The Spatial and Temporal Variability of Groundwater Recharge

Background / Need: Understanding the spatial and temporal distribution of groundwater recharge is a pre-requisite for effective groundwater management and modeling. Recharge, defined as the entry of water into the saturated zone, is influenced by a wide variety of factors including the vegetation, topography, climate, geology, and soils. Despite its dependence on these spatially variable parameters, recharge is typically assumed to be constant and uniform within a watershed. The recharge estimate is usually empirically derived, is a fitted parameter determined by calibration, or is calculated using baseflow of streams as a surrogate. Since the distribution, rate, and timing of recharge are dictated by the interaction of these variable parameters, recharge should vary temporally and spatially at the watershed scale and the use of a constant value for an entire watershed may be inappropriate. Using a combination of field work and integrated modeling, we developed a suite of techniques for estimating recharge and tested our methods by quantifying the spatial and temporal distribution of recharge at the watershed scale and a daily time step for the Trout Lake basin, a small forested watershed in northern Wisconsin.

Objective: Our main objective was to develop a methodology for estimating the spatial and temporal distribution of groundwater recharge. The methodology was tested by application to the Trout Lake basin for the period 1996 – 2000