High resolution temperature observations to identify different runoff processes

Abstract

Headwater catchments are important contributors to streamflow. They are small, but all combined they influence river flow significantly. To be able to make proper runoff predictions under different climate conditions and changing land use, it is important to have detailed understanding of the discharge processes in the headwater catchments. In this thesis we explore the possibilities of fibre optic Distributed Temperature Sensing (DTS) to obtain more insight in temporal and spatial discharge dynamics during stormflow. DTS is a technique capable of measuring temperature with high spatial and temporal resolution. It was developed in the 1980’s by the oil industry but only recently (in 2006) it has been introduced into the field of hydrology. The technique relies on short laser pulses that are sent through a fibre optic cable. Throughout the fibre optic cable small parts of the pulses are reflected by disturbances in the glass fibre, of which the exact position is obtained by measuring the travel time of the reflected light. The frequency shifts of the reflected light are then used to calculate the temperature of the fibre optic cable at the point of reflection. The DTS system used in this thesis has a spatial resolution of 2 m and a temporal resolution of 3 min. With these settings a precision of ˜0.1_C is obtained. All experiments described in this thesis were done in the Maisbich: a 565 m long, first order stream in Central Luxembourg. The lithology of the Maisbich consists of schist which is covered with a layer of loose rock clasts with variable clay content of a few meters thick and a thin layer of fine sediments. Summer baseflow in the Maisbich can be