The Brigalow Catchment Study: Effects of land development on peak runoff rate and its prediction in central Queensland, Australia

Abstract

Commencing in 1965 and continuing today, the Brigalow Catchment Study in central Queensland has measured both runoff volume and peak runoff rate from three catchments (11.7 to 16.8 ha) which were initially covered with native brigalow scrub. Thirty-eight years of data were used to assess the accuracy of three different methods for estimating peak runoff rate, and then, to quantify the changes in peak runoff rate as a result of clearing two of the three catchments for either cropping or pasture. Three methods were used to estimate the peak runoff rate for the 3 catchments: 1) multi-variable regression; 2) Soil Conservation Service Curve Number (SCS-CN) method; and 3) Spatially Variable Infiltration model (SVIM). Regression analysis showed that peak runoff rate was strongly correlated with total runoff volume, in addition to 3 rainfall related variables. Regression method yielded the best results of the three methods tested. Estimates using the SCS-CN method were strongly correlated with observed peak runoff rate for all catchments. However, the method typically underestimated for small events and overestimated for large events. Estimates using SVIM with linear kinematic wave routing were strongly correlated with observed peak runoff rate for all catchments. Prior to land use change, peak runoff rate from the three brigalow scrub catchments averaged 3.4 mm/hr. A significant increase in peak runoff rate from both the cropping and pasture catchments was clearly evident and attributed to land use change, with the average peak runoff rate increased by 9.1 mm/hr for the cropping catchment and 3.4 mm/hr for the pasture catchment. This equates to an increase of 263% and 164%, respectively, to estimates of their peak runoff rate had they not been cleared. Increases in the peak runoff rate were largest for smaller storm events with an average recurrence interval of less than two years under cropping and less than four years under pasture.