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Water and Land Resources Division

King County, Washington

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Water and Land Resources Division, King County, Washington

Lower White River Countyline reach projects
(from A Street downstream to Eighth Street)

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Overview    

The Countyline Reach of the Lower White River is bounded by the A Street and Burlington Northern Santa Fe (BNSF) Railway bridges at the upstream end (River Mile 6.33) and the Eighth Street Bridge at the downstream end (RM 5.0), and is so named because it spans the King-Pierce County boundary.

King County has proposed two levee setback projects within the Countyline Reach: the Countyline Levee Setback Project and the Right Bank Levee Setback Project. The combined result of these projects will be to reconnect more than 120 acres of floodplain to the White River channel. Both projects involve property acquisition, levee removal and setback, and floodplain enhancement and will provide improved flood risk reduction.

The Countyline and Right Bank projects are identified in and consistent with the primary objectives of the adopted 2006 King County Flood Hazard Management Plan and the 2013 King County Flood Hazard Management Plan: Update and Progress Report, as well as the Salmon Habitat Protection and Restoration Strategy for the Puyallup and Chambers/Clover Creek Watersheds (external link, PDF 869KB) - Water Resource Inventory Area 10 and 12.

Anticipated construction timelines: Updated Oct. 2014

  Countyline Projects  
Countyline* June 2015-Oct. 2016
Pacific Right Bank 2018-2019

*One year delay for Countyline is likely to allow completion of property acquisitions.

Problem statement

The White River carries a high sediment load, and sediment tends to deposit in this reach of the river causing the river bed to rise. As a result, the cities of Pacific and Sumner have experienced flooding in this area. The primary flood risk reduction strategy for this reach (as identified in the 2006 King County Flood Hazard Management Plan) is to increase the river’s capacity to accommodate flood flows and high sediment loads. This is best accomplished by acquiring land and modifying levees or revetments so the river is reconnected to its floodplain. This approach increases flood conveyance and storage, while opening up areas to accommodate sediment deposition.

The White River supports salmon species that are listed as threatened under the Endangered Species Act (chinook, steelhead, and bull trout), as well as coho, pink, and chum salmon and cutthroat trout. White River chinook are the only early (spring run) returning chinook in South Puget Sound, making chinook recovery a high priority in this river system. These projects directly address limiting factors identified in the WRIA 10 and 12 salmon recovery plan by restoring and providing off‑channel rearing habitat for spring and fall chinook, coho and steelhead. White River spring Chinook are the last remaining spring run in South Puget Sound.

Goals

Goals of Flood Hazard Management Plan
The key goals of the 2006 King County Flood Hazard Management Plan and the 2013 King County Flood Hazard Management Plan: Update and Progress Report remain:

  • to reduce the risks from flood and channel migration hazards;
  • to avoid or minimize the environmental impacts of flood hazard management; and
  • to reduce the long-term costs of flood hazard management.

Ecological Goals
The ecological goal in the Countyline Reach is to restore riverine processes and functions to the lower White River and its floodplain in order to enhance salmonid rearing habitat, in particular for spring and fall Chinook, coho, and steelhead.

This goal focuses on restoration of processes that create and sustain productive salmon habitats, including:

  • Channel migration
  • Large wood delivery
  • Erosion and deposition
  • Forest regeneration
  • Plant and animal production
  • Floodplain inundation

Individual projects are intended to enhance and reconnect:

  • Juvenile rearing habitat, such as side channels, backwaters and low-velocity margins
  • Adult migration and holding habitats, such as deep pools

Capital Recommendations

Because the lower White River is highly modified and constricted, the approach to resolving existing flood risks focuses on increasing flood flow and sediment load capacity. The strategy is two-fold: Acquire land or flood easements; and follow up with capital improvements to modify levees and retrofit revetments so that the river is reconnected to its floodplain. This will increase flood conveyance and storage as well as accommodate sediment deposition. Returning the lower White River to a more naturally functioning floodplain will also improve aquatic and wildlife habitat. These flood-risk reduction objectives are framed in the 2006 King County Flood Hazard Management Plan and the 2013 King County Flood Hazard Management Plan: Update and Progress Report and are also consistent with recommended salmon habitat recovery actions present in WRIA 10 Shared Strategy for Puget Sound.

Comprehensive solution

These projects provide a comprehensive solution to reach-specific issues including flood risk, habitat quality, and cost-effectiveness. Flood risk reduction will be achieved by constructing new levees that are set back from the main river channel. This strategy gives the river more room to move through its floodplain, increases the overall channel capacity, and provides areas for both flood storage and sediment deposition. Habitat enhancement goals will be achieved by improving currently degraded habitat and by allowing natural river processes to create fish and wildlife habitat, to result in an overall increase in quantity and quality of available habitat. Cost effectiveness goals will be achieved by constructing projects that work with, instead of against, the natural tendencies of the river system. Levee maintenance costs and flood damage repairs are expected to decrease because the river channel is not constricted, allowing more area to dissipate energy.

Flood hazard reduction benefits
Capital projects being pursued in this reach will include the setback of existing levees and construction of revetments to provide increased flood conveyance and storage. Allowing the river a broader floodplain corridor helps to reduce flood elevations and slow velocities that can be damaging to public and private infrastructure.

The current movement of sediment through the reach is confined to a channel that was constructed through the existing Stuck River corridor early in the 20th Century. Sediment accumulation is an on-going issue on the Lower White River. Historically, dredging has been used to maintain channel capacity. Yet due to the high sediment load of the White River, dredging provides only a short-term solution, historically requiring frequent mobilization of crews and equipment to maintain channel capacity. Reconnection of the river with a broader floodplain will have the effect of allowing sediment accumulation to take place over a much greater area, rather than in the confined channel where sediment deposition continues to reduce conveyance capacity. The capital projects proposed for this reach would provide an alternative to historic sediment management practices by providing a long-term solution at a substantially reduced cost to public funding sources.

Habitat benefits
The Right Bank and Countyline projects involve removal of existing angular rock and concrete slab (levee prism and revetment material) to allow the White River to meander through its floodplain, thus providing important habitat for young salmon to feed, grow, and find refuge from predators and high flows. Log structures will be installed in the floodplain to deflect high-energy flow paths to promote side channel formation and provide cover and slow water refuge for salmon. Native trees and shrubs will be planted to enhance the riparian buffer. This buffer will provide shade, wildlife habitat, and food sources for aquatic organisms.

Project sponsors and roles

The King County River and Floodplain Management Section is overseeing the design and construction of these projects which are being implemented on behalf of the King County Flood Control District (external link).

External links to related information

For more information about the White River, contact Jeanne Stypula, White River Basin Supervisor, King County River and Floodplain Management Section.