Abstract: Both the theoretic consideration and the field experience suggest that the application of Bruun Rule in the muddy coast, especially in the Changjiang deltaic coast, is a complicated problem, for such coast presents a significant difference from sandy beaches in its coastal dynamics, geomorphology, sediment characteristics and transport. This paper presents a special study and discussion on the original equilibrium profile associated with Bruun Rule and its application. The study suggests that although the strict equilibrium coastal profiles, as described in the classical theory for sandy beach development, do not exist on the deltaic coast, the coastal profiles do show certain stable morphological features, such as, the closure depth, the most important parameter in Bruun Rule, which provide a basis for the application of Bruun Rule in this coast. Because the coastal profiles vary greatly, even within the same onshore offshore profile, the coastal slope shows a large variation and this may give a great difference in the estimate of shoreline retreat rate if an arbitrary distance L_* is adopted. An integrated study of coastal dynamics, geomorphology and sedimentology in the coastal system suggests that, while estimating the shoreline retreat rate, the two closure depths of-8 m and-30 m should be considered in the open east coast of Shanghai, while on the north coast of Hangzhou Bay the single closure depth of-8m is enough due to the existence of 8m underwater platform of Hangzhou Bay: It is found that these two different closure depths are dynamically controlled by the two wave heights approximately with ≤1-year and≥10-year recurrence intervals, respectively. Furthermore, it is suggested that a study of longshore sediment budget is indispensable for obtaining a reasonable estimate of shoreline retreat rate within the studied coastal segment because historical evidence suggests that the dynamical changes in the middle to the upper part of coastal profile are largely controlled by this factor under a stable sea-level.

Key words: Bruun Rule, sea-level rise, coastal erosion, equilibrium profile, closure depth