| Abstract: | ABSTRACT: Interpretation of ground water level changes in a developed aquifer usually relies on reference to some benchmark such as “predevelopment” ground water levels, changes from fall to fall and/or spring to spring, or to determination of maximum stress during the pumping season. The assumption is that ground water levels measured in the monitoring well accurately reflect the state of the ground water resource in terms of quantity in storage and the effects of local pumping. This assumption is questionable based on the patterns shown in continuous hydrographs of water levels in monitoring wells in Nebraska, and wells installed to determine vertical gradients. These hydrographs show clear evidence for vertical ground water gradients and recharge from overlying parts of the aquifer system to deeper zones in which production wells are screened. The classical concept of semi‐perched ground water, as described by Meinzer, is demonstrated by these hydrographs. The presence of semi‐perched ground water (Meinzer definition, there is no intervening unsaturated zone) invalidates the use of measured ground water levels in regional observation programs for detailed numerical management of the resource. Failure to recognize the Meinzer effect has led to faulty management. The best use of data from the observation well network would be for detection of trends and education unless it is clearly understood what is being measured. |
