Multi-step outflow method

Multi-step outflow (MSO) is an indirect method to determine the hydraulic properties by inverse modeling using data from transient outflow. Currently, eight soil columns can be measured independently at the MSO facility, whereby four columns are additionally equipped to measure spectral induced polarization (SIP) in saturated / unsaturated soil cores.

In general, MSO measurements start from a saturated soil column which will be stepwise desaturated using either a peristaltic pump or compressed air, up to a maximal air pressure of 1 bar. Additional sensors such as time domain reflectometry (TDR) and tensiometers measure the matric potential and the water content, respectively. Water outflow from the soil core will be sampled in a burette, whereby its amount will be monitored by a pressure transducer. The course of the drying/wetting cycles and the data requisition are fully automated. The parameters of an appropriate model that describes the hydraulic properties are determined by numerical solution of the Richards equation using the measured outflow, matric potential, and water content data.