Effects of Floods on the High-Energy Cobble-Boulder Bedded, Urbanized Ellis Creek, British Columbia, Canada
Leif Burge, PhD
Stantec Consulting Inc.
Kelowna, British Columbia, Canada
Authors: Leif Burge, Megan Hendershot, Shawn Kilpatrick and Joe Kennedy
Stantec completed the Ellis Creek Master Plan for the City of Penticton. Ellis Creek flows westward approximately 5 km from a reservoir, through industrial and urban areas, to Okanagan River Channel in Penticton British Columbia, Canada. Sediment supply within the study area is limited to the bed and the banks of the channel downstream of the reservoir. Three historical dam breaches in 1921, 1941 and 1942 substantially impacted the geomorphology of the Ellis Creek channel. More recently, floods in 2017 and 2018 caused significant erosion of the channel bed and banks of Ellis Creek, exposing and breaking water mains and exposing gas lines. Large volumes of bed load were transferred downstream and deposited during the two events. Results from five assessments characterize the Ellis Creek channel, including: (1) a geomorphic field assessment, (2) a hydraulic assessment, (3) a bank erosion hazard assessment, (3) an aggradation or degradation assessment, and (4) sediment mobility and transport assessment. The channel was divided in to 13 reaches for analysis and grouped based on the assessments into natural, incised, deeply incised, transitional, aggraded, and channelized. A one-dimensional hydraulic (HEC-RAS) model was developed to assess existing site conditions along Ellis Creek. Current channel conditions present a flood risk to municipal infrastructure due to sediment deposition. Sediment is largely produced in an upstream section that is deeply incised, with banks up to 4 m tall. This substantial degradation confines the 200-year flows within the channel banks. The sediment produced in the incised section was deposited in the downstream aggraded section. Aggradation decreased the capacity of the channel. Widespread flooding is predicted during the design flood flow event downstream. Ten of 11 bridges on Ellis Creek do not convey the 200-year design flow event. The results of the assessments were used to develop conceptual designs for the restoration of the Ellis Creek channel. The designs were based on the geomorphically stable bed sediment patterns, including riffle pools, step pools and plane beds with boulder clusters. The restoration of the creek is estimated to take 20 years to complete.
About Leif Burge, PhD
Dr. Burge is a nationally recognized river scientist at Stantec with over 20 years of experience solving applied river problems and conducting research. Leif’s wide-ranging experience includes hydrotechnical assessment of bridges, hydrotechnical geohazard assessment, natural channel design, hydraulic modelling, channel assessment, sediment management, sediment transport, river stability, environmental impact assessment, assessment of dam breaches, flood response and recovery, and fluvial habitat projects.