Baseline suspended-sediment, solute, EC and turbidity characteristics for the Ngarradj catchment, Northern Territory, and the impact of mine construction

A stream gauging network in the Ngarradj catchment, Northern Territory, was established to determine stream baseline conditions to monitor impacts of the Jabiluka mine construction site. Data on stream suspended sediment concentration, electrical conductivity (EC) and turbidity were collected for four wet seasons (1998*2002). The network design enabled the influence of dry season fires on stream suspended sediment concentration to be observed. Water quality trigger values were established using upstream percentiles and a BACIP design using monthly median values. There was very low frequency exceedence of the 99.7th percentile trigger level, however, it cannot be definitively stated that this was due to mine site construction. A late dry season fire occurred contemporaneously with site construction confounding experimental design and elevated sediment loads resulting from the fire may have masked mine site impact. The data set provides good baseline information for future assessment at Jabiluka and demonstrates the need to view measured parameter values on a catchment-wide basis with knowledge of rainfall, discharge and fire distribution.