Is what you see really what you get? A new method of monitoring sediment dynamics in a macro-tidal, monsoon climate

Darwin is Australia’s most northern capital city with a population of 130, 000 people. Highly turbid coastal waters have been observed by locals from the coastline during the wet season for years. Although the link between... [ view full abstract ]

Darwin is Australia’s most northern capital city with a population of 130, 000 people. Highly turbid coastal waters have been observed by locals from the coastline during the wet season for years. Although the link between high turbidity and wet season weather appears obvious to observers, in most cases it has led to a variety of unverified opinions being accepted as true and correct. A reliance on observations rather than field data is unsurprising given accessibility constraints during the wet season and a diurnal tidal pattern with a maximum range of 7.9 m. With increasing industrial development, an evidence based theory on sediment dynamics in estuarine Darwin Harbour has become increasingly important. The central question to be addressed is: Are the effects of anthropogenic development on turbidity in Darwin Harbour significantly different from baseline turbidity levels, which are known to vary seasonally? To improve harbour management, the natural environment must be described while it is still in a relatively pristine state. The Australian Institute of Marine Science Darwin, Charles Darwin University and the Aquatic Health Unit of the N.T. Department of Land Resource Management have collaborated on a novel pilot study to collect facts about sediment dynamics in Darwin Harbour. We measured, for the first time in Darwin Harbour, relative suspended sediment and localised surface elevation change using an Acoustic Doppler Velocimeter and Rod Surface Elevation Tables (RSETs) respectively. The results show that it is possible to relate the increase in turbidity in the intertidal zone to localised erosion during in the presence of monsoonal rainfall and runoff events. It has highlighted the utility of time series data as a robust method of monitoring a naturally variable water quality parameter. This research has cleared the water for local scientists to work towards developing evidence based knowledge on sediment dynamics in Darwin Harbour. The results from this study have direct application to the existing Darwin Harbour monitoring and research program.