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.

At a regional scale, the state of the coast can be understood from a sediment budget point of view. For example, accretion occurs when more sand is transported into the system than is being transported out, while erosion occurs when more sand is leaving the system than coming in. Therefore, shore protection or stabilization can be achieved by balancing the sediment budget at an adequate spatial and temporal scale. However, the practice of balancing a sediment budget at a regional scale is quite complicated and has not been broadly applied till the recent 20 years. This chapter discusses the formulation of a regional sediment budget at beach–inlet systems. The inlet reservoir model, which accounts for temporal evolution of sediment volume at an ebb tidal delta, is discussed. At a local scale, sediment bypassing or backpassing and inlet channel dredging are often conducted, and these methods are reviewed in the context of regional sediment management.