Map 01 - ArcGIS layer showing contours of the mean May water levels during the 2000-2009 water years (feet)

Statistical analyses and maps representing mean, high, and low water level conditions in the surface water levels and groundwater levels in Miami-Dade County were made to help inform decisions necessary for urban planning and development. Sixteen maps were created that show contours of (1) the mean of daily water levels at each site during October and May of the 2000-2009 water years, (2) the 25th, 50th, and 75th percentiles of the daily water level at each site during October, May, and for all months during this same period, and (3) the differences in mean October and May water levels, as well as the differences in the percentiles of water levels from all months, between 1990-1999 and 2000-2009. The 80th, 90th, and 96th percentiles of the annual maximums of daily groundwater levels during 1974-2009 (a 35-year period) were computed to provide an indication of unusually high ground water level conditions. These maps and statistics provide a generalized understanding of the variations of water levels in the aquifer, rather than a survey of concurrent water levels. Water-level measurements from 473 sites in Miami-Dade County and surrounding counties were analyzed to generate statistical analyses. The monitored water levels included surface water levels in canals and wetland areas, and groundwater levels in the Biscayne aquifer. Maps were created by importing site coordinates, summary water-level statistics, and completeness of record statistics into a geographical information system, and by interpolation between water levels at monitoring sites in the canals and water levels along the coastline. Raster surfaces were created from these data using the triangular irregular network interpolation method. This surface was contoured using geographic information system software. These contours were imprecise in some areas because the software could not fully evaluate the hydrology given available information; therefore, contours were manually modified where necessary. The ability to evaluate differences in water levels between 1990-1999 and 2000-2009 is limited in some areas because most of the monitoring sites did not have 80 percent complete record for one or both of these periods. The quality of the analyses was limited by (1) deficiencies in spatial coverage, (2) the combination of pre- and post-construction water levels in areas where canals, levees, retention basins, detention basins, or water control structures were installed or removed, (3) an inability to address the potential effects of the vertical hydraulic head gradient on water levels in wells of different depths, and (4) an inability to correct for the differences between daily water-level statistics. Contours are dashed in areas where these limitations have created uncertainty. Although the ability of the maps to depict differences in water levels between 1990-1999 and 2000-2009, was limited by missing data, results indicate that water levels near the coast were generally higher during 2000-2009, and that water levels overall were generally lower except during October.This feature class contains the potentiometric contour lines for the average May water levels for the water years 2000-2009.