A comparison of high‐resolution specific conductance‐based end‐member mixing analysis and a graphical method for baseflow separation of four streams in hydrologically challenging agricultural watersheds

Abstract

Quantifying the relative contributions of different sources of water to a stream hydrograph is important for understanding the hydrology and water quality dynamics of a given watershed. To compare the performance of two methods of hydrograph separation, a graphical program [baseflow index (BFI)] and an end‐member mixing analysis that used high‐resolution specific conductance measurements (SC‐EMMA) were used to estimate daily and average long‐term slowflow additions of water to four small, primarily agricultural streams with different dominant sources of water (natural groundwater, overland flow, subsurface drain outflow, and groundwater from irrigation). Because the result of hydrograph separation by SC‐EMMA is strongly related to the choice of slowflow and fastflow end‐member values, a sensitivity analysis was conducted based on the various approaches reported in the literature to inform the selection of end‐members. There were substantial discrepancies among the BFI and SC‐EMMA, and neither method produced reasonable results for all four streams. Streams that had a small difference in the SC of slowflow compared with fastflow or did not have a monotonic relationship between streamflow and stream SC posed a challenge to the SC‐EMMA method. The utility of the graphical BFI program was limited in the stream that had only gradual changes in streamflow. The results of this comparison suggest that the two methods may be quantifying different sources of water. Even though both methods are easy to apply, they should be applied with consideration of the streamflow and/or SC characteristics of a stream, especially where anthropogenic water sources (irrigation and subsurface drainage) are present. Copyright © 2014 John Wiley & Sons, Ltd.

A new approach for continuous estimation of baseflow using discrete water quality data: Method description and comparison with baseflow estimates from two existing approaches

“…Cumulative Q BF-GHS and BFI GHS values were greater than Q BF-MEAS and BFI MEAS , respectively at 8 of the 12 sites. This finding is consistent with that of Kronholm and Capel (2014), who reported that GHS estimates of baseflow were greater than CMB estimates of baseflow in a stream draining an irrigated watershed in Washington that has a single extended ($5 months) high flow season, similar to that of a snowmelt-dominated hydrograph. Cumulative Q BF-GHS deviated most from Q BF-MEAS at the Dolores River sites (116-370% difference) and at GUN1 (70% difference, Table 5), where Q BF-GHS and BFI GHS were greater than Q BF-MEAS and BFI MEAS , respectively.…”

Optimal hydrograph separation using a recursive digital filter constrained by chemical mass balance, with application to selected Chesapeake Bay watersheds

“…This may be insufficient to characterize systems with more complex or diverse hydrologic compartments or components (such as interflow or subsurface stormflow, movement of soil moisture, macropore flow) or with human modification (including diversions, dams, point sources and sinks, artificial drainage, and others) (Bazemore and others, 1994;Cartwright and others, 2014;Freeze, 1974;Klaus and McDonnell, 2013;Sanford and others, 2012;Vasconcelos and others, 2013). In some of these cases, multiple components may need definition, possibly using multiple tracers in an end-member mixing analysis (Genereux and others, 1993;Hooper and others, 1990;Kronholm and Capel, 2015).…”

A conceptual framework for effectively anticipating water-quality changes resulting from changes in agricultural activities

“…Water moves vertically to drains on the timescale of hours to days and laterally on the timescale of hours to months. Kronholm and Capel (2014) demonstrated that hydrograph separation methods, specifically the method of Wahl and Wahl (1995), can be used to describe slowflow and fastflow moving to a stream dominated by drainflow. The slowflow component describes water moving through the subsurface in areas far from the actual drains.…”

“…The thick, black line follows the behavior of sediment in a hydrologic setting where fast flowpaths are an important component of total streamflow, at least for part of the year. As an example, fastflow to Granger Drain in central Washington occurs when excess irrigation water is present on the landscape (Kronholm and Capel, 2014). Irrigation water is relatively abundant as snowmelt from the Cascade Mountains.…”