Baseflow analysis as a tool for groundwater
Abstract
Baseflow analysis provides a very useful tool to help in the analysis of the extent of groundwater-surface water interaction. Baseflow contributes to streams to a highly variable extent. Baseflow is affected by many natural and anthropogenic factors, including climate, groundwater pumping and land use change. There are a number of baseflow separation techniques available that enable the proportion of groundwater flow to a river to be estimated from gauged streamflow data. The different methods are reviewed and the strengths and applicability of the different approaches identified.
It is also possible to analyse the baseflow data over time to remove the “noise” (principally due to climate variability) to determine the underlying trend (due, for example, to groundwater use in the catchment). There are several statistical methods available to remove the ‘noise” and hence identify the trend in baseflow over time. The combination of the use of baseflow separation, trend analysis and knowledge of catchment conditions provides a very powerful technique to identify and quantify groundwater impacts on stream flow. These analyses can then be used to assist management decisions.
Baseflow analysis data from several different catchments in Australia are presented to illustrate both the spatial and temporal variability. The spatial variability is obviously profoundly influenced by the hydrogeological setting. However where relatively uniform hydrogeology exists (eg the fractured rock Eastern Highlands of Australia) the spatial variability is also influenced by climatic factors, principally evapotranspiration. Streams where baseflow analysis has been reported are reviewed to indicate the natural and human induced change. Very little published data exists on trends in baseflow over time. Nonetheless one example shows a clear relationship with declining groundwater level.
Baseflow analysis is an under-used and poorly understood tool which provides uniquely valuable insights to the low flows of streams and the factors controlling these baseflows. The greater use of this tool will enable broader data sets to be developed which are useful to both surface water and groundwater understanding and to the intimate interaction thereof.
Authors
Dr Richard Evans & Brad Neal