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Discharge time series' are one of the core data sets used in hydrological investigations. Errors in the data mainly occur through uncertainty in gauging (measurement uncertainty) and uncertainty in determination of the stage–discharge relationship (rating curve uncertainty). Thirty‐six flow gauges from the Namoi River catchment, Australia, were examined to explore how rating curve uncertainty affects gauge reliability and uncertainty of observed flow records. The analysis focused on the deviations in gaugings from the rating curves because standard (statistical) uncertainty methods could not be applied. Deviations of greater/lesser than 10% were considered significant to allow for a measurement uncertainty threshold of 10%, determined from quality coding of gaugings and operational procedures. The deviations in gaugings were compared against various factors to examine trends and identify major controls, including stage height, date, month, rating table, gauging frequency and quality, catchment area and type of control. The analysis gave important insights into data quality and the reliability of each gauge, which had previously not been recognized. These included identification of more/less reliable periods of record, which varied widely between gauges, and identification of more/less reliable parts of the hydrograph. Most gauges showed significant deviations at low stages, affecting the determination of low flows. This was independent of the type of gauge control, with many gauges experiencing problems in the stability of the rating curve, likely as a result of sediment flux. The deviations in gaugings also have widespread application in modelling, for example, informing suitable calibration periods and defining error distributions. This paper demonstrates the value and importance of undertaking qualitative analyses of observed records. Copyright © 2012 John Wiley & Sons, Ltd.

Short-term (contemporary) and long-term denudation rates were determined for the Blue Mountains Plateau in the western Sydney Basin, Australia, to explore the role of extreme events (wildfires and catastrophic floods) in landscape denudation along a passive plate margin. Contemporary denudation rates were reconstructed using 40 years of river sediment load data from the Nattai catchment in the south-west of the basin, combined with an analysis of hillslope erosion following recent wildfires. Long-term denudation rates (10 kyr-10 Myr) were determined from terrestrial cosmogenic nuclides, apatite fission track thermochronology and post-basalt flow valley incision. Contemporary denudation rates average several times lower than the long-term average (5·5 ± ± ± ± ± 4 mm kyr − − − − −1 versus 21·5 ± ± ± ± ± 7 mm kyr − − −Recent studies have compared long-term denudation rates (10 kyr-10 Myr) determined from cosmogenic nuclides and apatite fission track thermochronology (AFTT), with contemporary rates (1-100 yr) calculated from stream gauging, sediment rating curves and sediment trapping (see, e.g., von Blanckenburg, 2005). Whilst some studies have observed similar short-term and long-term rates of denudation indicating steady state erosion (Bierman and Caffee, 2001;Matmon et al., 2003;Nichols et al., 2005), many have found either elevated contemporary rates attributable to human impact and land use change (Hewawasam et al., 2003;Gellis et al., 2004), or lower rates thought to be explained by the absence of high-magnitude, low-frequency (extreme) events in records that span only decades (Kirchner et al., 2001;Schaller et al., 2001). To substantiate the former, paired catchment type investigations have been conducted using undisturbed environments to give reasonable estimates of natural contemporary rates (Brown et al., 1998; von 1014 K. M. Tomkins et al. Blanckenburg et al., 2004). For the latter, determination of sediment yields from hypothetical extreme events has proved to be more problematic and, as a result, so has extrapolation of these contemporary records to long-term landscape evolution. In a study of denudation rates from the Rocky Mountains in Idaho, USA, Kirchner et al. (2001) found that modern sediment yields measured over 10 -84 years from stream gauging and sediment trapping were on average 17 times lower than the long-term sediment yield. They concluded that the mismatch in rates was the result of sediment delivery being dominated by extreme erosional events triggered by external forces such as severe storms and wildfires, which occur at time intervals greater than the length of the modern record. In south-eastern Australia, weather extremes including drought, floods and wildfires are a dominant characteristic of the landscape. Very low rates of contemporary denudation have been reported (Bishop, 1984; Wasson, 1994; Wasson et al., 1996), despite significant increases as a result of European settlement and land use change (Wasson, 1994). However, it is possible that these short-term records have not capt...

The rainfall‐runoff events following five fires that occurred within a 40‐year period in eucalypt forests of the Nattai catchment, southeastern Australia, were investigated to quantify the postwildfire hydrological response and to provide context for lower than expected erosion and sediment transport rates measured after wildfires in 2001. Daily rainfall and hourly instantaneous discharge records were used to examine rainfall‐runoff events in two gauged subcatchments (>100 km2) for up to 3 years after fire and compared with nonfire periods. Radar imagery, available from 2001, was used to determine the intensity and duration of rainfall events. Wildfires in the study catchment appear to have no detectable impact on surface runoff at the large catchment scale, regardless of fire severity, extent or time after fire. Instead, the magnitude of postfire runoff is related to the characteristics of rainfall after fire. Rainfall is highly variable in terms of annual totals and the number, size, and type of events. Rainfall events that cause substantial surface runoff are characterized by moderate‐high intensity falls lasting one or more days (≥1 year average recurrence interval). These are triggered by synoptic‐scale weather patterns, which do not reliably occur in the postfire window and are independent of broad‐scale climate dominated by the El Niño–Southern Oscillation (ENSO). This study highlights the importance of considering the characteristics of rainfall, as well as local factors, in interpreting the postfire hydrological response.