In November 2006 an intense storm dropped 45 cm (17.9 in) of rain over 36 hours at Mount Rainier National Park, Washington. The record floods from this event caused the park to be closed for six months, destroying roads and trails, damaging utilities, and cutting off access to park campgrounds. The region overall has seen increasing flood damage: six of the largest storms on record have occurred in the last 25 years (Parzybok et al. 2009). Flooding at Mount Rainier is not uncommon, but the November 2006 flood was by far the most destructive in park history and its effects are still felt today. Though one might conclude that the 2006 flood was an anomalous event in the park’s history, recent trends in flooding, aggradation (excessive sediment accumulation in riverbeds), debris flows, glacial recession, and warming temperatures are consistent with effects of climate change.
Because of steep topography, Mount Rainier hosts significant development in valley bottoms near rivers. Large portions of the mountain’s infrastructure are built in the rustic style of architecture from the early 1900s, and make up the park’s designated National Historic Landmark District (NHLD), the highest level of cultural resource protection. Much of this development occurred before recognition of hazards associated with building near rivers. For example, the Carbon River Road on the northwest side of the park was built along the grade of the river. Repeated flooding in the 1990s and subsequent destructive floods in 2006 and 2008 have damaged significant portions of the road, cutting off access to the northwestern portion of the park. The Longmire Complex, which is one of the main developed areas on the west side of the park, is located adjacent to the Nisqually River. This river is up to 30 feet in elevation higher than nearby roads and park buildings, which are only protected by a small levee (fig. 1). Park staff must determine how best to manage infrastructure in peril, including areas that have been designated as NHLD features.