Serving property owners, developers, buyers and sellers, realtors, businesses, and timber and resource managers since 1995.               

ALL ABOUT GEOHAZARDS

A survival guide for property owners and residents in western Puget Sound

For many of us, the headlines are all too familiar:

            "A procession of winter storms accompanied by heavy rains causes flooding along local rivers and streams, eroding slopes and endangering several homes."

            "A major earthslide covers a highway, cutting off access to a beach community."

            "Mudflows cascade without warning down a steep slope pushing several waterfront homes off their foundations, resulting in tragic deaths."

            "Along the edge of the sound, wave action, generated by high winds, undercuts the base of a high bluff causing landslides and threatening the safety of several homes at the top."

Each year, the pattern repeats itself, as Puget Sound area residents living in geologically-hazardous areas along unstable slopes, bluffs and shorelines brace for the worst. By spring, however, the events of the previous winter are seemingly forgotten as owners whose property has survived intact clear away the mud and debris and clamber back onto the beachfronts and bluff tops.

Of perhaps greater concern is the explosive growth occurring in these same high-risk areas as dozens of expensive new homes are eagerly snatched up by buyers seeking "spectacular marine, city and mountain views", unaware of the potential hazards of slope failure. As the density of homes increases along marine bluffs and shorelines, it is inevitable that losses from these events will become even more frequent.

"Civilization exists by geological consent - subject to change without notice!"

The geological processes that cause erosion, slides, slumps and mudflows are part of a continuing cycle we are unlikely to ever control. Recognizing that these events will likely continue to occur, local governments have enacted ordinances that regulate development in these "Critical Areas". While ordinances are a good first step, the best solution to the problem of geohazards is an informed public. Property owners and residents who understand the inherent risks of owning slope, bluff or waterfront properties, who can recognize geologically-hazardous conditions and who know how to reduce the potential for losses will be the best equipped to deal with the hazards in these areas.

Reducing the Risks

Identifying and describing potential geohazard areas and developing ways to mitigate them is the role of a professional geologist or geotechnical engineer. However, property owners can benefit from understanding some basic concepts that may reduce risks.

       1.    Maintain buffers and building setbacks:

               Most counties require minimum setbacks from critical geohazard areas, but in some cases these are not always adequate.

        2.    Preserve existing vegetation:

                Plant leaves, stems and branches reduce the impacts of rainfall on slopes while root systems hold soils in place. Plants also allow ground materials to dry out more quickly by wicking water from the soils.

        3,    Avoid artificial saturation of slope materials:

                Direct storm water runoff away from slopes or tightline this water to the slope base. Avoid landscaping that requires heavy watering or frequent use of sprinkler systems. Keep drainfields, septic tanks and swimming pools (that often leak) away from slopes and blufftops.

        4.    Avoid over-steepening of slopes:

                Construction of roads, driveways and building pads that result in over-steepening portions of a slope or undercutting the base of a slope may greatly increase the risk of slope failure.

        5.    Avoid off-season development:

                Removing vegetation, clearing, grading and filling at building sites should be avoided during periods when heavy rainfall may be expected. In the Puget Sound region, this period usually extends from mid-October through April. Work that leaves the ground surface exposed during the winter months should employ effective erosion-control measures.