Performance of In-Stream Habitat Structures Under Flood Conditions

Three field sites were monitored for water surface elevations during 1996 and 1997 and post high-water measurements of channel topography and structure position were compared using Terra Model for each year. The field locations included: St. Regis River, Montana; Zumbro River, Minnesota; and Sammamish River, Washington. Results from the St. Regis River and Sammamish River are reported here. Both 1996 and 1997 recorded higher than average flows at both sites with peak flows at 25 year recurrence period levels or greater. Topographic and photo surveys of the sites were used to measure the evolution of the channels and banks including patterns of deposition and erosion. Of the structures represented in these sites, including: boulder clusters, low flow deflectors, sills, and root wads, the boulder clusters showed the greatest changes in position or "instability" while the low flow deflectors effected the greatest local change in bed topography based on deviation from average cross sectional depths. The habitat enhancement projects were newly constructed in the Sammamish River in 1995 prior to the winter and spring peak flows.