Graduate Thesis Or Dissertation
 

Sediment production from forest roads in the upper Oak Creek Watershed of the Oregon Coast Range

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/br86b793p

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  • Unpaved roads are sources of chronic sediment in forested watersheds. Bare soil on roads is exposed to erosion from rainfall and runoff Published research on sediment production from forest roads focuses primarily on road characteristics. Since water drives the mechanics of sediment transport, hydrologic variables should correlate with sediment production. This project investigated the relationship between sediment production and runoff-producing storms. Road and hydrologic variables were correlated with total sediment production for nine road segments in the upper Oak Creek Watershed from November 2002 through June 2003. One of the road segments was monitored intensively during four runoff-producing storms. Field data were compared with total sediment production predicted by SEDMODL2 and WEPP:Road. Total coarse and settleable sediment produced from the nine road segments ranged from 0.025 kg (2.77 x 10⁻⁶ kg/m²/mo) to 15.0 kg (1.04 x 10-² kg/m²/mo) while total runoff volume ranged from 100 m³ (1.11 x 10⁻² m³/m²/mo) to 52,000 m³ (36.1 m³/m²/mo). Correlation between total coarse and settleable sediment and total runoff volume for all road segments was significant (R² = 0.51, p-value = 0.004). No other variables correlated as strongly with total coarse and settleable sediment. However, while hillslope gradient and cutslope height did not yield significant correlations with total coarse and settleable sediment as individual variables, when added to total runoff volume in a multiple linear regression model, the relationship was improved. Suspended sediment data was collected for four storms at one culvert. Results showed that suspended sediment concentration had time derivatives similar to those of culvert discharge, 1-hr rainfall intensity lagged one hour, and 2-hr rainfall intensity lagged two hours. Summed instantaneous suspended sediment concentration was correlated with cumulative rainfall. SEDMODL2 results of predicted sediment produced from the nine road segments ranged from 0.0 to 6.7 kg (4.4 x 10⁻⁴ kg/m²/mo). WEPP:Road results ranged from 160 kg (7.4 x 10⁻² kg/m²/mo) to 3020 kg (19.5 x 10⁻² kg/m²/mo). When compared with actual sediment data (0.025 kg to 15.0 kg), SEDMODL2 had much closer agreement. Further research is needed to quantify the total amount of suspended mineral sediment transported in runoff from unpaved forest roads in the upper Oak Creek Watershed.
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