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<br />After a subsequent flight and re-measurement, the amount of subsidence was calculated from the <br />difference in elevation at each point that had the same X, Y coordinates. <br />(5) Toooaraohic Base MaP From the original DTM data with additional "breaklines" such as <br />drains and ridges digitized in the analytical plotter, a contour map at a 5 foot contour interval was <br />plotted at 1"=200' scale, with the contours being generated automatically from the digitized X, Y, Z <br />points. Contours within Red Wash valley were plotted at one foot intervals so that gradient changes <br />can be detected once subsidence began. In addition, major planimetric details such as roads and <br />rivers were compiled on the map. <br />This map was used for location purposes, and was generated from the original photography only. <br />(8) Subsidence Contours Ascribed drawing was made at 1"=200' showing "subsidence <br />contours" at one foot intervals. These contours were based on the difference between the original <br />digital terrain model and subsequent models. BME proposed to provide three subsidence contour <br />maps, one for each survey following the baseline survey. <br />(7) CrossSections Cross-sections were generated along grid lines between X, Y coordinates, <br />• showing the terrain profile. Profiles from different flights could be combined on one cross-section plot. <br />These were plotted on paper at 1"=200' H and 1"=5' V, automatically on acomputer-driven flatbed <br />plotter. A separate vertical scale was selected along the subsidence profile to allow a visual <br />recognition of the amount of subsidence. <br />Various cross-sections were produced, each to show the first and subsequent subsidence intervals <br />compared with the baseline data. <br />(8) Accuracy A total of 22 ground control points were monitored immediately prior to each <br />flight. BME completed a Third Order survey on the 22 ground control points, certified by a <br />registered land surveyor, licensed to practice surveying in the state of Colorado. The root mean <br />squared error of the difference in elevations determined from the aerial methods and from <br />on-the-ground surveys was within +/- 0.25 feet. 95% of the elevations differences at these 22 points <br />was within +/_ 0.8 feet. <br />(g) Coordination with Surtace Observations and Other Monitoring Programs DMG had <br />expressed concem regarding probable impacts to the hydrologic characteristics of Red Wash. To <br />alleviate this concern, BME install nine alluvial wells in Red Wash to define the alluvium characteristics <br />and any changes that might occur in Red Wash as a result of subsidence. The nine-hole installation <br />• Midterm Review (8/2002) III-24 <br />