The modified Bruun Rule extended for landward transport

• Evolution of sandy beaches in response to relative sea level rise is reviewed.
• Limitations of the widely-applied Bruun Rule are discussed.
• A modified Bruun Rule is presented that allows for landward transport.
• Examples illustrate application of the modified Bruun Rule.
• Optimal application of new method requires quantification of landward transport.

The Bruun Rule (Bruun, 1954 and Bruun, 1962) provides a relationship between sea level rise and shoreline retreat, and has been widely applied by the engineering and scientific communities to interpret shoreline changes and to plan for possible future increases in sea level rise rates. The Bruun Rule assumes that all sand removed from the upper profile is deposited offshore as sea level rises, although overwash during storms and landward Aeolian transport clearly indicate otherwise. Herein, we examine processes associated with sandy beach evolution in response to relative sea level rise and propose a modified form of the Bruun Rule that considers the full range of parsing cross-shore transport, from completely seaward to completely landward depending on the prevailing storm and surge conditions and whether there is a surplus or deficit of sand in the profile with respect to the equilibrium beach profile. A methodology is proposed that more appropriately represents the long-term processes and beach response. However, an improved quantitative understanding of landward transport is required for optimal application of the proposed method.