Beaver Management in King County

By Jen Vanderhoof

Prior to the arrival of the fur trade in the Pacific Northwest, the North American beaver, Castor canadensis, was a common denizen of lakes, ponds, and riparian areas. But in the 1800s, beaver trapping throughout the West very nearly eradicated the species. Many people now think of them as invaders, as opposed to a native species slowly filling in all the spaces left empty 150 years ago. And their return has been so gradual that it is easy to forget they were historically an integral part of the landscape.

beaver_photo_-_Lauren_SmithBy building dams on streams, beavers formed networks of wetlands, increased ecosystem complexity, and contributed to increased biodiversity. Beaver ponds are well-documented to:

  • maintain stream flow during summer;
  • reduce downstream flooding and erosion by storing rainwater during high-flow events;
  • trap sediment and pollutants;
  • raise groundwater levels/replenish aquifers;
  • help create diverse plant communities; and
  • create habitat for coho salmon and other fish, birds, amphibians, mammals, and invertebrates.

However, there are also negative impacts from beavers in King County. Although no one in Washington state tracks beaver population numbers, there is a great amount of anecdotal evidence that population sizes continue to increase. As beavers reclaim their former habitat, their ponds impact human infrastructure that was built without beaver ponds present. The absence of considering potential beaver impacts combined with the beavers’ proclivity for creating dams at the narrowest points in streams – which tend to be culverts – may result in the backwater flooding of roads, farmland, and other private property. If the dams are removed, beavers build new dams. If beavers are removed, more beavers take their place.

Ideally, workable solutions can be found so that beavers can remain on the landscape and provide their ecological benefits while not negatively impacting private property and infrastructure. “Beaver deceivers” and pond levelers are excellent examples of engineered solutions for co-existing with beavers. However, such devices are not always effective in flat locations such as agricultural areas.

Further, because of the trees planted at riparian restoration projects, these projects can be become attractive to beavers, whose activities may subsequently impact the trees as well as potentially affect neighboring properties by flooding. And as King County continues to build restoration projects, plant trees, maintain roads, maintain and steward parks and natural areas, perform levee setbacks, provide assistance to farmers, and attempt to be good neighbors (all of which can impact, and be impacted by, beavers), the need is ever-increasing to find and adopt workable solutions to living with beavers.

King County Department of Natural Resources and Parks has convened stakeholder groups in the past to try and address emerging beaver issues. But over the years, the number of beaver related drainage complaints and beaver related inquiries have continued to increase. Therefore, in 2016 a “beaver management program” was approved, and in Spring 2017 the program was kicked off.


King County Beaver Management Program

Until now, many groups and individual King County employees working on beaver issues have been using a variety of tools. Not all tools have been equally effective, and some may have even exacerbated problems. The over-arching goal of the beaver management program is to find the best, most effective and science-based solutions for humans and beavers to co-exist in King County. The following tools will help agencies and landowners find ways to live with beavers:

  • A summary of beaver biology, life history, and ecology, to help better understand and predict behavior.
  • A summary of current management techniques such as beaver deceivers, pond levelers, and tree protection, plus the pros and cons of each and required permits.
  • A summary of state and local laws and policies.
  • Educational materials, including information for landowners.
  • New policies establishing when, where, and how King County engages in beaver management issues.
  • Ongoing monitoring of beaver activity and pilot projects to test effectiveness of new management techniques.

King County’s beaver website will soon be revamped and updated, and these written summaries and other newly developed tools will be placed online as they become available.

j-vanderhoof.pngJen Vanderhoof is an Environmental Scientist III/Senior Ecologist in King County’s Science and Technical Support Section. Jen’s work often focuses on issues related to wildlife and biodiversity (including beaver-related issues) and climate change. She frequently consults on wildlife and habitat-related questions and policies for King County Parks and Recreation Division, the Wastewater Treatment Division, the Director’s Office, and the River and Floodplain Management Section. Jen is currently the project manager for a shoreline and estuary restoration project at Saltwater State Park, and she is conducting the wetland and riparian analyses for the Bear Creek Basin Watershed Plan.

Echo Lake Stormwater Study

By Carly Greyell

Living in King County, rain is a natural part of life. But you might not realize that when rain collects on impervious surfaces, like roadways and roofs, it can pick up a variety of pollutants. Every day activities, like driving a car, walking the dog, and fertilizing your lawn, can contribute pollutants like heavy metals, oil, bacteria, solids, and nutrients. This polluted rain water is referred to as stormwater and King County and other local jurisdictions are working hard to reduce the amount of pollutants that stormwater adds to our local waterbodies, including lakes, rivers, and Puget Sound.

One way to treat stormwater is through bioretention where stormwater is filtered through a soil mixture that includes compost and sand. In 2012, the City of Shoreline installed a number of bioretention planter boxes (designed like concrete-lined rain gardens), along Aurora Avenue North, which is part of Highway 99. The bioretention planter boxes treat some of the stormwater that drains to Echo Lake. King County recently designed a study to see how effective the planter boxes remained three years after construction, and whether they could reduce stormwater pollutants that contribute to human health risks such as PCBs.


The King County Environment Lab (KCEL) Field Sciences Unit braved the rain to collect samples during eight storms from December 2015 to February 2017. Samples of both the untreated stormwater entering the bioretention planter boxes and the treated stormwater after it had filtered through the soil mixture were collected for chemical analysis. Pollutant concentrations between the treated and untreated stormwater were then compared to determine how effective the planter boxes were at removing pollutants from the stormwater.

The results were mostly positive: the bioretention planter boxes significantly reduced concentrations of most pollutants, including chemicals associated with oils and exhaust, total copper, total zinc, solids, and even PCBs. Average reductions for these pollutants ranged from 81 percent to 99 percent at each site. Levels of dissolved heavy metals were not always reduced, but concentrations in both the treated and untreated stormwater were very low. These findings are consistent with results from studies that evaluated new bioretention, suggesting the planter boxes are continuing to perform as expected, three to five years after installation.

Unfortunately, nutrients in the stormwater were not consistently reduced, and in many cases the stormwater treated by the planter boxes actually had higher concentrations than the untreated stormwater. This is particularly problematic for phosphorus, which, when elevated, can lead to increased algal blooms in lakes. This problem has been recognized with bioretention across the region, and local researchers are currently evaluating alternative bioretention soil mixtures for stormwater treatment in areas at risk for algal blooms.


Despite the good news in treatment, the maintenance requirements for these planter boxes were higher than expected. Water enters these installations from the busy roadway through cuts in the curb, which were easily blocked with dirt, leaves, and other debris. Without regular debris clearing, stormwater was blocked from entering the planter boxes, and bypassed treatment.

Thanks to the results of this and similar studies, stormwater engineers and managers are learning how to improve stormwater treatment techniques.

PCBs – Banned But Not Forgotten

pcbsPolychlorinated biphenyls, or PCBs, are a group of chemicals developed in the 1930s that had a range of uses, including additives for construction materials, such as paints and caulks. However, PCBs were linked with negative health effects such as cancer and hormone disruption, and in 1979, U.S. production was banned. Unfortunately, most PCBs do not break down easily, and older buildings and industrial sites remain important sources of PCBs.

In several local waterbodies, including Lake Washington, fish consumption advisories warn that certain fish species contain PCBs at levels that are unsafe to eat. Researchers are learning that one of the main ways PCBs enter these water bodies is through stormwater. However, PCBs are not currently regulated under stormwater permits. Studies, like the one described here, are important so that we can learn how best to reduce PCBs in stormwater, thus preventing human health issues.

Effective Stormwater Management

The Washington State Department of Ecology helps local municipalities like King County and the City of Shoreline manage their stormwater permits. Since 2013, most Washington state stormwater permitees have pooled resources to fund regional stormwater monitoring and studies that evaluate how well permit requirements serve to improve stormwater treatment. Washington state permitees selected the study described here for funding through this program.

carly-greyell.pngCarly Greyell is an ecotoxicologist in the King County Science and Technical Support Section. She has been supporting many of the Lower Duwamish source control projects and involved in ongoing toxics monitoring and projects assessing the effectiveness of stormwater treatment.




Modeling Climate Change Impacts on Extreme Precipitation, Stormwater Design Requirements, and Wastewater Conveyance

By Jim Simmonds

King County’s 2015 Strategic Climate Action Plan calls for assessments of climate change effects on large rainstorms in King County and the ensuing impacts on stormwater and wastewater management. These assessments were prioritized in response to recent findings from the University of Washington that large rain events known as “atmospheric rivers” are projected to hold an average of 22 percent more moisture by the end of the century (Warner et al., 2015).


Large rain events known as “atmospheric rivers” are projected to hold an average of 22 percent more moisture by the end of the century.

(Warner et al., 2015)

Most extreme precipitation events along the West Coast are associated with winter atmospheric river events. Atmospheric rivers are relatively long, narrow bands of moisture-laden air that can deliver intense rain when they intersect land. Atmospheric rivers that affect western Washington often originate in the subtropical Pacific Ocean near Hawaii; these are sometimes referred to as “pineapple express” events. About one-half to two-thirds of Western Washington’s annual precipitation falls during atmospheric river events.


King County partnered in 2016 with the University of Washington’s Climate Impacts Group to model hourly rainfall throughout the county under climate change conditions. This modeling was funded by King County’s Stormwater Services Section,Wastewater Treatment Division, and a grant from the Washington State Department of Ecology. The innovative modeling approach relies on “nesting” a regional weather model within two global weather models to allow for more refined predictions. The nested modeling approach is critical for understanding climate change impacts on storms in the Pacific Northwest.

This image of total precipitable water contained in the atmosphere shows a long band of wet air crossing the Pacific Ocean towards the Pacific Northwest, known as an “atmospheric river” (from Warner et al 2015).

The regional model used was the Weather Research and Forecasting model applied by the University of Washington, which is the same model used to make short-term weather forecasts for the region. The climate scenario modeled is based on ongoing, unabated global carbon emissions through the end of the century.

Preliminary modeling results show about 20 to 40 percent more rain will fall during each year’s heaviest hour of rainfall by the end of this century. Increases are also projected for less-frequent storms and longer-duration storms. For the official Seattle weather station at SeaTac, this means that the one-hour annual peak rain event is projected to increase by 2100. Model results to date do not suggest that “atmospheric rivers” will occur more frequently under climate change conditions, only that they are projected to deliver more precipitation.

These modeling results have important implications for stormwater management. In accordance with requirements by the Washington State Department of Ecology, King County requires developers to use a manual to size and design stormwater flow control and water quality treatment. The design relies on the past 68 years of rainfall data for ensuring proper sizing. Because future storm sizes are projected to increase, this implies that stormwater systems designed today may be undersized for future conditions. A sensitivity analysis of stormwater facility design to future rainfall conditions will be completed in 2018, along with an analysis of options for updating the design requirements.

Intense rainstorms can overwhelm the stormwater system and cause urban flooding.

King County also owns and operates the regional wastewater conveyance and treatment system for the greater Seattle area. Portions of the City of Seattle have combined wastewater and stormwater conveyance systems, which allow for substantially greater flows during rain events than dry periods. King County is investing heavily to reduce overflows from the combined system during large rain events, and is interested in incorporating future storm conditions in the planning process. To do this, the King County Wastewater Treatment Division will be modeling the wastewater conveyance and treatment system under both historical and projected future climate conditions to determine possible changes in flow timing and volume. The results from this modeling will be incorporated into future plans for maintaining and upgrading the facilities.


Read more about the King County SciFYI newsletter.

jim-simmondsJim Simmonds is the Water Quality Unit Supervisor of King County’s Science and Technical Support Section. He has over 25 years’ experience monitoring and modeling environmental conditions, managing environmental investigations, managing environmental data, and assessing potential impacts of stormwater, wastewater, and environmental contamination. He has been with King County for 17 years.


New Fish Resource Monitoring Program

By Jim Bower

fish-panoKing County is ground zero for managing both rapid urbanization and highly valued fish resources. The County and numerous other partners have spent millions of dollars on fish conservation and fish habitat projects, as well as floodplain restoration, land protection, stormwater controls, land use regulations, and other salmon recovery efforts. Do you ever wonder if all the steps we take to conserve the County’s environment and fish resources are making a difference? Are we on the right track?

King County’s Science and Technical Support Section has initiated a Fish Resources Monitoring Program to track and more importantly, drive improvement of the overall effectiveness of ongoing strategies to conserve our fish resources. The program will implement a suite of methodologies to determine if our strategies are producing an overall positive, cumulative effect on fish populations and fish habitat. Furthermore, the program will evaluate the return on County (and other partner) investments in fish resources; where and how the County can maximize the effectiveness of future investments in fish resources; and whether or not changes should be made to protection, mitigation and restoration efforts.


A technical team from across King County’s Water and Land Resources Division (WLRD) began work in early 2017 to develop an initial, multi-prong approach to address the program goals and questions. The team started by considering fundamental analysis options, such as project-level, status and trend, and intensively monitored watershed assessments. Over time, the program may tackle these challenging goals and questions from different scales and scopes, along with changing priorities. The acquisition of additional status and trends data across major watersheds in King County will also be explored. However, in the near term, the initial approach by the team is likely to involve two separate methods:

A meta-analysis of approximately 18 project-level monitoring efforts overseen by the River and Floodplain Management Section and Ecological Restoration and Engineering Services Unit within WLRD. This analysis is expected to utilize “log response ratios,” which measure the proportional changes of important ecological variables caused by a range of treatments (Hedges et al 1999). The results of individual monitoring efforts within the meta-analysis will be weighted based on the type of experimental control.

A variation of intensively monitored watersheds by replicating the 2014 study Assessing Land Use Effects and Regulatory Effectiveness on Streams in Rural Watersheds of King County, Washington (Lucchetti et al 2014). This approach will evaluate changes to important fish habitat variables after 10 plus years of implementation of “critical area” regulatory protections. This analysis will also initiate the assessment of fish population biomass, richness, and diversity among the study watersheds.

Both analyses are expected to help describe the performance of current resource management strategies and inform future adaptive management.

A concurrent program task is developing a spatially related fish population and habitat database. Over time, the database will incorporate historic and current fish resource information, including survey data, related reports, and supplemental narratives.  This will require coordination with other local and regional data collection efforts, such as those by Tribes, WRIAs, Puget Sound Partnership, and state and federal agencies. The data is anticipated to be associated with high-resolution hydrography and delivered to any desktop or online ArcGIS end-user in their own, customizable GIS environment.

A “Year 1” program status report will be completed in February 2018. Future bi-annual status reports will review ongoing data collection and assessments, describe data gaps, promote new opportunities for adaptive management, and ensure current and relevant resource management questions are still being asked. The periodic status report will also be the primary opportunity to propose future program monitoring and assessment methodologies based on current findings.

Read more about the King County SciFYI newsletter.

jim-bower.pngJim Bower is an Environmental Scientist III/Fish Ecologist in the King County Science and Technical Support Section. He is King County’s technical representative for the Lake Sammamish kokanee and WRIA 8 Chinook restoration planning areas. His work with native kokanee involves collaboration with numerous public agencies, private landowners, and conservation organizations; his work includes various long-term monitoring and coordination of annual kokanee recovery actions. Jim also provides technical support to WRIA 8 project planning, study design, monitoring implementation, and grant review.