Upward infiltration–evaporation method to estimate soil hydraulic properties

Figures & data

Table 1. Time intervals used in the simulation of the theoretical loam soil.

		Duration of each process (min)
Case	Scenario	Sorption	Overpressure	Evaporation
i	Cap0	40	0	0
ii	Cap0 + h	40	30	0
iii	Evap	0	0	36 000
iv	Cap0 + Evap	40	0	36 000
v	Cap0 + h + Evap	40	30	36 000

Figure 1. Diagram of the experimental set-up.

Table 2. Soil properties of the studied soils, applied pressures, evaporation rates and experimental times used in the upward infiltration overpressure step and evaporation processes.

Texture	Sand	Silt	Clay	CaCO3	Organic carbon	Soil tensions	Evaporation rate	Interval times
		(g kg^−1)				(cm)	(cm min^−1)	(min)
Fine sand	962	27	11	-	-	0, + 2	0.0036	3.3; 7.66; 2870
Loam	280	470	250	527	11.7	0, + 5	0.0069	15.23; 23.63; 9914
Clay-loam	205	497	298	228	19.9	0, + 5	0.00294	29.5; 48.5; 8574

Figure 2. Contours of the objective function Φ(K,α,n) for the upward infiltration curves in the (a) K–n, (b) α–n and (c) K–α planes, without (1) and with (2) an overpressure step of 5 cm at the end of the wetting process. The number of contour lines corresponds to a 70 × 70 parameter combination grid. The thick (red) line indicates the experimental contour line corresponding to a RMSE of 0.1 mm due to water level measurement.

Figure 3. Contours of the objective function Φ(K,α,n) for an evaporation process: one parameter is fixed and the other two are optimized in the (a) K–n, (b) α–n and (c) K–α planes. See Figure 2 caption for details.

Figure 4. Contours of the objective function Φ(K,α,n) for the upward infiltration curves plus the cumulative evaporation curves: one parameter is fixed and the other two are optimized in the (a) K–n, (b) α–n and (c) K–α planes, without (a) and with (b) an overpressure step of 5 cm at the end of the wetting process. See Figure 2 caption for details.

Table 3. Soil bulk density (ρ_b), saturated (θ_s) and residual water contents (θ_r), saturated hydraulic conductivity (K_s), the n and α parameters of the van Genuchten (1980) water retention curve estimated for a wetting (α_w) and a draining process (α_d) from the TDR-pressure cell (PC) and the inverse analysis (CR-E), respectively, measured on sand and 2-mm sieved loam and clay-loam soils. The α values in italics were calculated according to the Gebrenegus and Ghezzehei (2011) model. W & D: wetting and drying.

				θs (cm^3 cm^−3)
Soil	Method	Process	ρb (g cm^−3)	Wetting	Drying	θr(cm^3 cm^−3)	Ks (cm min^−1)	αw(cm^−1)	αd(cm^−1)	n [-]
Fine sand	PC	Draining	1.57	-	0.38	0.020	-	0.1081	0.054	2.33
	CR-E	W & D	1.60	0.378	0.42	0.001	0.6486	0.07406	0.037	2.6
Loam	PC	Draining	1.19	-	0.48	0.150	-	0.076	0.039	1.64
	CR-E	W & D	1.09	0.43	0.53	0.012	0.0969	0.0905	0.0468	1.52
Clay-loam	PC	Draining	1.31	-	0.52	0.360	-	0.102	0.055	1.32
	CR-E	W & D	1.26	0.54	0.52	0.008	0.0476	0.0741	0.0383	1.52

Figure 5. (a) Contours of the objective function Φ(K,α,n) for the cumulative upward infiltration plus the cumulative evaporation curves: one parameter is fixed and the other two are optimized in the α–n plane for a 2-mm sieved loam soil. See Figure 2 caption for details. (b) Experimental (circles) and optimized simulated (line) cumulative upward infiltration plus evaporation curves measured on a 2-mm sieved loam. (WCR: water capillary rise.)

Figure 6. Comparison between effective saturation (S_e) curves measured in (a) fine sand, (b) sieved loam and (c) sieved clay-loam soil with TDR pressure cells (circles) during a draining process and the corresponding curve obtained by inverse analysis (line) of the cumulative upward infiltration–evaporation curve in the draining branch of the water retention curve.

van Genuchten, M.T., 1980, A closed-form equation for predicting the hydraulic properties of unsaturated soils. Soil Science Society of America Journal, 44, 892–898.

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Gebrenegus, T. and Ghezzehei, T.A., 2011, An index for degree of hysteresis in water retention. Soil Science Society of America Journal, 75, 2122–2127.

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