Response of Trout Populations in a Colorado Stream from Conversion of a Highly-Confined, Channelized and Riprapped, Single-Stage Stream Segment to a Moderately-Confined, Three-Stage Stream with Functional Floodplain
Matt Kondratieff
Colorado Parks and Wildlife
Fort Collins, CO
Authors: Matt Kondratieff & Eric Richer, Colorado Parks & Wildlife, Fort Collins, CO
Many Colorado streams have been channelized to convey floods, protect infrastructure, and maximize crop production over the past two centuries. We report on a study assessing the effects of converting a highly-confined, channelized and riprapped, single-stage Rosgen F-stream (confinement ratio = 1.2; channel slope < 2%) to a moderately-confined, three-stage Rosgen Bc-stream (confinement ratio = 2.0; channel slope = 0.9%) on trout populations. Primary treatments within the high-intensity segment consisted of removal of riprap and excess bank material to create a new floodplain and shape a new active channel that aligned with current bankfull discharge. Response of trout population abundance from the high-intensity segment were compared to low-intensity and control stream segments. Channel cross-sectional geometry was not altered in the low-intensity segment (pre- and post-construction average confinement = 1.2). The low-intensity segment remained highly confined, riprapped, and constrained between two roadways. Pre-construction baseline data were collected at the high-intensity (two years), low-intensity (three years), and control (one year) segments. Post-construction fish population monitoring continued for a total of five years, evaluating fish population composition, density (number/mile), and biomass (lbs/acre) for populations within the three segments. Project effectiveness monitoring was based on data for Brown Trout (Salmo trutta) only as they are a wild and self-sustaining population (not stocked), a popular game species, and less sensitive to confounding variables such as whirling disease, metals toxicity, and water pollution. Post-project monitoring of Brown Trout populations suggest that habitat treatments have resulted in an increase in Brown Trout density and biomass in both high- and low-intensity treatment segments. Within the control reach, Brown Trout density and biomass did not change significantly over the five year monitoring period. The magnitude of change for Brown Trout density within the high-intensity segment (+182%) was higher as compared to the low-intensity segment (+104%). Brown Trout biomass increased even more within the high-intensity segment (+422%) as compared to the low-intensity segment (+76%). This evaluation suggests that the conversion of highly-confined, channelized and riprapped, single-stage streams to a reference-like historic condition can cause large increases in trout population abundance and biomass.
About Matt Kondratieff
Matt Kondratieff is an Aquatic Research Scientist for Colorado Parks and Wildlife in Fort Collins, CO. He completed his undergraduate work at U.C. Davis, received his Master’s from Colorado State University and he worked for three years as a fisheries biologist for Wyoming Game and Fish in Pinedale, WY. Matt has 14 years experience involving the design, construction, and monitoring habitat restoration and enhancement projects in Colorado. Recent research has focused on the biological response of aquatic organisms to stream habitat restoration treatments. Additional research interests are focused on the influence of in-channel structures, such as whitewater parks and water diversions, on fish populations and fish passage.