Comparison of Baseflow Separation Methods in the German Low Mountain Range

Michael Kissel,Britta Schmalz

doi:10.3390/w12061740

Abstract

The last several years in southern Germany brought below average precipitation and high temperatures, leading to considerable challenges in water resource management. Deriving a plausible baseflow estimate is important as it affects aspects of integrated water resource management such as water usage and low flow predictions. The aim of this study is to estimate baseflow in a representative catchment in the German low mountain range and identify suitable baseflow estimation methods for this region. Several different baseflow separation methods, including digital filters, a mass balance filter (MBF) and non-continuous estimation methods were applied and compared to estimate baseflow. Using electric conductivity (EC) for the MBF, June to September and November to May were found to be suitable to estimate the EC of the baseflow and runoff component, respectively. Both weekly and continuous EC monitoring can derive similar EC value component estimates. However, EC estimation of the runoff component requires more careful consideration. The baseflow index (BFI) is estimated to be in the range of 0.4 to 0.5. The Chapman and Maxwell filter, Kille method and the Q90/Q50 ratio are recommended for baseflow estimation in the German low mountain range as they give similar results to the MBF. The Eckhardt filter requires further calibration before application.

Highlights

In recent years southern Germany has experienced several dry years with below average precipitation and high temperatures resulting in extended and/or severe low flow periods
Since 2003 there have hardly been any unusually wet years in southern Germany [1]. This has led to considerable challenges in water management [2]. In this context assessing baseflow in a catchment is of increased importance as the baseflow may impact many different aspects of integrated water resource management, e.g., water usage, water quality and low flow predictions
The decision to discard the first two days of a recession period is based on the HLNUG [30] noting that direct runoff is relatively quick and two days is consistent with calibrated retention constants for the slow direct runoff component in Bach [35] for a neighboring catchment

Summary

Introduction

In recent years southern Germany has experienced several dry years with below average precipitation and high temperatures resulting in extended and/or severe low flow periods. Since 2003 there have hardly been any unusually wet years in southern Germany [1] This has led to considerable challenges in water management [2]. Graphical methods separate baseflow by identifying specific points in the hydrograph and connecting them via some predefined rule to account for the shape of the curve between these points [6,7,8]. These methods are often not suited for automation and are susceptible to subjective influences [9,10]. Recession analysis assumes that periods without precipitation and with receding flow can be analyzed to infer knowledge on aquifer properties [11]

Objectives

Methods

Results

Discussion

Conclusion