Project will enhance Whychus Creek

Whychus Creek is one of the most important features of the landscape of Sisters. The stretch where it runs through town is slated for enhancement.

The Sisters City Council reviewed concept designs for the Creekside Park and Campground Fish Passage and Restoration Project at their September 26 workshop. Mathias Perle, program manager for the Upper Deschutes Watershed Council (UDWC), made the presentation.

The City and UDWC are collaborating to restore and enhance the section of Whychus Creek between the Locust Street bridge and the Highway 20 bridge, where the creek runs between the park and the campground. This is a complex project that will involve a number of regulatory and permitting agencies.

The consolidated project addresses issues of concern for both entities. The UDWC wants to eliminate the current conditions along the creek, which cause erosion of the banks and damage to the riparian areas. They also want to improve the conditions for the passage of fish and in-stream aquatic habitat.

The City needs to protect the 12-inch sanitary sewer mainline which is currently hanging on the upstream side of the Locust Street bridge, leaving it vulnerable to damage from vandalism, debris or ice jams floating downstream, and vehicle traffic.

With the installation of the new ADA bathroom in the campground, the City also wants to make the pedestrian bridge ADA compliant. The current approaches to the bridge have steep grades, making use by someone in a wheelchair or with limited mobility very difficult if not impossible (see story, page 18).

A 10-inch PVC gravity-fed sanitary sewer line is buried underneath the creek between the footbridge and US 20. A four-foot concrete cap was installed on top of the PVC line to help protect it from erosive forces in the creek. Since the cap was installed in 2001, the surrounding streambed material has been scoured away and two feet of the cap rise above the streambed, creating a fish barrier and hazard to the creek and creek users. There are a number of alternatives for modifying the cap and/or its surroundings to improve fish passage.

The creek also lacks in-stream complexity, which can be important for regulating water temperature, a necessary factor for returning fish. Complexity, created by adding boulders and V-shaped weirs to create small pools, and stream bank rootwad clusters also provide biodiversity and aquatic habitat.

Heavy use of Creekside Park and the campground has led to degraded conditions of Whychus Creek and its banks. Campers and park visitors have created numerous creek access points. Combined with localized scour and erosion, various locations within the project reach are in need of bank restoration.

One highly visible area of bank failure began about five years ago on the northern creek bank near the concrete cap of the sewer line. The spot is currently marked with orange construction fencing to keep visitors from the eroded bank. Approximately 10 feet of bank recession has occurred.

Once the renovation work is completed, the creek bank on both sides will be planted with native plants to increase long-term bank stability and eventually disguise the restoration work. Combining split-rail fencing, controlled access points, signage, and revegetation will hopefully help control foot traffic along creek banks and prevent further user-created bank degradation.

The pedestrian footbridge across Whychus Creek between the park and the campground is about 40 feet long with a five-foot-wide covered wood walkway supported by two 26-inch-diameter tamarack logs that came from Green Ridge and were donated to the project in 1999. The structure sits on grouted rockery abutments on concrete footings.

The location of the abutments creates a constriction or pinch-point in the active creek channel. Scouring and undermining by the creek's accelerated flow between the abutments is occurring under the north abutment, although there doesn't appear to be any imminent danger to the bridge's stability.

The bridge foundations, wing walls, and approach ramps were reportedly constructed by the Civilian Conservation Corps in either 1939 or 1941. Sometime in the middle of the 20th century a bridge utilizing the abutments was built. In 1999, as a Boy Scout project, the bridge was rebuilt. The original design called for a true covered bridge with sidewalls containing windows. The plan was revised to include the open sides visible today.

The historic nature of parts of the bridge places it under the purview of the State Historic Preservation Office (SHPO). As the design of the new approaches advances, SHPO reps will determine the extent of mitigation required for changes made.

The existing bridge deck, at five feet wide, is adequate for light pedestrian traffic, but during events, bicycle use, and use by dog-walkers, the space can be restrictive, especially when people stop to enjoy the view of the creek. The concept design proposes adding two-foot wide "bump-outs" on either side of the bridge to accommodate users who would like to pause on the bridge.

To address all these issues, the City and UDWC have secured grants to hire the consultant that produced the conceptual designs presented to Council and will provide the final design, A 50 percent design package should be ready by December 12, 2018 and the final design completed by January or February 2019. The initial concept drawings can be viewed at the City of Sisters website: https://www.ci.sisters.or.us/community-development/page/activeprojects.