Publication Summary

In 1988 Chapter 173-511 WAC established minimum instream flow requirements for the lower reach of the Nisqually River, but a gage for the river mile (RM) 4.3 control point was never established. The purpose of this study was to collect and analyze data for this location, to determine whether instream flows were being met. The study method included using a pressure transducer to collect stage data from 8/8/00 through 11/5/01, excepting some minor data gaps and one significant lapse in December of 2000. The collected data suggests that Nisqually River flows were above the established minimum flows during all but portions of six days during the entire gaged period. Based on the potential for streamflow measurement error, however, there is actually a range of days over which the data suggest that minimum flows might not have been met.

In 1988 Chapter 173-511 WAC established minimum instream flow requirements for the lower reach of the Nisqually River, but a gage for the river mile (RM) 4.3 control point was never established. The purpose of this study was to collect and analyze data for this location, to determine whether instream flows were being met. The study method included using a pressure transducer to collect stage data from 8/8/00 through 11/5/01, excepting some minor data gaps and one significant lapse in December of 2000. The collected data suggests that Nisqually River flows were above the established minimum flows during all but portions of six days during the entire gaged period. Based on the potential for streamflow measurement error, however, there is actually a range of days over which the data suggest that minimum flows might not have been met.

Combined flows at the upstream USGS 12089208 and 12089500 gages can be used as an indication of flows at the lower Nisqually River site. A regression analyses of the Ecology data versus the combined USGS data produced the equation y = 19.85x0.5792, where y equals the expected flows near RM 4.6 and x equals the combined data from the two USGS gages. Based on the historical upstream flow data and this equation, the subject minimum instream flows were met all days at RM 4.3 control point from 6/9/88 through 8/8/00. This equation failed to detect a failure to meet minimum flows during January of 2001 (suggested by the corrected Ecology data), however, thus the results produced by this equation are not entirely accurate.