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U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2007–5159

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Field Survey of the 2006 Flood

On November 21, 2006, 2 weeks after the flood, a two-man crew from the USGS surveyed HWMs on the right bank from XS2 to XS3 using the same total station as used in the previous survey in 2004. On the day of the flood after the river had crested, Malcolm Leytham (Northwest Hydraulics Consultants) marked the high-water line with 1×2-inch hubs labeled with red poker chips (written comm., November 20, 2006). Five of these HWM hubs were found by USGS personnel, who also located 25 additional HWMs, each subjectively rated Excellent, Good, Fair to Poor (E, G, F, and P) based on the condition, type, and accuracy of the mark. A straight stationing reference line was drawn on a map along the line of HWMs to provide stationing for each HWM in a longitudinal profile (fig. 2).

Several 2×2-inch survey control hubs from the previous survey in 2004 were found and used to establish the survey control for the 2006 survey. The survey began near XS2 with two 2004 hubs that agreed within 0.025 ft in the horizontal and 0.038 ft in the vertical with the 2004 survey. The survey ended near XS3 on a 2004 hub (on a sand bank and found at an angle), checking the old coordinates within 0.082 ft in the vertical and 3.003 ft in the horizontal. The error in the horizontal is quite large, but this error may be partially due to movement of the hub in the sand bank. Positional checks were made between every total-station setup in the survey and they were all within 0.07 ft in the horizontal and 0.02 ft in the vertical. Ten setups were used along a baseline of about 2,100 ft to complete the survey. A 3-foot error in the horizontal length of the river (2,108 ft) used to determine the water slope in this reach equals an error in the slope of ±0.15 percent.

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