Sullivan Gulch Bottomland Restoration

 

Project Location: Sixes River, 42.8379, -124.5314

 

Background: Sullivan Gulch is a 700-acre watershed on the south side of the Sixes River estuary. The gulch owes its existence to prehistoric riverine activity that carved a large floodplain into the uplifted coastal terrace that terminates into the Pacific Ocean as Cape Blanco. The prehistoric floodplain is about 300 acres in size and dominated by wetland habitat. The terrace slopes down into the bottomlands, which include multiple small perennial and intermittent stream channels. The Sullivan Gulch bottomlands are a geologic anomoly on the southern Oregon coast that rival in scale and complexity to the estuarine and floodplain habitats to the north - in New River, the Coquille Valley and Coos Bay. The location of the bottomlands relative to the Pacific Flyway and Cape Blanco make them of particular importance to waterfowl and migratory songbirds; for breeding habitat as well as refugia from winter storms and summer winds. The bottomlands support extensive wetland plant communities, including two rare assemblages: Hardstem bulrush (Scirpus acutus) marsh and Pacific reedgrass (Calamagrostis nutkaensis) fen; as well as intact stands of late-seral Sitka spruce forest. The bottomlands also function as overwintering habitat for native fishes, including Oregon coast coho and large scale suckers. Overwintering habitat is of particular importance because the geology of the Siskiyou Mountains and the rate of tectonic uplift constrain valley development, and thus naturally limit floodplain size and connectivity; and because settlers ditched and drained most of overwintering habitat by the twentieth century and converted it into pasture for sheep and cattle.

 

Project Purpose: The Sullivan Gulch Bottomland Restoration project began in 2009 over concerns that the ‘inset’ beaver dams constructed within the incised Sullivan Gulch ditch channel were impeding juvenile fish from accessing the 200 acre wetland habitat upstream of the Cape Blanco road. Early discussions between State Parks’ personnel, local Oregon Department of Fish and Wildlife (ODFW) biologists, Curry Soil and Water Conservation District (Curry SWCD) staff, and the McKenzie Family led to a decision to broaden the project scope beyond fish passage; to include enhancement and restoration of habitat within the bottomlands that had been adversely affected by past agricultural activities. In April 2010 the Curry SWCD submitted a Technical Assistance grant to the Oregon Watershed Enhancement Board (OWEB) to fund project development and design. The grant was awarded in November 2010, and a series of stakeholder meetings were held in the winter and spring of 2011; which were attended by the above mentioned parties as well as the Coquille Indian Tribe, and later, US Fish and Wildlife Service staff.

 

After reviewing available literature and conducting coarse field assessments, the Stakeholder group decided to limit the geographic scope of the project area to the 40 acres on the west side of the plateau. In making this decision the Stakeholders reasoned that the wetlands to the south were already in decent condition and provided extensive ecological function; that developing a design for such a large, complex area would be too onerous given the available funding and desired project timeline; and most importantly, the Stakeholders recognized that downstream of the access road the incised Sullivan Gulch ditch channel constituted a significant threat to the hydrology of the upstream wetlands, and that this segment of channel also limited connectivity and therefore was the principal limiting factor to the utilization of the bottomland’s overwintering habitat. After narrowing the geographic scope the Stakeholders developed the following project goals: (1) Restore consistent seasonal fish passage between the Sixes River and the 200 acres of wetland located upstream of the Cape Blanco access road. (2) Enhance and restore fish and wildlife habitat within the project area. (3) Maintain the existing hydrologic conditions in the wetlands upstream of the road. (4) Minimize impacts to the McKenzie’s livestock operation.

To achieve these goals the stakeholders developed the following project objectives:

  • Construct fish passage and grade control that (a) provides upstream juvenile fish migration at winter base flow and greater discharge, (b) minimizes the risk that future beaver dams will create barriers, and (c) stabilizes hydrologic conditions upstream of the Cape Blanco road.
  • Increase and enhance instream habitat by restoring channel morphology, installing log structures, and revegetating the riparian zone.
  • Increase off-channel open water habitat and near-shore wetlands for fish rearing, waterfowl and shorebirds, amphibians, and plant diversity.
  • Preserve the existing riverine oxbow.
  • Revegetate the project area with native herbaceous and woody species to increase wildlife habitat (especially for migratory songbirds) and to limit invasive weeds.
  • Preserve and enhance quality pasture for livestock production.
  • Exclude livestock from stream channels, non-pasture wetlands, open water habitat, and riparian areas. 

With these objectives in mind the stakeholders developed a conceptual project plan that routed Sullivan Gulch through a new stream channel rather than modifying the existing ditched channel. This decision was based on the following considerations: • A new channel alignment (presumably through the oxbow feature) would increase the length of stream habitat by at least 200%, which by default would increase rearing habitat for juvenile fish. • A new channel alignment could utilize existing topographic depressions and ditched wetlands to develop backwater habitat. • Constructing fish passage in the existing Sullivan Gulch ditch channel would require more engineered channel than constructing fish passage in the proposed channel alignment, because the elevation gain would occur over a shorter distance.

 

Species that will benefit: Coho salmon, Chinook salmon, coastal cutthroat trout, Pacific lamprey, large scale suckers

Implementation of this project will restore consistent upstream passage for juveniles migrating into the bottomland overwintering habitat. By migrating into this habitat juvenile fish can avoid being flushed to the ocean prematurely, and they can put on significant growth that will increase their ocean survival. Restoration within the project area, including the construction of unconfined sinuous stream channels and open-water off channel habitat, will greatly improve rearing conditions downstream of the Cape Blanco access road, which should also translate into increased rearing and ultimately lower ocean mortality.

 

Chinook may also benefit from the project in late summer when the Sixes River becomes bar bound and traps out-migrating Chinook smolts in the estuary until the fall rains and/or high tides open the river's mouth. When this happens most of the project area, including the backwater habitats, will flood, and Chinook may move into the bottomlands to escape poorer water quality conditions in the estuary. Based on summer water quality data collected by the SWCD in the early 2000's, the estuary does, at least intermittently, exhibit moderate signs of eutrophication, such as high water temperatures, elevated nutrient levels, algal blooms, and wide swings in pH and conductivity.

 

Evaluating success: Our monitoring plan will begin with an as-built coordinate survey of the constructed project, which will be used to document that the project was built as designed and to record modifications to the design that occurred in the field. This survey and the project design will be used to interpret project fluvial performance. Physical measurements, including instantaneous flow readings, will be made on the roughened channel chute-pool structure to document that jump heights and velocities are passable under a range of winter discharge. Smolt traps will also be deployed intermittently for a decade or more to document winter usage in the upstream wetlands, and they will be used to assess winter and summer rearing in individual backwater areas. OPRD will also conduct bird inventories within the project area to evaluate how the habitat, particularly the backwater areas, are being used by waterfowl, shorebirds, and migratory songbirds.

 

Metrics to evaluate success: Our baseline fisheries data is insufficient to make quantitative pre and post comparisons, but it can be used to make some qualitative observations about juvenile overwintering, such as magnitude and species composition; and these can be compared to a control site located on a wetland tributary that enters the Sixes estuary from the north, approximately a 1/2 mile upstream. In lieu of a robust fisheries monitoring plan, we will use the as-built survey to show that the construction phase was successful, and if there are indications that the channel morphology or the hydrology of the project area and upstream wetlands is evolving contrary to our intentions, we can resurvey coordinates to document what is changing, and potentially isolate the reason(s) why. Since fish passage and grade control are the most critical project components, much of the success of the project will depend on the performance of the roughened channel, which as described above, will be evaluated using physical measurements, flow readings, and observations over a range of discharge.

 

Climate change strategies addressed by this project: 

3.2 Promote habitat connectivity and integrity.

3.3 Reduce non-climate change ecosystem stressors.

3.4 Identify and fill priority freshwater needs.

 

National Conservation Strategies addressed by this project:

  1. Protect intact and healthy waters.
  2. Restore hydrologic conditions for fish.
  3. Reconnect fragmented fish habitats.
  4. Restore water quality.

Sullivan Gulch project map


Fish Passage-Grade Control Rock Structure: The structure alignment was significantly over-excavated  and then reconstructed with rock. Rock sills were constructed across the alignment to act as grade control on the pool-riffle channel. Pumping was necessary for ~ 2 weeks to keep the area dry enough to work, and to wash finer material into the voids in the rock slope.

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Fish Passage-Grade Control Rock Structure: As the structure came up in elevation, wood and micro-habitat were added to provide hydraulic roughness in the channel.

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Fish Passage-Grade Control Rock Structure: Aside from the revegetation, and the addition of stream bed material (in the riffles), the structure is now complete. The rock features in the lower end of the alignment (pool-riffle) will be below groundwater, but they were designed/constructed to withstand southward migration of the Sixes River channel, which would change the overall slope of the lower Sullivan Gulch channel.

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The photo on the left shows the newly constructed Sullivan Gulch channel, one meander bend upstream of the rock drop structure. An inset floodplain surface was first excavated, then the channel was dug into that surface as pool-riffle morphology. Additional finish grading, wood placement, and revegetation has yet to occur. The photo on the right shows the deeply incised (~12 to 14 ft) pre-implementation Sullivan Gulch channel, which was filled and replaced by the newly dug channel in the next two photos.

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The left photo shows another segment of the new Sullivan Gulch channel. The pools were dug down to groundwater (as evidenced by the reduced, grey anaerobic soils) to create a cold water input. The photo on the right shows Backwater Area 3, which was excavated  along the toe of a northwest facing slopes, where groundwater it present. The in- tent of the backwater area is to provide waterfowl/bird habitat, and additional rearing for juvenile salmonids.

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The photo on the left shows wsed I-beams that were purchased used from a highway contractor in the Willamette Valley, where they were used to build temporary bridges and overpasses on I-5. The beams will be placed on pre-cast concrete blocks (photo on the right) and covered with a structural corrugated metal deck and crushed aggregate to provide a livestock.

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The crew is compacting 3/4” crushed rock to build a pad on which the concrete blocks in the fore- ground can be placed to create abutments for a second livestock bridge. This bridge will provide access across a tie-channel to Backwater Area 3. It will be constructed from the pre-stressed concrete slabs in the bottom photo, which also came from a temporary I-5 bridge project.

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The unnamed tributary channel is being constructed through an existing depression that is dominated by sedge. The sedge was grubbed out to create an alignment for the channel excavation, and the grubbings (sedge) were stockpiled for later use when the exposed surfaces get mulched and planted.

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Sullivan Gulch Bottomland Restoration Powerpoint

Sullivan Gulch Action Completion Report

Sullivan Gulch Final Report Maps