Springbrook Creek Site 0317

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King County Water Quality Monitoring

King County monitors the ecological health of Springbrook Creek in a variety of ways including collecting and analyzing water, sediment, and benthic invertebrate samples. Water quality samples have been collected from Springbrook Creek since 1977. Station 0317 is located near the mouth of the creek at the bridge. Beginning in 1987, sediment quality samples have been collected from Springbrook Creek. In 2002 King County began a benthic invertebrate monitoring program that included sampling in Springbrook Creek.

From time to time special studies have been conducted at various streams in King County. (Click here for information about Special Studies of Springbrook Creek.)

Springbrook Creek Watershed

The Springbrook Creek watershed is located in South King County in Water Resource Inventory 9 (WRIA 9) in and around the cities of Kent and Renton. The mainstem of the creek flows for 12.0 miles, with an additional 19.1 miles of tributaries. Springbrook Creek becomes the Black River at a point 0.65 miles upstream of the Green River. The Creek, via the Black River, enters the Lower Green River at River Mile (RM) 11.0 (Kerwin and Nelson 2000; Herrera 2005).

Historically, the Black River drained Lake Washington, combining with the Cedar River and Springbrook Creek before it’s confluence with the Green River to become the Duwamish River. Since the construction of the Lake Washington Ship Canal in 1916, the Black River receives very little drainage besides flows from Springbrook Creek (Kerwin and Nelson 2000, Herrera 2005).

The Springbrook basin drains an area of 15,763 acres and has two distinct physical settings. The eastern half of the basin has steep rolling hills rising to elevations about 525 feet above the valley floor. The western half of the basin is virtually flat. Panther Lake and some smaller ponds and wetlands are located in the eastern half. Panther Creek and Mill Creek (not to be confused with Mill-Hill Creek also in WRIA 9) are the major tributaries to Springbrook Creek. Panther Creek drains Panther Lake and enters into Springbrook Creek at RM1.3. Mill Creek is located entirely in the Green River valley and enters Springbrook Creek at RM 3.8 (Kerwin and Nelson 2000, Herrera 2005).

Land use in the Springbrook Creek basin consists of low to high-density development (Herrera 2005).

For more information about the Springbrook Creek watershed, visit the WRIA 9 website for the Lower Green River Subwatershed.

Fisheries

Coho salmon, cutthroat trout, and winter steelhead adults have been observed spawning in Springbrook Creek and it’s tributaries (Kerwin and Nelson, 2000). Resident and anadromous cutthroat have been observed throughout the basin. As summarized in the 2000 WRIA 9 Habitat Limiting Factors and Reconnaissance Assessment Report, there was roughly 17.9 miles of potential fish habitat within the Springbrook basin with 17.2 miles of this accessible to anadromous salmonids.

The Lower Green River Baseline Habitat Survey Report provides more detailed information about habitat conditions in the Springbrook Creek area.

Water Quality

Water quality samples are analyzed monthly for temperature, dissolved oxygen, pH, conductivity, turbidity, total suspended solids, ortho-phosphorus, total phosphorus, ammonia, nitrate-nitrogen, total nitrogen, and fecal coliform bacteria. Results are compared to state water quality standards. Water quality standards are designed to protect public health and aquatic life. Comparing monitoring results to water quality standards allows an understanding of how safe the creek is for recreational contact as well as for aquatic life.

State water quality standards were revised in 2003. Springbrook Creek was considered a “Class A” water body under the 1997 rules and is categorized as “Spawning Rearing and Migration Habitat” for aquatic life use and “Primary Contact” for recreational use under the 2003 rules. The creek is on the 2004 Washington Department of Ecology’s (Ecology) 303(d) list for violation of dissolved oxygen and fecal coliform bacteria standards.

Water quality conditions in Springbrook Creek have historically been characterized as poor (Metro 1989) with low dissolved oxygen concentrations, high temperatures, high fecal coliform bacteria, high turbidity, high total phosphorus and ammonia, and high conductivity. Current water quality charts illustrate similar water quality conditions. (Click here to view the current water quality charts). See Table 1 for a summary of water quality violations in the creek during the most recent water year.

A water quality data assessment conducted for the Green-Duwamish River in 2003 found that when evaluating most water quality parameters, conditions at Springbrook Creek (A317) were poor relative to the Soos Creek and Newaukum Creek stations (Herrera 2005). Total iron concentrations exceeded the Washington State chronic criterion in one baseflow sample. The herbicide 2,4-D was detected in two baseflow samples, while polycyclic aromatic hydrocarbons were detected infrequently at Springbrook Creek.

Long-term Trends

A 28-year (1979 - 2007) trend analysis was conducted with baseflow water quality data collected from Springbrook Creek. This analysis shows that there has been changes in water quality during that 28 year time period that indicate some decline in water quality. Total nitrogen concentrations have increased and and dissolved oxygen concentrations have decreased significantly. The pH values showed that the creek has become significantly more acidic though values are still within acceptable range of 6.5 to 8.5. Some improvements in water quality in Springbrook Creek were also observed in the 28-year trend analysis. Total suspended solids, turbidity, ortho-phosphorus, total phosphorus, ammonia, nitrate and fecal coliform bacteria have all decreased significantly.

Water Quality Index

A Water Quality Index (WQI) rating system was developed by the State Department of Ecology that evaluates several water quality parameters and gives a single rating of “high,” “moderate,” or “low” water quality concern. Springbrook Creek has consistently had a WQI rating of “high concern” due primarily to low dissolved oxygen concentrations and high nutrients during the summer months. To see how Springbrook Creek ratings compare with other stream sites, visit: the Water Quality Index page.

For more information about long-term trends, the Water Quality Index, or to view charts of current water quality conditions in the creek, please visit the links at the top of the page.

A review of the 2008 data shows the following violations of State water quality standards:

 

Stream Sediment

Sediment data were collected from Springbrook Creek as part of the Streams Sediment Monitoring Program starting in 1987. Data were compiled and analyzed for the years 1987 through 2002. Data were analyzed for trends, correlations, and were compared to sediment quality guidelines. No significant trends were identified during data analysis for any of the parameters tested. Results indicate that Springbrook Creek sediment exceeded two sediment quality guidelines (cadmium and zinc). However, of the 27 streams monitored in King County, Springbrook Creek was about in the middle with the 9th lowest metals concentration.

Benthic Invertebrates

The county monitors stream health by collecting samples of benthic invertebrates from selected streams as part of King County’s Benthic Invertebrate Program. Benthic invertebrates are an important link in the food chain for fish in the creek and are an excellent indicator of stream health.

In 2002, 2003, and 2006, benthic invertebrate samples were collected, analyzed, and benthic invertebrate index scores (BIBI) were calculated for Springbrook Creek. One sample was collected each year from the creek. Results indicate that conditions for benthic invertebrates in Springbrook Creek were very poor. The samples were dominated by species that are tolerant to degraded conditions. Also, very few individuals that are long lived or are sensitive to degraded conditions were present. Longer-lived species tend to take longer to reproduce and along with sensitive species are among the first to disappear when a stream ecosystem is altered by human activity such as urbanization.

Special Studies

Green-Duwamish Water Quality Assessment

In 2001 King County initiated a separate comprehensive study of the Green-Duwamish Watershed, called the Green-Duwamish Watershed Water Quality Assessment (GDWQA). Several reports evaluate data collected as part of the GDWQA. Springbrook Creek is included in this analysis.