Hydrodynamics and sediment processes at beach–inlet systems are dynamic and complicated. Beach–inlet systems are characteristic of mostly shallow and complicated bathymetry. As ocean waves propagate into shallow water with complex bathymetry, wave refraction, diffraction, shoaling, and breaking occur. The shallow water associated with the ebb tidal delta has significant influence on the pattern of wave propagation. Eventually in the vicinity of the shoreline and over the very shallow portions of the ebb tidal delta, waves break and generate intense turbulence that induce active sediment transport. Both wave and tide play significant roles in transporting sediments and causing morphology change at barrier–inlet systems. In general, wave-induced sediment transport dominates in areas far from the inlet where tidal currents tend to be weak. Within the deeper parts of inlet channels, tide-driven current constitutes the main mechanism for moving sediments. Over the ebb and flood tidal deltas, sediment movements are driven by both wave and current. This chapter reviews the above topics and commonly used equations on the hydrodynamics and sediment transport relevant to the beach–inlet system.

Although barrier islands occur under a variety of coastal settings, coasts with an ample supply of sand-sized sediment, a wide and gentle continental shelf, and a broad coastal plain are more conducive to the formation of barrier islands. When the above three conditions, combined with a slow sea-level rise rate of 1–3 mm/year, occur, barrier islands can be the dominant coastal features, such as along the US Gulf of Mexico and Atlantic Ocean coasts. Although not as common, barrier islands also occur along rocky coasts and river-delta coasts. This chapter discusses different morphologic and sedimentologic characteristics under different geologic and oceanographic settings. The various sub-environments, also referred to as morphologic features, that compose a barrier–inlet system are described, along with a morphodynamic classification of barrier island under different coastal settings. These morphologic features and the morphodynamic classification are used in the following chapters discussing sediment transport processes, sediment exchange among the different features and the associated pathways, and management of the sediment resources among the various morphologic features.

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.

The concept and application of resilience have been significantly expanded in the last three decades and the term is being used more and more broadly to represent a large-scale multi-disciplinary and comprehensive approach to both natural and human-related coastal issues associated with rising sea level, increased storm frequency and intensity, and human stressors. This chapter reviews the relevant findings from the recent global climate-change reports and introduces the resilience of barrier–inlet systems. In terms of the natural system, the survival of the very landform under the condition of accelerating sea-level rise is discussed via a conceptual model or a couple of numerical models. The resiliency of the human–natural barrier–inlet environment is far more complicated than just the natural system. The concepts and complicated framework outlined in the recent NRC (National Research Council) and USGCRP (US Global Climate Research Program) reports are reviewed, and illustrated with two case studies.

Prior to the 1950s, general shore-protection practice was to use hard structures to protect against beach erosion or storm damage. Generally, the hard structures can be divided into two categories. The first category functions through anchoring the position of either a shoreline or a dune-line, such as seawalls and revetments. The second category is mainly sand-trapping structures such as groins and detached breakwaters. Realizing that the accumulation of sand produced by a structure is at the expense of an adjacent section of the shore, since the 1970s, 90% of the US Federal appropriation for shore protection has been for beach nourishment. Although beach and dune nourishment has become by far the most dominant approach to shore protection, principles of hard engineering structures are still reviewed in this chapter. More recently, since the 2010s, Engineering with Nature (EWN), defined as the intentional alignment of natural and engineering processes to efficiently and sustainably deliver economic, environmental, and social benefits through collaborative processes, are being promoted and applied more and more. The concept and practice of EWN are introduced in this chapter.

The 2010 US Census indicates that 39% of the US population, or 123.3 million people, live in Coastal Shoreline Counties which comprise less than 10% of the US land area. This results in a population density that is 4.2-times the national average. Similar dense population occurs in coastal areas worldwide. Barrier islands constitute a major coastal environment. Barrier islands are separated by tidal inlets which serve as essential navigation channels connecting harbors within the estuaries and the open ocean. Barrier island beach and tidal inlet are parts of an inter-connected system and should be understood and managed as such. This book discusses beach–inlet interaction in terms of sediment exchange among various morphologic features and processes that drive the sediment exchange. Balancing valuable sediment resources in a beach–inlet system is essential to modern shore protection and coastal management.

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.