Evaporation — A Tool for Sustainable Drainage Management

Where the use of orthodox controlled hydraulic discharge to watercourse is not possible for the management of urban runoff, alternative strategies need to be considered. At Jersey Airport (Great Britain) the development of a new Fire Training Ground facility was constrained by a prohibition on the disposal of surface runoff to watercourse or ground water (because of low levels of persistent pollutants in the runoff) so a system using evaporation and water re-use was developed to create a unique surface water drainage system without a surface water outfall. Surface runoff from the training ground catchment, excluding that generated during practice, is contained and stored beneath the permeable paved surface in a storage cell and managed either through evaporation or through harvesting for use in fire fighting practice. Evaporation is achieved using a patented system of 20 water jets placed around the fire training ground that apply water from the cell to the paved surface. They are automatically switched on when the on-site weather station indicates that there is sufficient evaporative potential. Wind speed and direction are measured to enable the sprays to cover the paved areas within the site boundary. Further research has been undertaken that has demonstrated that significant evaporation is achievable in patented designs of underground storage cells. This paper describes the development and modelling of the use of evaporation as a runoff management tool with particular emphasis on spray-on-pavement systems and enhanced passive evaporation from underground storage cells. The use of spray on pavement systems has been proven as viable and the use of in-cell evaporation is under development.