Estimating Ground Water Recharge using Flow Models of Perched Karstic Aquifers
Menachem Weiss and Haim Gvirtzman

 

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ABSTRACT

Figure 1

Figure 2

Figure 3

The fraction of rain that is annually recharged to ground water is very difficult to estimate. In this study we have used long records (20-30 years) of precipitation and spring discharge to accurately reconstruct the transient character of yearly recharge. These data sets were used to calibrate numerical ground water flow models for four separate perched karstic aquifers in the Judean and Samarian Mountains of Israel, each on the less than 3 square kilometer scale (Fig. 1).

The stratification and karstic character of the local carbonate rock aquifers cause ground water to flow through discrete dissolution channels and to discharge at isolated springs. An innovative, dual-porosity approach was used to simulate flow in the rock matrix and through karstic channels. Perched conditions are also simulated innovatively using MODFLOW (Fig. 2).

Best fitting between measured and computed spring hydrograph data (Fig. 3) has allowed us to develop a set of empirical functions relating measured precipitation to actual recharge of the ground water aquifer. The generic methodology gives insight into changes in aquifer recharge rates between particularly wet or dry years.

 



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