Importance of Inundation Frequency Analysis for Constructed Wetlands

Constructed wetlands play a vital role in Australia to reduce the environmental impacts of urbanisation. They also provide habitats for wildlife, provide people with places for recreation, and help make people be more aware of the environment around them.

Wetlands in Australia are typically designed to treat the 3 month ARI peak storm events over a 72 hour detention time. Urban development has forced wetlands ‘online’ which effectively treat flows from the whole of catchment. Wetlands placed downstream of other water quality treatments, retarding basins, large catchments and coupled with successive rainfall events, generate base flows for extended periods. This causes increased frequency of inundation and detention times in excess of 72 hours. Additional stress on vegetation and treatment performance therefore occurs, especially during establishment periods.

This paper takes a case study from one of Melbourne’s northern growth area where a constructed wetland’s vegetation partially died due to increased inundation times during establishment. A holistic catchment analysis was carried out utilising Continuous Rainfall Simulation (using MUSIC) in order to determine the frequency of inundation of vegetation over a 10 year period and the effects of urban hydrology. The paper recommends design considerations and techniques for ‘online’ wetlands.