1. Abstract Upland areas of the Willamette Basin are associated with a long history of logging and related road construction. Sediment derived from forested areas can greatly impact the rates of geomorphic processes and water quality in downstream areas. Soil erosion on forest roads can come from many different sources, with controlling variables that include slope angle and spatial position. A key event that has been subject to much research is that of the 1996 storm and flood event in western Oregon. Intense rainfall caused widespread erosion in forested areas. Road erosion is dependent upon local geology, forest condition, and construction style. In addition, soil texture and degree of vegetative cover also played a role in controlling erosion rates. Forest roads in clear-cut areas were associated with significantly more sedimentation and higher erosion rates. Introduction The specific designs of forest roads and placement of them can significantly help lower the chances of sediment build up or erosion that results from natural storms. Poor planning of placement can endanger the natural habitat as well as the workers who use the roads. To be successful the planning must take into account several different factors and must be able to be altered when the actual construction begins. Currently many forest roads are threatened by flooding, landslides, and soil erosion making them unsafe and unstable to use (Figure 1). Many studies have been conducted to figure out the best placement of forest roads and how to protect pre-existing ones that have already been built in precarious locations. The information gained from these studies can help determine the natural factors forest roads face. Oregon forests have been good testing grounds because they weather severe storms and flooding. With each passing incident scientists can take away what worked and what did not and incorporate those factors into planning for new roads. Methods Used With such wide variety of natural factors, scientists have to obtain a large amount of information based on everything from soil conditions, weather, plant life, logging plans, location, and many others. To study erosion scientists use sediment traps to measure sediment production. The sediment traps were 1.5 cubic meter plastic bins that were first weighed with water and sediment and then water only. The flow came into the bins using culverts (Figure 2) which could often get clogged and caused additional flooding and sediment production, and then end up in sediment traps (Figure 3). One study tested two different types of soil textures and tested eleven different features that effect forest road sediment production: inherent erodibility and runoff producing capacity of soil and running surface; road segment length; road gradient; amount of cutslope and running surface; treatments of cutslope, running surface, and fillslope; flowpath geometry as embodied in insloping and outsloping and degree of rut development; slope position and aspect as they affect soil moisture; forest cover; time elapsed since construction; road use and weather (Luce, 1999). References Cited Akay, Abdullah., Aruga, K., Chung, W., Miyata, E., and Sessions, J., January 2007, Incorporating Soil Surface Erosion Prediction into Forest Road Alignment Optimization: Internet Web Resource, URL : Http://www.lib.unb.ca/Texts/JFE/ January2007/jfe18_1art03.pdf ( last Updated January 2007).Http://www.lib.unb.ca/Texts/JFE/ Black, T., and Luce, C., August 1999, Sediment Production for Forest Roads in Western Oregon: Water Resources Research, v. 35, No. 8, p.2561-2570. Jones, J., Swanson, F., and Wemple, B., 2001, Forest Roads and Geomorphic Process Interactions, Cascade Range, Oregon: Earth Surface Processes and Landforms, v. 26, p. 191-204. Oregon Department of Forestry, July 2000, Forest Road Construction: Internet Web Resource, URL : http/www.oregon.gov/ODF/STATE_FORESTS/docs/ management/roads_manual/RMSec4-Const.pdf (last Updated July 2007). Effects of Forest Roads on Hillslope Hydrology and Sediment Production in the Willamette Basin Prepared by: Allison McGonagle Results and Discussion of Data The first study found that the variability of sediment production is high from road segment to road segment. In this study there was not much sediment produced but when it was found there was a lot of it produced. They also found that soil that was coarser produced less sediment than soil that was fine so the soil texture had a large impact on sediment production. The second study found that fluvial features were used less than mass movement of sediments and ¾ of movements were mass while the remaining ¼ were fluvial. Most of the sediment that ended up on the roads was from debris flows while other avenues ended up off the road (Figure 5). Fillslopes accounted for 2/3 rd of sediment being removed from roads and hillslopes had most of the remainder. Older and mid-slope road have the bulk production of sedimentation and debris flow issues. Conclusion Both studies resulted in outcomes that helped users and builders of forest roads. The first study found that since there were many road segments studied and only a few were high risk for sediment production that it would more cost effective to focus engineering upgrades to the few roads that were sediment prone. The second study found that valley floor roads provide more effective sediment passages then the other two levels of roads. Now developers can focus on how to maintain and perfect the passages on the valley floors since they held up the best. Since the studies there has been more research on road alignment and its effect on erosion. These studies have been focusing on how a road connects with different sources such as streams and how erosion and sediments are transported as well as the costs of building new roads. Each of these studies is taken into account when Oregon Department of Forestry looks into planning for more forest road developments. During the process of new road construction the real life application comes through and the process is altered with the new information. Figure 3. A plot layout sample (Black and Luce, 1999). Figure 1. Photo of flooded road (Akay and others, 2007). Erosion Figure 4. Location map of testing sites (Jones, Swanson and Wemple, 2001) Figure 2. Example of a culvert (Akay and others). Methods Used Continued A second study looked more exclusively at road placement and used roads that were at different elevations and hillslope positions as well as road age and density factors (Figure 4). The elevations zone coordinated with different weather positions with the low elevation from 400-800m, middle elevation 800- 1200m and higher elevation >1200m. Then the basin was sectioned off into upper slope, mid-slope and valley floor zones. They then observed the February 1996 storm and recorded the results (Wemple, 2001). Figure 5. Example of a debris flow (O.D.F., 2000).