Feeder Bluffs on Puget Sound: Tools for Improved Management

Much of Puget Sound’s shoreline consists of mixed sand and gravel beaches, dominated by longshore sediment transport and organized into hundreds of discrete littoral cells. Sediment supply within these cells is often provided by erosion of the steep coastal bluffs, which are composed of abundant, coarse-grained Pleistocene sediment. Bluffs that provide beach sediment are referred to as feeder bluffs and are important to the long-term maintenance of Puget Sound beaches. At the same time, development of Puget Sound’s shoreline has led to widespread construction of seawalls and revetments to control bluff erosion, with the unintended consequence of reducing natural sources of beach sediment. Coastal managers are concerned that this will adversely impact beach conditions. Impair nearshore ecological functions, and reduce resilience to rising sea level. Until recently, regional mapping of feeder bluffs existed. In 2012-2013, we combined existing information with new data and completed a sound-wide coverage of eroding bluffs, along with related beach and coastal landforms. Mapping was conducted using detailed field observations, supplemented with geologic information and aerial photographs. Bluffs were categorized based on their potential ability to deliver beach sediment. We found that of Puget Sound’s 4000 km of shoreline, about 2200 km are beaches. Of these about 600 km are feeder bluffs and about 50 km were mapped as exceptional. About 35% of the region’s beaches were mapped as modified or armored. The maps of feeder bluffs will be provided on Ecology’s online Coastal Atlas, allowing access and integration with other nearshore data. In addition, web-based material provides background information on geology and beaches and guidance on how to interpret and apply his information. This will assist planners and resource managers in improving shoreline management, assessing Puget Sound nearshore health, and identifying coastal restoration priorities