Bioengineered Solutions in the Mill Creek Watershed

The health of streams in the Okanagan Lake of British Columbia, like those throughout North America, is influenced by human development. Urban, agricultural, industrial, and forestry activities have resulted in increased erosion and pollution, altered drainage patterns, and reduced riparian vegetation.

With urban, agricultural, and industrial activities, there are problems of drainage and periodic flooding that often result in property loss or damage. Many of the methods used to overcome these problems were for the sole benefit of property owners, and ecological and other habitat functions were not considered. Typically, stream (and drainage) management became strategies to protect property – or, as some may say, ³liability management.² Using piped networks and concrete or mortared rock walls eliminated valuable habitat for both aquatic and terrestrial life. These practices, although successful at curbing the flooding problems, reduced naturally occurring watershed functions and helped create an entirely different set of problems for the species that rely on streams during their life cycles.

The Mill Creek watershed has a drainage area of 86.3 mi.2, 24.3 mi.2 of which is within the City of Kelowna’s boundaries (Dayton & Knight, 1989). In addition to use by aquatic and terrestrial wildlife, the watershed is subjected to a variety of other uses, including forestry, drinking-water supply, livestock watering, agriculture, residential, industry, and irrigation (Ministry of Environment, Lands and Parks, 1996). Primary uses in the lower reaches include urban, industrial, and agricultural. All of these activities have resulted in increased erosion and pollution, altered drainage patterns, reduced riparian vegetation, and a lack of habitat for aquatic life and wildlife.

Historically the creek has supported a variety of recreational and course fish species, including Kokanee salmon, rainbow trout, brook trout, redside shiner, longnose dace, and northern squawfish. The main fish species of concern in Mill Creek are the fall-spawning Kokanee and the spring-spawning rainbow trout, as these populations have been declining dramatically over the past decade (UMA Environmental, 1996).

In 1996 the area experienced a cryptosporidium outbreak, which brought water-quality and watershed issues to the forefront of community concerns. The municipality recognized the importance of focusing efforts on restoring Mill Creek and initiated the Lower Mill Creek watershed Restoration Program in 1997. The program focuses on both the rural and urban areas that fall within municipal boundaries and commits to completing a major restoration and enhancement project each year to demonstrate techniques to improve watershed health. That same year, stakeholders in the upper watershed also initiated restoration and enhancement projects primarily using funds from Forest Renewal BC’s Watershed Restoration Program.

The chosen projects for 1997 and 1998 were based on site visits and partnerships established with local landowners. In 1997 the installation of a tree revetment stabilized a section of creek through a local turf farm, and erosion control blankets stabilized another section of creek in a rural farm area in 1998.

In 1998 the municipality received funding from Forest Renewal BC to complete a channel assessment procedure for the lower reaches of Mill Creek. This completed the channel assessment for the entire Mill Creek watershed, as the upper reaches were completed at an earlier date. The study identified priority restoration sites and provided the scientific information to support restoration efforts. The study also provided the technical information required by many different funding organizations. Overall, the channel assessment procedure’s general recommendations included stabilizing the streambank, planting riparian vegetation, and removing refuse and invasive weeds (Wildstone, 1999).

Tree Revetment

In 1997 the city’s Environmental Division tackled its first restoration project along Mill Creek. The focus of the project was to stabilize streambanks by using a tree revetment. Tree revetments provide numerous benefits including:

  • deflecting stream currents to protect banks from eroding;
  • dispersing the energy of the water as it flows in a natural meandering channel;
  • increasing water quality by significantly reducing sediment loading and related nutrient enrichment impacts by acting as a flow buffer (absorbing some of the force and decreasing the velocity);
  • producing turbulence and eddies with branches and limbs, which effectively intercept and trap sediment, further stabilizing the banks and securing the trees;
  • protecting adjacent property;
  • providing fish habitat from brushy top growth and other parts of the trees that create shade and providing diverse currents, bed shapes, and sediment deposits (McCullah and Kendrick, 1997).

Site Description

A local turf farm along Mill Creek was chosen as the site for the demonstration project because of the highly visible erosion, lack of riparian vegetation, livestock with direct access to the creek, good visibility, and cooperation with the local landowner. It was also hoped that the project would encourage nearby residents to partner in similar restoration efforts.

The project included several facets aimed at reducing erosion, enhancing water quality, restoring habitat, and minimizing property flooding. Chosen project components included a tree revetment, rock riprap keys, fencing to restrict livestock access, and replanting of indigenous species.

Project Steps

1. Regrading the Streambanks. An excavator regraded 230 ft. of nearly vertical streambank on either side of Mill Creek to a 3:1 slope. This provided a gentle slope on which to place the trees.

2. Fence-Post Installation. Fence posts were installed 20 ft. apart and approximately 1.5 ft. from the water’s edge with 1.5 ft. exposed.

3. Rock Riprap Keys. The creation of riprap keys using 6- to 30-in. rock installed at the upstream edge of both revetments ensured that streamflow would not undermine the revetment, compromising its stability. The use of silt fencing during installation of the riprap keys helped reduce sedimentation.

4. Tree Placement. Approximately every 1.5 ft., one tree was placed horizontally on the streambank slope, with the tip oriented slightly downstream. This provided an overlap of the trees, ensuring a continuous armoring of the bank. The coniferous trees used were mainly lodgepole pines that were 20 ft. long with 6- to 8-in. butts, 1- to 2-in. limbs at the trunk, and wide, thick branches. Other suitable tree species for a project of this nature would include cedar, fir, and yellow pine. The trees can be double-crowned or have some heart rot. Typically, trees that are ideal for revetments are what the forestry companies do not want. Freshly harvested trees were used because they are more flexible than older trees and are less likely to break apart.

5. Securing the Structure. To securely anchor the trees, the butts were cabled with 0.24-in. inert aircraft cable to 3.9-ft.-long, 17.7-in.-diameter deadman logs. Although slow and tedious, this is the most stable method of securing the trees. Other methods can be chosen depending on the hydrologic characteristics of the stream, such as burying the butts of the trees with large rocks. After cabling, the deadmans were placed in a 3-ft. trench, located 10 ft. away from the top of the streambank and were backfilled with soil.

6. Holding Tree Tips in Place. The final step to the revetment involved tightly tying a polypropylene rope between the fence posts installed in Step 2 and nailing it randomly to the trees to ensure that the tips of the trees were securely anchored.

7. Livestock Access. As part of the project, the landowner agreed to fence his livestock away from the creek.

8. Replanting. A replanting program occurred in the spring of 1998 using City of Kelowna Watershed Stewardship Volunteers. Low-growing indigenous species such as red osier dogwood, Oregon grape, rose, and snowberry were planted so that the landowner’s turf and hay crops were not shaded.

Inspection and Maintenance
The tree revetment is inspected regularly for scouring and undermining. The landowner and city staff continue to inspect the cable and fasteners for integrity and tension. In addition, the landowner continues to remove invasive weeds so that native plants can establish. Invasive weeds are superior competitors to native plants because they grow aggressively, and consequently they can be highly destructive to native plants and therefore need to be removed (Cranston and Ralph, 1996).

Habitat Recruitment Structures and Instream Complexing

Using recommendations from the Lower Mill Creek Channel Assessment, two projects were completed in 1999. The first project, a comprehensive restoration project at a former golf course slated for development, utilized habitat recruitment structures, instream complexing, and intensive riparian replanting to overcome extensive erosion, a lack of instream habitat, and a degraded riparian area.

Site Description
Along this stretch of Mill Creek, carefully manicured lawn and golf greens were maintained over the entire property all the way to the edge of the stream. Mature trees were constantly removed from the edge of the stream to allow open fairways for golfers. Within the stream channel, logs and debris were removed to prevent any threat of damming or flooding.

The city’s Environmental Division had an excellent opportunity for restoration at this high-priority site as the property was undergoing redevelopment.

Project Steps
1. Bank Regrading. With an excavator, the streambanks were regraded from a vertical slope to a 3:1 slope to increase the channel width and return the banks to a more natural slope.

2. Habitat Development. Large rock was placed at the toe of the slope, and large logs and woody debris were placed along the slope in order to stabilize the banks, reduce erosion, and recruit habitat for aquatic life. The large woody debris creates habitat by allowing hiding places and pools for fish. It also provides variation and diversity in flow depths and velocities. Some of the material was secured into place using anchored cables and large rock. This helps ensure that the material will not move during high water flows, causing a debris jam and flooding of neighboring properties. Using this technique stabilized 1,500 ft. of streambank.

3. Instream Complexing. A natural system provides many types of habitat. Using a combination of machinery and manual labor, the project carefully inserted large rock for weirs and boulder-cluster structures to replace the overabundant glide habitat with complex pools and riffles.

4. Replanting. More than 2,300 plants representing native species were replanted at this site, including red osier dogwood, willow, birch, hawthorn, alder, rose, pine, cedar, spruce, and fir. Planting took place in the fall of 1999 and spring of 2000 with labor provided by BC Environment Youth Team, Lonely Loon Fly Fisher’s Society, Creative Community Service Program, and other community volunteers.

5. Interpretive Signage. After the project was complete, interpretive signage was developed to raise public awareness on environmental issues relating to Mill Creek. The signage discusses the Mill Creek watershed, the fish that utilize the creek, the importance of riparian vegetation and instream complexity, and before and after photos of the restoration projects. Signage is important in encouraging the public to be stewards of the land and change their beliefs as to what constitutes a healthy creek. To bolster the stewardship initiative, the signage also contains information on how the public can be procurators of Mill Creek and other watersheds.
Monitoring and Maintenance
During the development process, 50 ft. of land adjacent to the creek will be dedicated to the city as a public route-of-access park, while an additional 50-ft. no-build zone will be set aside by the landowner. These precautions ensure that no restoration efforts will be compromised by development of commercial and light-industrial buildings. In addition, visual inspections of structures and plants, photo documentation, and electrofishing will help guarantee long-term project success.

Future Plans
The City of Kelowna Environmental Division is looking forward to completing additional watershed restoration and enhancement projects in the Mill Creek watershed. The Lower Mill Creek Channel Assessment Procedure provides the basis for choosing project sites. Four restoration projects for Mill Creek are in the works:

  • bank stabilization, instream complexing, and replanting at Leathead Road;
  • expansion of the project at the golf course to cover the entire property;
  • bank stabilization at Hunter Court;
  • expansion of the park naturalization program at the existing sites and to new park land.

Some similar techniques from past projects will be implemented along with new techniques, including the establishment of off-channel habitat, vortex weirs, and log deflectors.The future of the Lower Mill Creek Restoration Program depends on the amount of external funding that can be secured each year from various sources. If funding continues, as it has to date, it is hoped that the majority of recommendations made in the Lower Mill Creek Channel Assessment will be completed within the next five years. The knowledge acquired through the Lower Mill Creek Restoration Program will then be applied to other watersheds in the City of Kelowna.

About the Author

Fred Schaad, Michelle Kam, and Tracy Gow

Fred Schaad, Michelle Kam, and Tracy Gow are with the City of Kelowna Environment Division in Kelowna, BC.