Green covers improve drainage channels

Posted on June 1, 2016

In urban environments, the ubiquity of impervious surfaces increases rainfall runoff and the risk of flash flooding. These problems can be addressed by widening and deepening drainage canals, but usually at the risk of further habitat degradation. As a result, there ‘s increasing interest in low-impact environmentally-sensitive designs that simultaneously improve flood control and ecosystem values. One of these proposals involves installing a layer of vegetated soil on decking in the open spaces above existing canals, a configuration that essentially places a green roof over a concrete channel. The permeable cover filters floodwater and slows runoff into the channel, which helps to reduce flooding. At the same time, the green cover creates habitat for animals and plants, shades the stream, moderates water temperatures and improves visual amenity. The impacts of green cover designs on runoff flows have been simulated using a stormwater management model calibrated for Singapore’s Bukit Timah catchment, which contains open sections of concrete canal. Two rainfall patterns were modelled: a short duration–high intensity event and a long duration–low intensity event. The simulations showed that, on average, installing a green cover would reduce the maximum depth of water in the canal by 20% and the maximum flow at the catchment outlet by 21%. Maximum velocities in the canal would be lowered by 0.2–0.5 m/sec. Partial green cover designs, with openings that allow direct sunlight and rainfall into the channel, were also successful at reducing predicted peak flows. It seems that green channel covers can play a useful role in flood mitigation, aesthetic enhancement and improving ecosystem function in urbanised catchments

Reference: Palanisamy, B. & a,1, May Chui, T.F. 2015. Rehabilitation of concrete canals in urban catchments using low impact development techniques. Journal of Hydrology 523, 309–319.