Methodology con't

Finding the counties: An Ogallala Aquifer shapefile was created by selecting the Ogallala from the Major Aquifers shapefile. Displaying this file with the Texas Counties shapefile identified all counties located on the aquifer and an Ogallala Counties shapefile was created by selecting these in the NAME field of the Counties attribute table. see map

Finding well density: The Texas Wells shapefile was clipped to the Ogallala Aquifer shapefile and the number of wells per county were calculated. These values were input into new fields in the Ogallala Counties attributes to calculate well density by county (see Data Aquisition). The Ogallala Counties shapefile was then converted to raster using a ranked well density field for display.The result was a raster file showing ranked well density by county for each of the 47 Ogallala counties. see map

Finding Ogallala precipitation: The Texas Precipitation shapefile was clipped to the Ogallala Counties shapefile to determine countywide precipitation ranges. The values were ranked and added as a new field to the shapefile attributes and the data was converted to raster format and imported to Idrisi. The result was a raster file showing ranked precipitation over the entire area covered by the Ogallala Counties. see map

Isolating Ogallala surface water : The Texas Rivers, Lakes and Streams shapefile was clipped to the Ogallala Counties shapefile. The same operation was performed with the Texas Reservoir shapefile. The latter shapefile was inclued as the former did not contain data for large sized reservoirs. Each of these files were converted to raster format and imported to Idrisi. In Idrisi, each file was reclassified into a boolean format and then an overlay operation was performed to combine the two files. The file was then reclassed again into boolean format with the end result of one boolean surface water map. see map

Isolating Ogallala Groundwater Conservation Districts (GWCDs), Priority Groundwater Management Areas (PGMAs) and Proposed Inter-basin Transfers (IBTs): The shapefiles for each governance type were clipped to the Ogallala Counties shapefile, converted to raster and used to generate three separate Idrisi files. In Idrisi each map was reclassified into a boolean format. see maps:

GWD

GWCD - PGMA - IBT

All shapefiles were initially rendered in ArcMap version 9.1. The projected coordinate system used was the NAD 1983 Texas Centric Mapping System and the projection was Lambert Conformal Conic. These reference files were available on the SFU SIS lab S:// drive. Linear units for all files were in metres. After rendering, all shapefiles were converted to raster format using a cell size of 500 metres, converted to ASCII format, then imported into Clark Lab's Idrisi Kilimanjaro for multi-criteria evaluation. Because the NAD 1983 Texas Centric Mapping System reference file was unavailable in Idrisi, a new reference file for the coordinate system was added manually.