New research on how urbanisation impacts subtropical hydrology and ecology
After three years of detailed research and modelling, The Urban Water Security Research Alliance (UWSRA) has released a report with answers for South-East Queensland.
– Alan Hoban, Bligh Tanner Consulting Engineers
The answer for hydrology is complex: it depends. Urbanisation does change stream hydrology compared to pre-development (forested) conditions. Generally these changes result in catchments spending more time under high flow conditions, but not necessarily so. Catchments can vary depending on their topography and size. Placing the same urban development in two catchments is likely to lead to different outcomes, because catchment characteristics have a role in mediating the impact that urbanisation has on hydrology too.
The project was lead by Dr Brian McIntosh, a senior lecturer at the International WaterCentre.
In terms of ecology, Brian’s team found that subtropical stream species can be fairly resilient to the intense flows that can result from urban runoff, with macro-invertebrate assemblage characteristics like diversity and species richness remaining similar between urban and pre-development sites. However species composition does vary, with fewer sensitive species in urban streams, particularly in pools. Other factors, like water quality and temperature, appear more likely to be responsible for relatively poorer health of aquatic ecosystems in and downstream of traditional urban areas.
The report also presents an assessment of Queensland’s Frequent Flow Management Objectives, designed to maintain catchment hydrology in a pre-development state, and finds them only partially effective at best.