Discussion

As discussed earlier and shown in table 4, the absolute difference (or error) between net water-balance mean annual volumes for the first and second 22-year periods is 103,000 acre-ft. This value can be considered the magnitude of the water-balance inconsistency. Possible reasons for the inconsistency are listed in table 2. For purposes of identifying the cause and source of the water-balance inconsistency in this study, several assumptions can be made:

Ground-water levels have not increased during the 44-year study period. It is unlikely, therefore, that ground-water inflows to the river have increased and that they could be a significant factor in the water-balance inconsistency.
The magnitude of undocumented diversion and return flows in the study reach (flows not included in the water balance) is insignificant relative to the water-balance inconsistency.
The USGS flow record for the Klamath River at Keno, Oregon (the downstream streamflow-gaging station in the water balance), has been rated “excellent” or “good” throughout its history. Error in this record is insignificant relative to the water-balance inconsistency.
The USGS flow records for the Link River and westside power canal have been rated “excellent” or “good” throughout their history. Although these records were not used in the water balance, they can be used to assess some of the error in the Reclamation-PacifiCorp record for the Link River.

On the basis of these assumptions, the probable cause of the water-balance inconsistency is error in the eight diversion and return-flow records. Part of the 103,000 acre-ft water-balance inconsistency can be explained by an 11,000 acre-ft/yr error in the westside power canal flow record for water years 1984–2004. Another part can be explained by a 32,000 acre-ft error in the river flow portion of the Link River flow record. A residual of 60,000 acre-ft of error could then be distributed among the seven other returns and diversions: the Lost River Diversion Channel Lost River Diversion Dam return, Lost River Diversion Channel Miller Hill Pumping Plant return, Klamath Straits Drain F-FF Pumping Plant return, North Canal diversion, Ady Canal diversion, Lost River Diversion Channel Station 48 diversion, and Lost River Diversion Channel Miller Hill Pumping Plant diversion. Some of the 60,000 acre-ft of error might also be in the Link River flow record; the magnitude of the Link River flow is many times greater than that of the seven other flow magnitudes. Detailed data-collection documentation that could be used to identify specific sources of error during the 44-year period in the seven flow records is unavailable. However, it is notable, or possibly coincidental, that the error bias in all seven flow records is consistent among them and with known water-management changes in the Klamath Project and National Wildlife Refuges. All diversion flows increased over time, and all return flows decreased over time.

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