Upper Design Details

Upper Project Area (Dead Horse Canyon) Project Goals

In the upper project area design, we plan to improve the health of the canyon ecosystem, with a focus on sediment management by installing large woody material (LWM) structures in-stream. The goals of the upper project area are:

Trap sediment from landslides and erosion to prevent improvements in the lower project area from getting washed out
Slow the flow of water by raising the creek bed and reducing the slope of the channel
Reconnect the floodplain by raising the creek bed, reducing the risk of downstream flooding during storm events
Reduce some causes of erosion and sediment input
Create a healthier plant community through revegetation with native plants
Prioritize forest ecosystem preservation

The following section explains how each element of the project works together to achieve these goals.

Click each button below to learn about the upper design elements

Install large woody material structures within and along the creek to stabilize ravine walls and better manage and trap sediment: Stormwater from heavy rains, landslides, and erosion—especially in Lakeridge Park— can wash sediment and debris into the creek. If too much sediment builds up in the narrow lower channel of the creek, it can cause localized flooding and poor habitat conditions. Large woody material structures placed within the creek naturally trap sediment, prevent sediment deposits in the creek, and can help rebuild and stabilize the creek bed.

SPU engineers are evaluating configurations of large woody material structures in Dead Horse Canyon (Lakeridge Park) and ideal locations for placement along the creek to control sediment, reduce erosion, and create habitat. Achieving the sediment management goals will require larger structures that can capture more sediment, while smaller structures can be used to provide some additional benefits. Learn more about how LWM works here.

Stabilize sewer line and trail: This work would involve installing a wall of “micropiles” (small diameter metal tubes pushed into the ground to provide stability) underground in a portion of the steep slope of Dead Horse Canyon where the slope is unstable and threatens the sewer line and the trail. The “wall” extends through many soil layers and provides stability that prevents the upper layers of soils from continuing to move, which will prevent damage to the sewer line and trail.

Tightline drainage: A “drainage outfall” is a pipe that collects stormwater from neighborhood roads. “Tightlines” are pipes placed on the ground surface that connect to a pipe exiting from underground— such as an outfall—and carry the water to the creek directly. There are currently several uncontrolled drainage outfalls discharging water directly onto the slopes of Lakeridge Park from surrounding areas. This water erodes the canyon and contributes to the sediment deposits in Taylor Creek, slope de-stabilization, and landslides. SPU plans to “tightline” several of these drainage outfalls to prevent further erosion of the canyon while still delivering the water to the creek.

Upper Project Area (Dead Horse Canyon) Design Limitations

Designing and installing LWM structures that are large enough to capture sufficient sediment will be crucial for the success of this project. The design and size of the LWM structures is limited by the materials delivery method and LWM installation method. SPU originally recommended building the largest and most effective LWM structures with a temporary access road in Dead Horse Canyon to deliver the large logs and machinery. However, building this temporary road would require tree removal and severely impact the surrounding forest ecosystem. These impacts are not tolerable to the community and we are working internally and with community to develop alternative plans that accomplish the project goals while minimizing impacts to the tree canopy.