Sound mapping design of water features used over road traffic noise for improving the soundscape

This paper examines the effectiveness of water features in masking noise and improving the soundscape, when used over road traffic noise. The work focused on identifying how appropriate sound pressure levels can be achieved from a variety of water sounds generated by small to medium sized features (waterfalls, fountains, jets, a cascade and a natural stream). Sound pressure levels were calculated using standard propagation models and sound maps were developed for a 20 m × 20 m grid representative of a garden/park area. Maps displaying three acoustic zones were also created (‘water sound dominant’, ‘optimum’ and ‘road traffic noise dominant’ zones) for a wide range of road traffic noise levels (‘optimum’ = water sounds similar or not less than 3 dB below the road
traffic noise level). Results showed that most small to medium sized water features (individual or combined features) could be used in environments where road traffic noise levels are equal or lower than 65 dBA, with larger optimum zones typically achieved for lower road traffic noise levels, and with a linear decrease of the optimum zone’s width with road traffic noise level. Fountains with multiple upward jets, cascades and waterfalls with an edge made of small holes, tended to be most effective in improving the soundscape over road traffic noise levels ranging 40–65 dBA. Natural shallow streams, which tend to be very highly rated for relaxation, were only effective for road traffic noise levels of 40–55 dBA. Furthermore, waterfalls with plain and sawtooth edges and single narrow jets masked a wider range of road traffic noise levels (40–70 dBA), but previous research has shown that these tend not to be preferred compared to other water generated sounds.