Limiting Factors Analysis
These two documents identify the dominant processes and habitat characteristics that currently limit the production of coho salmon smolts in the Scappoose Creek basin and in Milton Creek. The concept of these plans is a limiting factor analysis, identifying habitat conditions that restrict the success of one or more coho life history stages.
Milton Creek was historically a direct tributary to the Columbia river, and currently a watershed draining into the Scappoose Bay. The sub-basin comprises of 21,561 acres and contains 17.8 miles of mainstem stream corridor and 6.6 miles within five tributary corridors utilized by coho.
Limiting Factors for Milton Creek
- Spawning gravels are very low in the upper mainstem of Milton Cr, suggesting that restoration prescriptions for this important segment of the Core Area should focus on improving trapping and sorting activities that boost gravel retention and functionality. These changes would allow currently functional summer and winter habitats to be adequately seeded.
- Elevated temperatures in the lower mainstem Milton Cr make this otherwise high-quality habitat unusable during the summer. Coho juveniles attempting to migrate upstream to cooler tributary systems encounter multiple physical barriers. Those that migrate downstream face temperature limitations beyond their physiological threshold and must move or perish. From a restoration standpoint, the most effective approach to deal with this highly important habitat disconnection is to work simultaneously in both the mainstem and Cox Cr.
Scappoose Creek is a tributary of Scappoose Bay in the lower Willamette River. The Scappoose Creek watershed is 40,663 acres and includes both the North and South Scappoose Creek sub watersheds, and contains 25 miles of mainstem stream corridor exhibiting the potential for anadromous use. Ten main tributary corridors provide an additional 14 miles of potential habitat.
Limiting Factors for Scappoose Creek
- The loss of beaver colonies. In a 2008 survey, only 24 beaver dams found in the entire Scappoose watershed’s 39 stream miles of anadromous salmonid distribution.
- Spawning gravels are very low in Cedar Cr suggesting that restoration prescriptions for this important segment of the Core Area should focus on improving trapping and sorting activities that boost gravel retention and functionality. These changes would allow currently functional summer and winter habitats to be adequately seeded.
The Council worked with Oregon Department of Fish and Wildlife (ODFW) and a qualified contractor to conduct aquatic habitat inventories and a rapid bio assessment (RBA) of approximately 50 stream miles in Milton Creek, as well as North and South Scappoose Creeks.
Aquatic Habitat inventories are a way to assess the quality and type of habitat present in a stream system. Aquatic habitat inventories interpret a large amount of data pertaining to the stream characteristics. The data collected includes (but not limited to); type of channel substrate, classification of reaches into types of pool, riffle, glide, cascade, and beaver dams. There is also a large amount of collateral data collected; percent shade, composition of riparian area etc. This type of information is very useful for restoration projects.
The (RBA) or Rapid Bio-Assessment protocol is a scientific method to gather data on fish distribution and potential barriers to fish on a watershed scale. The surveys continue upstream to the end of fish distribution. As the surveyor moves upstream the contractor snorkels every 5th pool and describes the number and species of salmonid present, as well as any potential barriers along the route. The RBA protocol then takes this sample of the watershed and uses that to estimate adult salmonid use of the watershed and how much potential the watershed has of supporting more juvenile salmonid. This set of surveys (RBA), and (Aquatic Habitat Inventory) provides information on current use of the stream by salmonid, habitat conditions, and identify limiting factors to spawning and rearing in the watershed. The final report provides details on each of the creeks that were surveyed.
South Scappoose Creek Restoration Plan
In 2000, the Scappoose Bay Watershed Council (SBWC) completed a watershed assessment for the streams and catchments that enter Scappoose Bay.
The watershed assessment identified several areas of concern affecting watershed and ecosystem health. Concerns include sediment delivery into Scappoose Bay, loss of high quality spawning and rearing habitat for salmonids, and incision within many of the primary channels. Of particular concern was the potential impact that channel incision has on channel and floodplain interaction and the ability of the stream to support and maintain the physical habitat features that provide for good aquatic habitat.
A five mile stretch of South Scappoose Creek that flows through the City of Scappoose was determined to have high priority for further assessment. This segment is characterized by an incised channel, severe bank erosion, lack of a continuous riparian corridor, a half dozen road crossing that have constricted the channel and floodplain, and urban encroachment into the historic floodplain. It was identified as a priority for further assessment due to local concerns about erosion and flooding and the opportunities to enhance conditions for salmon and other organisms that rely on high quality aquatic habitat.
Scappoose Bay Bottomlands Conservation and Restoration Plan
This plan, completed in 2004 by The Wetlands Conservancy, describes the Bottomlands in terms of historic conditions, ecologic processes, current plant communities, fish and wildlife use, and wetland values.
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The plan also summarizes the natural resource and open space components of the Columbia County Comprehensive Land Use Plan, and identifies the major economic conditions, potential opportunities and conflicts for conserving and enhancing sociological and ecological values, and threats to conservation.
Three reference sites within the bottomlands are described; these are sites that are in relatively good ecological condition, primarily because they lie in areas where diking was never done or drainage was ineffective.
Seven privately owned parcels and three publicly owned areas were identified as having the highest priority for conservation and restoration. These areas included the Malarkey and Hogan ranches, Oregon State Parks/Greenland in St. Helens, and the Sauvie Island Wildlife Area (SIWA). The private sites were the main focus of field surveys, and land value appraisals were conducted on four of these sites, where landowners were willing to consider protection easements.
Significant Study Results
- The characteristic habitats, including plant, wildlife, and fish species, for the Scappoose Bay Bottomlands were described.
- Field surveys were conducted of seven bottomland parcels that have the potential to be some of the best remaining habitats in the Lower Columbia River system.
- Conservation strategies were determined for the seven properties, detailing prescriptions for native plantings, crop conversions, reconnections, and managing control structures.
Fish Passage Barriers
The Scappoose Bay Watershed Council has been working to replace culverts and other fish-passage barriers that exclude salmon and other fish from prime spawning grounds in the upper tributaries.
SBWC has worked with a variety of partners to remove or replace 40 barriers, opening up over 55 miles of creek for fish access. We have been systematically working our way through the watershed over the last several years to replace priority barriers. In 2010-2011, we finished up work on Salmon and Cox Creeks and our next priority will be culverts along Dart Creek.
Site selection is based on the following watershed plans: A Comprehensive Assessment of Fish Passage Barriers in the Scappoose Bay Watershed (May 2001), Scappoose Bay Watershed Assessment (January 2000) and Strategic Plan (January 2008). The comprehensive barrier assessment, conducted on behalf of the Watershed Council, shows that barriers have a significant cumulative impact on fish habitat on most streams in the watershed. The assessment used biological criteria and findings of the Scappoose Bay Watershed Assessment to prioritize barriers for each sub-watershed and for the watershed as a whole. The priorities are based on whether the barrier is in a key sub-watershed (e.g. Scappoose Creek or Milton Creek), is a complete or partial barrier, and rank on a habitat index score (based on whether the barrier blocks access to upstream refugia and the length of potential upstream habitat).