Monitoring underwater nourishments using multibeam bathymetric and backscatter time series

Monitoring underwater nourishments using multibeam bathymetric and backscatter time series

Gaida, T.C. (TU Delft Aircraft Noise and Climate Effects)
van Dijk, T.A.G.P. (TU Delft Aircraft Noise and Climate Effects; Deltares; University of Illinois at Urbana-Champaign)
Snellen, M. (TU Delft Aircraft Noise and Climate Effects)
Vermaas, Tommer (Deltares)
Mesdag, Chris (Deltares)
Simons, D.G. (TU Delft Aircraft Noise and Climate Effects)

2020

Natural and man-induced coastal erosion endanger life and environment in coastal areas worldwide. For sedimentary barrier coasts, beach and underwater nourishments are an efficient coastal protection strategy. To optimize nourishments and to understand their impact on the marine environment, monitoring strategies are required. In this study, we investigate the potential of multibeam echosounder (MBES) data, providing both bathymetry and backscatter (BS), for monitoring the evolution of the nourished sediment and morphodynamics over time. A time series of seven MBES measurements, as well as two sets of box cores, vibrocores and seismic data were acquired of a channel-side nourishment near the Wadden Sea island Ameland (The Netherlands), between April 2017 and May 2019. In general, a high confidence of the acoustic reliability of the BS time series measurements is demonstrated. The unsupervised Bayesian classification method, supported by ground-truthing, is employed to produce a time series of sediment maps, revealing sediments ranging from sandy mud to sand with varying amounts of shell fragments. Based on the sediment maps, the nourished sediment could be distinguished from the natural sediment. Within one year, the shell-rich pre-nourishment seabed is recreated by washing out finer sediments, which are deposited towards the main tidal channel. Using the seismic data and vibrocores, the shell-rich pre-nourishment seabed could be identified in the subsurface after being buried by the nourishments, supporting the general findings. Furthermore, a rapid development of steep bedforms with increasing sediment sorting is observed in parts of the nourished areas. This study shows that high-resolution sediment maps obtained from a time series of MBES BS together with bathymetry reveal morphodynamic and sedimentary processes of nourishment evolution and can advance underwater nourishment strategies.

Acoustic backscatter
Bedform
Monitoring
Nourishment
Sediment classification
Wadden Sea

http://resolver.tudelft.nl/uuid:760e04ad-5f8f-466e-b601-aae7b1c4be6e

https://doi.org/10.1016/j.coastaleng.2020.103666

0378-3839

Coastal Engineering, 158

Institutional Repository

journal article

© 2020 T.C. Gaida, T.A.G.P. van Dijk, M. Snellen, Tommer Vermaas, Chris Mesdag, D.G. Simons