Utilizing street trees for sustainable stormwater management

Drainage problems arising from increasing levels of urbanization have exacerbated the limitations of conventional surface-water drainage measures. Street trees can be essential components to the management of stormwater in urban areas. Like their woodland forest equivalents, urban trees direct precipitation into the ground through trunk flow and absorb rainfall through their roots – making them an invaluable sustainability asset in the urban environment. Traditional drainage systems for surface water runoff have been designed to transfer rainwater from where it has fallen to either a soak-away or a watercourse as rapidly as possible. This method increases the risks of flooding, environmental damage, and urban diffuse pollution; since runoff water usually carries contaminants including oils, heavy metals, pesticides, fertilizers, chemicals and other urban matter. Specifically designed urban tree pit systems can effectively and sustainably mitigate these challenges. Sustainable urban drainage is about combining stormwater management with urban tree planting design. These systems can significantly reduce the velocity and flow rate of surface water runoff in urban areas and contribute towards meeting the required discharge rates, while filtering out harmful pollutants and contaminants carried in surface water, preventing particles in the water from passing through but allowing the water to be discharged into surrounding subsoil and absorbed by the trees’ root system, or into a specially designed flow-control chamber positioned on the outfall of the tree pit.