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Instream Restoration Riparian Restoration Fish Passage
Habitat Manipulation Study on Six Northern Colorado Mountain Streams   Jackson, Routt, Boulder, and Larimer Counties, Colorado
Primary Project Type: Instream Restoration
     Secondary Type:
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  In late summer 1988, study reaches were selected on each of the six high-elevati...  

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Primary Problem: Loss of Fish Habitat
     Secondary Problem:
Main Restoration Action(s): Habitat enhancement
Native Fish Focus: N/A
Is this project part of a watershed scale restoration? No
Project Dates: 1987 to 1995
  Initial Monitoring: 1986
Restoration Implementation: 1988
Follow-up Monitoring: 1988-1995
Lead Agency:
     Colorado State University
Project Partners:
  Colorado Division of Wildlife
U.S. Forest Service
Project Location: Six remote northern Colorado streams were selected for the habitat manipulation study. Study streams were South Saint Vrain Creek, Little Beaver Creek, North Fork of the Cache la Poudre River, Colorado Creek, Walton Creek, and Jack Creek. For a map of the study area, click here.
Project Description: Logging practices between 1860 and 1940 included cutting riparian forests, which resulted in the elimination of large woody debris input for instream pool formation. Biologists believe instream pools provide winter habitat for trout, enhancing over-winter survival and trout abundance. Log drop structures (also known as low log dams, log weirs, or low stage check dams) are a widely used stream restoration technique in moderate- to high-gradient streams. They are designed to enhance salmonid habitat by scouring a plunge pool below the log and impounding the water above it. Although there had been some evidence that these structures increased trout abundance and biomass, the mechanism behind this increase had never been understood. Prior to this study, there was never a controlled, replicated experiment testing the response of trout populations to habitat manipulation using log drop structures.
Project Goals: Researchers designed an eight-year, controlled, replicated study to evaluate the effectiveness of habitat manipulation using log drop structures on trout abundance, biomass, growth, survival and movement. Research was conducted on six high-elevation (2,425 to 2,925 meters), moderate-gradient (1 to 2.4 percent) streams in northern Colorado. The streams were chosen to be representative of small, mountain trout streams in the central Rocky Mountains, including a range of elevations, habitat conditions, and trout species.
Project Methods: In late summer 1988, study reaches were selected on each of six high-elevation streams: South Saint Vrain Creek, Little Beaver Creek, North Fork of the Cache la Poudre River, Colorado Creek, Walton Creek, and Jack Creek, based on typical characteristics that allowed habitat manipulation by fishery management agencies. Except on South Saint Vrain Creek, study reaches on each of the streams were 500 meters in length. The reaches were divided in half. One half the study reach was randomly designated as the habitat manipulation section where log drop structures were installed. The other half of the study reach served as the unmanipulated control. Click here for more information on project methods.
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  Log drop structure on Colorado Creek....  
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  Annual monitoring conducted on treatment and control reaches on all six streams ...  
Monitoring Data and Collection Methods: Annual monitoring conducted on treatment and control reaches of all six streams included habitat measurements, angler surveys, fish population surveys by electrofishing to determine abundance, and fin-clipping to determine growth, survival and movement. Click here for more information on monitoring.
Was this project effective and how was this determined? Manipulation of stream habitat to increase fish populations is a common practice. Hydrologists and fish biologists design restoration around the assumption that habitat availability limits trout abundance. Rarely do they conduct important pre-habitat manipulation evaluations to determine the limiting factors. This in-depth study is applicable regionally to installation of log drop structures in high mountain streams–-a common restoration method in the Rocky Mountain region. Results of the study show that log drop structures provide more quality habitat by decreasing stream velocity and increasing pool volume and cover. Once adult trout move into the new habitat, they tend to stay there rather than emigrate to another stream reach. Therefore, the increase in trout abundance is due to immigration, not due to increased growth rates, recruitment, or survival.

Results of the study have implications for fish management at a watershed scale. The study showed that fish moved into the habitat manipulation reach from long distances, rather than from the adjacent control reach. If these immigrant fish vacated their previous habitat because it had become unsuitable, then the habitat manipulation resulted in increased watershed-wide survival rates by providing new, suitable habitat for these fish. Alternatively, if the habitat that these fish vacated was still suitable, this habitat would become available for use by other fish. Again, this would increase watershed-wide survival rates. Thus, the effect of the habitat manipulation was not to simply concentrate the same number of fish into a smaller area. Watershed-wide fish survival rates were increased by the manipulation.
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  (Before) Typical characteristics of the study reaches were: narrow with coarse s...  
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  (After) U.S. Forest Service hydrologists and fishery biologists installed ten lo...  
Confounding Effects/Additional Information:
Project Specs (all specs are estimates):
  Overall Estimated Cost:
For more information on this project contact:
  Dr. Charles Gowan, Randolph-Macon College, Email:
Dr. Kurt Fausch, Colorado State University, Email:
This information was collected by: Kristin Keith
Project last updated on: 2/12/2007

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Updated: February 16, 2007
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