The impacts of armoring on Salish Sea beaches: overview, background, and methods

Shoreline armoring is widespread in the Salish Sea, but few data have documented actual impacts on physical or biological features of local nearshore ecosystems. Armoring marine shorelines can alter natural processes at multiple spatial and temporal scales; some, such as ‘starving’ the beach of sediments, may take decades to become visible, while others such as ‘placement loss’ are immediate. Two research teams have been studying a broad set of sites to document parameters that do and do not change when a shoreline is armored, and to determine under what conditions armoring has significant effects. Our methodology has been to compare paired adjacent armored and unarmored beaches. During the years 2010 - 2013 we completed surveys at 6 pairs of beaches in South Sound, 25 pairs in Central Sound, and 36 pairs in the North. At all sites we have data on habitat and setting (e.g., overhanging vegetation, location in the drift cell); beach topography; sediment size distributions; abundance and types of logs, wrack, and invertebrates in the wrack line; and juvenile clams at Mean Low Water. At some sites we have data on forage fish spawn. Overall, demonstrating physical differences between paired beaches is difficult given the very high natural variability among beaches, although obvious effects such as reduction in beach width are evident. Limited data show that wave heights are greater where they interact with armoring, and beach slope near the armoring tends to steepen. Many biological effects are clear at the upper part of the beach, while lower elevation effects (further from armoring) are progressively harder to demonstrate. Armoring impacts are less dramatic at the pairs of beaches in the northern Salish Sea. There does not appear to be a distinct threshold in elevation of armoring that causes increased impacts, but instead a gradient. Analyses of these diverse datasets are ongoing, and results are detailed in the following linked presentations