Author(s): S. F. Boelman; O. R. Stein
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Abstract: The St. Regis River in western Montana USA, has been impacted along most of its 59 kilometer length by various activities including several active and abandoned road and railroad grades. As a result, most of the river has been relocated and/or channelized. Several miles of fishery improvement structures were installed between 1972 and 1982 as mitigation for new highway construction. Biological assessments in 1976 and 1982 concluded that random boulder clusters and associated scour pools were effective mitigation for loss of trout habitat, though the longevity of these improvement structures was unknown. The stability of existing clusters and their impacts on channel stability, conveyance, and sediment transport are analyzed in the present study. Pressure transducers installed in November 1995 have continuously recorded river stage differences over a boulder cluster reach as compared to an upstream control reach. The data includes an event estimated to be in excess of a 25 year return interval. These data, in conjunction with detailed bed surveys and velocity measurements, assess the short-term impacts of boulder clusters on channel morphology and hydraulic performance. Stereoscopic aerial photography data has been collected on approximate 5 year intervals from a time pre-dating boulder placement. Long-term changes in channel morphology; including aggregation, degradation and lateral migration; and boulder stability are investigated using historical flow data, the stereoscopic aerial photography, and present-time bed surveys.
Year: 1997