Well Hydrographs

Just as river hydrographs are used to record and visualize variations in flow with time (as discussed in Module 4), a well hydrograph is a time series of hydraulic head recorded in a well. This provides information about the fluctuation of hydraulic head (equivalent to the water table in an unconfined aquifer), which reflects the combined effects of temporal variations in climate, recharge, and pumping (Figures 30-31). The U.S. Geological Survey maintains a database of active monitoring wells in major aquifer systems across the United States. Hydrographs provide information about seasonal patterns that may be associated with pronounced wet and dry seasons typical of some regions (for example, Central CA), as well as long-term trends driven by climate change, decadal-scale climate patterns like el nino, prolonged groundwater extraction, or human-induced modifications to natural recharge. We'll cover examples of the latter two processes in the next section of the module (Module 6.2: Water budgets).

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Figure 30. Hydrographs for 2013-2014 for a monitoring well near Sacramento, CA.
Source: USGS, 10/4/2014

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Figure 31. Hydrographs for 2013-2014 for a monitoring wells in Centre County, PA near State College. The red diamonds show the water level (hydraulic head) measured in depth below the land surface. Black triangles show the historical mean, and colored bars show historical percentiles for water level (red= <10%; orange = 10-24%; green = 25-75%; light blue = 76-90%; dark blue = >90%). Note that the water level in the Sacramento example is near the all-time historical low, whereas in Centre County the water level is near the historical mean.
Source: USGS, 10/4/2014

• Formative Assessment 2: Well Hydrograph Records