Integrating Best Available Science: New Tools for Land Use Planning & Emergency Management

Lidar-derived imagery of islands just north of Westport, OR. Image credit: Daniel Coe (WGS). Find more lidar images at Flicker | WA-DNR.

Part of the Washington State Department of Natural Resources (DNR), the Washington Geological Survey (WGS), publishes geologic information for decision-making, including geologic hazards, and mineral resources. Below are some highlights of recent publications and products of interest to land use planning staff, emergency management personnel, geologists, engineers, and others in the community.

New Tsunami Products

During the last year, WGS released several tsunami-related publications and products useful for emergency management, the land use planning community, and the general public. WGS released a tsunami hazard assessment for the modeled impacts from a Cascadia earthquake scenario to the northern outer coast and Strait of Juan de Fuca, along with a separate hazard assessment for the impacts from an earthquake on the Seattle Fault to the greater Puget Sound area. Both assessments show modeled tsunami inundation and current velocity. For more information, see Tsunamis | WA - DNR.

Additionally, WGS released tsunami evacuation walk time maps for several communities, including Long Beach, Tokeland, Ocean Shores, Westport, North Ocean Shores, and Grayland. Tsunami evacuation walk time maps show a more detailed view of the time it would take to evacuate on foot from the tsunami inundation zone. The maps also show how long it would take for the first tsunami wave to arrive. Emergency managers, planners, and local decision makers use these maps to plan evacuation routes, put in place critical infrastructure and resources, and plan response. The public should use these maps before the tsunami occurs, by learning the routes ahead of time for home, work, and school.

New Geologic Maps

Geologic maps show the composition and structure of geologic materials at Earth’s surface and at depth. These maps are foundational science from which most other applied geological work begins. Engineers, geologists, GIS analysts, planners, and others can use these geologic maps in their work.

In late 2022, WGS released three new detailed geologic maps at 1:24,000 scale: Chester Morse Lake quadrangle in King County, the Colockum Pass SE quadrangle in Kittitas County, and the McKenna and northern half of the Lake Lawrence quadrangles in Pierce and Thurston Counties.

In addition, the Washington Geologic Information Portal (Portal) has been updated to include about 60 more previously published geologic maps at 1:24,000 scale that will be available for viewing and download.

Landslide Mapping

In late 2022, WGS released a new interactive state map showing recently reported landslides as compiled by WGS using data from media sources and government agencies. The map contains data from 2015 to present and is updated regularly. Events are categorized by water year, which begins October 1st and ends September 30th the following year.

Additionally, WGS distributes inventories of landslide data for download and viewing on the Portal. These data include Landslide Inventory Mapping, a lidar-based, detailed mapping of landslides, which follows a published protocol, and Landslide Compilation layers, which include many mapped landslides from numerous sources. Late in 2022, WGS released the Landslide Inventory of Portions of Snohomish County, Washington. Data in that report is included in the Portal.

Lidar-derived imagery of a large alluvial fan along the Columbia River in Douglas County. Image credit: Daniel Coe (WGS). Find more lidar images at Flicker | WA-DNR.

Areas impacted by wildfires are particularly prone to debris flows, which are a rapid and often destructive type of landslide. The burning of vegetation (trees, shrubs, and ground cover) and forest floor materials can produce water-repellant soils, known as hydrophobic soil conditions. The formation of water repellant soils more than doubles the rate that water will flow into watercourses. Burned areas are also more prone to soil erosion due to this loss of the natural cover.

In the last few years, WGS’ Wildfire-Associated Landslide Emergency Response Team (WALERT) was established, and it now conducts rapid debris flow hazard assessments in areas recently burned by wildfires. WGS geologists develop summary reports noting the areas where property and lives may be at risk of geologic hazards such as debris flows. This information is transferred to the appropriate agencies to inform emergency response plans and mitigation measures. Reports can be downloaded from the Wildfire-Associated Debris Flows webpage after a post-wildfire assessment has been completed.

Wildfires can significantly change the hydrologic response of a watershed so that even modest rainstorms can produce dangerous flash floods and debris flows. Increased runoff, flash floods, and debris flow hazards may remain elevated for several years after the fire.

Aggregate Resource Mapping

WGS recently resumed aggregate resource mapping on a county basis. The goals include assisting local jurisdictions in mineral resource land designations and assessing regional capacity statewide to keep up with projected demand for aggregate resources.

Lidar-derived imagery of meander scars in the Yakima River floodplain. Image credit: Daniel Coe (WGS). Find more lidar images at Flicker | WA-DNR.

The aggregate resource projects use geologic mapping information, subsurface information from borehole data, and materials testing to show where sand and gravel or bedrock resources are either known or suspected to exist.

By the summer of 2023, Kitsap County’s aggregate resource map will be completed, with plans to subsequently map Skagit County. Find existing maps and our fact sheet on the WGS Aggregate Resources webpage.

Geologic Planning

Geologic planning involves cooperation between a variety of stakeholders. Geologists, land use planners, emergency management staff, and others work together to identify natural hazards, map mineral resource lands, recognize the importance of climate change, use best available science, and mitigate the impacts of natural hazards on communities. Check out the WGS geologic planning webpage to learn how WGS’s information can be integrated into local planning efforts.