Project:                                 Clerkenwell Green

Location:                              Clerkenwell Green, Islington

Power’s involvement:          Underground utilities surveys

Project completion:             August 2024

About the project

Clerkenwell Green is one of London’s oldest public spaces, dating back to the 12th century, and it is surrounded by some of Islington’s most attractive and interesting buildings. Back in 2017, the council consulted local people on proposals to improve the  Green by creating a more pleasant and greener local environment. These proposals received good support at the time, with 82% of the 433 respondents giving positive feedback.

As well as boosting biodiversity and improving air quality, the project at Clerkenwell Green was also designed to make the Green a more attractive space for the many people that use it every day. The improvements would also make the area quieter and safer for local people to walk or cycle, and for buggy and wheelchair-users to get about.

Our involvement

Powers completed a topographical survey of the Clerkenwell Green site in 2016 which was used to create the initial concept design. In August 2022 during the detailed design phase, Powers was commissioned by Islington Council to undertake a manhole/chambers survey and underground utilities detection (UUD) survey to provide as much understanding of what assets were located below ground as possible. The UUD data was inserted into the original topographical survey, once checks had taken place to ensure the survey measurements were still valid and correct. This invaluable knowledge was key to enabling the designers to maximise the design for the greatest benefit of the local residents.

As part of the environmental element of the work, the council also planned to install an underground sustainable drainage system (SUDS) retention tank, to provide temporary storage for excess water, which would in turn prevent flooding. The UUD survey played an integral role in determining the size of the tank, dependent on available space.

The challenges

As an important historical area, as well as the usual utilities sited below the surface, the Powers team also had to be aware of the potential for unmarked chambers and tunnels. As a public space home to residents and businesses, Clerkenwell Green remained open to the public while the surveys were being carried out, which meant the team needed to be vigilant from a health, safety and security perspective at all times.

The outcome

This major improvement project supports the Clerkenwell Green people-friendly streets low traffic neighbourhood, which was introduced as an 18-month trial in September 2020. The public space project, completed late summer 2024, introduces an additional 1,700sq.m of public space, representing a 68% increase and a 51% reduction in road space. Key highlights of the project included the planting of fifteen trees and introducing low-level paving on the Green, introduction of new paved areas, and replacement of some of the existing paving with new, more attractive York stone paving and granite setts.   The project also included the closure of the junction of Clerkenwell Road and Clerkenwell Green to motor vehicles, making it easier to walk, cycle, and use buggies and wheelchairs. Another welcome addition has been the installation of four new benches.

The UUD and chambers surveys enabled Islington Council to de-risk the project as much as possible at the start, by removing a huge level of uncertainty about the utilities, chambers and tunnels below ground. Being able to insert the later UUD survey data onto Powers’ existing topographical survey also gave the customer the following benefits:

  • The drawing details, layering styles and naming conventions were exactly the same between the two surveys. As the council already had Powers’ topographic survey, it was familiar with all markings, making the drawing easy to read and navigate.
  • Both surveys are on the same highly accurate control network grid, which ensures there is no disparity of level and position of, for example, manholes, between what’s surveyed underground and above aground.
  • Powers pick up manhole and services cover details as a part of its standard topographical specification, because its surveyors know that there may be UUD assets to add to it later. Not all topographical survey companies pick up private and public sewer manholes, for example, which can cause problems for Powers utilities surveyors when it comes to positioning them from above ground on another company’s topographic survey drawing.

Since completion, Clerkenwell Green has continued to be a busy local public space, hosted events including a summer party and featured on the front cover of Vogue.