Advantages and challenges of using soil water isotopes to assess groundwater recharge dominated by snowmelt at a field study located in Canada

Figures & data

Table 1. Validated empirical methods used to predict the hydraulic conductivity with the specific conditions of application. Note that D_α is the effective grain diameter (mm), where α is the cumulative weight percentage of smaller grain size. C_u: uniformity coefficient (= D₆₀/D₁₀); e: void ratio, n: porosity.

Method	Empirical formula	Conditions
Hazen	K (cm/s) = (D10)^2	1. Loose and uniform sand
	with D10 in mm	2. Cu ≤ 5
		3. 0.1 mm ≤ D10 ≤ 3 mm
NAVFAC DM7	K (cm/s) = 10^1.291e−0.6435(D10)^0.^5504–0.2937e	1. Sand and mixtures of sand & gravel
	with D10 in mm	2. 2 ≤ Cu ≤ 12
		3. D10/D5 ≤ 1.4
		4. 0.1 mm ≤ D10 ≤ 2 mm
		5. 0.3 ≤ e ≤ 0.7
Chapuis	K (cm/s) = 2.4622((D10)^2e^3)/(1 + e))^0.^7825	1. All natural soils without plasticity
	with D10 in mm	2. 0.003 mm ≤ D10 ≤ 3 mm
		3. 0.3 ≤ e ≤ 1
Beyer	K (cm/s) = 0.45(D10)^2log(500/Cu)	1. Uniform to moderately uniform sand
	with D10 in mm	2. 0.06 mm ≤ D10 ≤ 0.6 mm
		3. 1 ≤ Cu ≤ 20
Sauerbrei	K (cm/s) = 2.436n^3(D17)^2/(1 – n)^2	1. Sand and silty sand
	with D17 in mm	2. D10 ≤ 0.5 mm
USBR	K (cm/s) = 0.36(D20)^2.3	1. Medium size sand
	with D20 in mm	2. Cu ≤ 5

Figure 1. Mean monthly water isotope ratios in rainwater at Station CMP in comparison to long-term data from the Chapais station of the Global Network of Isotopes in Precipitation (GNIP). Only δ¹⁸O values are displayed, but δ²H values follow the same distribution, as shown by the local meteoric water line shown in Figure 2.

Figure 2. Water isotope ratios in precipitation, with the local meteoric water line (LMWL) and the water isotope ratios in the soil water at sites C1 and C2.

Figure 3. Water isotope profiles of (a) δ²H and (b) δ¹⁸O determined at sites C1 and C2. Note that y-axes have different scales and that the water isotope ratio profiles of pore-infiltrated water read chronologically from bottom to top of the vadose zone. Correspondences between isotope-profile-identified behaviours and time periods are noted in the figure.

Figure 4. (a) Volumetric water content profiles at sites C1 and C2, and (b) degree of saturation (S_r) profiles at sites C1 and C2. The left-hand scale of depth is for the C2 profile and the right-hand scale is for the C1 profile.

Figure 5. Volumetric water content profiles and snowmelt and precipitation data at (a) Site C2 and (b) Site C1. The correspondence between the infiltrated water and its origin (time period and age) is indicated on the two volumetric water content profiles.

Figure 6. Grain-size sieve analysis results for sites C1 and C2 for the different ranges where the samples were identified to be similar and belonging to the same class of soil.

Table 2. Soil properties obtained from grain-size sieve analysis and from soil drying.

Site	Depth b.g.s. interval (cm)	D5 (mm)	D10 (mm)	D17 (mm)	D20 (mm)	D50 (mm)	D60 (mm)	D10/D5 (-)	Cu (-)	n(-)	e (-)	K predicted average (cm/s)	K predicted total average (cm/s)
	0–85	0.043	0.070	0.094	0.105	0.180	0.220	1.628	3.14	0.42	0.72	4.78E-03
	85–125	0.048	0.072	0.091	0.096	0.130	0.160	1.500	2.22	0.46	0.87	5.77E-03
C1	125–155	0.056	0.081	0.105	0.107	0.170	0.190	1.446	2.35	0.42	0.74	6.07E-03	5.26E-03
	155–205	0.078	0.108	0.125	0.130	0.205	0.230	1.385	2.13	0.40	0.67	9.42E-03
	205–245	0.034	0.054	0.081	0.090	0.140	0.170	1.588	3.15	0.37	0.59	2.55E-03
	0–35	0.034	0.056	0.080	0.085	0.108	0.120	1.647	2.14	0.45	0.82	3.96E-03
	35–145	0.080	0.105	0.120	0.140	0.210	0.260	1.313	2.48	0.40	0.67	9.28E-03
C2	145–175	0.034	0.056	0.080	0.084	0.108	0.140	1.647	2.50	0.38	0.62	2.54E-03	8.47E-03
	175–295	0.105	0.170	0.205	0.210	0.350	0.400	1.619	2.35	0.39	0.64	2.21E-02
	295–415	0.105	0.170	0.205	0.210	0.350	0.400	1.619	2.35	0.38	0.61	2.11E-02

Figure 7. (a) Predicted Vol. WC curves at equilibrium for sites C1 and C2 and (b) predicted hydraulic conductivity curves at equilibrium for sites C1 and C2.

Table 3. Recharge for sites C1 and C2 calculated for different periods.

	Time period
Site C1	23 July–16 October (86 days)
Recharge (mm)	284
Precipitation (mm)	299
% Recharge	95
	Time period
Site C2	1 June–16 October (140 days)	1 April–31 May (61 days)
Recharge (mm)	239	120
Precipitation (mm)	571	300
% Recharge	42	42