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SHOREFACE PROCESSES IN ONSLOW BAYprimarily by wave-current interactions {Madsen and Grant,1976); the micromorphology (ripple geometry, biologicroughness. etc.) and sedimentary characteristics of the seabed{Nielsen, 1979; Wright, 1993); and the geologic frameworkof the shoreface {Pilkey et al. 1993; Riggs et al..1995). Figure 2 illustrates the combined effects of these factorsin determining the nature of the bottom boundary layerand the resultant bed stresses and sediment transport.A number of field studies have documented that significantsuspended and bed load transport occurs frequently onthe shoreface and inner shelf. These include Sternberg andLarsen {1975); Gadd et al. {1978); Lavelle et al. {1978);Cacchione and Drake {1982); Vincent et al. {1982); Wibergand Smith {1983); Cacchione et al. {1987; 1994); andWright et al.. {1986; 1991; 1994) among many others. Thesestudies, however, capture only a brief moment in the largescaleevolution of the shoreface. A decade-scale view ofshoreface processes and evolution is currently lacking. Thisis particularly true in engineering studies of coastal processes,which typically require a decade- scale understandingof shoreface evolution.Engineering models used to predict shoreline evolutionand to design replenished beaches usually assume I that theshoreface has an equilibrium shape related I to wave climateand surficial sediment grain size: {Dean. 1977; Zeidler.1982). As applied to the design of replenished beaches, theprofile of equilibrium is considered to be the stable configurationthat a beach will try to achieve under the influence ofincident waves {Dean, 1983). Maintenance of the profile ofequilibrium during shoreline retreat is also central to the conceptof Bruun Rule response to sea-level rise (Bruun, 1962).The equilibrium profile equation was first proposed byBruun (1954) for the Danish North Sea coast, and has theformh = Ayn (1)where h is water depth, y is the distance offshore fromthe shoreline, n is a variable shape parameter and A is a scalingparameter. Bruun (1962) used this equation to develop asimple model for coastal evolution, in which the shorefaceprofile responds to sea-level rise by moving landward andupward such that the profile shape remains constant down toa depth of no wave influence (beyond which little sedimentis supposedly transported). This simple relationship was oneof the first models of shoreface transgression, preceding themore "classic" geologic conceptualizations of Curray (1969)and Swift (1976).The Bruun Rule was, and still is, a good concept. It isnot a good quantitative model. The concept, as originallyconceived by Bruun, provided a strong conceptual basis forfurther thought about the nature of shoreface evolution. Subsequentwork, however, sought to verify its basic principles.For example, Dean (1977) used a least squares approach tofit the data of Hayden et al. (1975) to an equation of the formshown in (1), where n=0.67. Infixing the value of n, Dean(1977) left the sediment scaling parameter, A, as the onlyindependent variable in the equation. Dean (1987) related Ato sediment fall velocity by transforming Moore's (1982)sediment grain size data to the equationA = 0.067 w O.44 (2)where w is the sediment fall velocity in cm S-1. Essentially,this relationship implies that any shoreface profile can bedescribed solely on the basis of the grain size present.The profile of equilibrium concept makes several fundamentalassumptions about the nature of the shoreface and theprocesses acting on it (Dean, 1977; 1991; cf. Pilkey et al.,1993). Pilkey et al. (1993) argued that several basic assumptionsof the shoreface profile of equilibrium concept are notmet in most field settings. The assumptions include: 1) sedimentmovement is driven solely by diffusion due to waveenergygradients across the shoreface; 2) closure depth (aseaward limit of significant net sediment movement) existsand can be quantified; 3) the shoreface is sand-rich, andunderlying geologic framework does not influence the profileshape; and 4) the profile described by the equilibriumprofile equation (Dean, 1977) provides an approximation ofthe real shoreface shape useful for coastal engineeringprojects.The shoreface profile of equilibrium is a fundamentalprinciple behind most analytical and numerical models ofshoreline change used to predict large-scale coastal behavior(e.g., Hanson and Kraus, 1989 [the GENESIS model]) and todesign replenished beaches (e.g., Hansen and Lillycrop,1988; Larson and Kraus, 1989 [the SBEACH model]),including those used on beaches in Onslow Bay. There hasbeen no systematic field verification of the physical basis forthe equilibrium profile equation (Kraft et al., 1987; Wright etal., 1991; Pilkey et al., 1993). The concept, however, hasbeen accepted as valid and useful by many coastal researchers,and is used to predict coastal evolution in a variety ofcoastal settings (e.g., Rosen, 1978).The Bruun Rule effectively states that shoreface slope isthe only control of shoreline retreat and that for a given sealevelrise, beaches with gentle shorefaces will recede fasterthan those with steep shorefaces. In typical applications,retreat rates are based on the slope of the shoreface ratherthan the slope of the migration surface. As a result, on EastCoast shorefaces the Bruun Rule usually predicts a sea-levelrise to shoreline retreat ratio of 1: 200. However, the retreatactually occurs across the surface of the lower coastal plain,the slope of which in southeastern North Carolina, for example,averages about 1: 2000. The Rule is also flawed in itsassumptions concerning areal restriction of sediment movementon shorefaces, and in its lack of consideration for geologiccontrol of shoreface slope. In actual use, theassumption of the depth of no wave motion (closure depth)has decreased to between 4 and 8 m on East Coast shorefaces,in contrast to Bruun's original 18 to 20 m depthassumption. There is no basis in reality for using the Bruun21