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Comparison of the power consumption coefficient (PCC) method to totalizing flow meter (TFM) for estimating ground-water pumpage in the Arkansas River Valley, Colorado

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Comparison of the power consumption coefficient (PCC) method to totalizing flow meter (TFM) for estimating ground-water pumpage in the Arkansas River Valley, Colorado

Study Area: Arkansas River Valley
Period of Project: October 1996-September 2003
Project Number: CO316
Project Chief: Russell G. Dash
Cooperator: Colorado Department of Natural Resources, Division of Water Resources, Office of State Engineer

BACKGROUND:

The Colorado State Engineer (CDWR) has adopted rules governing the measurement of tributary ground-water withdrawals in the Arkansas River Valley. The rules are designed to provide information to properly administer water rights in the basin and to comply with the U.S. Supreme Court in the case of Kansas v. Colorado (Case No. 105-Original). The rules require the owners of wells to provide the total monthly pumpage for their wells, using information from either a totalizing flow meter (TFM) or using a power-consumption coefficient (PCC) and site energy records. Since 1994 when State rules became effective in the basin, most well owners have chosen to use the PCC method to determine their pumpage. Opinions by representatives of the State of Kansas stated that the PCC method was not acceptable to determine ground-water pumpage unless studies were performed to determine the comparability of estimates made using a PCC to estimates made by a TFM. In 1996, the U.S. Geological Survey (USGS), in cooperation with the CDWR, began a study to evaluate the comparability of pumpage using the PCC and the TFM methods.

During 1997-98, the USGS completed Phase I and published a report in 1999 that compared discharge and pumpage estimates by the TFM method to discharge and pumpage estimates using the PCC method at a network of more than 100 sites. However, there was insufficient data to adequately address potential errors associated with year-to-year variability in the PCC's or the reliability of using a PCC over multiple years to estimate pumpage. Additionally, because the Phase I study collected TFM data for only about 1-year it limited any observations of long-term variations in the permanently installed TFM's. In 1999, USGS continued the method evaluations with a Phase II study.

OBJECTIVES:

1. To evaluate long-term differences between the TFM and PCC methods for determining ground-water pumpage. This evaluation involves determining whether pumpage using the PCC method, as applied by the State of Colorado, is statistically different from pumpage determined using the TFM's over multiple seasons, and if annual differences in pumpage remain comparable.
2. To evaluate the long-term stability of the inline TFM's. This involves determining whether discharge measured by an inline TFM exhibits any significant variability over a 4-year period, and if so, to determine if there is a pattern to discharge change since the 1997-98 measurements.
3. To determine whether short-term variations in PCC's are different than long-term variations. This involves determining whether the PCC's measured at about 25 wells in the network change significantly during an irrigation season (short term), or over a period of multiple seasons (long term), and if so, determine if there is a pattern or relation to other variables, which could be used to correct for drift in the PCC method.