Limitations of the Miami Subdistrict End of Month Report

Several issues led to the October 2000 discontinuance of the End of Month (EOM) Report on ground-water conditions that had been produced by the Miami Subdistrict (FISC-WRS since 2003).

1. Production of the report occured only once per month, even during periods when timely information on water levels was critical to water supply management.

2. Seven to ten days of processing time were required to publish the report after the data were collected.

3. Single instantaneous tape-down readings were compared to computed monthly means of maximum daily water levels. A single measurement can be more indicative of a rainfall or pumping event than of true ground-water conditions.

4. Collecting instantaneous readings over a period of several days produced inconsistency in the data.

5. There existed only a limited capability for statistical analysis of the data collected.

6. A large network of wells has been required to offset the statistical deficiencies of the EOM report.

7. Some of the wells that had been part of the original monthly network have been lost because of well destruction or removal, or withdrawal of funding by various cooperators.

8. The output format was designed primarily for a text-based paper report rather than computer graphics.

One significant deficiency, related to item 5 is illustrated by the wells L-729 and L-1993 (Lee County, map). Because the EOM report compared the monthly mean of water levels, from 1974 to the present, to the most current tape-down reading, it did not show that water levels at both wells have declined over the past 20 years ( L-729 , L-1993 ). In the case of well L-729, water levels at this site are about 6 feet lower on average than in 1977 (Summary of Hydrologic Conditions, U.S. Geological Survey Water-Data Report FL-96-2B). Therefore, while a drop in mean yearly water levels of 4 feet since 1977 has not caused problems such as dewatering of a confined aquifer, saline intrusion, or loss of pumpage capabilities in public or private water-supply wells, a drop of 4 feet could now cause these types of problems. This illustrates why one needs to see not only the magnitude by which recent water levels may be deviating from the long term mean, but also the long-term trends in the data.

The deficiencies explained in items 3 and 4 above were made clear in 1997, when water managers received complaints from the public concerning loss of pumpage in privately owned water-supply wells and other related problems. The onset of the decreased water levels which caused these problems was too rapid to be depicted in the existing EOM report. During the period that followed the onset of these conditions water managers relied heavily on the information provided by the real-time recorders and requested, on an emergency basis, the installation of additional real-time recorders.