Performance of the infiltration and laboratory tests

Four field infiltration tests were tried at each experimental site. The adopted experimental layout is described below.

The first test was generally done on the soil surface under natural moisture conditions; then the soil was (almost) saturated with about 0.1m3 of water slightly poured out over a circular area of about 1 m2 around the infiltrometer. In order to help the process of saturation of the upper soil layers during the water pouring, and to prevent the runoff of the water over the surface, two holes (diameter 0.01 m, depth 0.15 m) were made along eight equally spaced directions. Then the second surface test, that is, the surface test under modified ''saturated'' soil moisture, was performed. The degree of saturation was afterwards verified in laboratory over a core sampled after the modified-moisture infiltration test. Finally, two other infiltration tests were performed at the same sites, but at lower soil depths, about 0.1 and 0.2 m deep.

Toce soil saturated conductivity map (m/s)

Monte Rosa (4633 m asl)

Toce soil saturated conductivity map (m/s)

Monte Rosa (4633 m asl)

Map Soil Conductivity Canada

Figure 9.4 Surface soil saturated conductivity map for the Italian Toce River basin (after Clerici and Cantoni 2000). For the values in legend, the Reynolds and Elrick method (see the text for details) is adopted

1.00E-9 peat

1.00E-8 rock with thin soil cover 1.00E-7 outcropping rock 1.00E-7 rock with thin soil cover 1.00E-6 discontinuous urban fabric 1.00E-6 outcropping rock 1.00E-6 rock with thin soil cover 1.35E-6 forest covered moraine 1.61E-6 grass covered alluvial soils 2.30E-6 cultivated areas 2.46E-6 grass covered slopes debris 2.79E-6 forest covered slopes debris 2.88E-6 grass covered alluvial soils 4.15E-6 grass covered moraine 1.00E-5 outcropping rock 1.29E-5 forest covered moraine 1.84E-5 grass covered moraine 2.92E-5 alluvial soils >1.00E-4 moraine >1.00E-4 slopes debris Glaciers Lakes

Lago Maggiore (184 m asl)

Figure 9.4 Surface soil saturated conductivity map for the Italian Toce River basin (after Clerici and Cantoni 2000). For the values in legend, the Reynolds and Elrick method (see the text for details) is adopted

For each site, surface samples of the soil were collected to perform soil moisture measurements, soil saturated conductivity and water retention tests in laboratory. Two more soil cores were taken, when the soil was deep enough, to measure the soil saturated conductivity after laboratory analysis also for the lower layers and to verify possible discontinuities in the profile of the grain size distribution.

In laboratory, the core samples were weighed and saturated for at least 16 h before performing the falling head permeability test. The sample was weighed another time to verify any change in the soil moisture and finally oven dried at 105°C for 24 h. Then the soil sample was divided into two parts: one being used to determine the grain size distribution curve, and the other to determine the water retention relationship. To perform this experience, the soil was previously sieved at the 2-mm sieve, then three samples (height about 1 cm, diameter 8 cm) of sieved soil were laid on a Richards' porous plate that was previously saturated. Then the samples were saturated by imbibition from the porous plate and a pressure of (10, 33, 50, 100, 500, 1500 kPa) was imposed in the Richards' apparatus. After drainage, the moisture of the samples was measured by oven drying.

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