Publication Summary

This report takes a comprehensive look at water quality issues for the Henderson Inlet watershed. The study found widespread fecal coliform bacterial contamination, which threatens shellfish harvesting. Total maximum daily load allocations are established, and recommended clean-up actions are prioritized.

The study also addresses water quality impairments due to temperature, dissolved oxygen, and pH. The report quantifies the geographic and temporal extent of low dissolved oxygen levels in Henderson Inlet and recommends several actions for improvement. Temperature, dissolved oxygen, and pH problems in the streams were partially due to natural conditions but could be improved by the identified recommendations.

As part of the Henderson Inlet watershed Total Maximum Daily Load (TMDL) project, the Department of Ecology conducted a water quality monitoring and modeling study from 2002 to 2005. This report summarizes the findings.

Fecal coliform bacteria criteria were not met throughout Henderson Inlet and its six tributaries: Woodland, Woodard, Meyer, Sleepy, Dobbs, and Goose creeks. The critical period for most areas was during winter storm events, but some areas such as Woodland Creek and lower Henderson Inlet had high bacteria levels during the dry season as well. Fecal coliform bacteria reductions are recommended for all sites. Areas for bacteria clean up are prioritized based on bacterial loading and concentrations.

The Woodland Creek temperature TMDL includes the lower portion of Woodland Creek which meets temperature standards. Originally the temperature TMDL included the upper portion of Woodland Creek. However, more analysis is required to determine a background/natural temperature condition for the upper portion of Woodland Creek.

Henderson Inlet shows evidence of low dissolved oxygen levels, but this report does not set load or wasteload allocations. This study quantifies the geographic and temporal extent of low levels of dissolved oxygen and recommends several actions to improve water quality.

Woodland, Woodard, Sleepy, and Dobbs creeks did not meet the dissolved oxygen criterion of 9.5 mg/L. Natural conditions are largely the cause in these four creeks. Woodland Creek dissolved oxygen levels start out low at Beatty Springs but should meet the dissolved oxygen criterion at river mile 1.6. Model simulations showed that nutrient reduction had little or no effect on dissolved oxygen levels. Increased shading and lowering biochemical oxygen demand to the creek would slightly improve dissolved oxygen levels. Woodard Creek dissolved oxygen levels are low at the headwater and increase downstream. A target dissolved oxygen level of 9.0 mg/L should be met at river mile 2.9.

For all six creeks sampled, pH levels fell slightly below the standard. This was due to natural conditions.

Link to EIM data for User Study ID DSAR2