FROM GEOLOGIC MAP TO GEOHAZARDS POLICY, A CASE STUDY FROM KIRKLAND WA

The basic geologic map still serves many purposes. But in areas with geohazards, that basic geological map is often the foundation for many derivative maps including those that lead to the designation of critical areas and ultimately impacting city codes and policies. Hence, the basic geological map needs to be as accurate and precise as possible. Recently, the City of Kirkland Washington contracted for an updated geological map and geohazards maps including landslide susceptibility and liquefaction potential. As part of the package, depth to groundwater and surface water occurrences were mapped. Then the City engaged with geologic consultants to use the maps and databases to delineate critical areas and to updated codes and procedures for permitting for property development. The City hosted multiple hearings in which the project geologists were key participants presenting the science and societal impacts to the public, to City commissioners, and to City staff. By having engineering geologists involved with the code changes, the City now has relevant and defensible regulations. For example in areas highly susceptible to landslides, the City requires: subsurface investigations, review of lidar mapping, a discussion of the presence or absence of landslides, slope stability analysis, and peer review. The City’s goal for the project was to protect the public and to reduce the risk of loss of life and damage to property.