Center for Spatial Analysis Technologies
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During November 2000 the flood
project team continued to work on revising available DEMs (from NMD) by
topographic quadrangle for the Flint River Basin in the 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. The next area of DEM revision work, as figure 1 shows, was in the Albany, Georgia area along the mainstem of the Flint River. The pre November 2000 flood inundation model indicated flooding well beyond the 100 year floodplain, as shown in figure 2. The revised flood inundation model run (December 2000) produced a new 100 year floodplain for the Albany vicinity, as shown in figure 3. The improved floodplain (figure 3) illustrates the importance of completing the process of DEM revision to produce a regionally accurate and consistent DEM for the river basin prior to beginning any comparative, qualitative analysis. Figure 4 illustrates the differences in elevation, in feet, of the scanned, vectorized and gridded DEM created from the 1:24,000-scale topographic contours relative to the original 1:24,000 DEM. Areas in blue show negative differences in elevation (i.e., the revised DEM elevations are lower) while areas in red show positive differences (i.e., the revised DEM elevations are higher). 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 met the first week in December with Mike Callahan, USGS, NMD Liason to Georgia and discussed NMD participation in developing 10-meter DEMs for the entire Flint River Basin. |
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Figure 1: Status of DEM revision in the Flint River Basin, Georgia |
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Figure 2: Map of the 100 year floodplain model (pre November 2000) in the vicinity of Albany, Georgia |
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Figure 3: Map of the revised 100 year floodplain model (December 2000) in the vicinity of Albany, Georgia |
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Figure 4: Difference map depicting difference in elevation in feet of revised DEMs minus existing DEM elevations |
U.S. Department of the Interior |
U.S. Geological Survey
URL: http://csat.er.usgs.gov/cindi/nov2000.html
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Page Last Modified: Tuesday, 23-May-2006 10:32:13 EDT
