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Historic
In general, riparian areas support high species abundance and diversity because of the varied sources of food, water, and shelter found in these streamside habitats. Based on Coast Survey charts of the lower Willamette River from 1870 to 1887, the riparian habitat of the Willamette River bottomland in this subwatershed was a mosaic of open water (Guilds Lake), wetlands, grassland, and forested areas(Graves et al., 1995).
In the Balch Creek canyon above the bottomland, the riparian habitat of hillside streams was closed canopy forest (Hulse et al., 2002). Much of the West Hills portion of this subwatershed burned sometime in the mid-1800’s (Hulse, et al., 2002) and there is no indication of composition of the riparian habitat in the burned area. The dominant soil types of the ridges and slopes of the West Hills are fine-textured and prone to failure when saturated or disturbed. As a result, landslides, mudslides, and slumps were common in the steep terrain of the West Hills (City of Portland, Bureau of Planning, 1992c). Slope failures typically occurred after periods of heavy rain and provided the primary source of rocks, gravels, and other substrates to the stream channel (City of Portland Bureau of Planning, 1992c). Wildfires would have exacerbated slope failure in certain situations.
Current
The Willamette River floodplain has been nearly completely filled and developed, with almost no remaining riparian habitat. Based on a visual estimate of 2002 aerial photography, the land cover in this part of the subwatershed consists of approximately 97% developed areas and 3% tree, shrub, and grass cover. Developed areas include buildings, parking lots, shoreline structures, and unclassified cleared areas.
Above the bottomland, the riparian habitat of Balch Creek and tributaries resembles historic conditions of mixed conifer deciduous forest, while confluence regions are dominated by deciduous species. This portion consists of a total of 88% tree and shrub cover, 7% industrial land, and 5% cleared or residential areas. The riparian habitat in many areas along Balch Creek is characterized as a "gallery" forest, consisting of a mix of red alder and black cottonwood trees (City of Portland Bureau of Planning, 1991).
Vegetation around the headwaters of Balch Creek is described as a second growth mixed conifer and hardwood cover with some remnant first growth Douglas fir trees (City of Portland Bureau of Planning, 1991). Common tree species include big leaf maple, vine maple, willow, western hemlock, red alder, western red cedar, and Douglas fir. Although large trees persist throughout the riparian corridor, grasses and shrubs, rather than intermediate sized trees (and species composition), comprise the understorey of these forested areas Metro’s inventory of regionally significant riparian resource areas within the subwatershed maps landscape features that contribute to key riparian functions as outlined in current scientific literature. The City has established protections for some riparian areas and is updating its inventories to include more current information on riparian area resources.
Assessment
Riparian areas, with landscape features such as streams, wetlands, water bodies, floodplain, tree canopy, vegetation, ravines and steep slopes, contribute to key functions including streamflow, flood storage, water quality, bank stabilization, erosion control, channel dynamics, microclimate, food web, and wildlife habitat. Urban development, pier and dock construction, filling, road building, and vegetation removal altered riparian habitat conditions.
As urban development increases (particularly in middle Balch Creek), riparian integrity will continue to decline; corridors will become more fragmented due to presence of roadways, residential dwellings will encroach onto the stream bank, vegetative cover will diminish (or become more characteristic of landscaping species) and impervious area will increase.
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Government 
