Discharge Data Collection and Analysis Strategies in Low Flow Studies

The objective of this paper is to determine the most appropriate data collection strategy and analysis techniques which should be used to assess the low flow regime of a catchment. The data used were: a) synchronous discharge measurements during low flow periods, and b) continuous daily flow records. The analyses based on both types of data were able to distinguish different low flow regimes within a 114 km² Danish catchment. Despite the limited spatial variation in climate and geomorphology there was a high spatial variability in low flows caused by differences in the lithology of sediments. This demonstrates the difficulties in using simple indices of catchment geology in regional low flow estimation. The results highlight the benefits of using synchronous discharge measurements, both for estimating low flows at ungauged sites, and for understanding groundwater flow paths. Analyses of daily flow records from six gauging stations in the catchment showed that a baseflow index was more useful than the flow duration curve for classifying low flow regimes when only short records were available. The paper illustrates the importance of estimating the uncertainty of discharge measurements when interpreting low flow data.