The Institute for Applied Ecology at the University of Canberra has conducted research to find out how changing the water level in urban ponds affects water quality. The findings will help us better manage the ACT’s many urban ponds.
Our ponds and wetlands
Cities like Canberra change the way water moves in our landscape. Lots of hard surfaces, like concrete and paving, mean rain doesn’t soak into the ground. Instead, it runs off into our stormwater system and urban streams.
Greater volumes of faster moving water pick up all sorts of pollutants along the way, including sediment, nutrients and rubbish.
Urban ponds are designed to filter that water before it enters our lakes and rivers. They slow the flow of water and allow sediment and nutrients to settle out. However, over time, pollutants build up and the pond doesn’t work as efficiently.
But there may be a way to extend the life of a constructed pond by mimicking what happens in natural waterbodies.
Seasonal wetting and drying
The water level in a natural pond changes regularly, due to evaporation and seasonal variations in rainfall. Man-made ponds tend to be located in urban areas and, as a result, generally remain full (thanks to increased volumes of run-off).
However, there is evidence to suggest that varying the water level increases a pond’s ability to trap pollutants, therefore improving water quality and extending its useful life.
Existing research tends to focus on natural waterbodies and/or a single monitored wetting and drying event (an isolated storm for example) rather than wet and dry cycles over time.
The Urban Stormwater Pond Research Project was a longer term study looking at multiple wetting and drying cycles in constructed urban ponds.
The research project
To find out how varying the water level affects water quality, the Institute for Applied Ecology at the University of Canberra is studied six urban ponds:
- Jarramlee Pond and Fassifern Pond in Dunlop
- Holdens Pond and School Pond in Coombs*
- Lyneham Wetlands and Dickson Wetlands
Two ponds (Fassifern Pond and School Pond) remained full and acted as controls.
The water level in the corresponding active ponds (Jarramlee Pond and Holden Pond*) were dropped by up to 1.5 metres, leaving 3-4 metres of exposed bank. Each pond was left to refill naturally before being drained again. This process was repeated during late summer and autumn in 2018 and 2019.
Lyneham Wetland and Dickson Wetland were also studied as, due to the harvesting of stormwater for nearby playing fields, the water level in those ponds already changes.
Researchers visited all six ponds weekly until May 2019 to collect water and sediment samples for analysis at the University of Canberra. They also took measurements of any plants growing around the edges of the ponds.
This work is currently being finalised.