Hemlock Dam Removal and Trout Creek Restoration

Background Information

Hemlock Dam was on the National Register of Historic Places. Before its removal, it was the only surviving concrete dam constructed by the CCC on the west coast. The fish ladder is one of the earliest fish ladders in the Pacific Northwest. The dam replaced an earlier timber splash dam located between 70 and 140 feet upstream. A picnic and camping area with small boat launch was first established upstream of the dam on the left bank in 1935. Hemlock Dam impounded a small, shallow lake, which was about 6.5 acres in size and the lake was used by an unknown number of local residents for recreation.

The reservoir behind Hemlock Dam filled with between 48,000 and 93,000 yd³ of sediment. There is a large range of uncertainty in the reservoir sedimentation volume because there is no pre-dam topographic survey of the reservoir bottom. The reservoir sediment is predominantly sand with a median grain size of 0.6 mm. Less than 10 percent of the sediment volume is silt and less than 10 percent is gravel and cobble. Sand deposition in the downstream portion of the reservoir has likely filled the reservoir’s sand storage capacity so that inflowing sand and finer-sized sediment tends to pass through the reservoir. However, the coarse delta in the upstream portion of the reservoir continues to grow at a slow rate. Gravel and cobble deposition was expected to completely fill the reservoir in 200 to 300 years.

Downstream from Hemlock Dam, Trout Creek enters a steep and narrow bedrock canyon where it flows into the Wind River 1.5 miles downstream from the dam. From this confluence, the Wind River continues down the steep and narrow bedrock canyon where the river mouth is in the backwater of Bonneville Reservoir, located on the Columbia River.

Hemlock dam no longer produced power or provided irrigation storage, but continued to affect steelhead by impeding upstream and downstream movement of the fish, increasing water temperatures in lower Trout Creek, and obstructing downstream movement of valuable stream sediments.

Trout Creek is located in the Wind River watershed in southwest Washington. The Wind River is a Tier I Key Watershed on the Gifford Pinchot National Forest, and as such is a top priority for aquatic habitat restoration. Trout Creek provides critical habitat for Lower Columbia River steelhead, a fish listed as Threatened under the Endangered Species Act. This project will improve conditions for the fish and restore natural riverine processes to lower Trout Creek. Trout Creek was once known for producing a disproportionately large share of the wild steelhead in the Wind River, and this project aims to help restore that mantle.

Restoring Trout Creek

Since the early 1990’s, the Forest Service along with partner agencies and organizations have focused restoration efforts on Trout Creek, in efforts to restore the historically exceptional steelhead habitat. Riparian, upland, and instream habitats in upper Trout Creek have been enhanced by projects intended to reduce fine sediment introduction to Trout Creek, to provide increased shade on the stream, to improve fish passage at road crossings, and to improve instream habitat by placement of woody debris complexes. Removal of Hemlock Dam and restoration of lower Trout Creek contributes to this whole-watershed approach to habitat restoration, and is the culmination of many years of planning.

Project Goal

The goal of the restoration project is to increase the viability and productivity of Lower Columbia River Steelhead in the Wind River.

To meet this goal, the restoration project has these objectives:

  • Improve passage for fish and other aquatic organisms
  • Reduce peak stream temperatures in lower Trout Creek.
  • Improve quality of channel bottom substrates throughout lower Trout Creek
  • Increase habitat complexity in lower Trout Creek

Project Elements

  • Remove Hemlock Dam along with associated buildings and structures
  • Excavate excess sediments from the reservoir area
  • Construct a channel in the area now occupied by the reservoir
  • Incorporate large woody debris in the channel and floodplain
  • Physically remove and/or treat invasive vegetation in the project area
  • Revegetate the area surrounding the new channel

Lower Columbia River Steelhead

The Lower Columbia River Steelhead was listed as a threatened species on March 19, 1998 by NOAA’s National Marine Fisheries Service. The Lower Columbia River Steelhead is considered a distinct population segment (DPS).

The DPS geographic area the Lower Columbia River Steelhead includes all naturally spawned steelhead populations below natural and manmade impassable barriers in streams and tributaries to the Columbia River between the Cowlitz and Wind rivers in Washington, and the Willamette and Hood rivers in Oregon. The Lower Columbia River Steelhead DPS also includes ten hatchery programs on rivers and streams within the same geographic area. History of the Site Hemlock Dam was built by the Civilian Conservation Corps (CCC) in 1937 to provide irrigation and power to the adjacent Wind River Nursery. With the closure of the nursery in the 1990s, the irrigation and power generation function was no longer needed. In the seventy years since the dam has been in place, sediment behind the dam has increased and water temperatures have risen to lethal levels for fish.

Planning

In December of 2005 Mt. Adams District Ranger Nancy Ryke signed a Record of Decision (ROD) today calling for removal of 70-year-old Hemlock Dam northwest of Carson, Wash.
Ryke chose Alternative C of the final Environmental Impact Statement (FEIS) for the Hemlock Dam Fish Passage and Aquatic Habitat Restoration Project. It called for dredging years worth of sediment that has built up behind the CCC structure before the dam itself was removed.

“Removing the dam and its sediment is the best way to fulfill our obligation to enhance fish passage for threatened steelhead,” Ryke said. “We have put a lot of effort into this study, and I believe it’s the right course of action to achieve our objectives for steelhead recovery.”

Hemlock Dam is located on Trout Creek, a tributary to the Wind River, approximately 10 miles northwest of Carson, Wash. The dam has been identified as an impediment to the migration and survival of Lower Columbia River steelhead, a fish that is listed as threatened under the Endangered Species Act.

Copies of the FEIS and ROD are available online.

Timeline

The restoration project involved key milestones including:

  • Facility Removal – Remove small buildings such as the pumphouse located just southeast of the dam.
  • Creek Diversion – Diverting Trout Creek upstream through 2 or 3 large pipes and returned below the existing dam.
  • Hemlock Dam Removal – Dismantling he 22-foot high Hemlock Dam.
  • Invasive Weeds – Removal of a growing population of invasive weeds.
  • Stream Channel – A large amount of accumulated sediment was removed upstream of the dam. The natural channel for Trout Creek was restored.
  • Riparian Restoration – Once the natural channel is established, native plants and trees that were planted will provide shade and complexity to the area.
  • Recreation Site – The Forest Service will work with interested publics to identify recreational development at the site.

Partners

The restoration of Trout Creek and the benefits to the federally listed Lower Columbia River Steelhead would not be possible without the financial support of the following partners:

  • Bonneville Power Administration
  • Salmon Recovery Funding Board
  • Yakama Nation
  • American Rivers
  • Ecotrust
  • U.S. Fish and Wildlife Service
  • NOAA Fisheries
  • Mid-Columbia Fisheries Enhancement Group

Document: 

Hemlock Dam Removal (PDF)