Groundwater hydrographs illustrate the historical record of aquifer water levels measured within a well. The example shown below illustrates two features of a hydrograph:
1. A long term of record is important when evaluating water level trends. In the above example, an overall, long-term view shows that following a period of steady water levels, conditions changed, causing water levels to decline until again conditions changed, resulting in a water level rise.
2. Seasonal impacts on aquifers are often depicted by a hydrograph. In the above example, water levels drop during summer as demands on the aquifer increase. These demands include irrigation, lawn watering, car washing, and so forth.