The lifetime of shoreface nourishments in fields with nearshore sandbar migration

Abstract

Migration of nearshore sandbars results from nonlinear interacting hydro- and morphodynamic processes in the surf zone of wave dominated sandy shorelines. To gain new insights in the largely varying temporal effects of shoreface nourishments within these areas, the principle component analysis is applied to sixteen data sets with i) natural sandbar migration on different timescales and ii) interfering shoreface nourishments. The statistical methodology is able to separate the non-stationary effects of shoreface nourishments from the natural stationary migration of the sandbars. Depending on other long-term morphodynamic changes and nourishment interactions in the data, the duration of these interferences (the nourishment lifetimes) can be quantified. Relating these nourishment lifetimes (Ln) with respect to the bar cycle return periods (Tr) of these areas (e.g. the relative nourishment lifetime) of twenty-one shoreface nourishments with several design parameters, and parameters of the sandbar system in which they were placed, remained inconclusive. A negative exponential fit with the bar cycle return period itself was the most significant (r2 = 0.41). Assuming a linear system of the parameters increases the predictive capability (r2 = 0.67). The most influential parameters in this relation are the nourishment concentration (+), the nourishment depth (+), the concentration of the migrating sandbars (−) and the bar cycle return period (−), thereby indicating the prominent roles of both nourishment design and natural sandbar system in the inter-site variability of shoreface nourishment lifetimes.