The Brigalow Catchment Study: A comparison of four methods to estimate peak runoff rate for small catchments before and after land use change in the Brigalow Belt bioregion of central Queensland, Australia

Abstract

Study region: Brigalow Belt bioregion of north-eastern Australia. Study focus: Dynamic SedNet is used to model erosion from 42.4 Mha of grazing land in the Great Barrier Reef catchments to guide the $3 billion Reef 2050 Long-Term Sustainability Plan 2021–2025. Improving Dynamic SedNet by incorporating the Modified Universal Soil Loss Equation requires spatially derived peak runoff rate. This study evaluated four simple methods to estimate peak runoff rate at a site representative of the 15 Brigalow Belt bioregion catchments that intersect with the 35 Great Barrier Reef catchments. Performance was assessed against measured data from three long-term catchments of the Brigalow Catchment Study both pre-clearing (1965–1982), when all catchments were virgin brigalow scrub prior to land use change, and post-clearing (1984–2004), after one catchment was converted to cropping and another to grazing. New hydrological insights for the region: Useful estimations were obtained from the scaling technique (R2 = 0.90; NSE = 0.79), multiple regression models (R2 = 0.90; NSE = 0.63), and the variable infiltration rate method (R2 = 0.88; NSE = 0.71). Estimations using the curve number and graphical peak discharge method gave an R2 of 0.85; however, NSE was typically negative because the method systematically underestimated runoff rate. Despite different data requirements and complexity, all four methods were easily applied with parameters derived from widely available rainfall data, measured runoff volume data, and basic physical descriptors of the catchment.

Keywords

• Tree clearing
• Modelling
• Hydrology
• Acacia spp
• Paddock to Reef
• Peak discharge