Comparison of different base flow separation methods in a lowland catchment

摘要

Assessment of water resources available in different storages and movingalong different pathways in a catchment is important for its optimal use andprotection, and also for the prediction of floods and low flows. Moreover,understanding of the runoff generation processes is essential for assessingthe impacts of climate and land use changes on the hydrological response ofa catchment. Many methods for base flow separation exist, but hardly onefocuses on the specific behaviour of temperate lowland areas. This paperpresents the results of a base flow separation study carried out in alowland area in the Netherlands. In this study, field observations ofprecipitation, groundwater and surface water levels and discharges, togetherwith tracer analysis are used to understand the runoff generation processesin the catchment. Several tracer and non-tracer based base flow separationmethods were applied to the discharge time series, and their results arecompared.The results show that groundwater levels react fast to precipitation eventsin this lowland area with shallow groundwater tables. Moreover, a goodcorrelation was found between groundwater levels and discharges suggestingthat most of the measured discharge also during floods comes fromgroundwater storage. It was estimated using tracer hydrological approachesthat approximately 90% of the total discharge is groundwater displaced byevent water mainly infiltrating in the northern part of the catchment, andonly the remaining 10% is surface runoff. The impact of remote rechargecausing displacement of near channel groundwater during floods could also bemotivated with hydraulic approximations. The results show further that whenbase flow separation is meant to identify groundwater contributions tostream flow, process based methods (e.g. the rating curve method; Kliner andKnezek, 1974) are more reliable than other simple non-tracer based methods.Also, the recursive filtering method (proposed by Eckhardt, 2005) can becalibrated well using the results of tracer investigation giving goodresults. Consequently, non-tracer based base flow separation methods thatcan be validated for some events may provide a powerful tool for groundwaterassessment or model calibration/validation in lowland areas.