Hydrograph separation using tracers and digital filters to quantify runoff components in a semi‐arid mesoscale catchment

Abstract

Chemical hydrograph separation using electrical conductivity and digital filters is applied to quantify runoff components in the 1,640 km2 semi‐arid Kaap River catchment and its subcatchments in South Africa. A rich data set of weekly to monthly water quality data ranging from 1978 to 2012 (450 to 940 samples per site) was analysed at 4 sampling locations in the catchment. The data were routinely collected by South Africa's national Department of Water and Sanitation, using standard sampling procedures. Chemical hydrograph separation using electrical conductivity (EC) as a tracer was used as reference and a recursive digital filter was then calibrated for the catchment. Results of the two‐component hydrograph separation indicate the dominance of baseflow in the low flow regime, with a contribution of about 90% of total flow; however, during the wet season, baseflow accounts for 50% of total flow. The digital filter parameters were very sensitive and required calibration, using chemical hydrograph separation as a reference. Calibrated baseflow estimates ranged from 40% of total flow at the catchment outlet to 70% in the tributaries. The study demonstrates that routinely monitored water quality data, especially EC, can be used as a meaningful tracer, which could also aid in the calibration of a digital filter method and reduce uncertainty of estimated flow components. This information enhances our understanding of how baseflow is generated and contributed to streamflow throughout the year, which can aid in quantification of environmental flows, as well as to better parameterize hydrological models used for water resources planning and management. Baseflow estimates can also be useful for groundwater and water quality management.

HydroMix v1.0: a new Bayesian mixing framework for attributing uncertain hydrological sources

“…The stable isotope composition of hydrogen and oxygen in water (subsequently referred to as 'stable isotopes of water') are used as tracers in hydrology. Other commonly used tracers include electrical conductivity (Hoeg et al, 2000;Laudon and Slaymaker, 1997;Lopes et al, 2018;Pellerin et al, 2007;Weijs et al, 2013) and conservative geochemical solutes such as chloride and silica (Rice and Hornberger, 1998;Wels et al, 1991). Classically, Eq.…”

“…A key challenge in hydrology is to infer source contributions to understand the flow paths to a given water body using a source attribution technique. A classic example is the two-component hydrograph separation model to quantify the proportion of groundwater and rainfall in streamflow, often referred to as "pre-event" water vs "event" water (Brewer et al, 2011;Burns et al, 2001;Buttle et al, 1995;Dusek and Vogel, 2018;Joerin et al, 2002;Klaus and McDonnell, 2013;Lopes et al, 2018;Schmieder et al, 2016;W. et al, 2009).…”

Improved Process Representation in the Simulation of the Hydrology of a Meso-Scale Semi-Arid Catchment

“…In the Kaap valley, lithic leptosols and rhodic nitisols dominate [22,23]. In terms of soil texture ( Figure 1D), 53% of the catchment is covered by sandy clay loams, 39% by clay loams, and the remainder of the catchment has clays, sandy clays and sandy loams [22,23,25]. [26]; and (D) Soil texture based on Soil Grids 250 m dataset [22,23]; the predominantly occurring textures are: Clay (Cl), Sandy clay (SaCl), Clay loam (CL), Sandy clay loam (SaClLo) and Sandy loam (SaLo).…”

Hydrograph separation: an impartial parametrization for an imperfect method

“…To remedy this, several studies use parametric graphical/empirical methods and calibrate them with chemicophysical data (Saraiva Okello et al (2018);Miller et al (2015); Chapman (1999)). It allows one to extend the hydrograph separation on time periods where chemicophysical data are not available, or to perform temporal downscaling -when daily streamflow 25 data or monthly tracer concentrations are available, for instance.…”