PREDICTION OF WATER YIELD REDUCTIONS FOLLOWING A BUSHFIRE IN ASH-MIXED SPECIES EUCALYPT FOREST

A two-parameter model of the long-term yield trend following a bushfire is proposed. It is shown to satisfactorily fit rainfall-runoff data for eight catchments affected by the 1939 fires. In addition, the fits confirm earlier findings of significant yield reductions and, moreover, suggest possible recovery in yields. Despite insufficient hydrologic data to confirm these recovery trends, forest age and composition data indicate that recovery in yield should be practically complete by the time the ash forest reaches maturity. Using a generalized least squares approach, regional models for the long-term yield trend parameters L//m//a//x (the maximum yield reduction) and log K (the response time) are developed. A simple simulation model based on the regional models is then developed enabling evaluation of the effect of future bushfire (and logging) on catchment yield. Additional study results are discussed.