Stormwater Temperature Monitoring in Federal Way, WA

From 2002 to 2005, the City of Federal Way, WA, Surface Water Management embarked on a stream temperature study within the West Hylebos Creek drainage basin, an important salmon-bearing stream located in a high-density Puget Sound metropolitan area. The study was conducted to generate meaningful information that may be used to help protect the health and integrity of our aquatic ecosystems and the organisms—specifically, endangered salmon—that once thrived in Federal Way waters.

Cool surface-water temperatures are a fundamental characteristic of Pacific Northwest aquatic habitats—complex ecosystems that include populations of fish, amphibians, insects, zooplankton, and phytoplankton. Stream temperatures are critical because they influence fish in many ways, especially cold-water salmonid species and trout. Heat is considered a pollutant under Section 502(6) of the Clean Water Act.

Human activities and the urbanization of land such as that in Federal Way have been associated with increased stream temperatures. Expanding impervious areas (e.g., roads, driveways, parking lots, and rooftops) within the city due to watershed development have directly impacted the West Hylebos Creek drainage basin. This has resulted in more frequent flooding, higher peak-flow volumes, increased sediment loadings, loss of aquatic/riparian habitat, changes in stream physical characteristics (channel width and depth), and decreased base flows—all leading to elevated stream temperatures (Schueler 1987).

The generated data may become useful if Hylebos Creek fails to meet water-quality standards for temperature and is placed on the state’s list of impaired water bodies—the Clean Water Act Section 303(d) list. Placement on this list would require the city to implement total maximum daily loads to meet water-quality temperature standards.

The City of Federal Way faces many challenging hurdles with the temperature issue. “When I gaze into my crystal ball and try to foresee impending issues for the utility, elevated stream temperatures give me great concern,” says Paul Bucich, the city’s surface-water manager. “The causes are truly nonpoint, making the solutions for our watersheds difficult and widespread.”

Although not yet mandated to conduct such a study, the city concluded that the collection of comprehensive stream temperature information would be consistent with one of the goals outlined in its Surface Water Management Plan: “to protect, preserve, and enhance the beneficial uses of surface water for recreation, fish and wildlife habitat, aesthetic enjoyment, aquifer recharge, and open space,” as well as to provide a protective stance on dealing with potential temperature issues.

The objectives of the study include:

1. Establish whether West Hylebos Creek water temperatures from 2002 to 2005 meet Washington state aquatic life use criteria and salmonid thermal requirements.
2. Determine if there are annual differences for each monitoring station, and differences in water temperature between monitoring stations (upstream-downstream), that are statistically significant during the monitoring period.
3. Identify general patterns between collected stream temperature data and watershed factors, and/or human activities, influencing temperature.
4. Describe the management practices and measures or control technologies that may be used to reverse any warming trends in the basin, watershed, or stream segments.

The Study Area
Federal Way, population 85,800, is located in the southwestern corner of King County on a plateau between Puget Sound and the Green River Valley, 25 miles south of downtown Seattle. The West Hylebos Creek system in the city is composed of 4,300 acres of drainage area, over 9.45 miles of stream corridor, two natural lakes, four manmade lakes, two major wetlands, and various unnamed ponds. Figure 1 illustrates the surface-water resources of Federal Way, and Figure 2 illustrates the West Hylebos Creek drainage basin and monitoring site locations.

The majority of the most highly intensive commercial uses are located in the mid- to upper basin, a largely developed portion of the city with more than 90% impervious surface coverage. This area includes highways, parking lots, and buildings that generate large volumes of stormwater and urban pollutants. Because of high storm flows, high nonpoint-source pollutant concentrations, and low summer base flows, aquatic habitat is limited or nonexistent in the northern half of the Hylebos Creek sub-basin.

By contrast, mid- to lower reaches of both the West Branch Hylebos Creek and North Fork Hylebos Creek systems sit in low-density residential and other low-intensity uses such as agriculture, forest, or grassland. Because their uses generate less stormwater per acre, these less-developed drainage areas help buffer the watershed against stormwater impacts.

At the 100-year return interval, the stream flow rate at South 373rd Street at the lower end of the basin in the city (which includes flow from both the West Branch and the North Fork) is predicted by hydrologic computer modeling to be approximately 443 cubic feet per second (CH2MHill 2003). Because of urbanization in and around Federal Way, infiltration of rain into subsurface systems has decreased, but groundwater continues to be the major source of stream flow during summer months (King County 1990). Two major groundwater sources located in the lower stream reaches—West Hylebos Wetlands (93 acres) and Spring Valley (95 acres)—help preserve what is left of the area’s shrinking salmon habitat and spawning grounds.

The Way Things Used to Be
Less than 30 years ago, West Hylebos Creek was one of the most productive small salmon streams in the central Puget Sound region, hosting annual runs of thousands of coho and chum salmon and hundreds of chinook salmon and cutthroat trout (FOHW 2006). By comparison, habitat within present-day Hylebos Creek is less productive for fish and wildlife.

Ted Enticknap, a lifelong Puget Sound resident, moved to Spring Valley in 1967. Local raconteur and diligent historian of local weather and flooding events, he fondly remembers walks on his property to the banks of the North Fork Hylebos Creek to witness salmon completing their final journey up the stream.

Figure 1. Surface Water Resources of Federal Way

The year-round cool groundwater seeping into the creek from the Spring Valley wetlands provided an excellent location for spawning. “Back in the good old days, I’d just stand there at one spot and watch them come through in pairs every five minutes,” Enticknap remarks as he recalls the large salmon runs four decades ago. “It’s a strange facet of nature. They’d fight like heck to protect their nest to see that another generation would live,” he says, “and then later, when the fish died after the eggs were fertilized, the whole valley would stink with rotting carcasses.”

Due to their dwindling numbers, chinook salmon (Oncorhynchus tshawytscha) were listed as threatened under the Federal Endangered Species Act in 1999, and coho (Oncorhynchus kisutch) are a candidate species for possible inclusion in the List of Endangered and Threatened Species.

Currently, salmonid populations (a mix of native and stocked species) are small because of the basin-wide influences of urbanization. Local volunteers at stationary observation stations throughout the West Hylebos Creek system have provided estimate numbers of returning salmon between 2002 and 2005. The group has documented an average of 10 chinook and 80 coho counted over this six-year period (FOHW 2006).

Reasons for Increased Stream Temperatures
Long ago, changes in a watershed’s land use were understood to affect salmon populations. European rivers were once full of Atlantic salmon, but within the hundred-year span between 1700 and 1800, stocks were depleted to levels that sparked restoration efforts. Concurrently, salmon populations were declining in the New World. In little over two centuries after colonization, New England’s salmon were commercially extinct (Montgomery 2003).

Harmful effects of human actions—impacts of the timber industry, agricultural-related soil erosion, and alterations in the watershed—were all cited as reasons for over half of the original salmon habitat along the Eastern Seaboard being destroyed by 1850. Increased stream temperatures were documented as one of the many negative impacts to which these natural stream systems and salmon populations were subjected (Marsh 1864).

Figure 2. Temperature Monitoring Sites, West Hylebos Creek Drainage Basin

The unfortunate events that led to the devastation of Atlantic salmon in Europe and New England are relevant to the current situation facing the Pacific Northwest. With a distinct sense of déjà vu, the landscape of Puget Sound has changed dramatically in the last century. By the late 1980s, almost half of the previously forested watershed in Federal Way had been developed (APWA 1998).

There have been many specific studies examining the fate and transport of heat in natural waters due to lost aquatic habitat. The following list includes the most common environmental variables that drive water temperature in streams (Bilhimer, Sullivan, and Brock 2005).

• Air temperature above the stream surface is the greatest factor in increasing water temperature (Bartholow 1989).
• Solar radiation—radiant energy that passes directly from the sun to the earth—is a major thermal input to an unshaded body of water during the day when the sky is clear.
• Stormwater flows raise receiving water temperatures due to the transfer of heat that impervious surfaces (pavement, asphalt, and roofs) absorb from solar radiation.
• Riparian vegetation in sufficient density and height near a stream all combine to produce shading that reduces the transfer of solar heat to the surface of the water.
• Expanding watershed development increases winter flow volumes and runoff velocities, scouring and widening downstream channels. Lower depths and lower summertime flows—caused in part by streambank erosion, sediment loading, and widening—allow streams to be more quickly influenced by higher ambient air temperatures and solar heating.
• Stormwater retention/detention facilities, lakes, and ponds are affected by ambient air temperatures and solar heating. Temperature effects on these slower-moving bodies of water are profound. Impacts are seen when heated water is discharged to other water bodies such as streams.
• Groundwater has an important cooling effect on stream temperature (depending on the rate of inflow relative to the flow in the stream and the temperature differences between the two).

Impacts of Increased Stream Temperatures
Water temperature is an important factor influencing the health and survival of all aquatic organisms, including native fish and amphibians. Temperature controls metabolic rates and reproductive activities and determines which species can survive.

Chinook salmon spotted in West Branch Hylebos Creek

Temperature effects on salmon are lethal at levels above 21.1 degrees Celsius (°C) or 70 degrees Fahrenheit (°F). But water-quality standards are based on the sub-lethal effects of elevated temperatures–effects that reduce the ability of the fish to successfully reproduce and limit survivability and growth of offspring (Boyd and Sturdevant 1997). When these sub-lethal levels are reached, the following effects on salmon become evident:

• Warmer temperatures lower dissolved oxygen content by decreasing the solubility of oxygen in water, thereby decreasing the supply of oxygen available to aquatic organisms. This impacts both salmon and its food supply.
• Warm water can cause the fish’s need for dissolved oxygen to increase. This effect disrupts its metabolism, and can affect adult migration and spawning.
• Temperature can influence embryonic development, reducing the survival rate of eggs and the growth of juveniles.
• Higher temperatures influence the activity of toxic chemicals, bacteria, and parasites in water. This stresses the organism, increasing the incidence of fungal infections and disease.

Water-Quality Standards
West Hylebos Creek is considered a Class A (excellent) surface water in the state of Washington pursuant to Chapter 173-201A Washington Administrative Code (WAC). The 1997 water-quality standard (currently in effect) for Class A surface water limits temperature to a maximum of 18.0 degrees C (64.4 degrees F) due to human activities.

In 2003, the Washington Department of Ecology (DOE) completed the first major overhaul of Washington’s water-quality standards in a decade. As a result, temperature criteria were developed to protect salmon and trout spawning, non-core rearing, and migration of endangered coldwater species.

The EPA has only partially approved the revised DOE standards, which change from a daily maximum to a seven-day average of daily maximum temperatures (7-DADMax). The 7-DADMax is the arithmetic average of seven consecutive daily maximum temperature measurements and is calculated by averaging a day’s daily maximum temperature with the daily maximum temperatures of the three days prior to and the three days after that date. The proposed 7-DADMax temperature standard for Hylebos Creek is defined as 17.5°C (63.5°F).

Data-Collection Methods
A continuous temperature monitoring protocol was established that utilized optical TidbiT StowAway Loggers and YSI 6-series multi-parameter sondes. All temperature thermistors were programmed to record measurements at 30-minute sample intervals.

The monitoring instruments were positioned at 12 in situ stream or storm drainage structure monitoring sites (Figure 2). The locations were selected to maximize ease of access and to minimize the potential for vandalism. Where possible, placement was made within the main channel of stream flow to avoid measurement bias from the warmer stream edges and from thermal stratification.

The maintenance frequency was governed by both hydrologic environment and other factors that subject field instruments to fouling, corrosion, submersion in sediment, battery failure, or physical disruption. The data were manually downloaded during regular site visits (approximately every 30 days) and uploaded to a PC, where they were further managed to remove outliers, abnormalities, and deviations.

Quality Control Procedures
The goal of the quality control program was to generate consistent, representative, and comparable temperature data that the City of Federal Way could use to evaluate the effectiveness of habitat restoration efforts and surface-water quality in the project stream over the long term. In some cases, the data were lost from the logger in the field for various reasons (damage, theft, battery failure, or repair). In these instances, gaps were filled with representative data obtained from the secondary YSI temperature probes (if installed at the site).

The first quality control exercise undertaken to ensure the generation of reliable temperature data included side-by-side analyses of data recorded at the same location by both the optic TidbiT logger and YSI thermistors. By comparing recorded sets of data to a given tolerance range, the quality control tests confirmed that the field-deployed temperature instruments were producing quality measurements within specified tolerance limits, and that YSI thermistor data could be substituted to fill optic TidbiT logger gaps where necessary to ensure an uninterrupted span of continuous readings.

The second quality control test involved immersing the TidbiT loggers into a controlled ice bath to verify whether they were recording within their specified limits. As the loggers acclimate (approximately 120 minutes), the temperature of the ice bath will settle to around 0°C. All TidbiT loggers passed the quality control procedure as the readings did not deflect from the specified 0°C ± 0.23°C accuracy range (Onset 2006).

Data Analysis
Temperature data were analyzed in a variety of ways to determine

• whether there was a year-to-year trend (increasing or decreasing temperature) at each monitoring site;
• upstream-to-downstream trends (increasing or decreasing temperature) between each monitoring site; and
• if water-quality standards were exceeded at individual monitoring stations, including impacts to salmon health and survival.

Temperature Trends Over Time
The objective of the temperature-trend analysis for West Hylebos Creek in Federal Way was to determine if there is an increasing or decreasing trend over time for the daily maximum temperature at each of the sampling locations. The Seasonal Kendall Tau test was used to determine the type of trend (Kaslik 2006).

Several sites do not experience flow during the summer. In addition, some locations have missing data because of equipment failure or downloading transfer problems. For these reasons, the trends analysis portion of this study is not entirely conclusive–but strong inferences may be made.

To ensure independence, water-quality data were selected that were one month apart. For each stream-sampling station, one date per month was randomly selected that was shared by all locations. The maximum temperature from the selected date was used for the trends analysis.

For a trend to be significant, the p-value for the Seasonal Kendall Tau test statistic must be less than 0.05 and the 12 monthly Kendall tests must be homogeneous with a common trend. If the Seasonal Kendall Tau test statistic is significant, the magnitude of the trend is given by the Kendall Slope. A negative slope corresponds to a decreasing temperature (), and a positive slope corresponds to an increasing temperature (). A trend that is neither increasing nor decreasing is called a stationary trend (Ø).

The only significant trend was found at the SeaTac Inlet location, a water-quality treatment and storage facility located on property at the Commons Mall. Here, the median of all annual changes in temperature showed an increase of 0.513°C per year over the four-year period. All other locations showed a stationary trend (neither increasing nor decreasing) (Table 1).

A review of the city’s geographical information system (GIS) database reveals that the amount of increase in impervious area tributary to the SeaTac Inlet was negligible during the study period. Due to this finding, stormwater flows from these impervious areas cannot be identified as causing an increasing temperature trend over time.

Changing weather patterns were also considered. The average annual ambient air temperatures during the study period indicate a slight upward track during the same time frame. Although it is likely that seasonal weather patterns are the primary influence, further analysis would be required to determine whether the ambient temperature trend was significant enough to increase stormwater temperature at this location (NOAA 2006).

Temperature Variations Between Stations
An approach for determining the temperature changes between stations was used with a station-to-station comparison for days on which data are available at both stations. This analysis shows the change from the upstream station to the downstream station. A negative number means the temperature decreased, and a positive number means the temperature increased.

This analysis is important in illustrating how surface-water temperatures increase and decrease as the water is being exposed to different land uses and features while being transported through the drainage system. A monthly and yearly summary for all the available data is shown in Tables 2 and 3.

When examining the data for temperature variations between stations, it is important to note that some locations (SeaTac, Belmor, 336th, Kitts, and 356th) reflect seasonal drainage patterns (there is generally no flow during summer). For this reason, sufficient data were not available to generate monthly and yearly summaries for these locations that included the summer period (July, August, September).

The following trends are noteworthy:

• West Branch—Flow from Kitts Outlet drains through West Hylebos Wetlands Park before it reaches the Brooklake station. Due to the mitigating effects of wetlands and groundwater inflows, the trend shows an average decrease of 1.86°C over the sampling period, dropping considerably during the critical summer months (Figure 3).
  
  

  Figure 3. Difference in Daily Maximum Temperatures Between Hylebos Stations Kitts Outlet to Brooklake, 2002-2005

  
  
• West Branch—Flow from Brooklake drains through the stream segment from South 356th to SR99 at Montessori that contains very little development. Excellent riparian cover and groundwater inflow contributes to the average stream cooling effect during the year of 0.835°C (Figure 4).
  
  

  Figure 4. Difference in Daily Maximum Temperatures Between Hylebos Stations Brooklake to Montessori, 2002-2005

  
  
• West Branch—From Montessori, stream temperatures are heavily impacted by the lack of riparian vegetation that limits shading and allows more sunlight to reach the stream as it flows to 373rd. This stream segment shows a warming of 0.650°C over the period, peaking during summer (Figure 5).
  
  

  Figure 5. Difference in Daily Maximum Temperatures Between Hylebos Stations Montessori - 373rd, 2002-2005

  
  
• North Fork—There is a downward trend of 0.490°C over the monitoring period between 356th Outlet to 359th due to the flow through a stream segment with good riparian cover and groundwater inflows (Figure 6).
  
  

  Figure 6. Difference in Daily Maximum Temperatures Between Hylebos Stations 356th Outlet to 359th, 2002-2005

  
  
• North Fork—From 359th, stream temperatures rise before reaching 373rd. This stream segment shows a warming of 0.690°C over the period (Figure 7). It is evident that a lack of riparian vegetation allows a substantial amount of sunlight to reach the creek (downstream of the confluence between the North Fork and the West Branch), causing larger impacts to stream temperatures in summer. It is possible that additional contributions to stream heating originate from North Fork sources, but these will not become known until more monitoring points are established.
  
  

  Figure 7. Difference in Daily Maximum Temperatures Between Hylebos Stations 359th -373rd, 2002-2005

  
  

Exceedances Above Temperature Standards
Each downstream monitoring site where salmon habitat is present (Brooklake, Montessori, 373rd, 359th) was closely examined for exceedances above both the existing state water-quality temperature standards and the proposed standards developed to protect salmonids. The data generated in this study were examined comparatively with both chinook and coho patterns of use and their critical life stages (spawning, migration, rearing) in West Hylebos Creek. By analyzing both weather data and flow data against stream temperature data, strong correlations can be made that point to two distinct phenomena: (1) elevated ambient air temperatures combined with solar heating, and (2) warm stormwater runoff following rain events.

On five different periods during the duration of the study, stream temperatures exceeded the DOE standards due to elevated ambient air temperatures and solar heating during the spring and summer (Table 4).

Table 5 illustrates that on four different periods during the duration of the study, stream temperatures exceeded the DOE standards due to warm stormwater runoff experienced after rain events in the summer.

Impacts Due to Solar Heating and Hot Ambient Air
West Hylebos Creek at the Brooklake station exceeded state water-quality standards a total of six times during the study period (2002 to 2005) due to the effects of solar heating during hot and sunny summertime weather patterns. The primary heat source points to Brooklake, a 0.71-acre lake at the most downstream point in the West Hylebos Wetlands Park. Heated surface-water discharges from this water body during periods of warm weather caused temperature exceedances. Although the creek system upstream of Brooklake undergoes an average decrease of 1.86°C as it flows through West Hylebos Wetlands Park, summertime exceedances caused by solar heating effects in Brooklake offset the dramatic cooling effect of wetland-created groundwater seeping into the stream.

The same weather patterns have also created temperature problems at the 373rd station, where solar and ambient air heating of slow-moving surface water downstream of SR99 contributed to several exceedances during the study period. This section of stream is dramatically void of riparian cover and susceptible to warming. Additionally, several upstream private ponds (both on the West Branch and North Fork) may be contributing warm-water discharges in the summer to the creek system.

Even though the West Branch further upstream of this station undergoes an average decrease of 0.835°C as it flows through West Hylebos Creek from the Brooklake station to the Montessori station, the drop in temperature is not sufficient to cancel the summertime heating due to elevated ambient air temperatures and solar heating experienced along the exposed stream channel at 373rd.

Impacts Due to Warm Stormwater Runoff
Significant rain events occurring in summer generated heated stormwater that caused exceedances at the Brooklake station on four occasions during the study period. Warm stormwater flows transferring heat from heavily commercialized impervious surfaces in the upstream drainage basin eclipsed the beneficial effects of cooler groundwater flows entering the creek system in Hylebos Wetlands Park.

Hylebos Salmon Pattern of Use and Elevated Temperatures
The two critical salmonid species inhabiting Hylebos Creek, chinook and coho, have evolved to take advantage of the Pacific Northwest’s cold-water environment in different ways. The temperature study shows that the unique pattern of stream usage and the life history strategies of these two species may be impacted by elevated stream temperatures.

Adult fall chinook swim upstream into the West Branch Hylebos Creek to reaches north of the Montessori station, holding and spawning in the fall (October through December). Fry emerge from March through April and begin their downstream migration several weeks after emergence. Juveniles may rear in the stream from two months to a year.

Hollie Shillie, water-quality technician with Federal Way, retrieving temperature data, West Hylebos Creek

Adult coho salmon generally enter West Hylebos Creek in the fall and spawn in fall and winter (September through January) throughout the West Branch (up to Brooklake) and North Fork (up to South 364th). Fry emerge in the spring, and juveniles will rear for one to two years prior to migrating to sea during the spring.

Only one short three-hour duration of elevated stream temperature occurred during coho spawning and egg incubation (September 11, 2004) at the Brooklake station. This exceedance was a result of warm stormwater flow during a large rain event. Reduced egg viability is not likely due to the short duration of the exceedance.

The study identified a number of temperature exceedances in both the West Branch and the North Fork that may impact both coho and chinook juvenile migration and spawning. The longest duration occurred between August 24 and August 31, 2004, as a result of warm stormwater flow during a significant rain event. The elevated stream temperatures recorded did not approach lethal limits (23 to 26°C) but did exceed criteria developed to protect juveniles from disease and optimal growth at the monitoring locations.

Both chinook and coho adults migrate into the Hylebos Creek system beginning in September. Again, there was a total of three hours of elevated stream temperature during this migration period (September 11, 2004) at the Brooklake station. This exceedance was a result of warm stormwater flow during a significant rain event, but an overall reduction in adult migration due to cumulative temperature stresses in the stream (blockage, delay, disease, and impaired swimming performance) is not likely because a prolonged exposure period did not exist.

Stream habitat with boulders, large woody debris, and pools that provide cold-water refuge for salmon exist throughout much of the West Branch and North Fork stream segments. It is hoped that salmon will seek these colder pools of water during periods of temperature exceedances. But the problem area will continue to be the open stream channel both north and south of the 373rd monitoring station. Here, a large section of the creek exposes salmon (when present) to high summertime temperatures due to the lack of adequate riparian cover and stream habitat features.

Salmon Restoration Projects
Studies have shown that lack of riparian shade, excessive sediment load, increased wintertime stream flow, and decreased summertime flow can all adversely affect stream temperature. If designed properly, stream restoration projects can be effective in reducing stream temperatures.

The City of Federal Way has implemented a number of restoration and engineering projects over the past 10 years that have been designed to improve water quality and aquatic habitat in the Hylebos basin:

• In 1996 and 1997, the level of flood protection for affected sections of the West Hylebos drainage system was improved with the installation of two extensive regional stormwater detention and wetlands/stream restoration projects. Combined, they supply over 80 acre-feet of storage capacity and provide environmental resource protection within the West Hylebos stream/wetlands corridor that results in downstream habitat benefits.
• In 2003, 12 engineered large woody debris (LWD) structures were installed along 500 linear feet of West Branch Hylebos Creek between Brooklake and South 356th Street to improve channel morphology, low-flow fish passage, salmon spawning, and rearing habitat.
• A year later, West Hylebos Creek underwent a major restoration with the stabilization of more than 2,500 linear feet of streambank north of the Montessori station and downstream of South 356th Street. Work involved the removal of invasive vegetation and importing over 15 LWD installations in the form of log weirs, jams, and revetments to stabilize the creek and improve fish passage.

Ted Enticknap and Dan Smith discussing salmon habitat along the North Fork Hylebos Creek

A large-scale project is slated for the near future in the vicinity of South 373rd Street. It will create and restore wetland and stream areas along this problematic stretch of West Hylebos Creek. The project as designed will return approximately 1,400 feet of degraded creek channel and pastureland back to its natural state, thereby reducing temperatures by improving riparian conditions.

In addition, the creek at this location will be realigned to follow a more natural, meandering path, with shade cover from native plants and trees. Stabilized streambeds with overhanging vegetation will enhance salmon habitat diversity, lending to greater salmon growth and higher survival. The placement of large woody debris will improve pool habitat and provide cool-water refuge areas that support spawning and juvenile rearing. New salmon habitat will be generated by creating wetland areas adjacent to the stream. The work at South 373rd Street is to be completed by the fall of 2007.

The Future
Wild salmon are a great symbol of the waterways of Washington, and their survival is an important indicator of health for Pacific Northwest streams and rivers. As this article describes, the decline of salmon populations can be attributed in part to human changes to the landscape that have elevated stream temperatures.

Currently, the Puget Sound region contains a population of 2.5 million people. Its population is expected to surpass 4.1 million by 2010 and should approach 4.7 million by 2020. By 2030, nearly 5.1 million people are expected to call the Puget Sound region home (Washington Office of Financial Management 2006).

Although the city will certainly experience similar upward population trends (resulting in increasing impervious infrastructure necessary to accommodate expanding economic development and transportation needs), a GIS database analysis of residential and commercial parcels in the Hylebos basin indicates that less than 5% (approximately 243 acres) is designated as developable. This may mean that stream temperature exceedances associated with summer stormwater runoff from impervious surfaces may soon become static, making the problem more manageable in this watershed.

Air temperature and solar radiation are also significant factors in increasing water temperatures. The average temperature of the earth’s surface has risen by 0.6°C since the late 1800s. Proponents of climate change expect an increase of another 1.4 to 5.8°C by the year 2100 (UNFCCC 2006).

With even a minimum predicted warming trend, numerous plant and animal species already weakened by pollution and loss of habitat may be at risk for extinction. Even though long-term weather patterns are difficult to predict and impossible to control, ongoing stream temperature monitoring will become a useful tool for the city to track changes, measure impacts, and devise solutions that protect aquatic life.

The stream temperature study within West Hylebos Creek undertaken by the City of Federal Way has identified and documented stream segment “hot spots.” It provides fundamental information that will be used for the continued identification of temperature trends and inputs to the watershed, and the implementation of adaptive management practices and control technologies designed to preserve the viability of salmon populating this important stream system.

Ted Enticknap, at age 83, continues to participate as a Stream Team volunteer, traversing the channels of the North Fork in Spring Valley collecting water samples. “It’s a way of life, I guess. And I’m geared to Ma Nature. I enjoy the trees, the bushes, the water, the springs,” he says, while explaining his profound advocacy for the stream.

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Enticknap remains encouraged that continued temperature monitoring in West Hylebos Creek will help sustain the environment that he defends with a passion. “Salmon have been here for a thousand years, and I’m rather dissatisfied that we have a lot less than we used to. We’ve done everything to protect this valley. It gets complicated, but I’m not bright enough to figure it all out.”

Paul Bucich, Federal Way’s surface-water manager, believes that the city will initiate the implementation of basin-wide strategies addressing temperature problems. “Federal Way is committed to protecting and enhancing the natural resources within it and working with neighboring jurisdictions to find ways to improve habitat across the watershed,” he says. “Current options being pursued include acquisition of good-quality habitat, the encouragement of low-impact development alternatives where viable, and the continuing study of the temperature in our streams and ponds to better understand the problems so that we can pursue appropriate solutions.”

Author's Bio: Dan Smith is the Surface Water Quality Program Coordinator for the City of Federal Way, WA.