Moisture characteristic curves for Apache Leap Tuff: Temperature effects and hysteresis, Superior, Arizona

Abstract

Laboratory methods were used to define matrix hydraulic properties for low-permeability Apache Leap Tuff core segments. Moisture content/matric potential relationships, including hysteresis, and measured hydraulic conductivity data were determined at a constant laboratory temperature of 20°C. To investigate the effects of temperature on those relationships, additional retention data were obtained at 5°C and 45°C. Measured retention data at all temperatures were applied to the van Genuchten model RETC, which performs curve-fitting and calculation of the flow parameter hydraulic conductivity. Although data at 5°C proved to be inconclusive, increasing the temperature from 20 to 45°C produced a shift of the moisture characteristic curve toward a higher potential for a given water saturation. Model-calculated hydraulic conductivity also increased as temperature increased, with respect to water saturation. The temperature-dependent change in the viscosity of water proved inadequate to explain the increases of hydraulic conductivity with temperature.