LANDSLIDES AND LAND USE IN COLORADO SPRINGS, COLORADO

The City of Colorado Springs lies at the boundary between the Great Plains and the Rocky Mountains. The western part of the city occupies a series of dissected foothills underlain by weak Cretaceous claystones, which are prone to landslides. Whereas early growth avoided the foothills, these areas have become increasingly built out during the 1970s-1990s, fueled by premium land prices for infill and view lots.

Several areas in the city have experienced damage from landslide movements during the 1990s. Some episodes of landsliding, particularly during 1995 and 1999, correspond with wet winters or long-duration spring rainstorms. However, human-caused factors such as slope modification and lawn irrigation appear to have played a part in several episodes.

The Colorado Geological Survey (CGS) has responded to these events in a variety of ways. In several instances, CGS has provided emergency evaluations of landslide threats and hazards to the City, homeowners, and FEMA. Following the 1995 landslide episode, CGS hosted a geologic-hazards conference and field trips in Colorado Springs for private geotechnical practitioners, the development community, and City staff and decision-makers. As a result of this outreach, which resulted in an increased awareness of landslides and other geologic hazards, the City enacted it first geologic-hazards ordinance in 1996. The CGS now assists the City on an as-needed basis to provide third-party technical reviews of geologic-hazard and geotechnical-development reports under this ordinance. Following the 1999 disaster, the CGS provided landslide-hazard assessments and is currently completing a GIS map of landslides and landslide-susceptible areas for the City.

Landslides remain a controversial topic in Colorado Springs. FEMA has spent $4.5 million in acquiring affected properties following the 1999 episode, and public awareness of landslides has grown. However, the City and its business community and populace are strongly protective of property rights for new and existing land uses. This means that area-specific landslide investigations and recommendations must be based on solid scientific and engineering assumptions and principles in order to justify the resulting, and sometimes unfavorable, land-use decisions.