COST OF LIFE & DAMAGES Floods Deaths are rare $100’s of Millions in Damages Stream Bank Erosion

1. CASE STUDY: FLOODING Flood Inundations/FEMA Floodplains • Floods • Form floodplains • Deposit rich soils • Create river habitats • Support aquatic life • Protecting urban development within the floodplain • Hardened banks • Minimal channel change • Reduced channel dynamics • Impaired ecological conditions • Property loss increases as increasingly valuable structures are constructed within the floodplain Fig. 1: Historical extent of flooding along the central Willamette River. (Gregory, n.d.) CASE STUDY: STREAMBANK EROSION Bioengineering for Streambank Erosion Control • Streams naturally migrate from side to side over time • Often, a home will be built away from a river, but the river will migrate towards the home and eventually erode the ground under the home. • Bioengineering combines biological, mechanical and ecological concepts to stabilize soil and control erosion along streambanks • Native, flood resistant plants are used along the streambank to prevent erosion, thus controlling channel migration. • Also supports wildlife and fish habitat Fig. 2: Woody plants used to create a hard structure to prevent undercutting and flanking. (Leech, 1997) Earth Kills!!! Geomorphic Hazards of the Willamette Basin, Western Oregon Prepared by: Kristin Mooney Western Oregon University, Spring 2008 ABSTRACT Every year, lives are lost, and many people lose a great deal of money in property damage due to naturally-occurring surface processes. Decreasing the risk posed by these hazards costs money, but can save lives. Geomorphic hazards in the Willamette Basin include flooding, debris flows, landslides, and stream bank erosion. Risk increases with population growth and expansion into hazard-prone areas; for example, floodplains, hill-slopes, riparian areas or any combination of these. Increased mitigation and risk reduction is increasingly more important to the safety and welfare of Oregonians. Strategies for reducing these hazards often fail, mainly due to lack of scientific information and unawareness by policy makers. Many times local governments, which are not well informed, are put in charge of handling the hazard. Such strategies often do not take into account the actual risk posed by the hazard, the underlying geomorphic processes, or the appropriate mitigation technique. We live in Oregon and it is important for us to be aware of the geologic hazards that we may encounter. It is also important for us to have knowledge on how these hazards can be properly mitigated, so that we can make informed decisions. This poster provides examples of case studies related to geomorphic hazards in the Willamette Basin. CASE STUDY: DEBRIS FLOWS & LANDSLIDES Forest Clearing and Regional Landsliding • Landslides occur on steep, unstable terrains that have thick soils or excess pore pressures • Clearing forests • Removes the canopy that prevents rain from pounding the bare surface • Removes trees that would uptake water, leaving the soils saturated • Decreases root strength (decomposition) which decreases soil cohesion • Cleared areas have an increased landslide frequency when compared to un-cleared forested slopes INTRODUCTION As the number of people living in the Willamette Valley grows, hazardous areas are becoming more and more populated. Lives are lost and a serious amount of money is spent on repairing damages caused by these hazards. Flooding, Streambank Erosion and Debris Flows & Landslides are a major problem for the Willamette River Basin and mitigation of these problems takes a considerable amount of time. Fig. 3 Cleared area with multiple landslides. (Burbank, 2007) HAZARDS • Floods • Lowland flooding of major stream valleys and torrential floods in mountain valley channels • Stream Bank Erosion • Construction stability in severe erosion areas • River migration over time • Edges of mountainous terrain • Debris Flows & Landslides • Combinations of climate, slope, and rock type • Mostly moderate-slope slumps and steep-slope debris flows • CONCLUSIONS • Good Geologic Hazards maps that focus on the specific hazard for a specific site need to be developed • The public needs to be educated so they are better prepared to assist those making decisions regarding the hazard • Mitigation of geologic hazards needs to be mandatory through development restrictions, building codes, ordinances and regulations • COST OF LIFE & DAMAGES • Floods • Deaths are rare • $100’s of Millions in Damages • Stream Bank Erosion • Money is spent on prevention • Debris Flows & Landslides • 1-2 deaths/year • $1-10 Million in Damages • REFERENCES • Beaulieu, John D and Dennis Olmstead. Special Paper 31 Mitigating Geologic Hazards in Oregon: A Technical Reverence Manual. Special Paper. Portland: Oregon Department of Geology and Mineral Industries, 1999. • Burbank, Karl. Free Public. 16 December 2007. 27 May 2008 <http://seattletimes.nwsource.com/ABPub/2007/12/14/2004074235.jpg>. • Gregory, S., et al. "Flood Inudations/FEMA Floodplains." Atlas. n.d. • Leech, James R and Hollis H Allen. Bioengeneering for Stream Bank Erosion Control. Technical Report. Vicksburg: US Army Core of Engeneers, 1997. • Montgomery, David R, et al. "Forest clearing and regional landsliding." Geology 28.4 (2000): 311-314. MITIGATION Properly following the steps below will insure hazard management and reduction in risk. Determine the type and extent of the hazard Select team members with a background in dealing with the specific type of hazard Consider a variety of different strategies Select the best strategy for dealing with the particular hazard Permanently set the strategy into action by delegation