Carbon River Right Bank Floodplain Connection Project

About the Project

This project is currently on hold through the end of 2023.

The purpose of the project is to connect Carbon River main channel flows to its floodplain and an existing side channel, located on the right bank side of the river. The goal is to connect at least six acres of floodplain for a two-year flow event and stage, using at least six engineered log jams. The reason for connecting the floodplain is for the benefit and enhancement of fish habitat. Benefits also include reduction of flow pressure and damage to the opposite left bank side river levee.

The project is identified and listed as part of the draft Pierce County Habitat Conservation Plan (HCP). The project will provide fish habitat mitigation credits under the plan and is located in subject reach of the Carbon River that is known to be of high-quality habitat and productive for salmonid usage respective to spawning.

Floodplain Connection is accomplished by constructing and placing at least six Engineered Log Jams (ELJ) in the main stem close to the Carbon River active channel (three Apex Jams and three Deflector Jams). Size of ELJ’s varies from large size Apex Jams (approx. 15 feet by 25 feet) to smaller size Deflector Jams (approx. 8 feet by 10 feet).

Due to river dynamics, rivers are ever changing and can be inherently dangerous places to recreate. River flow combined with natural inputs of sediment, rock, and wood can pose natural hazards to those who choose to recreate on the river. As part of the proposed Carbon River Floodplain Reconnection project, engineered wood structures are incorporated in the design concepts to help manage flows and provide habitat benefits. These structures can pose hazards similar to what are found naturally in river systems.

Orthoimage of Project Location

Location

The ortho-photo mosaic imagery shows the Carbon River channel and its right bank (north side) floodplain area. The image starts at the top from the downstream end at Bridge Street in Orting (near River Mile 3.0) to the upstream end near River Mile 4.6. The image captures existing river channel conditions and features on June 25, 2021.

Features

This image includes water flows, prevalent gravel bars, large woody debris, trees, vegetation and a major side channel. The existing river levee is also shown on the left bank side (south side) of the river.

The major side channel feature is shown near the center of the image in which it meanders through the right bank floodplain area. The side channel intersects with the main river channel near River Mile 3.5.

Explore

The viewer can dynamically zoom in and out and pan along the river channel to see a greater level of detail by clicking on the image.

InundationExtentsComparison_2year_AA_EC Opens in new window

Click on Map to review in detail

Project Features

6 Engineered Log Jams (ELJs)
- 3 Deflector Wood Structures
- 3 Apex Wood Structures
2 pilot channels
Lowest construction complexity (location and number of pilot channels and ELJs, permitting)
Smallest area of potential disturbance during construction
Smallest cost
6 ELJs in main Carbon River channel

Meets main HCP goal

Increased inundation in right bank floodplain area
- Increase of up to 3.6 acres for yearly flows
- Increase of 7.8 acres at two-year flow
Moderate increase in access to floodplain features for aquatic species
Moderate increase in diversity of in-channel wood
Small increase in water levels and water velocities along left bank levee
Increase in 100-year flood levels in undeveloped portions of 5 private parcels