Dry Creek Greenway Trail Fluvial Audit
cbec was contracted by PSOMAS to assess the potential risk and prioritize mitigative measures for the City of Roseville multi-use trail along approximately 4.5 miles of Dry, Cirby and Linda Creeks between Darling Way and Spahn Ranch Road.
cbec used a processed-based geomorphic assessment including desk-based analysis of historical aerials, LiDAR data and specific stream power coupled with a field-based fluvial audit. The fluvial audit is a ‘fit-for-purpose’ methodology that characterizes indicators of physical processes and anthropogenic controls and impacts on channel behavior. This approach was used to inventory features such as channel reach type (e.g., pool-riffle, plane bed), sediment sources (e.g., bank erosion, tributary inputs), and in-channel sediment storage. We also assessed river engineering measures (e.g., channel straightening, bank protection, grade control structures, levees, etc.) to facilitate a more nuanced understanding of human impacts to physical processes and the resulting influences on dynamic channel behavior. The survey was conducted on foot and utilized a field tablet computer equipped with GIS mapping software to record observations, photos and locations using GPS.
The resulting field data and desk-based findings were used to characterize the channel’s geomorphic regime and to develop a trail alignment risk assessment methodology with five risk classifications. An initial evaluation of risk was made on the basis of primary criteria (bank erosion and proximity of trail to the edge of the channel) which was then corroborated or modified through consideration of secondary criteria. Six trail locations with extreme or high risk were identified as well as 48 segments with moderate risk (a number which includes trail segments adjacent to higher risk areas as well as clusters of multiple areas exposed to moderate risk). To address the extreme or high levels of risk to the trail at these six sites, concept-level mitigative measures were developed and prioritized.