Laserfiche WebLink
2024 Hennepin County All -Jurisdiction Hazard Mitigation Plan <br />Volume 2 — Hazard Inventory <br />4.1.1.8. Future Trends Ble <br />4.1.1.8.1. TRENDS AND PROJECTIONS: The most significant trigger for landslide activity in <br />Hennepin County is precipitation. Documented trends in precipitation in Minnesota, as well as <br />projections into the future show an increase in overall rainfall, plus an increase in intense <br />precipitation events. Recent landslide activity in Minnesota and Hennepin County has risen. It <br />appears likely that landslide activity will continue to grow in tandem with precipitation trends. <br />4.1.1.8.2. EVENT PROBABILITIES: More analysis of the recently developed data is needed to <br />determine landslide event probabilities in Hennepin County. <br />4.1.1.9. Indications and Forecasting <br />Further work is needed among the Hennepin County landslide assessment team to develop modeling and <br />forecasting methods. <br />4.1.1.10. Detection & Warning <br />Additional work is needed among the Hennepin County landslide assessment team to develop detection <br />and warning criteria. Indications of changes in key factors will be accomplished in large part by the <br />Hennepin -West Mesonet network of environmental sensors. <br />4.1.1.11. Critical Values and Thresholds <br />4.1.1.11.1. Slope. Also called the angle of repose, slope is a critical factor for landslide <br />susceptibility. In Hennepin County, landslide activity starts to increase above 20% slope, and is <br />most numerous on slopes between 30-40%. Slopes may be either natural or artificially created by <br />human activities. <br />4.1.1.11.2. Soil type: Soil type is important to landslide susceptibility for several reasons. <br />Differences in the porosity and permeability of soils is important since it describes the degree to <br />which soil types will either slowly retain or quickly shed water. Other characteristics such as soil <br />structure may contribute to slope failure. Many soils in Hennepin have been disrupted or altered <br />in some way by human activities. <br />4.1.1.11.3. Soil moisture: Soil moisture is a critical factor in Hennepin County landslides. Among <br />other things, when water replaces air within soil pores, the overall weight of the soil increases. <br />Increasing the weight of near surface soils can increase the likelihood of the material moving <br />downslope and forming a landslide. The Hennepin County landslide assessment is developing <br />specific soil moisture criteria for alert purposes. <br />4.1.1.11.4. Precipitation. Precipitation is one of the most critical factors in triggering landslides <br />in Hennepin County. Duration, intensity, and recurrence of precipitation are important elements <br />in precipitation -initiated landslide events. The Hennepin County landslide assessment is <br />developing specific precipitation thresholds for alert purposes. <br />4.1.1.11.5. Springs. Springs discharge water along slopes, increasing erosion and helping to trigger <br />landslides. Springs in Hennepin have been mapped in detail. <br />16 <br />