Predicting Morphodynamics for Beach Intertidal Systems in the North Sea: A Space-Time Stochastic Approach

Abstract

The ability to accurately predict beach morphodynamics is of primary interest for coastal scientists and managers. With this goal in mind, a stochastic model of a sandy macrotidal barred beach is developed that is based on cross-shore elevation profiles. Intertidal elevation was monitored from monthly to annually for 19 years through Real Time Kinematics-GPS (RTK-GPS) and LiDAR surveys, and monthly during two years with an RTK-GPS. In addition, during two campaigns of about two weeks, intensive surveys on a daily basis were performed with an RTK-GPS on a different set of profiles. Based on the measurements, space and time variograms are constructed in order to assess the spatial and temporal dependencies of these elevations. A separable space-time covariance model is then built from them in order to generate a large number of plausible future profiles at arbitrary time instants t+τ, starting from observed profiles at time instants t. For each simulation, the total displaced sand volume is computed and a distribution is obtained. The mean of this distribution is in good agreement with the total displaced sand volume measured on the profiles, provided that they are lower than 45 m3/m. The time variogram also shows that 90% of maximum variability is reached for a time interval τ of three years. These results demonstrate how the temporal evolution of an integrated property, like the total displaced sand volume, can be estimated over time. This suggests that a similar stochastic approach could be useful for estimating other properties as long as one is able to capture the stochastic space-time variability of the underlying processes.

Characterization of Intertidal Bar Morphodynamics Using a Bi-Annual LiDAR Dataset

“…Nevertheless, the complete destruction of intertidal bars has never been observed anywhere. At Groenendijk, the bars were also observed on aerial photographs and field measurements back to the 1950s [16,17] and annually from 1990 to the present [13,18]. This is evidence that bars are permanent features of the intertidal beach along Groenendijk and not only on a time scale of years but decades.…”

“…Recently, ref. [18] have found that the dissimilitude between elevations measured at the same position on a profile at Groenendijk was about 25% and 90% for measurements separated by a time lag of one month and three years, respectively. Thus, the profile elevations become uncorrelated for a time lag exceeding a few years.…”

Application of Artificial Neural Networks to Predict Beach Nourishment Volume Requirements

“…It could be an important factor in deciding which beach sites the coastal managers should develop. There are different techniques and approaches used for predicting beach changes and beach nourishment requirements; from simpler techniques such as linear least squares to more sophisticated models such as stochastic approaches, and finally machine learning techniques [4][5][6][7]. Many models include on longshore and cross shore transport for beach change prediction, as well as equilibrium beach profile expressions [8][9][10][11].…”

Beach-Dune System Morphodynamics

“…The third published paper is entitled "Predicting Morphodynamics for Beach Intertidal Systems in the North Sea: A Space-Time Stochastic Approach" by Bogaert et al [3]. The authors developed a stochastic model of a macrotidal sandy-barred beach based on crossshore elevation profiles.…”