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Instream Restoration Riparian Restoration Fish Passage
Effects of Boulder Weir Placement on Aquatic Habitat and Biota   Coos and Douglas Counties, Oregon
Primary Project Type: Instream Restoration
     Secondary Type:
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  Results of this research suggest the placement of boulder weirs appears to be an...  

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Primary Problem: Loss of Fish Habitat
     Secondary Problem:
Main Restoration Action(s): Boulder weirs, Habitat enhancement
Native Fish Focus: Steelhead
Is this project part of a watershed scale restoration? No
Project Dates: 2002 to 2003
  Initial Monitoring:
Restoration Implementation:
Follow-up Monitoring:
Lead Agency:
     Northwest Fisheries Science Center NOAA Fisheries Service
     U.S. Bureau of Land Management, Coos Bay District
Project Partners:
  U.S. Bureau of Land Management Oregon State Office
Coquille Watershed Association
Roseburg Resources
Plum Creek
Lone Rock Timber
Other private land owners
U.S. Environmental Protection Agency
Project Location: The project locations are on thirteen paired treatment and control reaches in seven different streams in the lower Umpqua and Coquille River basins in coastal Oregon. The stream reaches were low elevation (less than 500 meters), low gradient (1 to 3 percent slope), and were situated in sand and siltstone geology on U.S. Bureau of Land Management or U.S. Forest Service land. Click here for a map of the project area.
Project Description: The following case history was created using text from Rehabilitation of Bedrock Stream Channels: the Effects of Boulder Weir Placement on Aquatic Habitat and Biota by Roni, et. al of the Northwest Fisheries Science Center National Marine Fisheries Service and Van Slyke and Olmstead of the U.S. Bureau of Land Management, Coos Bay District. To view this report in its entirety, click here. [465 kb PDF]

In forests of the Pacific Northwest United States, twentieth century forestry activities such as splash damming and stream cleaning have resulted in stream channels devoid of wood and boulders and have often produced narrow stream channels scoured to bedrock. Several instream habitat improvement techniques have been employed to try to improve or restore these stream channels. Adding large woody debris (LWD) and other log structures have been particularly common methods of improving stream channels. In areas where LWD of adequate length and diameter is not readily available, boulder clusters, weirs, and other structures have been used. The placement of boulders has been particularly prevalent in streams dominated by sedimentary rock in coastal southwest Oregon, where boulders placed in the configuration of weirs are intended to function similar to key pieces of wood. Anecdotal information suggests that streams along the Oregon coast contained many larger boulders prior to splash damming and stream cleaning. However, there is considerable discussion as to whether boulder and weir placement mimics natural conditions or is entirely artificial.

The effectiveness of wood placement on fish abundance has been examined in several recent studies (e.g., Cederholm et al., 1997; Reeves et al., 1997; Solazzi et al., 2000; Roni and Quinn, 2001; Roni, 2003). Most of these studies demonstrated increases in juvenile coho salmon (Oncorhynchus kisutch) abundance following wood placement. In contrast, research on the effectiveness of boulder weir placement has been limited to a handful of case studies, which have often focused on physical variables with limited information on fish responses (Roni et al., 2004). These limited studies on boulder structures have suggested potential benefits for steelhead, brown trout, and Atlantic salmon, but more rigorous evaluation was needed for these and other species.

Stream morphology and biotic communities can differ according to geology and channel type (Hicks and Hall, 2003; Montgomery et al., 1996; 1999). For example, basalt and sandstone stream channels in coastal Oregon have different morphological characteristics and fish community structure. Sandstone channels have more pools, a lower gradient, and are typically dominated by coho salmon (Hicks and Hall, 2003). Most evaluations of fish response to restoration have occurred in alluvial reaches or in stream channels with basalt or glacial geology. Moreover, these studies have generally occurred in relatively small streams (bankfull width less than 12 meters), and boulder structures are often placed in larger channels (Roni et al., 2002; Roni et al., 2004). The response of biota to placement of instream structures is likely to differ among geologic types but has not been examined in sandstone channels or in larger stream channels. Research examining the response of macroinvertebrates to placement of boulder structures has been less extensive, but has produced similarly equivocal results. The difference among results of previous macroinvertebrate studies underscores the need for additional research on macroinvertebrate response to restoration.
Project Goals: The goals of the project were to examine the effects of boulder weir placement on physical habitat, water chemistry and nutrients, fishes and macroinvertebrates. The effectiveness of boulder weir placement was examined by comparing physical habitat, chemical, and biotic metrics in 13 paired treatment (boulder weir placement) and control reaches in seven southwest Oregon watersheds in the summer of 2002 and 2003. Site geology was sedimentary – most being sandstone and siltstone.
Project Methods: Extensive post-treatment design was used to compare the responses of habitat, macroinvertebrates, nutrient levels, and juvenile fishes to boulders and boulder weirs placed in southwest Oregon streams. This design, which has been used widely to assess habitat alterations on salmonids, involved comparison between treatment and control reaches at a large number of sites after restoration. Thirteen paired treatment and control reaches in seven different streams in the lower Umpqua and Coquille River basins were sampled once in the late summer of 2002 or 2003.

Treatment was defined as the artificial placement of boulders and boulder weirs within the active stream channel. Treatment and control reaches 200 meters long (greater than 10 times the bankfull channel width) were selected in each stream (400 meters total). Study reaches, located at least 200 meters apart, were used to assure that fish movement between treatment and control reaches was minimal during the study period. In streams with multiple treatment and control reaches, treatment-control pairs were located two or more stream kilometers apart. Paired treatment-control reaches within a stream were of similar slope, width, riparian vegetation, discharge, and length. All streams in the study region had a similar legacy of splash damming, stream cleaning, and other forestry activities that have resulted in highly uniform, incised, bedrock-dominated channels with few boulders or woody debris. The proximity of the reaches insured that discharges between reaches were essentially identical, though the distribution of point velocities might have differed.
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  Extensive post-treatment design was used to compare the response of habitat, mac...  
 
Click here for an enlarged photo
  Therefore, boulder weirs are merely the first step to restoring bedrock or incis...  
Monitoring Data and Collection Methods: Habitat units were classified within each stream reach using a modification of the methods and habitat types described by Roni (2002) and Bisson et al. (1982). Discharge was estimated with a flow meter immediately following each survey. All boulders and boulder weirs within the wetted channel were enumerated, the length and width measured, and their origin (i.e., natural or artificial placement) noted. The diameter class and length of all pieces of natural and artificially placed large woody debris (LWD) within the wetted stream channel were recorded. Fishes in each habitat were enumerated using snorkel surveys and benthic macroinvertebrates were collected in late summer and early fall. In conjunction with invertebrate sampling, three water samples were taken from the downstream, middle, and upstream end of each study reach. Statistical analyses were performed to understand differences and make correlations between all the variables measured. To learn more about the methods of monitoring for the boulder weir study, click here. [47 kb PDF] For results of the statistical analysis, click here.
Was this project effective and how was this determined? Boulder weir placement produced the predicted changes in physical habitat including increased pools, LWD, and boulders as well an increase in fish abundance. However, they appeared to have little effect on water chemistry, nutrient levels, and macroinvertebrate abundance or diversity. Had the placement of boulders been coupled with placement of large amounts of organic material (wood and leaves) or organic or inorganic nutrients, changes in water chemistry and primary productivity might have been detected. Significantly higher numbers of juvenile coho and trout (greater than 100 millimeters) were detected in response to boulder weir placement, suggesting that boulder weirs are an effective method of creating summer habitat for juvenile coho salmon and age 1 and older juvenile trout. However, there was a lack of response of young-of-year trout and longnose and speckled dace, a reflection of their preference for shallow habitats.

Results of this research suggest the placement of boulder weirs is an effective technique for increasing local abundance of species that prefer pools (juvenile coho and trout greater than 100 millimeters). Previous studies have indicated that they also trap large amounts of gravel and aggrade the stream channel. They do not, however, increase habitat complexity (wood cover). Therefore, boulder weirs are merely the first step to restoring bedrock or incised stream channels and weir placement should be coupled with measures to improve habitat complexity and protection of riparian areas to provide long-term inputs of LWD.
Click here for an enlarged photo
  Large woody debris (LWD) was surveyed for length and width, location in channel,...  
 
Click here for an enlarged photo
  Fishes in each habitat were enumerated using snorkel surveys. Common species obs...  
Confounding Effects/Additional Information:
Project Specs (all specs are estimates):
  Overall Estimated Cost: Project costs not available.
For more information on this project contact:
  Dan VanSlyke, Fish Biologist, U.S. Bureau of Land Management Umpqua Field Office Coos Bay District, Email: Dan_VanSlyke@or.blm.gov
This information was collected by: Kristin Keith
Project last updated on: 10/27/2006

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Updated: February 16, 2007
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