Examining the contributions of glacial till water to storm runoff using two‐ and three‐component hydrograph separations

Abstract

Abstract. Two-and three-component hydrograph separations based on 1 8 0 and dissolved silica are used to investigate the contributions of glacial till water to the storm runoff of a headwater stream on the Canadian Shield. Two-component isotopic hydrograph separations based on 1 8 0 indicate that the volume and flux of event water could be accounted for by direct precipitation onto saturated areas. Three-component hydrograph separations distinguish between event water, preevent soil water, and preevent till water. These results show that groundwater fl ow through coarse-textured glacial tills can make a significant contribution to stream discharge during runoff events (29 and 62% in this study) despite the lower hydraulic conductivities of the tills compared to the overlying soils. The three-component hydrograph separations also demonstrate that the relative contributions of preevent soil water and preevent till water changed during one runoff event such that the average water chemistry of the preevent component varied during the event. Two-component hydrograph separations using dissolved silica indicate that seasonal changes in the till water contributions also occur and are related to groundwater levels. Measurements of vertical hydraulic gradients during runoff events indicate that the increase in flow from the tills to the soils is minimal and cannot account for the large and rapid increase in till water flow into the stream. Till water that has discharged to the soils prior to the event is probably being flushed from the soils into the stream during events.

Mixing Model Approaches to Estimate Storm Flow Sources in an Overland Flow‐Dominated Tropical Rain Forest Catchment

“…The tracer concentrations of the postulated endmembers or components do not change during events, and their spatial variability is small compared to the differences between end-members or components. The validity of the temporal invariance assumption obviously depends on event duration: If it is in the range of hours [e.g., Pionke et al, 1993;Hinton et al, 1994], this assumption is more likely to hold than if it is in the range of days [Mulholland, 1993] or weeks [e.g., Hendershot et al, 1992]. It also depends on the choice of sources.…”

“…The basic technique, introduced by Finder and Jones [1969], consists of a hydrograph separation based on a mass balance approach. Their original twocomponent model, one preevent-water and one event water component, has been applied widely [e.g., Hooper and Shoemaker, 1986;Caine, 1989;Wels et al, 1991;Hendershot et al, 1992;Pionke et al, 1993]; it has been expanded to three components in cases where either the discharge of one of the components was known [DeWalle et al, 1988] or two tracers were used simultaneously [Generewc et al, 1993;Hinton et al, 1994]. The usefulness of this mass balance approach to predict preevent and event water components hinges critically on the assumption that the selected tracers behave conservatively 'Previously at the Department of Geography, James Cook University of North Queensland, Townsville, Australia.…”

“…For Walker Branch, three end-members, namely, vadose zone, saturated soil zone, and bedrock zone, determined stream water chemistry [Mulholland, 1993]; the same sources were identified by a mass balance approach based on radon 222 and calcium [Genereux et al, 1993]. For the Harp 4-21 catchment, Hinton et al [1994] singled out a preevent till water, a preevent soil water, and an event soil water component, using silica and oxygen 18. For the Fish Run catchment, two preevent water components, groundwater and soil water, and an event water component, channel precipitation, were identified based on oxygen 18 [DeWalle et al, 1988].…”

Vulnerability of groundwater resources to interaction with river water in a boreal catchment

“…Streams show systematic variation in the DSi concentration as a function of flow, with higher concentrations under baseflow conditions and the lowest concentrations under high flow (Neal et al, 2005). Therefore, DSi could serve as a potential tracer to estimate the contribution of GW to river flow, as observed earlier by Hinton et al (1994).…”

“…This has been acknowledged in a number of recent surveys in which riparian areas vulnerable to floods in the studied river catchment have been identified (i.e., Mäntylä and Saarelainen, 2008). Climate change is predicted to result in increasing annual precipitation and elevated temperatures during the twenty-first century (Jylhä et al, 2004), as well as an expected intensification of extreme precipitation events (Beniston et al, 2007), which will significantly increase the flood risk in some southern Finnish watersheds according to Veijalainen et al (2010). Frequency of summer floods due to the extreme precipitation and winter floods due to mild winters are expected to increase in the tributaries of the River Vantaa (Veijalainen et al, 2009).…”