Saturated and Unsaturated Hydraulic Conductivities and Water Retention Characteristics of Weathered Granitic Bedrock

Abstract

As a first step toward describing water flow processes in bedrock, we determined the hydraulic properties of three trimmed samples of weathered granitic bedrock (referred to as Samples A, B, and C, in order of size) in the laboratory. Silicone rubber was used to fill the space between each sample and the surrounding cylinder wall, ensuring accurate measurement of hydraulic properties of the samples. All samples showed similar saturated hydraulic conductivity values of 1 3 10 24 cm s 21 , with the saturated water flow in all samples obeying Darcy's Law. Unsaturated hydraulic conductivity and water retention functions of Sample A were determined by means of a multistep outflow experiment. Parameters in both functions were optimized by comparing observed and computed cumulative outflow rates. The resulting computed cumulative outflow rates using the optimized parameters showed a good match to the observed cumulative outflow data. Moreover, the derived water retention function agreed closely with the function measured by the pressure plate method. We conclude that the methods proposed in this study are effective for determining the hydraulic properties of weathered bedrock. The bedrock water retention curve exhibited small changes in volumetric water content throughout the measurement range where the pressure head, c, was greater than 2200 cm. The bedrock hydraulic conductivity function showed a small decrease in hydraulic conductivity in the very wet range of c greater than 230 cm, and then declined gradually with decreasing c.

Estimation of mean residence times of subsurface waters using seasonal variation in deuterium excess in a small headwater catchment in Japan

“…These characteristics are similar to those of the weathered granitic bedrock described by Graham et al (1997). The minimum value of the saturated hydraulic conductivity of the bedrock, measured using four undisturbed 100 cm 3 field cores, was 5Ð8 ð 10 6 m s 1 (Katsura et al, 2005). In contrast, the saturated hydraulic conductivity of the forest soil at the Kiryu Experimental Watershed was 4Ð7 ð 10 4 m s 1 (Ohte et al, 1989).…”

Effects of bedrock groundwater on spatial and temporal variations in soil mantle groundwater in a steep granitic headwater catchment

“…For 33.5 -38.0 m depths in R2, a weakly weathered (C M class) bedrock layer was observed. The K s value of the bedrock core samples, measured in the laboratory using the method of Katsura et al [2006], was 8.9 Â 10 À5 (at depth of 3.93 m in borehole R1) and 2.9 Â 10 À4 cm s À1 (2.63 m in R2) for the highly weathered layer; 3.4 Â 10 À4 (27.06 m in R1) and 2.1 Â 10 À6 cm s À1 (21.73 m in R2) for the moderately weathered layer; and 2.2 Â 10 À9 cm s À1 (36.80 m in R2) for the weakly weathered layer.…”

A numerical investigation to illustrate the consequences of hydraulic connections between granular and fractured-rock aquifers

“…This particular case has been documented, for example by Nastev et al (2004Nastev et al ( , 2005, Katsura et al (2005) and Cloutier et al (2006). In this situation, the shallow weathered bedrock ensures a hydraulic continuity between this bedrock and a granular aquifer above.…”