Noise

THEL’s goal is to ensure that noise from the Project’s lower powerhouse would be largely imperceptible to nearby residences under normal weather conditions.

Powerhouses generate noise via their machinery that includes, but is not limited to, generators, turbines and fans. Most important for this project is the ability to reduce sound levels outside of the powerhouse building. The primary method for this is through insulating materials in the building itself.

Studies of industrial noise sources in residential areas found façade insulation in buildings to have the most significant effect on noise levels and annoyance ratings (e.g., sound-insulated windows can reduce the sound by more than 30 decibel (dbA)) (European Union, 2017). Sound-damping in the building, especially with respect to ventilation, would likely be required for the lower powerhouse.

So how loud is loud?

A natural environment (e.g., birds, trees, wind) has an average daytime level of 40 dBA, and an average night-time level of 30 dBA. The figure below shows a comparison of common noise sources and their dBA levels. While the average ambient decibel level at the nearest residences on Warm Bay Road are not known at this time, it is expected to be similar and/or lower than the average night-time decibel level for a natural, quiet environment.

The nearest residences on Warm Bay Road are approximately 200 m away from the lower powerhouse. The distance that sound travels depend on acoustic design measures as well as the topography, the size of openings, the amount of vegetation, the prevailing winds, and other similar factors (Power Engineering, 2000). For that reason, the location and layout of the proposed lower powerhouse is as important to reducing the potential for noise to residences as the acoustic design measures. The lower powerhouse is ideally situated in this regard, as it is located below the residences at the base of a hill on the Pine Creek flats, reducing the potential for sound to travel. The site is also surrounded by forest, which further reduce this potential.

The noise control system for the lower powerhouse will be determined during the current detailed design phase. However, it should be noted that the lower powerhouse would use Francis turbines, rather than the Pelton turbines used at the existing powerhouse and proposed upper powerhouse. Because Francis turbines are submerged, and the tailrace is a low-flow channel, the potential noise associated with the turbines and flows from the tailrace are likely to be reduced. Other systems still to be designed would include noise abatement measures in the building, e.g., an acoustic building envelope, acoustically treated ventilation system and acoustic doors.

During the detailed design phase, the existing ambient noise levels at the nearest residences, as well as the location of the most sensitive noise receptors (not necessarily based on distance from the powerhouse) will be determined. This information will ensure the design reaches the target decibel level for these receptors through noise abatement – in other words, will ensure a quiet design. Measures may include, for example, the direction the vents should face, additional sound-damping/insulation on a particular wall, and minimizing the size and shape of clearings. This would be designed by an acoustic engineer.

The lower powerhouse would not only be designed to be quiet, but also discreet – it would not be visible from Pine Creek beach. As well, the powerhouse would generally not be operational during the summer months, the primary period of use at Pine Creek beach.