{"id":277,"date":"2020-11-11T17:18:52","date_gmt":"2020-11-11T17:18:52","guid":{"rendered":"https:\/\/books.gw-project.org\/groundwater-surface-water-exchange\/chapter\/box-4-measurement-errors-in-synoptic-surveys\/"},"modified":"2020-12-21T19:03:44","modified_gmt":"2020-12-21T19:03:44","slug":"measurement-errors-in-synoptic-surveys","status":"publish","type":"chapter","link":"https:\/\/books.gw-project.org\/groundwater-surface-water-exchange\/chapter\/measurement-errors-in-synoptic-surveys\/","title":{"raw":"Box\u00a04 Measurement Errors in Synoptic Surveys","rendered":"Box\u00a04 Measurement Errors in Synoptic Surveys"},"content":{"raw":"Standard stream gauging techniques introduce errors that range from 2% to 20% (Sauer and Meyer, 1992). A good reference for stream gauging methods is the USGS publication by Turnipseed and Sauer (2010). They suggest flow measurement errors usually average between 3 and 6%. When evaluating whether observed streamflow changes are meaningful, gains or losses must be outside of individual measurement error ranges. For example, if streamflow measurements contained an error of +\/- 6%, and the upstream discharge measurement was 30 m3<\/sup>\/s (+\/- 1.8 m3<\/sup>\/s) and the downstream measurement was 28 <\/a>m3<\/sup>\/s (+\/- 1.7 m3<\/sup>\/s), the net groundwater exchange computed by difference (assuming no other inputs or outputs within the reach) would be -2 m3<\/sup>\/s. If the 6% error is applied to the stream gauging measurements the upstream measurement could be as high as 31.8 m3<\/sup>\/s and the downstream measurement as low as 26.3 m3<\/sup>\/s. That means that for a measurable difference in streamflow to be observed the value obtained would have to exceed the difference of the discharges with the 6% error applied (31.8 m3<\/sup>\/s -26.3 m3<\/sup>\/s = 5.5 m3<\/sup>\/s). Unfortunately, the error ranges of inflow and outflow measurements did not allow differentiation of gain or loss when a difference of 2 m3<\/sup>\/s was observed. Depending on site conditions, increasing the distance separating the measurements may resolve the issue if sufficient additional streamflow gains\/losses occur. Roberts and Warren (1999) noted that additional errors are introduced if flow conditions are changing during the period of measurement.\r\n

Return to where text links to Box 4<\/a><\/p>","rendered":"

Standard stream gauging techniques introduce errors that range from 2% to 20% (Sauer and Meyer, 1992). A good reference for stream gauging methods is the USGS publication by Turnipseed and Sauer (2010). They suggest flow measurement errors usually average between 3 and 6%. When evaluating whether observed streamflow changes are meaningful, gains or losses must be outside of individual measurement error ranges. For example, if streamflow measurements contained an error of +\/- 6%, and the upstream discharge measurement was 30 m3<\/sup>\/s (+\/- 1.8 m3<\/sup>\/s) and the downstream measurement was 28 <\/a>m3<\/sup>\/s (+\/- 1.7 m3<\/sup>\/s), the net groundwater exchange computed by difference (assuming no other inputs or outputs within the reach) would be -2 m3<\/sup>\/s. If the 6% error is applied to the stream gauging measurements the upstream measurement could be as high as 31.8 m3<\/sup>\/s and the downstream measurement as low as 26.3 m3<\/sup>\/s. That means that for a measurable difference in streamflow to be observed the value obtained would have to exceed the difference of the discharges with the 6% error applied (31.8 m3<\/sup>\/s -26.3 m3<\/sup>\/s = 5.5 m3<\/sup>\/s). Unfortunately, the error ranges of inflow and outflow measurements did not allow differentiation of gain or loss when a difference of 2 m3<\/sup>\/s was observed. Depending on site conditions, increasing the distance separating the measurements may resolve the issue if sufficient additional streamflow gains\/losses occur. Roberts and Warren (1999) noted that additional errors are introduced if flow conditions are changing during the period of measurement.<\/p>\n

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