Publication Summary

The Department of Ecology conducted water quality monitoring and modeling for the Wenatchee River Basin in 2002-2004. This report summarizes the data quality assurance and findings of that study.

Reserve load capacities for biochemical oxygen demand and nutrients are recommended for the upper Wenatchee River and upper Icicle Creek to maintain water quality standards during critical conditions.

Loading sources and assimilative capacities for inorganic phosphorus were determined for the lower Wenatchee River and lower Icicle Creek. Large reductions in phosphorus loading are needed to meet the assimilative capacities of the lower Wenatchee River and Icicle Creek during critical conditions.

As part of the Wenatchee River Total Maximum Daily Load (TMDL) study, the Washington State Department of Ecology conducted a water quality monitoring and modeling study during 2002-2004. This document summarizes the quality assurance of the data, and reports findings of the monitoring and modeling.

Dissolved oxygen concentrations in the upper Wenatchee River and Icicle Creek (Class AA reaches) are likely to be lower than the 9.5 mg/L criterion during the summer due to the high land elevations and high water temperature. Implementation of the Wenatchee River temperature TMDL will improve dissolved oxygen in the tributaries. Reserve load capacities for biochemical oxygen demand (BOD) and nutrients to maintain water quality standards are recommended for the Class AA reaches of the Wenatchee River and Icicle Creek.

Observed data and model simulations showed that dissolved oxygen and pH exceedances in the lower Wenatchee River and Icicle Creek (Class A reaches) were caused by periphyton (attached algae) growth. Phosphorus is the most limiting nutrient that controls periphyton growth and biomass. Loading sources and assimilative capacities for inorganic phosphorus were determined for the Wenatchee River and Icicle Creek by using the QUAL2K water quality model.

Modeling of critical conditions in the lower Wenatchee River and Icicle Creek showed assimilative capacities of 7.7 kg/day and 0.65 kg/day of inorganic phosphorus, respectively, representing 80% and 55% reductions from current loading conditions, respectively. The model also showed that assimilative capacities for the lower Wenatchee River and Icicle Creek can be represented by instream maximum inorganic phosphorus concentrations of 3.1 ug/L and 4.4 ug/L, respectively.

Link to EIM data for User Study ID WENRTMDL