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I i___l ' ~ ~ J ~ people are naturally drawn to these areas and feel refreshed and comforted by them. ~ r f, Likewise they are repelled by dark, crowded ~ ~ w~,;_ areas of low biological diversity. A certain amount of the discomfort associated with overgrown or invasive-dominated natural areas in the park may be related to this phenomenon. I__1 ~ ~ ~ ~ ~ i 3' English ivy, shown here, can ~ Riverbank Stabilization _ spread quickly throughout the V Since the construction of the I-105 freeway ~ landscape by birds. Ideally, In 1962, the banks of the Willamette River should be controlled ~ before 't has a chance to set in the western portion of Skinner Butte Park Q fruit. have been rapidly eroding. To construct ~ the freeway, a portion of the north river bank U Scotch broom, English hawthorn and was extended into the river and armored Norway maple are quickly taking over large with rip-rap, thus increasing the speed of i.'_ ~ areas of the butte and river banks. Today, water flow through this area and directing very little remains of the original habitats it towards the south bank. Several flood ~ that were once plentiful within the park. events triggered large-scale erosion along Although there are a number of factors that this bank. Atypical pattern occurs when a contribute to this, including management, large cottonwood tree is undercut and falls development and human use, the threat into the river, leaving a large gap of exposed I . posed by invasive plants is seen as soil on the high bank. High water forms an ~ perhaps the greatest. eddy in the gap that accelerates the forces of erosion in a downstream direction. 1_.= Invasive plants cause other, more human- Several efforts have been undertaken to related problems, as well. Almost always, correct this problem, including the the areas that people perceive as most dark installation of gabion baskets (rock filled and unfriendly are dominated by invasive wire baskets) in the early 1970s, and an plants. As a result, legitimate users tend emergency stabilization project using rip- to shy away from natural areas in the park, rap in the later 1990s. Although the more Current erosion control and these areas are frequently given over recent effort appears to be resisting the includes armoring banks with to undesirable uses such as illegal forces of erosion, the gabion baskets riprap as shown here. This is camping, drinking and drug use. Studies appear to be undercut and are in danger seen as an emergency have shown that humans have an affinity of failure. measure. Non-structural for the natural beauty of healthy, diverse, ,I reinforcement improves habitat and is the preferred native plant communities. Interestingly, Along-term solution to this problem will be method. necessary to protect the park from further P. i i _ - erosion. Current management policies for ~ ~ ~ 8 riparian areas, including those associated ~ ~ ~ with the listing of native Willamette River . - salmon species through the Endangered ~ Species Act, discourage the use of _ . structural stabilization techniques such as rip-rap and gabions. Non-structural - stabilization such as terracing and planting of stabilizing, vegetation is a preferred method that helps increase riparian and aquatic habitat value. In particular, the ~ creation of lower flood terraces is known ~ ' to provide refuge and salmon fry migrating towards the ocean. i ~ , Skinner Butte Park • Master Plan 2001 39 ~