(Converted into web page from Ecology Publication #95-107: Surface Water and Groundwater on Coastal Bluffs: A Guide for Puget Sound Property Owners).
During the weeks following Christmas, 1994, we received numerous telephone calls from coastal property owners concerned about recent landsliding on their bluffs. Residents reported large and small slides, damaged stairways and bulkheads, old trees that had been undermined, and settling of yard areas near the bluff edge. On further discussion, we found that most of these slides occurred during two short periods of heavy rain in late December.
In each case it appeared that problems had been exacerbated by poorly designed or improperly constructed drainage systems. Although property owners were often aware of potential problems, they did not fully appreciate the relationship between drainage and slope stability and they often did not understand the operation nor the limitations of their existing drainage system. In many cases, it appeared that simple measures might have greatly reduced the amount of damage.
Coastal slopes on Puget Sound are inherently unstable areas. Our experience suggests that careful management of site drainage is probably the most cost-effective approach to minimizing bluff hazards. Even where circumstances dictate significant structural stabilization efforts, such as shoreline bulkheading or regrading of slopes, site drainage remains an essential component of the solution.
At Ecology, we would like to encourage both safe and environmentally sound shoreline development. Dealing with drainage wisely has little adverse impact on our beaches and shorelines and bears few of the environmental consequences associated with extensive shoreline bulkheading or major clearing and grading of coastal slopes.
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