Shoreline development and the alteration of nearshore processes through armoring can reduce longshore transport and sediment deposition. Cumulative impacts of these shoreline changes may only become evident over long periods of time, and spatial variation in trends may be complex, especially in cases of large beach complexes with interacting features. The Jackson/Lafarge tombolo and its associated Argyle Lagoon, on San Juan Island, Washington, have been stable for more than 106 years. Although the feeder bluff for the tombolo has been substantially reduced through gravel mining, associated beach loss that might be expected through wave erosion appears to have been at least temporarily mitigated by sand and gravel deposited to facilitate upland transport and barging at the proximal end of the tombolo. However, alterations to the shoreline at the proximal end of the tombolo may shift the existing dynamic equilibrium between deposition and erosion to a trend of net loss of beach substrate. This change would result in increased vulnerability and possible loss of an uncommon lagoon habitat.
The purpose of this study was to develop and apply analytical techniques to measure possible cumulative impacts of a gravel-mining operation on Jackson/Lafarge Beach, a small sandy barrier typical of those found along Washington State’s Puget Sound coast. Using a combination of aerial photo interpretation, GIS, and field measurements, this project examined the cumulative impacts of these changes to the Jackson/Lafarge beach drift cell more than 40 yrs later, including long-term spatial changes in geomorphic landforms, and corresponding impacts to beach and nearshore profiles, substrate, and distribution of coarse woody debris.
Gabriel, A.O., and L. Bodensteiner. 2009. Cumulative effects of gravel mining and barging operations, Jackson/Lafarge Beach, Washington, 1960-2003. Shore & Beach , 77 (1), pp. 9-18.