Gravel beaches have long been recognized as one of the most efficient forms of "natural" coastal protection, exhibiting a remarkable degree of stability in the face of sustained wave attack and as a result have been suggested as a form of shore protection. Such structures are variously termed "cobble berms", "dynamic revetments" or "rubble beaches" and essentially involve the construction of a gravel beach at the shore, in front of the property to be protected. These structures are effective in defending properties because the sloping, porous cobble beach is able to disrupt and dissipate the wave energy by adjusting its morphology in response to the prevailing wave conditions. Since the particle sizes used in their construction are generally small and their placement does not require special attention, dynamic revetments are much easier and cheaper to construct than a conventional riprap revetment or seawall. Furthermore, because dynamic revetments are analogous to a natural cobble beach, they are aesthetically pleasing compared with "hard" engineered solutions, which may lessen the rigors of permitting such structures for coastal protection. There remain, however, unanswered questions about their design particularly along the high-energy Oregon coast. This includes the sizes and types of gravel to be used, their slopes and crest elevations, the volume of material to be included in the berm, and where the material may be obtained to construct such features.
An examination of the morphological and sedimentary characteristics of 27 profile lines at 13 gravel beach study sites along the Oregon coast revealed that the heights of the gravel beaches ranged from 5.7 to 7.1 m (19-23 ft), while the slopes of the beaches varied from 7.7º to 14.1º. Mean grain-sizes were found to range from -4.9Ø (30 mm) to -7.0Ø (128 mm), and were classified as well sorted to moderately well sorted. However, a comparison of these parameters among stable versus eroding gravel beaches revealed no clear discernable pattern. In contrast, it would appear that a key difference in the stability of the gravel beaches was the volume and width of gravel contained on the beach, with beaches containing larger volumes of gravel (> 50 m3.m-1 (538 ft3.ft-1)) and larger widths (> 20 m (66 ft)) being the most stable. Based on this analysis, a crest elevation of ~7.0 m (23 ft), mean grain-size of no less than -6.0Ø (64 mm), and a beach slope of 11º was recommended in future designs of dynamic revetments for the Oregon coast. While numerous quarry sites were identified that could supply crushed rock for the building of a dynamic revetment, rounded gravels were more difficult to locate and tended to be located furthest from the coast increasing the costs that would be incurred to transport the material. Without doubt, the largest constraint that likely limits their adoption is the cost of transporting the gravels to a particular site.