A beach–inlet system is composed of several sub-environments, including beach and nearshore, tidal inlet and ebb and flood tidal deltas, and coastal dunes. Building upon Chapter 2, this chapter discusses in detail the sedimentologic characteristics and morphodynamics of the various sub-environments composing a beach–inlet system. Commonly used concepts in quantifying beach morphology and its changes, including equilibrium beach profile, depth of closure, and the Bruun Rule, are reviewed. Coastal dunes and their morphodynamics are discussed in the context of beach–dune interaction. Morphologic and sedimentologic characteristics of tidal inlets and their associated ebb tidal delta and flood tidal delta are described in detail in terms of various morphology features. General patterns of sediment exchange for wave-dominated and mixed-energy beach–inlet systems are introduced.

Building upon regional scale discussions in Chapter 2, this chapter discusses the interactions between barrier beaches and tidal inlets at a local scale from the perspective of inlet stability, and mechanisms and pathways of sediment bypassing across tidal inlets. Inlet stability can be significantly influenced by local geologic conditions such as outcropping of erosion resistant bedrocks or stiff mud, in addition to hydraulic conditions as controlled by tidal prism. Local geology such as shoreline exposure of bedrocks and stiff mud can also influence beach morphodynamics by controlling its planform. However, tidal inlets and their ebb tidal deltas impose the major interruption to the continuity of longshore sand transport. How sand moving along the beach can reach from one barrier island to another constitutes the main issue for beach–inlet interaction, and subsequently the erosion or accretion of barrier beaches. Several conceptual models have been developed and are discussed in this chapter. The rapidly improving numerical modeling provides a promising tool to quantify sediment bypassing and is introduced here.