Graduate Thesis Or Dissertation

 

Scaling hydrologic impacts from road segments to a small watershed Público Deposited

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/hh63t1326

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  • The impact of forest roads on the hydrology of forested watersheds has long been studied. While forest roads have been reported to alter storm runoff at the road segment scale, the potential for changes to be detectable at the small watershed scale has been debated. The purpose of this study was to quantify the road affect at the road segment scale and estimate how those affects are expressed at the mouth of a watershed. This study took place in the McDonald-Dunn Research Forest located in the Oregon Coast Range near Corvallis, Oregon. Claire Creek, a small watershed within the Oak Creek Watershed, and two road segments with the associated inboard ditches and upslope contributing areas were selected to represent the roaded watershed. Runoff from both road segments enters small headwater streams at stream crossing culverts. Discharge was measured from the headwater streams and from the road segments at the stream crossing culvert for five storms during the winter of 2004 – 2005. Discharge was also measured at the mouth of Claire Creek, an adjacent roadless watershed, Finley Creek, and at a gauging station on Oak Creek near the boundary of the McDonald-Dunn Forest. The difference in time of occurrence of peakflows and the length of the stream between the culverts and the mouth of Claire Creek was used to estimate a ‘real’ travel time of the peakflows for all five storms. Kinematic wave equations were used to model travel times of peakflows from the culverts to the mouth of Claire Creek, with and without the influence of the road. At the road segment scale the road affect was detectable for changes in peakflow magnitude, quickflow, and total stormflow, but the affect of the road on changes in the timing of occurrence of the peakflow was inconsistent. At the watershed scale the road affect could not be calculated for changes in peakflow magnitude, quickflow, or total stormflow because of the unavailability of pre-road runoff data. The modeled travel time of peakflows that included discharge from the road were shorter than the modeled travel time of peakflows of stream discharge alone by less than 10 minutes for all five storms. The road effect on real travel times of peakflows was inconsistent and did not correlate to the magnitude of the increase at the road segment or at the mouth of the watershed. These findings agree with earlier studies that have reported a road affect on storm runoff at the road scale, and suggest that the road affect at the mouth of a watershed may not be detectable. The findings also suggest that other factors are influencing runoff at the mouth of a watershed more than the addition of ditch runoff at stream crossing culverts.
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