Publication Summary

Between September 2000 and November 2001, Washington State Department of Ecology (Ecology) measured discharge and developed continuous stage records on Rocky Ford Creek and Rocky Coulee Wasteway, tributaries to Moses Lake. In addition, Ecology performed a synoptic flow study on Rocky Ford Creek and took a series of discharge measurements at the South Outlet of Moses Lake (USBR Site 07). Measurements at the South Outlet included both Acoustic Doppler Current Profiler (ADCP) measurements and instream measurements within the control structure.

Between September 2000 and November 2001, Washington State Department of Ecology (Ecology) measured discharge and developed continuous stage records on Rocky Ford Creek and Rocky Coulee Wasteway, tributaries to Moses Lake in Washington State. In addition, Ecology performed a synoptic flow study on Rocky Ford Creek and took a series of discharge measurements at the South Outlet of Moses Lake (USBR Site 07). Measurements at the South Outlet included both Acoustic Doppler Current Profiler (ADCP) measurements and instream measurements within the control structure.

Monitoring supported a Total Phosphorus Total Maximum Daily Load (TMDL) Study developed by Ecology. The study assessed the assimilative capacity of Moses Lake with respect to the in-lake total phosphorus (TP) criterion of 50 ug/L (Carroll, 2001). Calculation of lake inflows and outflows allowed the determination of lake TP maximum loading.

Seven to eight instream flow measurements were taken at both continuous recorder stations. Rating equations were developed by relating discharge to stage. United States Geological Survey (USGS) records were used to determine discharge from Crab Creek. Standard hydraulic equations were used to calculate discharge from the gated control structures at both the North Culvert and the South Outlet (USBR Site 07) of Moses Lake. The maximum flow of Rocky Coulee Wasteway was just above 2300 cfs, and the minimum flow was 8.5 cfs.

The maximum flow at Rocky Ford Creek was 94 cfs, and the minimum was 33 cfs. A low-flow rating and a high-flow rating, based on eight instream measurements, were developed for the Rocky Coulee Wasteway site. Based on polynomial regression analysis, both ratings produced an r2 of 0.99. The polynomial rating equation for Rocky Ford Creek, based on five instream measurements, also produced an r2 of 0.99.

The average total inflow to Moses Lake via Rocky Ford Creek, Rocky Coulee Wasteway, and Crab Creek was 452 cfs during water year 2000-2001. The outflow through the North Culvert and the South Outlet averaged 536 cfs. The estimated outflow exceeded the measured inflow by 84 cfs. This difference can be attributed to unmeasured inflow from minor streams, ground-water inflow, and errors in the calculations.