Center for Spatial Analysis Technologies
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During December 2000 the flood
project team continued to work on revising available DEMs (from NMD) by
topographic quadrangle for the Flint River Basin north of the town of Montezuma,
Georgia area as indicated in figure 1.
The revision is done by digitizing topographic contours from
7.5 minute topographic maps, gridding the area to suitable resolution,
and preparing new DEM’s for each map.
The new DEMs were inserted into the basinwide DEM,
constructed earlier. These new quadrangles were originally smoothed using methods proscribed by NMD. However, after comparing data re-gridded from the digitizing process to the smoothed data considerable differences were noted. Figure 2. shows the original DEM data from the Reynolds quadrangle (for location, see figure 1), while figure 3 depicts the revised scanned, vectorized and gridded DEM for Reynolds. Finally, figure 4 shows the differences (revised minus the original DEM values). Note that values range from -40 meters to +30 meters, primarily in the area of the Flint River and its flood plain where the original DEM elevations are on the average 30 meters higher than the revised DEM elevations. These differences are extremely important in accurately defining the 100-year flood plain. The DEM revision work is being shared with NMD by the flood team and the Georgia Tech GIS Clearinghouse (GTCH) digital orthophotography team which is working on an active and complementary (USGS cooperative) project to prepare color DOQs for the state of Georgia. These DOQ’s will aid the flood team with the planned future flood inundation visualization capabilities. The ongoing liaison with NMD is needed to improve the process of DEM development in order to begin the organized support of hydrologic applications, such as flood inundation modeling. The plan is to begin to establish and to refine the process using the DEM’s of the Flint River Basin. NMD has offered to partner with the state of Georgia to improve available DEM’s. The flood team will meet in January with Nick Faust of GTRI to discuss visualization efforts for the coming year. |
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Figure 1: Status of DEM revision in the Flint River Basin, Georgia |
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Figure 2: Original DEM elevations for the Reynolds Quadrangle |
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Figure 3: Revised (Scanned, Vectorized and Gridded) DEM elevations for the Reynolds Quadrangle |
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Figure 4: Difference map depicting difference in elevation in meters of revised DEMs minus existing DEM elevations |
U.S. Department of the Interior |
U.S. Geological Survey
URL: http://csat.er.usgs.gov/cindi/dec2000.html
Page Contact Information: webmaster-ga@usgs.gov
Page Last Modified: Thursday, 14-Jun-2007 15:28:29 EDT
