Loading...
Please wait, while we are loading the content...
Similar Documents
Variability of differences between two approaches for determining ground-water discharge and pumpage, including effects of time trends, Lower Arkansas River Basin, southeastern Colorado, 1998-2002
| Content Provider | Semantic Scholar |
|---|---|
| Author | Troutman, Brent M. Edelmann, Patrick Dash, Russell G. |
| Copyright Year | 2005 |
| Abstract | 3 100 wells and a lag of 4 years between PCC measurement and pumpage estimation, the mean difference was 9.8 percent of total network pumpage and the standard deviation was 2.3 percent of total network pumpage. Under the assumption of normality, there was a 95-percent probability that the difference between total network pumpage measured by the PCC approach and that measured using a TFM would be between 5.2 and 14.4 percent. These estimates were based on a bias of 2.2 percent per lag year estimated for the period 1998–2002 during which hydrologic conditions were known to have changed. Using the same assumptions, the estimated difference in total network pumpage for a 4-year lag for 1,000 wells would be between about 8.4 and 11.3 percent greater than pumpage measured using a TFM; the estimated difference in total network pumpage for a 3-year lag would be between about 6.1 and 8.8 percent greater than pumpage measured using a TFM; and the estimated difference in total network pumpage for a 2-year lag would be between about 3.9 and 6.4 percent greater than pumpage measured using a TFM. Discharge measured with a TFM was compared with discharge measured by portable flowmeter using the dependent variable diffQ. The overall mean of diffQ using all three portable flowmeter methods was –0.015, or about 1.5 percent less than TFM measurements. Three types of portable flowmeter were used: a pitot tube/manometer device (method C), an ultrasonic flowmeter (method P), and a propeller-type meter (method M). Statistical modeling of diffQ revealed that there were significant differences among portable flowmeter methods. Portable flowmeter method P tended to be about 1.9 percent below average of all three methods, meaning that flowmeter method P tended to measure a smaller discharge than the TFM as compared to other portable sampling methods. Discharge measured using method C was about 1.7 percent above average as compared to other portable sampling methods, and method M was about average. The median diffQ value for methods C, M, and P was 0.5 percent, –0.6 percent, and –4 percent, respectively. Overall, portable flowmeter discharge measurements made with method C provided the smallest differences in diffQ. Portable flowmeter discharge measurements made with method P provided the largest differences in diffQ and indicated a fairly strong negative bias, or a tendency to underestimate discharge with respect to TFMs. The variable diffQ indicated no observable persistent temporal trends when all sites were combined; however, individual sites often exhibited upward or downward temporal trends that were modeled with random time slopes. Pumping water level accounted for only a negligible amount of the variance of diffQ, indicating that pumping water level had very little influence on differences in discharge. Overall, the quality of discharge measurements associated with TFMs did not degrade over time (1998–2002); however, problems did occur with some TFMs. CDWR staff documented 27 problems with TFMs during 1998–2002. Equipment problems, including debris clogs and reasons unknown, occasionally resulted in loss of TFM data. Debris clogs in the meter components generally were observed early in the irrigation season during startup operations. |
| File Format | PDF HTM / HTML |
| DOI | 10.3133/sir20055063 |
| Alternate Webpage(s) | https://pubs.usgs.gov/sir/2005/5063/pdf/5063_508.pdf |
| Alternate Webpage(s) | https://doi.org/10.3133/sir20055063 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
