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Ecological Retooling of a Small Town
Greenway project along a creek running through Yreka, California

Landscape Architecture by Tom Hesseldenz and Associates


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The city of Yreka (pop. 7,500) is along Interstate 5 in far Northern California, just 21 miles from the Oregon border. Yreka is the Siskiyou county seat. The area is rich in ecological diversity, being situated at the junction of the Cascade Range (14,179 ft. Mount Shasta in the background), the Klamath Mountains and the High Desert. Yreka Creek flows through the center of town before joining the Shasta and Klamath rivers. The creek is spawning habitat for salmon (Chinook and coho) and steelhead trout.


When a handful of local community members got together in the late 1980s to launch a greenway project along a creek running through their small town of Yreka, California, they envisioned a single linear greenway comprised of a trail and small buffer. Yreka (pop. 7,765) is just 21 miles south of the Oregon border, sitting at an elevation of 2,500 feet.

Tom Hesseldenz and Associates (THA), a collaborative ecological landscape architectural firm based in nearby Mount Shasta, provided initial planning input, then proceeded to help the community expand that vision into a comprehensive integrated network of greenway elements contained in the recently-adopted Yreka Creek Greenway master plan.

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The entrance sign at one of the Greenway trailheads was made by Ralph Starritt of Starritt Studio. At top is the logo for the Greenway, composed of salmon backed by cottonwood, willow and alder leaves, the most common riparian trees along the Greenway.


The master plan contains a variety of design solutions that reduce flood hazards, improve water quality, restore fish and wildlife habitat, provide creekside trails with linkages through town and yield various economic benefits to the local community. An innovative nonstructural method of reducing flood hazards that had been developed by THA on previous Yreka projects led to the city of Yreka obtaining a $5 million grant from the California's Department of Water Resources to prepare the master plan, as well as acquire key lands, complete environmental compliance for the city-wide network, and implement a portion of greenway build-out.

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Yreka was founded during the California Gold Rush in 1851. This statue is by Yreka sculptor Ralph Starritt and was installed in 1976 by the Yreka Jaycees.
Photo: Public domain, Wikimedia.org


As lead consultant on the master plan, THA worked closely with the city of Yreka and its main greenway partner, the Siskiyou Gardens Parks and Greenway Association. The other members of the collaborative team assembled by THA were:
• GeoTerra (city-wide aerial photogrammetry and planimetrics)
• Foresight Surveying, Inc. (air photo target surveying/mapping)
• Natural Resource Geospatial (GIS services, including a Google Earth KMZ rendition of the master plan)
• Schlumpberger Consulting Engineers (civil engineering)
• Hydmet, Inc. (hydrologic analyses)
• GeoServ and Streamwise (stream geomorphologic analyses)
• GeoGraphics Unlimited and Erica Fielder Studio (MP document preparation and interpretive plan)
• The city brought in Michael Baker International and ECORP for environmental compliance of the California Environmental Quality Act (CEQA), National Environmental Policy Act (NEPA) and regulatory permits.

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Yreka Creek has an incised stream channel, rock and concrete armoring along its banks and a culvert draining directly into the creek. The channel has lowered to the point that it can undermine structures, cause downstream sedimentation and severe bank erosion and widening. Grant funding has been obtained to create an accessible floodplain, relocate the culvert outfall to the backside of the new floodplain and construct a new trail.


The flood reduction design solution developed by THA involved taking advantage of the incised condition of Yreka Creek to construct a new accessible floodplain at the lowered level of the creek. [Editor's note: "Incised" simply refers to a waterway that has cut through sediment or bedrock, leaving the riverbed now even lower in relation to the floodplain.] Many urban streams are incised due to increased peak flows from impervious surfaces. Raising or rerouting the channel to reaccess its historic floodplain is not possible since the floodplain has already been built-out.

Modeling conducted by THA's team showed that in the case of Yreka Creek, the full width of the historic floodplain was not needed to reduce flooding and achieve channel stability. Excavating a new floodplain at least 175 feet wide and 8-10 feet below the surrounding grade (2-4 feet above the incised creek bottom) was determined to be what was needed to restore stream geomorphology, and surprisingly, would also contain up to a 100-year flood event.

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A 25-year flood event occurred in Yreka in 2005, resulting in $1 million in property damage and claiming the life of a young woman who was swept away. A flood one foot higher and the houses in the photo (upper right) would have been flooded. That flood was the catalyst to include methods of flood hazard reduction in the Yreka Creek Greenway master plan.
Photo: Jerry Mosier, Siskiyou Gardens, Parks and Greenways Association (SGPGA)


The floodplain width required could be achieved by excavating along one or both sides of the creek, depending on the disposition of creek side landowners and what types of structures or other improvements were in the way. The newly created floodway could then be developed as part of a greenway, complete with trails and native riparian revegetation. Surrounding businesses and private residents would benefit from reduced risk of flood damage and associated flood insurance costs, plus derive economic benefits from being located along a greenway.

To date, this design solution has been implemented by THA along a half-mile of Yreka Creek and a quarter mile of its largest tributary, Greenhorn Creek. This involved the excavation of over 85,000 cubic yards of material. At one location, THA proposed using around 50,000 of those cubic yards as engineered fill on an adjacent undeveloped commercial property, saving the city $250,000 in hauling costs and saving the landowner a similar amount in constructing a building pad above the 100-year flood zone. This solution convinced that affected landowner to participate in the project, and brought 3 additional creek side landowners to the table that had previously been reluctant to participate.

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This is the existing FEMA 100-year flood zone along a portion of Yreka Creek next to Interstate 5.
Image from Google Earth; GIS overlay by Natural Resource Geospatial


Other innovative design solutions included in the master plan:
• Retrofitting storm drains to allow street runoff from smaller more frequent storm events (the runoff that contains the most contaminants) to flow above-ground through previously de-watered natural ephemeral drainages where it will be slowed down, contaminants will be filtered out, and runoff will soak into the ground to reduce winter peak flows and raise summer base flows in the creek. These drainages will also be restored with native vegetation to provide urban wildlife corridors. Runoff from large storm events will still be routed into existing storm drains to prevent localized flooding.

• Development of extensive bioswales, starting with retrofitting school campuses, that function in the same manner as natural ephemeral drainages and consist of gravel-lined channels, floodplains vegetated by native plants, and numerous small detention basins with metered outlets. This design solution was chosen where adequate space was available (such as at schools), in lieu of using engineered rain gardens with layered media that are more costly to install, require higher ongoing maintenance, and create less wildlife habitat due to limitations on what can be planted in the layered media. Schools also derive educational benefits from participating in bioswale planting, conducting water quality monitoring, and having on-campus wildlife observation opportunities.

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The floodplain has been lowered, widened and an overflow channel lined with gravel added. This was prior to hydroseeding and constructing a paved trail under the trees along the creek.


• Relocating storm drain outfalls to the back edge of newly lowered/widened floodplains, and installing bioswales with small detention basins leading from the relocated outfalls across the new floodplains to the creek.

• Retrofitting the spillway of a popular 26-acre reservoir in a city park for salmon and steelhead passage, including stocking with fin-clipped sterile hybrid trout and requiring catch-and-release of wild salmonids (which are by definition salmon, trout, chars, freshwater whitefishes and graylings) so that recreational fishing can continue at the reservoir.

• Converting the existing levee-protected underground disposal system of the city's wastewater treatment facility along Yreka Creek to a series of natural freshwater marshes and restored accessible floodplain, similar to the Arcata Marsh project on the coast near Eureka, California (not to be confused with Yreka). Eureka is 102 miles south southwest of Yreka.

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This is a recently completed bioswale and detention basin at Evergreen Elementary School. All of the school's runoff originally flowed directly onto the adjacent street prior to retrofitting the campus with a network of bioswales and basins. The same location after a snow shows the detention basin working, and use of the bioswale for snow storage, where it can slowly melt without causing dangerous ice conditions in the school parking lot.


In taking an integrated comprehensive approach, the master plan solves multiple problems simultaneously and in a more cost-effective and efficient manner than a piece-meal approach. It will also streamline the regulatory process, not only with respect to regulatory compliance for greenway buildout, but also in helping the city and local developers address TMDL (Total Maximum Daily Load) and MS4 (Municipal Separate Storm Sewer System) water quality requirements. The approach taken will also improve grant-writing success, yield greater local economic benefits and build stronger community support.

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The modeled reduction in 100-year flood extent--to be implemented in 2018--is shown by the light blue dash lines (existing 100-yr. flood limit) and the dark blue dashed lines (final 100-yr. flood limit). Several buildings will be removed to lower and widen the floodplain.


The updated Greenway Master Plan was enthusiastically adopted by the Yreka City Council in early 2017. The master plan documents and Google Earth KMZ version can be found on Yreka's website at www.ci.yreka,ca.us. When fully implemented, the master plan will achieve the following:
• 11 miles of perennial stream corridor restoration (1.5 miles completed to date; 3.25 miles underway)
• 4 miles of intermittent stream corridor restoration
• 5 miles of ephemeral drainage restoration involving storm drain retrofits. (Ephemeral drainage refers to water that flows on occasion, such as runoff running in gullies down a slope, versus permanent flowing waters of streams and creeks.)
• 5 miles of bioswale and small detention basin networks (1/2 mile completed to date at 2 schools)
• 860 acres of floodplain and riparian restoration (50 acres completed to date)
• 14 miles of paved multiuse trails (2 miles completed to date)
• 6 miles of unpaved trails (1 mile completed to date)

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The cross-sections show the method of floodplain lowering and widening to create a new accessible floodplain at the level of an incised stream, i.e., a streambed that has further distanced itself from the floodplain by cutting through sediment or bedrock. The diagrams also show the extent to which the 100-year flood height can be lowered and contained within the newly created floodway, based on hydrologic analyses conducted for the Greenway master plan. The lower diagram shows how spoils can be disposed of nearby to reduce project costs, while also creating elevated building pads for future development.
Renderings: Kim Solga Artworks


These improvements to Yreka's urban landscape will go far toward making the town more sustainable, not only in terms of flooding and water quality, but also by promoting nonmotorized transportation and bringing more nature into the built environment. It turns out that a small town is an ideal location to develop new approaches to making cities more ecologically sustainable, due to lower land costs, less complex creekside development, and less regulatory hurdles than conditions found in large cities. Nonetheless, these design solutions can be used in larger cities and neighborhoods with similar streams and drainage issues elsewhere in the U.S. and beyond.
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Girl Scouts volunteers wash off after helping replant a portion of the Greenway. The boardwalk is an ADA-compliant "float-aside" laminated plank that is cabled to an abutment. It floats to the side during high flows without damaging the boardwalk or the stream bank, and is easily set back in place with a backhoe when the flows drop. Incorporating this design solution into the project provided more opportunities for trail users to be close to the creek and take loop hikes.
Photo: Jerry Mosier, SGPGA




As seen in LASN magazine, January 2018.






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