The role of groundwater in storm runoff

Abstract. Multiple water sources and the physiographic heterogeneity of glacierized catchments hamper a complete conceptualization of runoff response to meltwater dynamics. In this study, we used environmental tracers (stable isotopes of water and electrical conductivity) to obtain new insight into the hydrology of glacierized catchments, using the Saldur River catchment, Italian Alps, as a pilot site. We analysed the controls on the spatial and temporal patterns of the tracer signature in the main stream, its selected tributaries, shallow groundwater, snowmelt and glacier melt over a 3-year period. We found that stream water electrical conductivity and isotopic composition showed consistent patterns in snowmelt-dominated periods, whereas the streamflow contribution of glacier melt altered the correlations between the two tracers. By applying two-and three-component mixing models, we quantified the seasonally variable proportion of groundwater, snowmelt and glacier melt at different locations along the stream. We provided four model scenarios based on different tracer signatures of the end-members; the highest contributions of snowmelt to streamflow occurred in late spring-early summer and ranged between 70 and 79 %, according to different scenarios, whereas the largest inputs by glacier melt were observed in mid-summer, and ranged between 57 and 69 %. In addition to the identification of the main sources of uncertainty, we demonstrated how a careful sampling design is critical in order to avoid underestimation of the meltwater component in streamflow. The results of this study supported the development of a conceptual model of streamflow response to meltwater dynamics in the Saldur catchment, which is likely valid for other glacierized catchments worldwide.

Section: Two-and Three-component Mixing Models and Underlying Assumptmentioning

confidence: 99%

Towards a tracer-based conceptualization of meltwater dynamics and streamflow response in a glacierized catchment

Penna

Engel

Bertoldi

et al. 2017

“…To estimate the fraction of older water that contributed to streamflow, a simple two-component hydrograph separation was carried out (Sklash and Farvolden, 1979) based on fortnightly data of each of the three seasonal tracers. This allowed one to obtain time-varying values of φ:…”

Section: Using Stable Isotopes and Chloridementioning

confidence: 99%

Time series of tritium, stable isotopes and chloride reveal short-term variations in groundwater contribution to a stream

Duvert

Stewart

Cendón

et al. 2016

Abstract.A major limitation to the assessment of catchment transit time (TT) stems from the use of stable isotopes or chloride as hydrological tracers, because these tracers are blind to older contributions. Yet, accurately capturing the TT of the old water fraction is essential, as is the assessment of its temporal variations under non-stationary catchment dynamics. In this study we used lumped convolution models to examine time series of tritium, stable isotopes and chloride in rainfall, streamwater and groundwater of a catchment located in subtropical Australia. Our objectives were to determine the different contributions to streamflow and their variations over time, and to understand the relationship between catchment TT and groundwater residence time. Stable isotopes and chloride provided consistent estimates of TT in the upstream part of the catchment. A young component to streamflow was identified that was partitioned into quickflow (mean TT ≈ 2 weeks) and discharge from the fractured igneous rocks forming the headwaters (mean TT ≈ 0.3 years). The use of tritium was beneficial for determining an older contribution to streamflow in the downstream area. The best fits between measured and modelled tritium activities were obtained for a mean TT of 16-25 years for this older groundwater component. This was significantly lower than the residence time calculated for groundwater in the alluvial aquifer feeding the stream downstream (≈ 76-102 years), emphasising the fact that water exiting the catchment and water stored in it had distinctive age distributions. When simulations were run separately on each tritium streamwater sample, the TT of old water fraction varied substantially over time, with values averaging 17 ± 6 years at low flow and 38 ± 15 years after major recharge events. This counterintuitive result was interpreted as the flushing out of deeper, older waters shortly after recharge by the resulting pressure wave propagation. Overall, this study shows the usefulness of collecting tritium data in streamwater to document short-term variations in the older component of the TT distribution. Our results also shed light on the complex relationships between stored water and water in transit, which are highly non-linear and remain poorly understood.

“…To estimate the sources of runoff in the four different sub-catchments during different events, a one-tracer, twocomponent hydrograph separation was conducted (Sklash and Farvolden, 1979). The stream water was separated into pre-event and event water fractions on the basis of the measured δ 2 H signatures.…”

Section: Hydrograph Separationmentioning

confidence: 99%

“…The signature in the stream water immediately prior to the events was used as C pe , based on the assumption that the influence from event water at that time is negligible (Pinder and Jones, 1969;Sklash and Farvolden, 1979). For the April and May events sparse precipitation samples were available and C e was calculated as a weighted mean and a bulk value, respectively.…”

Section: Hydrograph Separationmentioning

confidence: 99%

“…To obtain information about runoff sources at the catchment scale a common approach is stream hydrograph separations, often conducted by use of stable isotopes and chemical tracers (Sklash and Farvolden, 1979;Uhlenbrook and Hoeg, 2003). However, such hydrograph separations only reveal the integrated catchment response of the point-to-reach-scale groundwater-surface water dynamics, and have rarely been conducted in lowland agricultural catchments.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Detecting groundwater discharge dynamics from point-to-catchment scale in a lowland stream: combining hydraulic and tracer methods

Poulsen

Sebok

Duque

et al. 2015

Abstract. Detecting, quantifying and understanding groundwater discharge to streams are crucial for the assessment of water, nutrient and contaminant exchange at the groundwater-surface water interface. In lowland agricultural catchments with significant groundwater discharge this is of particular importance because of the risk of excess leaching of nutrients to streams. Here we aim to combine hydraulic and tracer methods from point-to-catchment scale to assess the temporal and spatial variability of groundwater discharge in a lowland, groundwater gaining stream in Denmark. At the point-scale, groundwater fluxes to the stream were quantified based on vertical streambed temperature profiles (VTPs). At the reach scale (0.15-2 km), the spatial distribution of zones of focused groundwater discharge was investigated by the use of distributed temperature sensing (DTS). Groundwater discharge to the stream was quantified using differential gauging with an acoustic Doppler current profiler (ADCP). At the catchment scale (26-114 km 2 ), runoff sources during main rain events were investigated by hydrograph separations based on electrical conductivity (EC) and stable isotopes 2 H/ 1 H. Clear differences in runoff sources between catchments were detected, ranging from approximately 65 % event water for the most responsive sub-catchment to less than 10 % event water for the least responsive sub-catchment. This was supported by the groundwater head gradients, where the location of weaker gradients correlated with a stronger response to precipitation events. This shows a large variability in groundwater discharge to the stream, despite the similar lowland characteristics of sub-catchments indicating the usefulness of environmental tracers for obtaining information about integrated catchment functioning during precipitation events. There were also clear spatial patterns of focused groundwater discharge detected by the DTS and ADCP measurements at the reach scale indicating high spatial variability, where a significant part of groundwater discharge was concentrated in few zones indicating the possibility of concentrated nutrient or pollutant transport zones from nearby agricultural fields. VTP measurements confirmed high groundwater fluxes in discharge areas indicated by DTS and ADCP, and this coupling of ADCP, DTS and VTP proposes a novel field methodology to detect areas of concentrated groundwater discharge with higher resolution.