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2024 Hennepin County All -Jurisdiction Hazard Mitigation Plan <br />Volume 2 — Hazard Inventory <br />4.1.1.11.6. Bedrock. The depth from the surface to bedrock is an important factor in some kinds <br />of slides. Exposed bedrock is required for rock falls for instance. A shallow depth to bedrock may <br />also facilitate flows and other forms of slides as well. <br />4.1.1.11.7. Surface conditions: Vegetation on slopes usually assists in stabilizing them against <br />failure. Plants with deep root systems, often native species, are recommended to help slow slope <br />erosion. Conversely, removal of vegetation that results in bare and exposed soil increases the risk <br />of landslides and mudslides. <br />4.1.1.11.8. Soil temperature: The action of winter and spring freeze -thaw cycles seems to help <br />trigger some rock falls or topples. Thus, these types of landslides are the only ones that appear <br />to happen outside of the normal rainfall/thunderstorm season of Hennepin County. The freeze - <br />thaw cycles allow water, trapped in voids and crevices in rock, to expand and push rock apart, <br />sometimes triggering a fall. <br />4.1.1.12. Prevention <br />Further work is needed among the Hennepin County landslide assessment team to develop prevention <br />methods. <br />4.1.1.13. Mitigation <br />4.1.1.13.1. Avoidance (Prevention). The most effective mitigation measure against landslide <br />fatalities, injuries, infrastructure disruption and property loss are avoiding development and <br />certain human activities at sites prone to landslides. This is a preventive action. Avoidance may <br />be accomplished through evidence -based zoning policies that utilize local area landslide hazard <br />assessments that trigger site -specific landslide investigations when appropriate if development or <br />other uses are proposed at sites inside identified hazard zones. Specific actions include avoiding <br />cutting into slope sides or at the food of slopes, and not placing excessive weight on the top of <br />slopes by erecting structures there. <br />4.1.1.13.2. Education and public alerts. Education of zoning officials, landowners and need <br />accurate local information in order to make sound decision regarding their development and <br />activities in landslide susceptible terrain. A simple knowledge of landslide risk also sets the <br />foundation for appropriate action when a public alert is issued. Public alert thresholds, messages <br />and distribution methods must be developed. <br />4.1.1.13.3. Active mitigation methods. Geometric methods include changes in slope angle to <br />reduce the chances of landslides. Hydrological methods consider surface, shallow and deep - <br />water drainage and attempt to improve the ability of landslide -susceptible sites to drain water <br />effectively. Finally, mechanical methods include the use of rock anchors, netting, retaining walls, <br />or pilings. In general, these methods are expensive and are suitable only of sites of limited size in <br />areas where development is of high importance. <br />4.1.1.14. Response <br />Further work is needed among the Hennepin County landslide assessment team to develop Response <br />17 <br />