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Special Paper 49, Beach and shoreline dynamics in the Cannon Beach littoral cell: Implications for dune management, by Jonathan C. Allan, Fletcher E. O’Brien, and Laura L. Gabel.

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EXECUTIVE SUMMARY

This study provides an assessment of the physical processes contributing to changes in the morphology of beaches and dunes in the Cannon Beach littoral cell, located in southern Clatsop County, Oregon. The work presented here updates an earlier investigation by Rosenfeld (1997). Since 1939, the City of Cannon Beach has experienced significant accumulation of sand along its beaches, especially in its dunes north of Haystack Rock (Figure 1 and Figure 33). In particular, north of Ecola Creek, the combination of a large sand supply and the proliferation of European beach grass (A. arenaria) has contributed to the formation of dunes that have reached heights of 16 m (53 ft, relative to the North American Vertical Datum of 1988 [NAVD88]) In response to considerable sand buildup north of Ecola Creek, the City of Cannon Beach initiated a process to evaluate their existing dune management plan on the basis of updated scientific information on physical processes and coastal geomorphology occurring along the Cannon Beach littoral cell. The overarching objective is to use the updated information to help establish new guidelines for the relocation of excess sand that periodically builds up along the coastline. This sand buildup within the dune is presently affecting the views of local residents, while sand blowing inland has become a nuisance, migrating where it has begun to inundate buildings and properties. The broad findings of this study include the following:

Because of the variability in the forces that both sustain and erode beaches and dunes on the Oregon coast and our uncertainty in changes that will likely affect the beach over longer time scales (10 to 30 years), an adaptive management approach based on a sound knowledge of beach and dune processes, guided by systematic monitoring and evaluation of the system as a whole is essential.

 

Figure 1. Location map of the Cannon Beach littoral cell on the Oregon coast showing subcells, place names, and beach profile locations.

 

Figure 33. Beach sand volume compartments identified for the Cannon Beach littoral cell showing the net sand volume change from 1997 to 2016. Green indicates accretion, red denotes erosion. Sand volumes are calculated for the area above the 4 m (13 ft) contour to the back edge of the dunes, physical features such as concrete paths, back edge of gravel berms, or the bluff toe.

 

Special Paper 49 is part of a series of DOGAMI publications that describe beach and shoreline dynamics along the Oregon coast: