Work has commenced on a temporary arena and cross country course for a major Equestrian event in Greenwich Park that will take place during July and August of this year.
EPG is engaged to provide a sustainable water management system by Andrews Bowen Ltd, the contractor responsible for the supply and installation of all equestrian footings (performance surfacing) for the scheme.
The design remit for this prestige project is complex and very demanding due to the temporary nature of the development and the unique constraints associated with the Royal Park’s heritage and environmental setting, combined with exacting performance requirements of the surfacing and construction tolerances to meet international equestrian eventing standards.
Major elements of the sustainable water management design are to be constructed within steel structural platforms to be provided by The Structures Group (TSG). Over the past 18 months several substantial test events have been undertaken by the client to assess all aspects of the proposed systems and this has enabled TSG’s structural design team and EPG to develop an integrated, complimentary water management design to manage the surface water run-off from the platforms, which includes water harvesting to be re-used for the environmental conditioning of the equestrian footings system.
The footings comprise a unique high performance sand and fibre mixture manufactured by Andrews Bowen, which require specific moisture content to achieve optimum performance. The water management elements will be installed by for Andrews Bowen by SEL Environmental Ltd, a specialist environmental contractor.
Test Event 2011 – Arena deck with Equaflow layer and hydrophilic geotextile system
Test Event 2011 – Arena deck with Andrews Bowen Sand & Fibre system being laid above the Equaflow water management system
Some of the key challenges are as follows:
- No excavations whatsoever are allowed within the Park
- Existing ground levels vary significantly with gradients up to 6% in areas of the proposed arenas and training areas, whereas international standards require maximum gradients of 1% for equestrian performance areas
- Numerous protected trees exist in and around proposed performance areas that require suitable root protection provision
- The water management system must comply with current best practice source control SUDS guidance
- The performance surfaces must manage a 100 year storm event with zero discharge to existing sewers
- Water supply for irrigation of the performance surfaces is limited
- Truck cycles must be kept to a minimum to avoid congestion and minimize environmental impact
- Wherever possible the construction materials must be manufactured from recycled materials, be recyclable and reusable
The solution developed by EPG involves the following innovative features:
- As all performance areas including the training facilities and the main arena are to be constructed to a 1% gradient; surface water run-off needs to be managed on a slope to prevent point loading to the existing grassed areas and avoid erosion issues and overland flooding to downslope structures and features. The run-off also needs to be harvested for irrigation of the overlying sand and fibre performance surfaces.To achieve this EPG has designed a system whereby the surface run-off is immediately collected within a modular high strength drainage/attenuation layer known as Equaflow (supplied by Andrews Bowen), which receives and conveys the surface water directly beneath the sand and fibre surfacing. However, to prevent the water migrating entirely to the low end of the platforms; a series of regular ‘check dams’ will be created using welded robust membrane that will capture and control the level of the water at regular intervals. An arrangement of hydrophilic (wicking) geotextiles installed throughout the Equaflow layer will transfer water ‘on demand’ into the overlying sand and fibre surface. An overflow arrangement will collect excess surface water into an underlying rainwater harvesting system that will incorporate wet risers at the edge of the platforms to facilitate recovery via suction pumps mounted on the plant that will be used for surface maintenance.A secondary overflow arrangement will convey further excess volumes to a an arrangement of perforated drains beneath the platforms to allow gravity controlled diffuse infiltration to the existing park surfaces; in effect, mimicking the natural rainfall management cycle. The system is designed to wholly manage the 100 year event + 10% allowance for climate change within the platform attenuation layer with final discharges to the diffuse soakaways limited to Green Field Run-Off Rates, in compliance with SUDS best practice.
- There are two types of structural platform proposed that will incorporate the above drainage design; two are steel and timber platforms designed by TSG; a further seven platforms are to be constructed using a lightweight upfill system designed by EPG. The lightweight upfill, known as Permavoid, comprises modular high strength plastic structural ‘blocks’ that have a high tensile lateral interlocking tie arrangement to create a structurally competent raft.The modules are 150mm thick and will be assembled into varying cumulative thickness along contours predetermined from detailed topographical land surveys at each platform location. Thin layers (averaging no greater than 75mm) of imported granular material will be used to regulate construction formation levels. The gravel will be laid on a robust separation/filtration geotextile.This design ensures there is no long term damage to the existing grassed areas and prevents any high loads from overlying construction and maintenance plant from impacting on existing tree roots i.e. the system also provides root protection.
- The introduction of the lightweight modular upfill in lieu of conventional granular fill provides in excess of a 20-fold reduction in truck cycles.
- All of the materials incorporated in the upfill and drainage systems are manufactured from recycled materials and/or are recyclable and reusable.
- Key figures (approximate):
- Platform Areas (Steel/timber) – 12,200 sq.m
- Upfilled Platforms – 18,000 sq.m
- Lightweight upfill – 6500 cu.m
- Modular attenuation (additional to fill) – 3600 cu.m
- Rainwater Harvesting – 100 cu.m
- Equestrian Surfacing – 12,000 tonnes
- Reduction in number of 20t truck loads – 700*
- Construction period – 11 weeks
- Deconstruction period – 7 weeks
*Based on equivalent volumes of gravel vs Permavoid lightweight fill
The whole system is to be installed under a strict construction quality assurance (CQA) protocol and the completed system will be subject to rigorous performance testing by a specialist academic team appointed by Andrews Bowen, which comprises an amalgamation of equestrian experts from Anglia Ruskin University, The University of Central Lancashire and Myerscough College.
Installation photographs during May 2012 main event build up
Lightweight upfill being installed to contours on one of the platforms. Upfill varies in height up to 1.5m
Water management arrangement at check dam position showing valve detail that controls attenuation and diffuse discharge. The pipes run through the whole system and have perforated walls with openings sized to ensure even distribution of discharge water. The white elements are the hydrophilic wicking geotextile that runs above and beneath the upper attention layer that is separated from the lower lightweight upfill by a robust welded waterproof membrane.
Rainwater harvesting tanks under construction beneath main arena steel/timber platform
Main arena under construction