Sedimentary geomorphology of mangrove coasts in perspective of energy dissipation

Energy dissipation has been widely studied in coastal sedimentary geomorphology. It has been assumed that thresholds in energy dissipation may exist in geomorphological evolution; however, whether energy dissipation evolves towards a minimum, maximum, or both, aroused a big debate in a long history. We summarized the previous publications to revisit the energy dissipation problem in coastal geomorphology, and proposed a concept of ‘impedance matching’ to explain the problem regarding minimum and maximum values of energy dissipation. Once the geomorphological system showed a maximal mechanical energy storage but a minimal thermal energy dissipation, it could be a ‘resonance impedance matching’ system. Otherwise, it could be a ‘gradience impedance matching’ system. The Ω classification of beaches obtained by dimensionless settling velocity was a typical example for these two ‘impedance matching’ systems. Based on the new concept, we reviewed geomorphological studies on mangrove ecosystems, and revealed the ‘impedance matching’ and the energy dissipation across the interfaces of tidal creek–tidal flat–mangrove systems. In addition, we discussed how the energy dissipation could affect the growth of mangroves through hydrodynamics and thermal dynamics, and pointed out that the three-dimensional structure of tidal creek–tidal flat is very important to maintain the stability of mangrove ecosystems and therefore should be considered in the future mangrove restoration projects.