Bletchley, Brunel Roundabout

Location: Bletchley, Milton Keynes

Milton Keynes Councils’ Master Plan was to redevelop and regenerate land in and around Bletchley Town Centre building on the opportunities created by the development of east-west rail and the work undertaken in the Bletchley Fixing the Links project a series of works to up-grade the pedestrian and cyclist links between Bletchley Rail Station and the town centre.

In line with the NPPF (National Planning Policy Framework), development of Bletchley town centre would enable new shops, services and facilities to serve the population of the proposed new residential areas identified in Plan.

A high quality public realm was proposed to develop the relationship of buildings to the public realm to increase pedestrian activity thus providing a thriving and safer outlook.  The plans held detailed information relating to ground levels, adjoining developments and site boundaries to trees, planting and other existing features on site and surrounding areas.

The quality of hard and soft landscape was a fundamental contribution to the value of the development. Not just to soften the landscape and shield street parking, careful consideration was taken regarding the daily burden to the environment such as the movement of vehicles, people, storm water and road gritting. Reflection was also given to the practicality of maintenance over the long term without affecting the quality and visual features.

GreenBlue Urban were brought into the team to provide design support and technical input to the tree pit design. The project opened an excellent opportunity to combine tree planting with best practice in water sensitive urban design. By utilising the new RootSpace tree system, large volumes of uncompacted soil could be provided, with a high strength air deck support allowing flood dispersion and air replenishment to the soil zone.

One of the key success criteria for allowing long term water attenuation within soil, is to maintain uncompacted soil structure. This means that the macro pores as well as the micro pores, so critical to water and air transport and storage within the soil, are protected. Soil composition and installation are therefore an area that GreenBlue offer support and give guidance on, as it is fundamental to both tree health and SUDS performance.

With the Bletchley project tree pit design, a modular, scalable root zone construction allowed tree pits to be linked below ground and can accommodate a large volume of storm water. In this project, the system has eight trees, and has a minimum combined storm water capacity of 19,511 litres. Thats a staggering 2438 litres of attenuation per tree.

This water capacity is likely to be significantly more, but current calculating methodology ensures a baseline figure which engineers can rely on. The figure does not allow for tree canopy interception (which can account for 70% of the first hour of a rain event) or ground percolation and recharge, which is site variable.

As GreenBlue often remind clients one of the wonderful things about using trees in this application is that every year the tree grows, canopy volume expands, and rainfall interception capacity increases!

Milton Keynes have successfully completed this scheme and installed what could arguably be described as a truly multi role example of green and blue infrastructure. If one considers the multiple benefits trees bring to urban space, not least in improving air quality, increasing real estate values and many other health and social economic benefits, it is difficult to imagine anything else that could bring the equivalent value and benefit to the urban realm.

Council: Milton Keynes

Contractor: Ringway Jacobs Ltd

Sub Contractor: Smith Construction Group Ltd