By PhD Candidate Donghwan Kim,
Read Time: 3 minutes, about 410 words.
Often during flood events, water from agricultural catchments will erode productive agricultural soils and carry large loads of sediment and nutrients to downstream estuaries and coastal areas. This can threaten the provision of safe drinking water for humans and the ecology of marine ecosystems, as well as sometimes necessitating costly sediment dredging and disposal operations.
My PhD focuses on better understanding the problem of nutrients and sediments being exported under a range of flow conditions from different land uses such as forestry, grazing and cropping. My research focuses on a region in the state of Queensland in Australia, the Laidley Creek catchment. This particular area is recognised as a major horticultural area for South East Queensland and is also known as a hotspot for sediment and nutrients export to the mid-Brisbane River.
“Capturing flood events in the Laidley catchment presents huge logistical challenges.”
Capturing flood events in the Laidley catchment presents huge logistical challenges. Firstly, the Laidley Creek has only flowed two to three days a year after 2019, a result of prolonged drought. Secondly, forecasts of storms have often been inaccurate and storm flows never occurred even after significant rainfall. Much of this rainfall replenished groundwater aquifers, but not enough to generate surface flows. Thirdly, when the flow eventually came, collecting samples became dangerous as water levels rise with turbulent flood flow rapidly. Numerous field investigations never eventuated or failed for more than two years. However, recently I successful sampled flood water during a prolonged and intensive rainfall (220 mm for 10 days) in March 2021. I was able to collect samples manually in some locations and by autosampler in a forest stream.
The photo collage below show different stages of dry and wet conditions in Laidley Creek and its inflows. The photos in the upper line are Laidley Creek at Mulgowie, where discharge increased from 0 to 200 cubic meters per second in a few hours. The photos in the second and third rows show the water discharge over one day, during and after the rain.