By Ruth Longoria

Last week’s early Sunday morning mudslide on Forest Avenue may have only affected a dozen homes, but it serves as a wake-up call to all Island homeowners.

Most of the perimeter of the Island is considered to have a problem with slope stability, said Glenn Boettcher, city maintenance director. That could be a problem when the Island’s abundance of upper-middle class to multi-million dollar homes are perched atop or situated below unstable soil.

“Mercer Island is basically a flat space with steep slopes and a lot of glacial tilt. That’s true throughout the Northwest, but with water involved there’s a lot of potential for earth movement,” said Rich Conrad, Mercer Island city manager.

Conrad was on the scene Sunday morning to ensure the homeowner was given technical advice from a geo-technical engineer and information on whom to call for a contractor to stabilize the hillside. City maintenance crews were able to clear the street and driveways so emergency services could get through if needed, while keeping people away from areas that could dangerous.

But, Conrad said, that’s about all the city can do in a situation where the slide is on private property, and caused by an individual homeowner’s irrigation system. The Forest Avenue slide is believed to have been caused by a leak in the homeowner’s sprinkler system.

Landslides occur in every state, but the coastal and mountainous areas of California, Oregon and Washington are among the primary regions of landslide occurrence and potential, according to the U.S. Geological Survey’s Web site.

Slides generally occur when rivers, ocean waves, melting snow pack, or heavy rains saturate and erode the soil of a steep slope. The site lists a variety of causes of slides, including geological (weak, sensitive or weathered materials), morphological (tectonic or volcanic uplift, glacial rebound, vegetation removal, freeze-and-thaw or shrink-and-swell weathering), and human (excavation of a slope, loading of soil, deforestation, irrigation, artificial vibration and water leakage from utilities). Water causes a downward and outward movement of the slope-forming materials — such as rock, soil and artificial fill — which leads to a sliding, toppling, spreading or flowing that can push along trees, shrubs, people, vehicles, homes and other buildings.

Every year, landslides in the U.S. are responsible for an average of about $3.5 billion damage, and 25 to 50 deaths. Most of the fatalities occur while people are sleeping, the site information says. Although it is impractical to stay awake constantly to avert danger, the Federal Emergency Management Agency’s web site suggests residents stay alert when possible during times of intense rainfall and damp weather and listen for unusual sounds that might indicate moving debris, such as trees cracking or boulders knocking together. However, moving debris can flow quickly and without warning. In the Forest Avenue mudslide, the homeowner heard running water, apparently from the leaking sprinkler system, only moments before his backyard trees began to disappear and slide down the hillside into his neighbors’ yards.

Although there were numerous slides in the past, there have been significantly fewer slides on the Island in the past decade, Conrad said, because of a storm water utility system installed 10 years ago that helps get rain effectively from rooftops to the lake, he said.

“When it rains, water drains. So, it’s a benefit to have the storm water system in place, but we still have soil conditions that allow water to build up,” Conrad said. “And when you have standing water seeping into hillsides, eventually you’re going to have slides.”

And, if you hear water running that isn’t coming from inside your home, check your meter and see if it is spinning, that’s a sign that water is going somewhere, Conrad said.

“If you’ve got water running, call for help. If we get calls, we’ll send out the water utility guys to see where the problem is,” he said. “We may not be able to fix it, but we can point folks in the right direction.”

Slide prevention

Here are some ways to prevent damage and protect your property if you are in a landslide-prone area:

? Clean out catch basins so you don’t have leaves and other debris stopping water from flowing out of the basin.

? If you have an irrigation system, periodically have it tested to make sure it is operating correctly.

? Install flexible pipe fittings to avoid gas or water leaks. Flexible fittings will be less likely to break.

? Plant ground cover on slopes and build retaining walls.

? In mud flow areas, build channel and deflection walls to direct the flow around buildings. However, remember that if you build walls to divert debris flow and the flow lands on a neighbor’s property, you may be liable for damages.

? Contract with a private consulting company specializing in earth movement for options and advise on landslide options and corrective measures you can take. Companies should be those specializing in geo-technical engineering, structural engineering or civil engineering. Taking steps without consulting a professional could make your situation worse.

? Make sure you have the right kind of insurance. Mud flow is covered by flood insurance policies from the National Flood Insurance Program. Flood insurance can be purchased through a local insurance agency.

What to do after a mudslide

FEMA offers some suggestions of what to do if you are involved in a mudslide.

? Call 9-1-1. Contact local fire, police or public works. Local officials are the best people to assess the potential danger. They also can give you an idea who to contact for cleanup and other involved issues.

? Evacuate. Get out of the path of a landslide or debris flow. However, realize that it may be dangerous to drive, and roadways may be blocked.

? Inform affected neighbors. Your neighbors might not be aware of the potential danger and advising them of the threat may save lives. Help neighbors who need assistance to evacuate.