Issues of Ecological Concern Regarding the Proposed Luebbers Development in Corvallis, Oregon

Executive Summary

May 2003

The Conservation Biology Institute (CBI) was approached by the citizens living in the Live Oak Drive area of Corvallis, Oregon, to review a proposed housing development planned for their area. The review had to be completed within a two week period and was to be focused on the ecological considerations and concerns invoked by the proposed development and not whether the development should or should not be approved.

The proposed development is located in the headwaters of Dixon Creek just outside the urban growth boundary (UGB) for the City of Corvallis. The development site contains two intermittent tributaries that flow directly into the West Fork of Dixon Creek. The proposed development would require substantial road improvement to Live Oak Drive immediately adjacent to Dixon Creek, including a section within the UGB. The development plan also proposes to construct Live Oak Court over steep slopes, which would connect Deer Run Street with Live Oak Drive. No plan for stormwater management or drainage plan for the road design have been provided. Wetlands are located on the east side of Live Oak Drive near the proposed development and should require a detailed wetland delineation and possible mitigation plan. No endangered species survey has been performed and will likely be required. The southeasterly side of the proposed development site is very step and has a history of landslides. The site has been identified as “sensitive” by Benton County Planning Commission staff due to its steep slopes (most of the site contains >20% slope) and highly erodable soils. No detailed sewage disposal plan for the proposed housing development was provided.

Dixon Creek Setting

Dixon Creek originates in the hills of northwest Corvallis, and the watershed contains 2,712 acres. Three main tributaries (the East Fork, Middle Fork, and West Fork) flow southeast and converge just south of Walnut Boulevard at which point the mainstem of the creek flows through largely low-density residential and commercial properties of the city (approximately 1/3 of the watershed) before draining into the Willamette River near the sewage treatment facility. The proposed Luebbers development is located in the headwaters of the West Fork of Dixon Creek.

Historically, Dixon Creek behaved much like the Willamette River and many of its other tributary streams, channels naturally meandered across a wide floodplain resulting in a wide variety of habitats including numerous wetlands. After most storm events, water drained from the surrounding uplands slowly compared to current flow conditions. Areas flooded, but they did so less severely over wider areas. Through extensive human engineering, the natural pattern and hydrologic dynamics of rivers and streams throughout the Willamette Valley was greatly transformed. Today, the river and many of its tributaries have been constrained into fewer, deeper channels. The loss of stream channels and natural hydrologic processes has had major ecological consequences not the least of which were a reduction of water quality, change in the hydrologic regime, and loss and alteration of critical habitat for numerous aquatic species including salmonids.

Major Ecological Considerations

• Dixon Creek is not used by Chinook salmon for spawning or rearing. During high water, however, Dixon Creek provides important refugia for Chinook salmon.

• According to the Oregon Department of Fish and Wildlife, cutthroat trout utilize Dixon Creek (including spawning) up to and including the headwaters.
• The proposed development lies in the headwaters of Dixon Creek, a tributary of the Willamette River. Headwaters typically support rich and varied communities of plants and animals. The headwaters of Dixon Creek are the most ecologically intact reaches of an otherwise significantly degraded stream.
• The required road improvement to Live Oak Drive would have a major impact on an important stretch of riparian corridor along Dixon Creek, described by the Corvallis Natural Features Inventory as “High” in water quality and wildlife habitat.
• Both during construction and long after, there will be an increase in sedimentation to Dixon Creek. Road improvements to Live Oak Drive, construction of Live Oak Court, driveways and housing surfaces will all lead to increased erosion.
• Chemical contamination will increase with inputs from oil and other pollutants washing off the increased impervious surface, more heavily traveled roadways, and from the runoff of commonly used household lawn and garden chemicals.
• Potential improper location and maintenance of sewage septic systems would translate into increases in fecal coliform bacteria and E. coli, both of which are already at unacceptable levels in Dixon Creek.
• With the increase in impervious surface and disruption of a significant portion of Dixon Creek, peak flows will increase and streambed scouring will worsen.
• Thermal regulation will be impaired by the removal of streamside vegetation during road construction and improvement.
• The disruption of riparian vegetation will worsen an already bad situation with regard to invasive exotic weeds.
• The proposed development has the potential to disrupt the forest linkage zone between northern rural forestry areas and urban wildlife habitat identified by the Corvallis Natural Features Assessment.

For more information, please contact James Strittholt.