Mapping software shows where logging and landslides collide

Investigative Reporters and Editors, Inc. The IRE Journal, Winter 2009 by Mayo, Justin

A massive winter storm pounded the Pacific Northwest with torrential rainfall and hurricane-force winds in December 2007. Lewis County, about 90 miles south of Seattle, was the hardest hit with some areas recording up to 20 inches of rain in 48 hours. The flooding buried some towns under 1 0 feet of water and caused tens of millions of dollars in property damage.

In the surrounding hills, the storm triggered landslides adding mud, logs and debris to the destructive floodwaters that destroyed homes and farms in the valley below. Seattle Times reporter Hal Bernton had covered a similar storm in 1996 for The Oregonian. With so much mud and debris, he believed landslides would be a major part of this story.

Vmes photographer Steve Ringman, who covered the storm along with Bernton, took a helicopter ride to document the slides. He photographed dozens of landslides, many on recently clear-cut slopes. One photo in particular resonated with readers. It showed a 1 06-acre clear-cut on a steep mountain slope with a half-dozen landslides spilling into the river below.

Timber giant Weyerhaeuser owned the site and had logged it three years before. Bernton found that a company geologist had said the site contained "no potentially unstable areas" in the application submitted to the state prior to logging. But the site did contain steep and unstable slopes - some well above the 35-degree state threshold for potentially unstable slopes.

The photo raised concerns about Weyerhaeuser's logging practices and triggered reviews of how well the Washington Department of Natural Resources regulates the industry.

For Bernton, questions remained: Was this site an anomaly? Did Weyerhaeuser clear-cut steep, unstable slopes? If so, how many of these slopes had landslides during the storm? Was DNR providing adequate oversight?

Answering these questions proved challenging.

The majority of the landslides occurred on private timber lands, which were mostly owned by Weyerhaeuser. This area, the Chehalis River basin in southwest Washington, encompasses about 74,000 acres of mountainous terrain. The storm damaged many of the logging roads in and out of the area.

We turned to geographic information system mapping for help. Mapping was invaluable as it allowed us to analyze what happened on the ground. The story could not have been done without it.

The bulk of our analysis relied on DNR's own map layers and databases, most of which were freely available on the department's Web site. We began with a GIS layer of all forest practice applications in the state. Applications are submitted to DNR when a landowner wants to cut trees, build roads, spray chemicals, etc.

In ESRI ArcView, we captured only those applications that were in the Chehalis River and Stillman Creek watersheds where the storm was most intense. Using a DNR map of all watersheds in the state, Arc View's Select By Location function allowed us to include only those applications within the Chehalis and Stillman drainages. We only included clear-cut sites, not applications for selective harvests or road-building.

The CIS data showed us the location and boundaries of the clear-cuts but little else. To find out who the landowner was, whether a geologist visited the site or what DNR did in their regulatory review, we had to look at the actual applications. Recent applications were available on DNR's Web site. Forthose prior to 2003, we filed public disclosure requests and built a database from the paper records.

A source at DNR gave us a shapefile with landslide data the department had gathered during aerial surveys in the days after the storm. More than 730 slides occurred in the Chehalis River basin. By overlaying the landslides with the application data, we found that nearly half of the slides were in recent clear-cuts.

This finding was to be expected. After all, decades of studies show logging can increase the risk of landslides. Because of this, Washington state forestry regulations are designed to restrict logging on potentially unstable slopes when public safety or public resources are at risk.

Instead of including all clear-cuts, we wanted to narrow the analysis to those logging sites with the most slide-prone terrain. To do this, we used a CIS layer of hazard zones. These zones were put in place in the mid-1990s by scientists at Weyerhaeuser and the state. The goal was to create an agreement between industry and regulators that would help guide logging in specific watersheds.

The hazard zones that came out of that plan assigned areas with a high, moderate or low potential for landslide risk based on factors including topography and steepness. We wanted to see if Weyerhaeuser's logging practices accounted for unstable slopes. Instead we found more examples similar to Ringman's initial photo.

By overlaying these zones on the clear-cuts, we focused on 87 logging sites that were in the most slide-prone terrain. To do this, we calculated how much of each clear-cut fell into the various hazard zones. We included only those clear-cuts where at least 50 percent or more of the acreage was in a moderate- or high-hazard zone. Out of those 87 logging sites, 42 had landslides from the storm. Despite making up only 8 percent of the total acreage in the. Chehalis River basin, these sites accounted for 30 percent of the slides.