New baseflow separation and recession analysis approaches for streamflow

Abstract

Understanding and modelling the relationship between rainfall and runoff has been a driving force in hydrology for many years. Baseflow separation and recession analysis have been two of the main tools for understanding runoff generation in catchments, but there are many different methods for each and no consensus on how best to apply them. A new baseflow separation method is presented, which is justified by being based generally on the more objective tracer separation methods and by being optimised by fitting to the recession hydrograph. Using this baseflow separation method, the thesis is advanced that recession analysis should be applied to the separated components (quickflow and baseflow), because of their very different origins and characteristics, rather than to the streamflow itself because analysing the latter alone gives misleading results. Applying baseflow separation before recession analysis sheds new light on water storage in catchments and may resolve some current prob- lems with recession analysis. It may also have implications for rainfall–runoff modelling. Among other things it shows that both quickflow and baseflow reservoirs have non- linear (quadratic) characteristics in the studied catchment (Glendhu, New Zealand).