Year of Award

2000

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Forestry

Department or School/College

W.A. Franke College of Forestry and Conservation

Committee Co-chair

Tara Barrett, Thomas H. DeLuca

Publisher

University of Montana

Abstract

In recent years more efforts have been made to return unneeded roads to natural states through obliteration or total recontouring methods. Yet, few data exist to support the road obliteration process. The purpose of this study was to assess some of the relative physical impacts of road obliteration for the O'Brien Creek (Montana) watershed. Three road treatments were chosen: recontoured road at 0 months, recontoured road at 12 months, and existing roads broken down into four segments ( cutslope, fillslope, road center and road tread). Two types of geologic formations were sampled (Bonner and Mount Shields) along with two slope categories (<45% (low) and >45% (high)). Each combination of factors was sampled 5 times for a total of 100 samples. Simulated rainfall was applied to each plot in order to assess erosion potential as sediment yield and runoff. Site characterization measurements, such as bulk density, sieve analysis, and organic matter content, were also taken. One-way analysis of variance was used to compare treatment means for the Bonner geologic formation while two-sampled T -tests were used to compare treatment means for Mount Shield samples. Recontoured roads (0 months) consistently had higher runoff and made more sediment available for erosion than any other treatment for both geologic formations. Statistics also showed that in the Bonner there was no significant difference in the recontoured road (12 months) and the natural slopes in the < 45% category for both runoff and erosion. The high slopes for Bonner were split, with no significant difference in the runoff, but significant difference in the erosion. For the Mount Shields there was no significant difference in the recontoured road ( 12 months) and the natural slopes in the > 45% category for both runoff and erosion. The low slopes were split, with no significant difference in the sediment, but significant differences in the runoff. In all cases it was found that recontoured roads (0 months) produced sediment and runoff comparable or higher than the road segments. But, after allowing for 1-year of revegetation, the volume of runoff and erosion greatly decreased to near natural slope conditions.

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© Copyright 2000 Jennifer Hickenbottom