Landslide Database to Inform Mitigation Decision-Making, Improve Whole Community Awareness

Landslide Database to Inform Mitigation Decision-Making, Improve Whole Community Awareness

US 89 in northern Arizona closed after a 150-foot section of pavement buckled the morning of Feb. 20, 2013 in an area about 25 miles south of Page. The roadway reopened in March 2015.

When a landslide south of Page, Ariz., collapsed a portion of U.S. Route 89 on Feb 20, 2013, it created a real mess for the Arizona Department of Transportation (ADOT). The damage forced ADOT to close a 23-mile stretch of highway that took—in the end—nearly 2 years and $25 million to repair, reroute and reopen, which it did on March 27, 2015.

Landslides on (and beyond) the scale of the one that broke US 89 are not unheard of in Arizona or any western state for that matter. Major landslides in Oso, Wash., and along West Salt Creek in Colorado in 2014 further raised the public profile of landslides, helping the Arizona Geological Survey (AZGS) win a Pre-Disaster Mitigation (PDM) grant to create an Arizona Statewide Landslide Inventory Database (AzSLID).

PDM planning and project grants are awarded annually on a nationally competitive basis. The Arizona Department of Emergency and Military Affairs (DEMA) manages the grants, functioning as the intermediary between FEMA and the subapplicant; in this case, AZGS. AZGS is required to account for 25 percent of the total project cost.

The finished AzSLID will include locations and scientific descriptions of every known landslide in Arizona’s geologic history. Dr. Ann Youberg, an AZGS research geologist and the principal investigator for the project, said the AzSLID represents the first landslide survey and risk assessment ever conducted in Arizona.

The hope is that the data will inform governments’ decision-making now and in the future as part of state, local and tribal hazard mitigation plans. AZGS plans to present their findings to county and tribal emergency managers when the AzSLID is complete.

“It is our hope that it (the AzSLID) will provide more factual and data-driven information that will reveal areas of concern, resulting in awareness and the opportunity to mitigate potential future impacts,” explained Sue Wood, DEMA Mitigation Planning Coordinator. “It can also be used as a tool to inform and educate the counties and tribes on potential risks in their jurisdictions.”

Meanwhile, just one county and three tribes felt landslides were significant enough of a threat to include in their current hazard mitigation plans. It’s not surprising when you consider there’s only ever been one federally-declared landslide incident in Arizona.

Youberg can only estimate what future landslides could cost in damages to public infrastructure and private property. “The economic and social impact of landslides throughout the U.S. is poorly understood,” she says, “but each year there are an estimated 25 to 50 fatalities with billions of dollars in costs, rivaling annual flood losses.”

Ultimately, DEMA will incorporate data from AzSLID into the 2018 update of the State of Arizona Hazard Mitigation Plan, which includes landslides among 15 statewide hazards most likely to affect (i.e., endanger lives, damage or destroy property, and disrupt local economies) a community. The term “landslide” is used in the plan to describe any event characterized by the “downslope movement of earth materials due to gravity,” such as rock falls, mudslides and debris flows.

The other 14 statewide hazards are dam failure, disease, drought, earthquake, extreme heat, earth fissures, flood, hazardous materials incidents, levee failure, severe winds, subsidence, terrorism, wildfires and winter storms.

Since work on database began, AZGS has entered 75 percent (or 4,420) of the documented landslides, covering about 528 square miles, into AzSLID. AZGS is, at the same time, using Google Earth to search the state for signs of undocumented landslides. The work is sometime tedious, but has also produced widespread evidence of landslides.

“We were surprised by how many landslides there are in Arizona,” said Youberg. “Landslides are more common than generally thought but often occur in remote areas.” But, she added, severe wildfires, development of the wildland-urban interface and above-normal precipitation could bring about more debris flows in the future. When the leftovers of Hurricane Norbert swept through Phoenix last fall, AZGS documented debris flows in South Mountain Park in Phoenix.

AZGS will also add the landslide geolocation data to its Natural Hazards Viewer, a public information tool used to share data on the locations of earth fissures, active faults and earthquake epicenters, and highest flood and wildfire risk. AZGS developed the Hazards Viewer in cooperation with DEMA and FEMA for emergency managers, hazard mitigation planners, developers, real estate agents and property buyers.

“Once someone has built in a landslide-prone area there is not much that can be done, without a lot of money, to mitigate the hazard,” explained Youberg. “It is important to work with your realtor, and possibly a geological engineer, to identify and understand the potential geologic hazards of a property before you buy.”

AZGS will update the Hazards Viewer with new landslide data as new landslides happen or are discovered as part of AZGS’ normal geologic mapping program.