Apparatus for constant-head solute transport and soil water characteristic determination

We developed a system to impose, maintain, and monitor constant matric head (h) and water content (Θ) within large soil cores during saturated or unsaturated flow. Critical elements include: (i) delivery of water and chemicals to the column inlet using a modified disk permeameter, (ii) paired time domain reflectometry (TDR) and transducer tensiometer sensors; and (iii) solenoid valves at the outlet for uninterrupted negative pressure and simultaneous collection of large effluent volumes. Use of TDR and tensiometry provides detailed water retention data and allows hydraulic conditions within the soil to be continuously monitored during single or multiple experiments using the same soil column. Our experiences have emphasized the need to measure soil column h rather than infer its status based on applied pressure.