Year of Award

2019

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Environmental Studies

Department or School/College

Environmental Studies

Committee Chair

Len Broberg

Committee Co-chair

Vicki Watson

Commitee Members

Len Broberg, Vicki Watson, Anna Klene

Keywords

Montana, Dam Removal

Subject Categories

Water Resource Management

Abstract

Using existing water quality data, historical aerial photographs, and recent orthoimagery, this research assessed how the environmental conditions of Rattlesnake Creek near Missoula, Montana have changed over nearly 90 years of human alteration of the Rattlesnake valley. To characterize stream health, the following indicators were investigated: fish genetic composition and species distribution, water temperature, streamflow, and nutrient levels. Five overlapping aerial photos from 1929 were georectified and compared to 2015 orthoimagery to assess changes in channel form (particularly channel straightening) and land cover across the Rattlesnake Creek valley bottom. Results indicate that trout species in Rattlesnake Creek have hybridized, in particular, rainbow trout, Yellowstone cutthroat trout, and native westslope cutthroat trout. Furthermore, upstream movement by native trout has been severely limited by the lower Rattlesnake Creek Dam, located 3.5 stream miles above the creek’s confluence with the Clark Fork River. Average orthophosphate levels have decreased, while average nitrate levels have stayed roughly the same. Although stream discharge data are limited to a few years at various sites, recent data suggest an increase in annual peak discharge and a shift in peak discharge to earlier in the season compared to historical data. Stream temperatures were difficult to compare over time due to lack of data. The aerial photo analysis demonstrated small changes in channel form between 1929 and 2015 relative to the dramatic shift in land cover from grassland to developed during that time.

The lower Rattlesnake Creek Dam is planned to be removed, beginning in the summer of 2019. In addition to assessing changing conditions, this work also describes pre-removal baseline conditions, which may be used in the future to evaluate the effects of this dam removal. Although not all data acquired were suitable to describe long-term trends, they will likely still be of use if compared to future data, post-dam removal.

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© Copyright 2019 Christopher D. Miller