the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 26 Sep 2025
Hydrogeological characterization of alpine karst using the transient analysis of flow and transport
Abstract. Karst springs in alpine catchments are important for maintaining groundwater-dependent ecosystems in fragile environments and for sustaining baseflow in mountain rivers. Despite its importance, rugged and inaccessible terrains pose major challenges in hydrogeological studies of alpine karst. This study developed a practical approach for characterizing an alpine karst system in the Canadian Rocky Mountains that had no previous information aside from the location of the spring outlet. Using geological maps, satellite images, simple water balance, water sampling and analysis, and dye tracer tests, it was possible to estimate the extent of the spring catchment and infer the hydrogeological characteristics of the karst system. Of particular importance was the information obtained from the fluctuations of spring discharge and electrical conductivity in response to diurnal snowmelt cycles. Synthesis of the diverse data set indicates that the karst system has a large volume of groundwater stored in the fractured rock matrix that buffers the interannual variability of precipitation and sustains steady baseflow throughout the year. The karst system consists of fractured rock matrix, saturated conduits acting like pipes, unsaturated conduits acting like open channels, and many pools delaying the propagation of transport and hydraulic signals through the conduit network. The approach developed in this study will be applicable to other alpine karst systems in snow-dominated catchments in rugged and inaccessible terrains.
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Status: open (until 07 Nov 2025)
- CC1: 'Comment on egusphere-2025-3767', Giacomo Medici, 02 Oct 2025 reply
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CC2: 'Comment on egusphere-2025-3767', Stephen Worthington, 04 Oct 2025
reply
This paper presents a wide range of data from a karst spring in Canada. I feel that the greatest strength of the paper is on the detailed analysis of the celerity and velocity of percolation recharge, and that the discussion on these should be expanded and better integrated with the discussion on the slow fraction of flow from isotope data. I have two major concerns with the paper:
Comment 1) Groundwater flow velocity
line 472-473 "the flow velocity through the karst conduit network is expected to be on the order of 1 m s-1 during May–December when Q varies between 0.3 and 3 m3 s-1."
The prediction of 1 m/s conduit velocities comes from calculations at lines 455-475. The calculations use the Darcy-Weisbach equation, which calculates flow in a pipe as a function of pipe size, hydraulic gradient, and friction (roughness) factor. Estimates of hydraulic gradient (lines 464-468) were based on values from Castleguard Cave (0.03: Ford et al., 1983), high flow conditions at Maligne (0.025: Smart, 1988), and Hölloch (0.0004-0.006: Jeannin, 2001). However, a later interpretation of Castleguard Cave (Ford, 2000; Worthington, 1991) suggested that hydraulic gradients during the formation of the cave could have been 0.0005 or less. Furthermore, a compilation of data in 20 karst aquifers showed that hydraulic gradients along major flow paths to springs are typically 0.0001-0.001 at low flow and 0.001-0.01 at high flow (Worthington, 1991). Moreover, field studies have shown that the Darcy-Weisbach friction factor can vary by more than three orders of magnitude in karst conduits (Jeannin, 2001, Table 3), and pipe size and hydraulic gradient also have a wide variation in their values. Consequently, the uncertainty in the 1 m/s conduit velocity is very large.
Given the lack of information on friction factors and hydraulic gradients at the site, a better approach is to consider measured groundwater velocities from other studies. It is very rare for velocities of 1 m/s to be measured from tracer tests, and velocities are usually between 0.003 and 0.3 m/s. This is true globally (Ford and Williams (2007, p. 125) and also in the Canadian Rocky Mountains, such as in the cited references by Smart (1983, 1988) and Worthington (1991). Furthermore, conduit diameter has been measured by a scuba diver in the conduit feeding Watridge Spring (line 470), and this gives a velocity of 0.028 m/s at moderately low flow (0.3 m3/s) and 0.28 m/s at high flow (3 m3/s), assuming a circular conduit. These measured velocities give more accurate values for assessing the aquifer than the 1 m/s estimate made at line 473. The similarity of the measured velocities to velocities in other karst aquifers mean that there is no need to suggest retardation or invoke pools to explain the measured travel times.
Comment 2) Subsurface residence times
line 359-361 ". It is impossible to determine the residence time of water, considering the possible variability of tritium contents between Ottawa and the WKS, but in an approximate sense, it seems likely that most spring water samples had a residence time of five to ten years."
line 502 "This [del 18O variation] is consistent with the tritium content suggesting a residence time of multiple years (Figures 8d and 9)."
These two comments are the only specific references in the paper to residence times for the groundwater discharging at Watridge Spring. However, Figure 7d shows day by day residence times (which can also be referred to as transit times) for snowmelt and glacier melt from May to September 2021, with dye traces (Figures 5 and 7d) confirming the rapid transit times for specific recharge locations.
 There have been several previous studies that have measured lag times between surface snow or glacier melt and variation in spring flow in carbonate aquifers, including Gremaud et al. (2009), Krainer et al. (2021), Smart and Ford (1986), Vigna and Banzato (2015), and Zeng et al. (2012). However, this study includes an exceptional data set on subsurface residence times for snow and ice melt (Figure 7d) and on the lag time for the pressure pulse for snow and glacier melt to reach a limestone spring (Figure 7c). Furthermore, seasonal variation in major ions, tritium, and del 18O (Figure 8), could help define the fractions of young water with an age of 0.4 to 4 days (Figure 4d) from older water with transit times up to several years.
The wide range of residence times in carbonate aquifers has been widely described in the literature and they are sometimes referred to as dual- or as triple-porosity aquifers. Małoszewski and Zuber (1985) and Zuber et al. (2011) presented the theory to interpret the ages of injected and environmental tracers in dual-porosity bedrock aquifers, and useful studies in carbonate rocks in mountain environments that have included transit times and the fraction of flow in each component include Maloszewski et al. (2002) and Lauber and Goldscheider (2014).
I think that it would be well worth adding a new section to Section 5 that specifically discusses subsurface residence times and fractions of spring flow involved. This would consider both vadose zone residence times and groundwater residence times and use most of the data sets collected, thus providing a suitable concluding section to the Discussion. If the authors adequately address the above comments, then this paper would be a fine contribution to the literature.
Other comments
Comment 3 - line 359-361 "It is impossible to determine the residence time of water, considering the possible variability of tritium contents between Ottawa and the WKS, but in an approximate sense, it seems likely that most spring water samples had a residence time of five to ten years."
This statement needs to be clarified that it is referring to tritium, and so reflects the residence of the slow-moving water through the matrix and narrow fractures. The residence time of snow and glacier melt has been very well determined in this aquifer. The three tracer tests give subsurface residence times of some days (Figure 5a), and the EC signal at the spring during the spring freshet demonstrates a snowmelt residence time of 0.5 to 2 days, rising to 3-4 days later in the summer when glacier melt predominates (Figure 7d). This strength of the study needs to be better emphasized, such as by adding a section to the Discussion that describes residence times.
Comment 4 - line 465 ", a map of the Castleguard Cave (Ford et al.,1983, Figure 3) suggests a gradient of ~0.03"
This needs to be updated with the conclusions on gradients in Ford (2000), as noted above, or else omitted.
Comment 5 - line 484-485 "meaning that the diel fluctuations of discharge would have a delay of less than an hour between BP14 and WKS. This is contrary to the observed delay of 12–15 h (Figure 7c)"
The radon data suggests that "most of the conduit flow occurs under pipe-flow conditions" (lines 453-454), and active karst conduits are frequently predominantly below the water table, so the lag time of <1 hour along the main conduit seems probable. However, BP11 and BP14 are 593 m and 575 m above Watridge Spring, respectively, suggesting that there is a vadose zone that is likely to be hundreds of metres thick at these locations. Thick vadose zones are typical in karst aquifers in mountain settings, and the more than 400 caves around the world that are >600 m deep provide a graphic illustration of the widespread presence of deep vadose zones in carbonate aquifers (Burger, 2025).
Flow peaks in karst springs due to snow or glacier melt in mountain areas usually occur in the evening or night, reflecting a lag that is typically 6-12 hours after the mid-afternoon peak of snow or ice melt (Gremaud et al., 2009; Krainer et al., 2021; Smart and Ford, 1986; Vigna and Banzato, 2015; Zeng et al., 2012). These lags predominantly reflect the much slower hydraulic responses in the vadose zone compared to the saturated zone. Consequently, most of the 12-15 hour lag shown in Figure 7c is likely to be in the vadose zone, such as the several hundred metres from the surface at BP14 down to the water table. Thus, the alternative explanation for the 12-15 h lag offered at lines 491-492 is the most probable explanation.
Comment 6 - line 525 - " transport velocity (0.05 – 0.15 m s-1) is much slower than the order of velocity (1 m s-1) expected for conduit flow or open-channel flow. Therefore, there likely are many pools within the conduit network, causing the physical retardation of solute transport."
See Comment 1.
Additional references cited above, to consider for inclusion
Burger, P., 2025, https://cave-exploring.com/index.php/long-and-deep-caves-of-the-world/world-deep-caves/, accessed October 3, 2025.
Ford, D., Lauritzen, S-E., Worthington, S., 2000 Speleogenesis of Castleguard Cave, Rocky Mountains, Alberta, Canada. In: Speleogenesis: Evolution of karst aquifers (Eds. Klimchouk, A.B., Ford, D.C., Palmer, A.N., Dreybrodt, W.), National Speleological Society, Huntsville, Alabama, USA
Lauber, U., Goldscheider, N., 2014. Use of artificial and natural tracers to assess groundwater transit-time distribution and flow systems in a high-alpine karst system (Wetterstein Mountains, Germany). Hydrogeol. J. 22, 1807-1824.
Małoszewski, P., & Zuber, A., 1985. On the theory of tracer experiments in fissured rocks with a porous matrix. Journal of Hydrology, 79, 333-358.
Maloszewski, P., Stichler, W., Zuber, A., and Rank, D., 2002. identifying the flow systems in a karstic-fissured-porous aquifer, the Schneealpe, Austria, by modelling of environmental 18O and 3H isotopes. Journal of Hydrology, 256, 48-59.
Vigna, B. and Banzato, C., 2015. The hydrogeology of high-mountain carbonate areas: an example of some Alpine systems in southern Piedmont (Italy). Environmental Earth Sciences, 74(1), pp.267-280.
Zeng, C., Gremaud, V., Zeng, H., Liu, Z. and Goldscheider, N., 2012. Temperature-driven meltwater production and hydrochemical variations at a glaciated alpine karst aquifer: implication for the atmospheric CO2 sink under global warming. nvironmental Earth Sciences, 65(8), 2285-2297.
Zuber, A., Różański, K., Kania, J., Purtschert, R., 2011. On some methodological problems in the use of environmental tracers to estimate hydrogeologic parameters and to calibrate flow and transport models. Hydrogeol. J. 19, 53-69.
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Citation: https://doi.org/10.5194/egusphere-2025-3767-CC2
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General comments
Very good research on karst hydrology. Please, follow my specific comments to fix minor issues and bring the impact out.
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Specific comments
Lines 23-54. Specify the most novel aspect of the research.
Lines 42-43. "complex flow pathways consisting of fractured rock matrix and conduits". Insert recent literature on fracture and conduit flow in palaeozoic and mesozoic carbonate aquifers  Â
- Medici, G., Munn, J.D., Parker, B.L. 2024. Delineating aquitard characteristics within a Silurian dolostone aquifer using high-density hydraulic head and fracture datasets. Hydrogeology Journal, 32(6), 1663-1691.
- Jourde, H., & Wang, X. (2023). Advances, challenges and perspective in modelling the functioning of karst systems: a review. Environmental Earth Sciences, 82(17), 396.
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Lines 56-100. What about minor faults? Any link with the small-scale karst landforms that you describe?
Lines 538-539. There are several other relevant researches on karst in mountain ranges in the Jura and the French/Swiss Alps. It would be good to enlarge the comparison.
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Figures and tables
Figure 2c. Syncline beds or tectonic foliation on the back? Please, specify if there is a link between the figure and the conceptual model in Figure 1.
Figures 3 to 5. Make the figures and the graphs larger.
Figure 6. You need to report the days on the horizontal axes on the graph of water temperature.
Figure 7. You need to report the days on the horizontal axes for all the graphs.
Figure 9. Make this graph on tritium larger.
Figure 10a. Is it clear enough the link between the conceptual models in Figs 10c and 14.
Figure 14. Write on top of the cartoons what the two block diagrams represent.Â