To act as a larger floodplain for the Truckee River, The Truckee River Flood Management Authority (TRFMA) sought to widen the Vista Narrows by introducing 4,000 feet of new levee and 2 miles of terracing. To help determine the levee and terracing design, Kleinfelder investigated and reviewed the site’s geotechnical and geologic conditions and conducted seepage and slope stability analysis for levee and/or floodwall sections and slope stability analysis for cut slope terracing.
To conduct proper exploration and assessment, Kleinfelder needed adequate site access which was made difficult with the various site owners and operators. For example, the project required significant coordination with the Union Pacific Railroad (UPRR) in order to gain access to some necessary exploration locations in near proximity to the railroad tracks. Additional coordination was also required between landowners, archaeologists, and contractors due to very few access points along the project alignment.
Challenging site conditions included glacial outwash soils consisting of sand, gravel, cobbles, and boulders as well as meta-volcanics and meta-andesite bedrock. This required Kleinfelder to assess conditions using a variety of test methods that included over 25 borings, 24 backhoe test pits, 13 seismic refraction lines, and about a dozen hand excavations. Continuous coring was performed through these materials in order to obtain full intact samples for classification and future lab testing. The site also contained a potential landslide feature requiring a detailed subsurface investigation that was factored in the terrace design.
By leveraging a variety of methods to effectively assess site conditions, Kleinfelder’s team of geologists and engineers provided TRFMA with a range of flood control design solutions that included a floodwall, new levee construction with seepage control alternatives for the levee alignment, landside grade improvements, relief wells, and new terracing geometry. The proposed terracing was comprised of cuts within rock and soil, some reaching over 100 feet in height.