2014/05/28 Council Agenda Packet

Typical Mitigation Strategies There are four basic strategies to mitigate for a particular landslide: • Stabilization • Protection • Avoidance • Maintenance and monitoring Only stabilization seeks to counter one or more key failure mechanisms and improve stability of the slope. The latter three strategies (protection, avoidance, and maintenance and monitoring) allow slope failure and seek to avoid, protect against or limit the associated impacts. The last mitigation strategy, maintenance and monitoring, is different than a "do-nothing" alternative; a "do-nothing" alternative is a management approach/decision, not a mitigation strategy. Stabilization (Capital Improvement Projects) Typical landslide stabilization measures include grading the unstable portion of the slope to a lower gradient, construction of rock buttresses and retaining walls, and drainage improvements. Examples shown below entail grading with slope armoring/buttressing (Figure 6) to address a large deep-seated landslide at railroad milepost (MP) MP 24.5; and patterned reinforcement of high -tensile -steel wire mesh that could potentially be used to address the abundant shallow -type landslides that originate upslope of BNSF's ROW (Figure 7). With the exception of drainage improvements, stabilization measures are typically moderate to high cost, but provide a long- term solution with low, long-term maintenance costs. Cessation of adverse human activities by diverting stormwater away from steep slopes, maintaining appropriate native vegetation, and properly disposing of debris off -site are also considered measures that would improve stability. p. 16