Ground-Water Elevation and Slope

Author:  Steve Custer
Data Compiled by:  David Moody, Matt Trebesch, Robert Snyder,  Gretchen Burton, Steve Custer
Earth Sciences and the Geographic Information and Analysis Center, Montana State University, Bozeman, MT

Last modified 22 January 2001; 02 January 2010

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Example Questions the Database Can Answer

  1. What was the ground water slope in 1953?
  2. What was the ground water slope in 1977?
  3. What was the ground water slope in 1995?
  4. What was the elevation of the ground water in 1953?
  5. What was the elevation of the ground water in 1977?
  6. What was the elevation of the ground water in 1995?

Why are there different dates for Ground-Water Elevation and Ground-Water Gradient?

Ground-Water Elevation (1953) (Does not cover the whole LWQD)

This grid shows the ground-water elevation as measured in shallow wells in 1953 by Hackett and others (1960; U.S. Geological Survey Water Supply Paper 1482). Metadata

Ground-Water Elevation (1977) (Does not cover the whole LWQD)

This grid shows the ground-water elevation as measured in shallow wells in 1977 by Dunn (1978) as part of the Blue Ribbons of the Big Sky project.  Wells measured by Hackett and others (1960; U.S. Geological Survey Water Supply Paper 1482) were revisited in the same month and measured on about the same date as Hackett's original measurements. Metadata

Ground-Water Elevation (1995) (Does not cover the whole LWQD)

This grid shows the ground-water elevation in 1995 as measured by Slagle (1995) as part of a follow-up study of the hydrogeology of the Gallatin Valley. Metadata

Ground-Water Slope 1953 (Does not cover the whole LWQD)

The ground-water slope was calculated from the elevation grid of groundwater elevation for 1953 data. Slope values are in degrees.  The decimal slope can be found by taking the tangent of the slope in degrees.   Data is based on the 1953 information provided by Hackett, 1960. Metadata

Ground-Water Slope 1977 (Does not cover the whole LWQD)

The ground-water slope was calculated from the elevation grid of groundwater elevation for 1953 data. Slope values are in degrees.  The decimal slope can be found by taking the tangent of the slope in degrees. Data is based on the 1977 information provided by Dunn 1978. Metadata

Ground-Water Slope 1995 (Does not cover the whole LWQD)

The ground-water slope was calculated from the elevation grid of groundwater elevation for 1995 data. Slope values are in degrees.  The decimal slope can be found by taking the tangent of the slope in degrees.  Data is based on the 1995 information provided by Slagle et al. 1995. Metadata

About the Data

These grids were constructed by digitizing the published ground-water contour lines, and ground-water elevations.  The digitized data was converted to a grid using ANUDEM.  The program uses xy location, elevation from the DEM of the area, and digitized ground-water-elevation data  to create a grid of ground-water elevation using a Laplacian Spline.  The gradients were calculated from the grid elevation data using Spatial Analyst.

The data was digitized from three sources:

Hackett, O.M., Visher, F.N., McMurtrey, R.G., and Steinhulber, W.L., 1960, Geology and ground water resources of the Gallatin Valley, Gallatin County, Montana: U.S. Geological survey Water Supply Paper 1482, 282 p.  Original map scale 1:126,700 polyconic projection.

Dunn, D.E., 1978, Ground-water levels and ground water chemistry, Gallatin Valley Montana: Blue Ribbons of the Big Sky Area wide Planning Organization report, #11, 62 p.  Original map scale 1:126,700 polyconic projection.

Slagle, S.E., 1995, Geohydrologic conditions and land use in the Gallatin Valley, South Western Montana: U.S. Geological Survey Water-Resources Investigations Report 95-4030. Original map scale 1:100,000 UTM Zone 12 NAD27.

The Hackett et al. (1960) and Dunn (1978) maps were digitized from maps in polyconic projection and the data was reprojected to UTM Zone 12 NAD83.  The settings for polyconic conversion in Arc/Info were:  Central Meridian: 111 degrees 00  minutes 00 seconds; Latitude of Projection Origin: 45 degrees, 22 minutes, 30 seconds;  False Easting: 0; False Northing: 0.  The Slagle (1995) map was digitized from UTM Zone 12 NAD 27 and reprojected to UTM Zone 12 NAD83.