A Re-Evaluation of Bruun's Rule and Supporting Evidence


  • Roger N. Dubois


Barrier island, barrier transgression, beach erosion, gradation, mass movement, nearshore, ramp, sea-level rise, sediment budget, shoreface, transgression


Bruun's rule postulates that in order to maintain an equilibrium shore profile in the face of rising sea level, sediments must be eroded from the heach and shoreface and deposited on the ramp so as to increase the ramp elevation in direct proportion to the rise in sea level. After evaluating results presented in support of the rule, it is argued here that at this time there is no hard evidence which links rising sea levels with the transference of sediments from the shoreface to the ramp. Data do show, however, that the rule is applicable to the beach and nearshore zone. Further, the limited depth of sediment transport that has an effect on shore erosion may be located near the base of the shoreface, not on the ramp as suggested by the rule. If this is the case, then there is no need to elevate the ramp in proportion to a rise in sea level. Consequently, in the face of rising sea level, the shoreface should transgress while the ramp may be simply abandoned by wave action.