Landslide hazards in Oregon are a severe threat to property and human life. Landslides are any mass of soil, rock, or debris that moves down a slope or stream channel. They can occur when driving forces exceed resisting forces, causing earth materials to fall, slide, or flow down a slope. Two types of forces are at work: driving forces and friction forces. Landslides are classified based on the type of movement and the transported materials.
Landslides can occur on-site or off-site. On-site hazards refer to landslides that occur on or near a development site and are typically slower-moving, causing most of the property damage in urban areas. Existing landslide hazard maps mainly focus on on-site hazards. On the other hand, off-site hazards typically begin on steep slopes far from homes or developments and often move rapidly. Recent events have highlighted the importance of off-site landslide hazards, where landslides that started a long distance away from homes and roads caused significant damage and loss of life.
Local planners and decision-makers can use this information to understand how landslides can impact current and future development in their communities. Identifying landslide hazards in the area is the first step towards developing effective plans and policies to prevent or mitigate damage caused by landslides.
What aggravates landslide hazards in Oregon?
Landslides can occur due to both natural conditions and human activities. Certain geological formations and steep slopes are more susceptible to landslides than others, with landslides occurring on steep slopes being more dangerous. Human activities, such as development and construction, can accelerate the incidence of landslides and their impact on people and property.
There are four conditions affecting landslides: natural conditions, slope alterations, grading and drainage, and changes in vegetation.
Natural conditions can cause landslides or re-activate historical landslide sites. Rainfall-induced landslides tend to be smaller, while earthquake-induced landslides may be more significant but less frequent. Landslides are common along stream banks, reservoir shorelines, large lakes, and seacoasts. Volcanic eruptions can also trigger large-scale landslides.
Excavation and grading on slopes for development can result in steeper slopes than the pre-existing natural slopes, increasing the risk of landslides. The added weight of fill placed on slopes can also increase landslide hazards.
Drainage and groundwater alterations can also increase the risk of landslides. Any activity that increases water flow into landslide-prone slopes can increase landslide hazards. Broken or leaking water or sewer lines can be especially problematic. Ineffective stormwater management and excess runoff can also cause erosion and increase the risk of landslide hazards.
Removing vegetation from steep slopes can increase landslide hazards. After timber harvesting, landslide hazards in steeply sloped areas were highest for a period of 10 years. Areas that have experienced wildfire and land clearing for development can have longer periods of increased landslide hazards because forest recovery may take a long time or may never occur.
Oregon’s Land Use Laws Regarding Landslide Hazards
The state has laws and regulations to address the risks associated with landslide hazards in Oregon, including comprehensive plans and ordinances to manage their risks. In particular, they must address areas with “known” natural hazards as a part of the comprehensive planning process.
The Debris Avalance Action Plan
The state of Oregon passed landslide legislation in response to property damage and fatalities from the 1996 flood and landslide events. The initial state response was the Debris Avalanche Action Plan, established by an Executive Order issued by Oregon Governor John Kitzhaber on March 4, 1997. The Governor’s Debris Avalanche Action Plan included specific recommendations for state and local governments to reduce the occurrence of debris flows and reduce the risk to the public when debris flows occur.
Goal 7
Goal 7 is the Statewide Planning requirement that directs local governments to address natural hazards in their comprehensive plans. Goal 7 states, “Developments subject to damage or that could result in loss of life shall not be planned or located in known areas of natural disasters and hazards without appropriate safeguards. Plans shall be based on an inventory of known areas of natural disasters and hazards.”
Senate Bill 1211
Senate Bill 1211 was passed in 1997 to reduce the risk of future landslide hazards. The legislation dealt with rapidly moving landslide issues around steep forestlands and not in typical urban or community settings. Senate Bill 1211 granted authority to the State Forester to prohibit forest operations in certain landslide-prone locations and created the Interim Task Force on Landslides and Public Safety. SB 1211 charged the Interim Task Force with developing a comprehensive, practicable, and equitable solution to the problem of risks associated with landslides.
Senate Bill 12
Senate Bill 12 directs state and local governments to protect people from rapidly moving landslides. The bill has three major components affecting local governments: detailed mapping of areas potentially prone to debris flows (i.e., “further review area maps”); local government regulating authority; and funding for a model ordinance. The legislature allocated funding to the Department of Geology and Mineral Industries (DOGAMI) to prepare the “further review area maps.” It provided $50,000 for a grant to a local government to develop a model program to address rapidly moving landslides. Senate Bill 12 applies only to rapidly moving landslides, which are uncommon in many communities but very dangerous in areas where they occur.
To reduce the risk of severe bodily injury or death resulting from rapidly moving landslides, Senate Bill 12 requires local governments to:
- Exercise all available authority to protect the public during emergencies;
- Decide when to require a geotechnical report and, if a report is required, provide for a coordinated review of the geotechnical report by DOGAMI or ODF, as appropriate, before issuing a building permit for a site in a Further Review Area;
- Regulate through mitigation measures and site development standards the siting of dwellings and other structures designed for human occupancy in Further Review Areas where there is evidence of substantial risk for rapidly moving landslides; and
- Maintain a record, available to the public, of properties for which a geotechnical report has been prepared within the jurisdiction of the local government.
Know all the land use rules governing your property with help from Richard Stevens & Associates.
Implementing laws and regulations about landslide hazards in Oregon is only one method officials may govern what you can and can’t do with your land or home. If you have questions about using your property, contact the professionals at Richard Stevens & Associates. We’re a land use consulting firm located in Medford, Oregon. Our team can guide you through obtaining rural and urban land use planning permits throughout all Southern Oregon counties and beyond. With expertise at your side, you’ll be able to navigate the complex systems to obtain the land use permits you need for your next project. Give us a call at 541-773-2646 to get started!
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