Tim Abbe

Engineered logjams (ELJs) were developed to mimic natural logjams, which alter hydraulics and bedforms in large alluvial rivers. First applied in the Upper Cowlitz River in 1996, ELJs have since become widely used for restoring the geomorphic and ecological functions of large wood in streams and rivers, particularly in the Pacific Northwest. There are a wide range of ELJ architectures that depend on project goals and settings.  The structures help stabilize incised channels, retain sediment, enhance floodplain connectivity, and improve hyporheic exchange. In large rivers, ELJs promote channel anabranching, form stable forested islands, and create complex pools and can provide habitat-friendly erosion protection. Recent projects demonstrate that ELJs reduce flow velocity, increase wetted areas, raise water tables, and provide cool water refugia, supporting ecological complexity and climate resilience. This talk will explore the history, science, and performance of ELJ projects.

Dr. Tim Abbe is a professional engineering geologist and hydrogeologist with nearly 40 years of experience in environmental science and engineering. After completing a bachelor’s degree in geology Tim did his master’s degree focusing on sediment transport in the Columbia River estuary.  He then worked in the San Francisco Bay on wave erosion and tidal marsh restoration. He completed a PhD at the University of Washington, focusing on the mechanics, hydraulics, and geomorphology of large wood in rivers, where he pioneered engineered logjam (ELJ) technology. Since 2000, he has worked in the private sector on water resources, river restoration, and ELJ advancements.  Tim co-authored Washington State’s channel migration guidelines and the National Wood Manual.