Making maps of tomorrow -- today

Abstract

This study is part of an assessment of water supply needs and sources in which the St. Johns River Water Management District (SJRWMD) has been required to identify areas expected to have inadequate water resources to meet the water supply demand in the year 2010. SJRWMD conducted this assessment using seven regional numerical MODFLOW ground water flow models and several local analytical ground water flow models. Two of the most important aspects of the ground water evaluation were (1) the projection of the 2010 potentiometric surface of the Floridan aquifer and (2) the change in the potentiometric surface of the Floridan aquifer between 2010 and the current hydrologic condition. A GIS approach was selected to synthesize the results of the various analyses. The numerical and analytical ground water flow models were run to produce a data set of hydraulic heads. A data set in excess of 800 water level monitoring well points was used as the base and quality control for the study. A monitoring well coverage with 1988 water levels was processed using the ARC/INFO triangulated irregular network (TIN) module, then contoured to generate a 1988 potentiometric surface map of the Floridan aquifer. The grid and resultant hydraulic head values for each grid cell of the numerical models were imported into GIS format. Control well points were matched against model grid cells to select hydraulic head values for the year 2010 to be contoured. Using the algebraic function in the GRID module of ARC/INFO, the 2010 surface was subtracted from the 1988 surface to generate a surface representing the projected change in the potentiometric surface of the Floridan aquifer between 1988 and 2010.