Pioneering Projects: Doing it Differently and New Ways of

TOM PALMER FdSc BSc (Hons) Project Design Engineer Essex County Council tom.palmer@essex.gov.uk 03330 139511

SMALL PROJECT OF THE YEAR British Construction Industry Awards 2018

Pioneering Projects: Doing it Differently and New Ways of Working Kingsmoor, Harlow Pluvial Flood Alleviation Scheme

•  5 year, £19m programme

•  Individual schemes funded from programme and topped up with grants from the EA

•  Projects selected by prioritising Critical Drainage Areas identified within SWMP’s and s19 report locations

•  Feasibility and Option Optimisation studies undertaken with gate reviews prior to design and delivery stage

5 year capital programme scheme locations within Essex

Harlow, Kingsmoor Pluvial Flood Alleviation Scheme

Essex Capital Programme

Harlow, Kingsmoor Pluvial Flood Alleviation Scheme

Location and Problem

•  Kingsmoor is an area in the south west of Harlow, Essex

•  Heavily developed between 1950 and 1980

•  Rural upstream, developed downstream

•  Recorded internal property flooding to 20 properties from surface water and 20 from sewers, most from a single storm event in 2006

•  Residential estate access road frequently made impassable due to flooding

•  Issues with silt and debris from farmland upstream entering piped systems

•  Modelled risk to 179 properties and 9 businesses from a 1% AEP event

Kingsmoor Critical Drainage Area (CDA)

Harlow, Kingsmoor Pluvial Flood Alleviation Scheme

Kingsmoor Area Flooding Photos

Photographs courtesy of Harlow DC

Harlow, Kingsmoor Pluvial Flood Alleviation Scheme

Scheme Development

•  Feasibility and Option Optimisation studies undertaken by Jacobs

•  Determined that a large earth bund and storage area provided the greatest benefits

•  Reviewed in conjunction with Harlow District Council and leaky dams and pond de-silting aspects were proposed to better mitigate against silt

•  The number and positioning of dams changed after discussions with Harlow DC based on known flood flow routes

•  Potential dam locations identified and finalised following site meetings

Location of proposed measures

Harlow, Kingsmoor Pluvial Flood Alleviation Scheme

Constraints and Considerations

Key site constraints

Site Constraints:

•  Local Nature Reserve (LNR) •  Ancient Woodlands •  SSSI’s (pedunculate woodland) •  Crematorium •  Footpaths and public access •  Proximity to residential areas •  Local ecology (hedges, trees, wildlife)

Considerations:

•  Use and type of machinery •  Working methods •  Noise and working hours •  Vehicle movements and re-use of spoil •  Sustainability (design and construction)

Harlow, Kingsmoor Pluvial Flood Alleviation Scheme

Mitigation Measures

•  Early engagement with stakeholders and partners

•  Dam positions adjusted to reduce impact to woodland and utilise existing morphology and features

•  Use of volunteer group to help clear woodland areas

•  Use of wood sourced from within woodlands as part of existing management plan

•  Use of heavy horses to move materials into position and dams installed by hand

•  Footpath diverted with unadopted path on bund crest

•  Work stopped for funeral processions

•  Grassland Management Plan created for Local Nature Reserve area

Photo courtesy of Place Services

Harlow, Kingsmoor Pluvial Flood Alleviation Scheme

Opportunities and Wider Benefits

•  Woodland clearances chance to improve wider area (in line with SSSI status)

•  Ecology and biodiversity in woodland and ponds

•  Local amenity, promotion of woodland, awareness raising

•  Education: woodlands frequently visited by schools

•  Footpath inconsistencies, chance to correct

•  Earth bund seeded with grasses and wildflowers

•  Innovative Grassland Management Plan for whole LNR rather than compensatory like for like area replacement

•  Improved wildlife corridors Site boundary (red) and Local Nature Reserve (blue)

Harlow, Kingsmoor Pluvial Flood Alleviation Scheme

Scheme Photos: Leaky Dams During Construction

Photos courtesy of Harlow DC

Harlow, Kingsmoor Pluvial Flood Alleviation Scheme

Scheme Photos: Dams and Ponds Post Construction

Leaky dams and pond de-silting works immediately after completion (November 2017)

Harlow, Kingsmoor Pluvial Flood Alleviation Scheme

Scheme Photos: Leaky Dams and Ponds

Leaky dams and ponds (June 2019)

Harlow, Kingsmoor Pluvial Flood Alleviation Scheme

Scheme Photos: Earth Bund During Construction

Top and bottom far left photos courtesy of TopBond PLC.

Harlow, Kingsmoor Pluvial Flood Alleviation Scheme

Scheme Photos: Earth Bund Post Construction

(June 2019)

Harlow, Kingsmoor Pluvial Flood Alleviation Scheme

Scheme Summary and Key Outcomes

•  Leaky dams completed November 2017, bund completed July 2018

•  Total scheme costs £440k, pond de-silting and leaky dam aspects £42.8k

•  Flood protection to 43 properties from a 5% AEP event, depth reductions to over 110 others

•  Carbon assessment: 94.4t of CO2 saved

•  Flood mitigation measures can be delivered in sensitive areas!

•  Flood alleviation works as an opportunity for wider benefits to ecology, biodiversity, water quality and amenity, and for raising flood awareness

•  Partnership working essential to project success Toads and mint returning to a pond

Harlow, Kingsmoor Pluvial Flood Alleviation Scheme

Thank You

TOM PALMER FdSc BSc (Hons) Project Design Engineer Essex County Council Flood and Water Management Team tom.palmer@essex.gov.uk 03330 139511

Kingsmoor Flood Alleviation Scheme SMALL PROJECT OF THE YEAR British Construction Industry Awards 2018