Figure 2 (Left) is a portion of a completed potentiometric surface map. The gray lines are lines of equal ground water head in the aquifer. Blue arrows have been added to the map to indicate the direction of ground water flow. Figure 3 (Below) represents a 3-D block diagram view along line A-B in Figure 2. Figure 3 shows both a side and top view of the direction of ground water flow in shallow and deep aquifers. The topography has a greater control on the direction of flow in the shallower aquifer than it does in the deeper aquifer (arrows labeled Regional Flow indicate direction of flow in the deeper aquifer).
How the Maps are Produced
Location data from the water well log database is used to create a water-well point coverage. In order to have the maximum amount of data points, geocoding software is run on the well log database. This allows for the best point coverage to be generated.
The horizontal component of flow can be different for different discrete zones or aquifers. Because of this, wells completed in the bedrock aquifers (e.g. limestone or sandstone) and the unconsolidated aquifers (e.g. sand and gravel) were mapped separately. The elevation of the water level in each water well is plotted on 7.5-minute topographic maps, which are then contoured to create the potentiometric surface map. Each map is then digitized to create a GIS file. A paper layout, available as a PDF, has been generated for all completed counties. Both the GIS file and/or the PDF can be downloaded from the Division's website.
Applications of Potentiometric Surface Maps:
Ground water potentiometric surface (water level) maps indicate the elevation and direction of ground water flow. These maps could be used to calculate the gradient or slope, determine ground water recharge and discharge areas, and as input data into ground water modeling programs. These maps could also be used to assist in preparing water resource plans, to assist in preparing technical studies, the mapping of stress areas, and in possible ground water diversion issues. Since these maps were created from existing data collected over a fifty-year period, field verification of the ground water flow direction should be conducted before the drilling of monitoring wells to satisfy compliance monitoring.