Estimation of vertical water flow in slopes from high-resolution temperature profiles

Vertical water flow is a decisive factor for slope stability and instability, but its characterization in the field remains a challenge. Quantifying flow rates in slopes is commonly impeded by insufficient resolution during field investigations or the limited insight obtained from near-surface geophysical methods. This study aims to develop a convenient method to investigate vertical water flow in slopes on the sub-meter scale. We present a numerical method to estimate flow rates based on temperature-depth profiles. In order to account for typical small-scale variabilities and complex boundary conditions in slopes, these profiles are obtained by high-resolution temperature measurements with passive distributed temperature sensing (passive-DTS). The transient heat tracing data is inverted in space and time to derive trends of perturbing vertical flow. The method is successfully validated in a laboratory tank with a series of experiments under well-controlled hydraulic and temperature boundary conditions. It is demonstrated that upward and downward flow rates greater than 1.0 x 10(-6) m.s(-1) can be properly estimated, and the influence of moving water on the thermal profiles can be identified even to a flow rate of 1.0 x 10(-7) m.s(-1).