Bridging the Gap between Noise and Planning
So many impacts from the construction industry have clear and obvious, well-defined and judgable outcomes.
The same can be said within the noise and planning sector. For much of the work we do, there are clear sets of criteria, with assessment methodologies.
If, for example, someone wants to install an air conditioning plant? Ok, there is an assessment to British Standard 4142:2014. If housing is to be built close to a road? Ok, noise levels within the houses can be assessed, through British Standard 8233:2014.
But how do you assess the noise impact of a footbridge?
Some of our jobs require nuance and foresight, or retrospective action to remedy unexpected outcomes.
Finzels Reach development footbridge: Bridging Noise & Planning
Assessing the noise impact of a footbridge, namely a new footbridge spanning the floating harbour in Bristol as part of the Finzels Reach development, was our role.
The curved bridge is currently under construction, and will form a public right of way from the main shopping area in Bristol towards Temple Meads Railway Station through a converted brewery site along the edge of the harbour.
Many beautiful footbridges span waterways within Bristol and across other UK cities. We learnt that, due to their construction, some of these create a lot of noise when people walk over them, or ride bikes over them. This seems to be because of the texture and material of the bridge deck, and the way that this generated vibration can interact with the structure. So, the first thing we needed to know was – how is the bridge built, and how loud will it be?
Discussions with the project architect and bridge contractor identified the construction and several locations where this had been constructed and could be measured. We then needed to find a site where we could physically place a microphone to undertake measurements of bridge noise without noise from other nearby sources. This ruled out any bridge over a road and any bridges at significant height.
Luckily for us, we discovered that a section of towpath along the floating harbour was constructed from timber fixed to supporting metal beams. It was bordered by office buildings on both sides of the river which minimised noise from nearby roads, and there was a mooring alongside where we could undertake our measurements. All we had to do was wait for the lunchtime rush for people to walk and cycle past us.
Once we had accurate measurement data we then had to determine how to assess this type of noise. The sound of people walking or cycling on a public right of way is considered part of the general noise within an urban area. The WHO1999 guidelines call this ‘Community Noise’, and provide guideline values for daytime and nighttime periods.
It was considered that the most significant effect would be that of the impulsive ‘maximum noise level’, if people were walking along the bridge at night.
Using the plan of the bridge and nearby housing we calculated the noise level at the façade of the nearest flat, based on the measured data.
Then, using information provided for the façade construction and layout of the flat, we determined that noise within the flat from the use of the bridge will not adversely affect the occupants, and thus could allow the planning condition to be discharged.
You can see that the outcome of this monitoring could have had a massive impact on the planned construction.
The project involved a lot of planning and a literature review. The outcome could be presented in a simple, clear and concise format based on accurate measurements that could be understood by any interested parties, and was able to satisfy the council that noise was not of concern.
We believe that is the skill in the environmental assessment of unique problems. A project can involve a lot of work, including measurement and prediction, but ultimately the assessment has to be simple enough for everyone to understand so that people can be confident in the conclusions it draws.
Picture courtesy of The Bush Consultancy, Finzels Reach & Cubex