University of Illinois, Urbana-Champaign: News

Rob Olshansky, expert on landslide hazards

3/28/2014  8:00 am

Rob Olshansky, a professor of urban and regional planning at the University of Illinois, has published extensively on planning and policy for unstable ground, dating back to his 1987 dissertation, “Landslide Hazard in the United States: Case Studies in Planning and Policy Development,” and including law review and legal newsletter articles emphasizing the need for local governments to address landslide hazards. In the aftermath of the deadly Oso, Wash., landslide on March 22, Olshansky discussed the role of urban planning in safeguarding citizens from these unpredictable and potentially fatal events with Dusty Rhodes, arts and humanities editor at the News Bureau.

How could this tragedy have been avoided?

image of professor rob olshanskyThe best way to avoid such tragedies is through the approval process for residential subdivisions. If such a subdivision – along a river, and close to a slope – were being proposed today, I would hope that the siting and design would be carefully evaluated. In California, for example, such a process would be governed by a local subdivision ordinance as well as by the California Environmental Quality Act. The county would also have a “safety element” in its general plan, as well as a hazard mitigation plan required by the federal government. The process would involve a geological assessment of the site and would be subject to public review. Given the history of sliding, it is likely that such a process would result in a denial of the subdivision application, unless the slope were to be stabilized. It would be possible to stabilize the slope, though probably too expensive for this rural subdivision.

The more difficult question is what to do with an existing subdivision once a slope instability hazard is discovered, as apparently happened in this case a few years ago. For this, there are no easy answers. A similar case is that of the La Conchita landslide in southern California, which killed 10 people in a 2005 event. This area, which also slid in 1995, has since been posted as unsafe, with no new development allowed, but residents continue to live there. All the possible solutions are costly to someone: Evict all the residents, buy out all the residents, relocate the residents from the most hazardous locations or reconstruct the slope. The current owner of the unstable slope has been exploring ways to stabilize it.

Was there any way this slope could have been reinforced? Or should local government have prohibited building in its path?

Yes, the slope could probably be stabilized, by some combination of subsurface drainage, diversion structures and slope reconstruction. In such a location, local government can and should prohibit new development, unless the slope is made to be safe. This is now common practice in much of the U.S.

Are there laws or insurance regulations pertaining to landslide danger zones?

There is no landslide insurance available in the U.S., other than “mudslide” coverage under the National Flood Insurance Program. Unless owners are clever enough to obtain this latter coverage, standard property insurance explicitly excludes coverage for earth movement. This is why landslide cases always end up in court: Owners lose their life investment, and have nowhere else to turn.

California has lots of policies that apply to such zones, including requirements to plan for natural hazards, subdivision regulations and procedures for evaluating new developments under the California Environmental Quality Act. California also maps selected landslide areas under the state’s Seismic Hazard Mapping Act, and the building code requires thorough geologic review of such sites.

California also authorizes “geologic hazard abatement districts,” which are special taxing districts that allow property owners to collectively finance slope repairs. I’m not as familiar with Washington, but I know that the state has mapped landslide hazards, and local governments have the ability to strictly regulate new development threatened by possible landslides. They do not, however, have an equivalent of California’s geologic hazard abatement districts.

How many such danger zones are there in the U.S.? Despite the fact that we have no mountains, are there any unstable places like this in Illinois?

The U.S. Geological Survey publishes maps of landslide-prone areas. Most states have some of these. Illinois has very few landslides; most occur on bluffs along the Mississippi River. The Illinois State Geological Survey, located on our campus, maintains an inventory of landslides in the state.

How could the Oso landslide have been predicted?

The hazard was certainly identified in their county hazard mitigation plan. But it also appears that the subdivision has existed for quite some time. So this is the same difficult situation as the La Conchita case: Once you discover that a hazard exists, what should you do about it? We know where landslides can potentially occur, but can’t predict when.

It’s difficult and costly to either repair a slope or move residents from a potentially hazardous location when you are not sure what the probability is. Would you do it if you thought there was a 50 percent chance of a slide in the next 30 years? What if it was 20 percent? 10 percent? 1 percent? Most likely, you would consider the problem, talk to your neighbors, wait for additional studies, assume the local government is handling the problem appropriately, and hope that a slide doesn’t occur this year. In most years, you would be right.

The main lesson here is to be extremely careful when creating new subdivisions of property on or near potentially unstable slopes. Once a subdivision exists, it is very difficult to put the genie back into the bottle. No local government wants to have a landslide. At a minimum, it can be extremely costly to taxpayers; at its worst, a tragedy can occur.