Science behind the project
Why does Taylor Creek need to be restored?
Without restoration, erosion of the canyon resulting from decades of urban development, historical logging efforts, stormwater runoff, and increasing frequency and intensity of storm events due to climate change will result in tons (literally) of sediment being delivered to the mouth of the creek at Lake Washington. The sediment coming downstream blocks the channel and the Rainier Ave S culvert, causing flooding that impacts homeowners, businesses, pedestrians, and traffic. Sediment that accumulates at the mouth of the creek blocks salmon from entering the stream and is a sign of an unstable watershed. Erosion is an exponential process: it will continue creating a steeper slope and faster moving water which results in even more erosion. Naturally occurring landslides will further destabilize the banks of the creek. Installing a natural sediment management solution such as large woody material (LWM) structures in the canyon could slow and even stop this erosion and damage to the channel and delta and could prevent flooding. This can reverse the effects of past mismanagement of the canyon and allow the system to become more naturally self-sustaining. Without intervention, it would take decades—if not centuries—for the creek to recover.
Developing a solution
SPU is planning to implement a long-term, effective sediment management approach. To do so, we’re working with engineers, ecologists, and geomorphologists to develop a restoration plan that would replicate natural conditions. We’re also working with SPR, regulatory agencies such as the Army Corps of Engineers and the Department of Fish and Wildlife, and members of the community to understand the project requirements and determine the best solution for the land and for the community.
Prior to logging and development, beaver dams and accumulations of logs and branches would have managed sediment and erosion naturally. Engineered LWM structures are a commonly used sediment management method that mimic the way that logs naturally fall into creek channels and change their shape over time.
Large woody materials or some other type of sediment retaining structures within the channel are necessary to capture sediment and start building up the creek bed to reduce the erosive force of the water. If we are not able to curb erosion in the creek, it may result in further downstream salmon habitat damage and increased flooding. We will continue to consider new ideas for erosion and sediment control that include community input.
Possible interventions outside the canyon
SPU is also exploring other stormwater management solutions in collaboration with King County. Coordinated efforts between King County and the City of Seattle to better address basin-wide drainage and sediment issues is needed, and SPU has met with members of the Water and Land Resources Division at the County to initiate discussions. Stormwater planning will take time to initiate, design, and implement and should involve the community. The timeline and approach of a large-scale planning process is beyond the scope of this project. However, we recognize near-term solutions are needed, as the creek is already damaged. SPU is proposing to kick-start the creek channel restoration by deploying LWM as described above and by rehabilitating two direct stormwater discharges to help immediately reduce erosion near the east ravine wall. As we engage with King County, we will look for other similar early action efforts that might help to reduce erosion in the canyon.
To learn more about current conditions in Taylor Creek and the science behind the restoration project, please explore the following pages.