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University of Oregon North Campus Conditional Use Permit Project
<br />Riparian Assessment and Management Report
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<br />of all these functions reduces downstream flooding and peak instream flow volume, leading to effective flood
<br />storage.
<br />Naturally-vegetated riparian areas are common throughout the PSA along the Willamette River. However, these
<br />areas have been historically reduced to narrow strips along the river, reducing flood storage function. The fields
<br />within the PSA are flat and can contribute to storing flood flows given their undeveloped nature, lack of excessive
<br />amounts of impervious surfaces, and ability to infiltrate flood flows directly on site. However, infiltration rates
<br />may vary throughout the upland parts of the PSA due to various levels of soil compaction.
<br />4.4Groundwater Recharge
<br />Riparian and floodplain areas are important groundwater recharge areas that allow precipitation to infiltrate soil
<br />and pass to the water table. Uncompacted soils are porous and absorb moisture. Organic debris, vegetation, and
<br />native stream substrates can slow down surface runoff, providing additional time for infiltration of precipitation
<br />events and flood flows.
<br />With the PSA, the riparian zone’s relatively dense vegetation slows runoff rates and promotes infiltration. The
<br />upland areas of the PSA are undeveloped and have compacted soils in some locations due to historic mining,
<br />gravel and concrete production, and industrial land uses. These compacted soils can reduce the recharge of
<br />groundwater within the PSA. However, the PSA occurs in an urban area with extensive development and
<br />associated impervious surfaces. As such, there is a lack of local undeveloped floodplain areas that have the
<br />capacity to infiltrate precipitation or flood flows. Therefore, the riparian and floodplain areas in the PSA are critical
<br />for supporting infiltration and groundwater recharge in the urban project area.
<br />4.5Sediment and Contaminant Removal
<br />Sediment loads to streams are often increased by roads and land management practices (e.g., grazing, logging,
<br />etc.) that disturb soils and create vectors for overland erosion and sediment transport. Trees, shrubs, and grasses
<br />act as a filter by reducing water flow rates and encouraging infiltration allowing sediments, nutrients, pesticides,
<br />pathogens, metals, and other pollutants to settle out prior to reaching water bodies. Vegetated riparian areas are
<br />common throughout the PSA and contribute to this riparian function. In addition to the well-vegetated riparian
<br />zones, there are several small potential wetland depressions and drainages within the PSA that may function to
<br />remove sediments from overland flows. Due to their depressional nature, these potential wetlands reduce the
<br />velocity of water allowing the sediments to settle in place.
<br />4.6Fish and Wildlife Habitat
<br />Streamnet (2012) lists the Willamette River as habitat for spring and fall Chinook salmon (rearing and migration;
<br />spawning and rearing, respectively) and summer and winter steelhead (migration only) within the PSA. Bradshaw’s
<br />lomatium has been reported as historically occurring near the PSA and bull trout have been recorded within the
<br />PSA (ORBIC 2017). Several other species were documented during the July 2017 field effort. It is expected that
<br />other mammals such as deer (Odocoileus sp.), coyotes (Canis latrans), muskrats (Ondatra zibethicus), rabbits
<br />(Sylvilagus bachmani), and small mammals from the family Sciuridae (such as squirrels and chipmunks) utilize the
<br />riparian and floodplain areas. Woody debris, benches, overhanging banks, rocks, and dense, stratified vegetation
<br />are present along the Willamette River riparian corridor within the PSA; providing food, water, and shelter to a
<br />large diversity of wildlife and serve as migration routes and stopping points between habitats for a variety of
<br />wildlife. Based on the riparian habitat functions observed within the PSA, it is expected that the riparian zone
<br />provides resting and wintering habitat to Canada goose, northern pintail (Anas acuta), mallards, herons (Ardea
<br />sp.), and other waterfowl; and breeding habitat to songbirds during the spring and summer. The riparian zone
<br />also provides potential habitat for reptiles and amphibians, such as gopher snakes (Pituophis sp.), garter snakes,
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