Long-term (>years) bathymetric data sets collected in six multiple near-shore sandbar systems were analyzed with complex empirical orthogonal function analysis to quantify intersite differences and similarities in cyclic offshore progressive bar behavior. The observations came from a 37-year annually sampled data set of four regions along the Dutch coast (spanning 70 km of coastline), an 18-year fornightly to monthly sampled data set at Duck, North Carolina (alongshore extent ∼ 1 km), and a 7-year daily sampled data set of a single cross-shore profile at the Hasaki coast of Japan. The first complex mode, typically representing 50-70% of the total depth variance, described the long-term offshore progressive behavior and allowed for an objective separation of the barred part of the profile from the shoreward- and seaward-located nonbarred parts by considering a threshold bar amplitude below which the spatial results from the first mode were not considered reliable. The sandbars at the six examined sites share common lengths and nondimensional amplitude characteristics, which can be described by a negatively skewed Gaussian function. The absolute amplitude dimensions and the cycle return intervals differ, however, considerably between the sites. The key geometric parameters that steer this intersite variation are the time-averaged mean depths at the shoreward and seaward side of the bar zone (d̄shore and d̄sea, respectively) as well as their difference d̄bz. The degree to which intersite differences in d̄shore, d̄sea, and d̄bz are related linearly to intersite differences in bulk statistics of external forcings (wave, tide, sediment, and bed profile characteristics ) is inconclusive.
- Eigenfunction analysis
- Nearshore morphology