Abstract
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. The new baseflow separation method presented here (the bump and rise method or BRM) aims to accurately simulate the shape of tracer-determined baseflow or pre-event water. Application of the method by calibrating its parameters, using (a) tracer data or (b) an optimising method, is demonstrated for the Glendhu Catchment, New Zealand. The calibrated BRM algorithm is then applied to the Glendhu streamflow record. The new recession approach advances the thesis that recession analysis of streamflow alone gives misleading information on catchment storage reservoirs because streamflow is a varying mixture of components of very different origins and characteristics (at the simplest level, quickflow and baseflow as identified by the BRM method). Recession analyses of quickflow, baseflow and streamflow show that the steep power-law slopes often observed for streamflow at intermediate flows are artefacts due to mixing and are not representative of catchment reservoirs. Applying baseflow separation before recession analysis could therefore shed new light on water storage reservoirs in catchments and possibly resolve some current problems with recession analysis. Among other things it shows that both quickflow and baseflow reservoirs in the studied catchment have (non-linear) quadratic characteristics.
Highlights
Interpretation of streamflow variations in terms of catchment characteristics has been a major theme in hydrology for many years in order to improve catchment and stream management
It is believed that it is not justifiable to treat the streamflow as a single component, but that at least two components should be considered by applying baseflow separation to the hydrograph before analysis
It accurately simulates the shape of the baseflow or preevent component determined by tracers. This should mean that it gives more accurate baseflow separations and BFIs, because tracer separation of the hydrograph is regarded as the only objective separation method
Summary
Interpretation of streamflow variations in terms of catchment characteristics has been a major theme in hydrology for many years in order to improve catchment and stream management. Recession analysis aims to model the decrease of streamflow during rainless periods to extract parameters descriptive of water storage in the catchment. Transit time analysis determines transit time distributions of water in the stream and catchment in order to quantify flowpaths and storages through the catchment. To fully understand and satisfactorily model the movement of water and chemicals through catchments, it is necessary to understand in detail the water stores and flowpaths (Fenicia et al, 2011; McMillan et al, 2011; Beven, 2012; Hrachowitz et al, 2013)
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