||Static Tension Lysimeter
||Controlled Tension Lysimeter
|How it Works
|A simple collection pan is buried in the soil to collect water draining from the root zone.
||A collection device, typically a cyclinder, is buried in the soil. Flow divergence is reduced by creating a static tension with a vacuum pump or a wick (which acts as a hanging water column).
||Suction Plates are buried in the soil. A control system measures soil water tension and uses the vacuum pump to match the suction of the plates with the tension in the surrounding soil. Leachate is collected in and underground control room.
||A large core of soil deep enough to encompass the root zone is removed. It is placed on a precision load cell which weighs the lysimeter continously. In UMS lysimeters, the lower boundary is controlled with an active suction system to match tension in the native soil. Porous concrete well rings maintain temperature dynamics.
|Most basic measurement of drainage; simple and inexpensive.
||Relatively simple and inexpensive.
||Very accurate drainage measurement method.
||Best possible quantification of the hydrologic cycle for climage change, ecohydrology, and contaminant transport studys.
|In unsaturaged soil water will flow around the lysimeter (flow divergence). Even with the best setup, commonly less than 10% of the drainage is collected.
||Flow divergence is reduced by not eliminated. Flow convergence is possible (though uncommon).
||Expensive to install and maintain, power-intensive.
||Most expensive to install and maintain.
|Flow divergence problems can be mitigated somewhat by using a large measurement footprint (several m2) and vertical walls (all the way to the surface is the best).
||Addition of divergence control tube minimizes convergence and divergence.