abstract of which is provided in Appendix D);

• Bird monitoring programme implemented to report on presence/absence of bird species within the basins; this will enable continued assessment of the mitigation implemented and highlight any requirements for further control measures (details have been provided for monitoring and target levels within the 2017 BHMP).

4.3 Subject to the implementation of the basin design upon which this assessment was based, in addition to the control measures outlined above and within the previously issued BHMP, the risk of bird strikes from the proposed development and subsequent drainage design are considered to be very low.

5. References

CAA CAP 772 Wildlife Hazard Management at Aerodromes Revision 2 dated October 2017

Bird Hazard Risk Assessment and Bird Hazard Management Plan, Airfield Wildlife Management Ltd dated February 2017

6600556-MLM-ZZ-XX-RP-C-0001 Flood Risk Assessment and Drainage Statement Revision 00 dated 14 February 2020

6600556-MLM-ZZ-XX-RP-9000- Networks 1-6 Half Drain Summary FOS 2

6600556-MLM-ZZ-XX-DR-C-9005-P05 OFFSITE BASINS

3 Page 24, ‘Open Terrain’ section of the CAA CAP 772 Wildlife Hazard Management at Aerodromes Revision 2 dated Oct 2017 4 00 ‘Infiltration Basins’ section of 6600556-MLM-ZZ-XX-RP-C-0001 Flood Risk Assessment and Drainage Statement Revision 00 dated 14 Feb 2020


Page 5

Appendix A – Site Location and Wider Landscape Plan


Page 6

Appendix B – Offsite Basins Drainage Design


Page 7

Appendix C – Surface Water Drainage Network Key Plan


Page 8

Appendix D – Filtration Rates

Previous Proposed Offsite Basin

Northern Offsite Infiltration Basin

Southern Offsite Infiltration Basin


Page 9

Appendix E – Maintenance of Infiltration Basins

Note: Abstract taken from the Surface Water Maintenance Plan within the FRA

manor farm, drayton hopkins homes ltd...manor farm, drayton, bird hazard risk assessment 2020 page 1...

Documents