By Scott T. Prinos |
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SUMMARYThe U.S. Geological Survey cooperative continuous ground-water level monitoring program in Miami-Dade County, Florida, expanded from 4 wells in 1939 to 98 wells in 2001. Historically, network design was coordinated with five different cooperative agencies to address the monitoring needs of these agencies. A correlation analysis of water-level data from wells in the existing network was performed to aid in the assessment of network redundancy by indicating which wells provide similar data. Because the water-supply and water-management systems in Miami-Dade County increased in complexity during the period that ground-water data were collected, temporal variation in the degree of correlation had to be considered. It was also necessary to consider the spatial variation in correlation because the water-supply and water-management systems as well as natural differences in precipitation, evapotranspiration, and hydrogeology can act spatially to affect the degree to which water-level data correlate. Using S-PLUS 2000 statistical analysis software, correlation analyses were performed for daily maximum water-level data from 98 monitoring wells for the period November 1, 1973, to October 31, 2000 (water years 1974-2000). Water-level data from each well were subdivided by year and season (wet and dry seasons). The analysis allowed the comparison of data that were not totally complete, but rejected from consideration any seasons that were missing more than 5 percent of the data. For each year and season, correlation analyses were performed on the data from all wells where data were available. Final correlation matrices for the wet and dry seasons were created. For the comparison of water-level data for each well pair, the correlation matrix provides: (1) the average of the correlation coefficients determined, using all noncensored seasons for the period analyzed; (2) the number of noncensored seasons; and (3) the standard deviation of the noncensored seasonal correlation coefficients. Graphs showing the variation of correlation through time were prepared for selected wells where water-level data were correlated with that of numerous other wells using an average coefficient of 0.95 or greater for the comparison. The average wet- and dry-season correlation coefficients were plotted spatially using geographic information system software. For each monitoring well, this software could readily show the location of any other monitoring wells that provided water-level data that correlated with a coefficient of 0.95 or greater for the comparison. Using this approach, wells with water-level data that correlated to this extent were almost always found to be located in relatively close proximity to each other. The data from the majority of the wells in the network (65 wells) generally were not correlated with that of other wells during the wet and dry seasons with an average coefficient of 0.95 or greater. Five areas were identified, however, where in both seasons the water-level data from wells within the area correlated with that of other wells within the area with a coefficient of 0.95 or greater, but not with data from wells outside the area. These areas were located in the Highly correlated water-level data in two or three ground-water level monitoring wells could generally be beneficial rather than overly redundant. The added water-level data can aid in quality assurance and provide data for those periods when one of the other monitoring wells has been damaged or destroyed. Therefore, the level of redundancy in or near the Although the greatest number of potentially redundant wells were near the West Well Field (21 wells), the short period of record available for analysis for most wells in this area generally resulted in determination of averaged correlation coefficients using only a few seasons of data. If the relations that were established for a few seasons of data remain consistent during future droughts, floods periods, and water-management changes in this area, then the case for redundancy would be stronger. Of the six wells near the Hialeah-Miami Springs Well Field, water-level data from well The correlation analysis of available data indicates that there are areas where the water-level data from certain wells may be redundant. In general, however, comparison of data is needed for longer periods of record than currently exist. For the few instances identified where the data have remained highly correlated on average over a lengthy period of record (specifically in wells Next: References Cited |
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