Comparison of Selected Methods for Estimating Groundwater Recharge In Humid Regions

Method:	Category:	Spatial Scale:	Temporal Scale:	Quantity Estimated:	Ease of Use:	Data Needs:	Cost:
Zero-Tension Lysimeters	Unsaturated Zone	Point	Day to Years	Potential Recharge	Difficult	Low	High
Gravity lysimeters are a method of estimating recharge by directly measuring the vertical flow of water through a large, relatively undisturbed section of the unsaturated zone at a depth below most root systems. Percolate collected from the lysimeters ideally represents water that passed beneath the root zone and is assumed to closely represent a direct estimate of the volume of recharge reaching the water table, although not necessarily the timing of its arrival. Gravity lysimeters are one of the few methods that provide an estimate of recharge by direct collection of infiltrating water. Disadvantages of the lysimeters, in addition to expense and difficulty of installation, are that they provide only a point-estimate of recharge and their installation disturbs the soil, which may affect the collection of percolate for several years.