Abstract
Recently, mega feeder nourishments have been proposed as a new strategy to nourish sediment-starving beaches. This strategy involves the placement of a large, concentrated sediment volume at a single location along the coast. Wind, waves and currents act as the natural agents to spread the sediment alongshore over the course of years to decades. This article presents the morphological development of the first full-scale implementation of this strategy, examining the 20 × 106 m3“Sand Engine” feeder nourishment and its impact on adjacent coastal sections. The analysis is based on 37 high-resolution topographical surveys, executed in a 17 km coastal cell. These unique data describe the alongshore spreading in the first five years and the response at different elevations of the coastal profile. The analysis shows rapid transformation of the nourishment’s planform shape, changing rapidly into a smooth (Gaussian-like) shape which is gradually extending alongshore over time. Within five years, sediment has been distributed to a 5.8 km stretch of coast from the initial 2.2 km peninsula footprint. Changes in cross-shore and alongshore extent varied strongly over depth, with the strongest morphological response at the mean sea level (MSL) isobath and limited morphodynamic activity at deeper water, below −8 m MSL. This depth-dependent response has resulted in decreasing subtidal slopes in eroding areas, accretive areas contrastingly show a slope increment. These results yield important insights in nourished sediment mobility at different depths near the coast and distribution over a larger coastal cell. However, this single-design assessment cannot address the wide range of mega nourishment design parameters essential for morphological development of its coastal cell. This work suggests limiting cross-shore extent, since it is uncertain whether nourished sediment at deeper water will become active in the coastal system. A continuation of the current monitoring and future research might shed more light on this.
Highlights
Introduction nal affiliationsCoastal nourishments are common practice at many locations around the globe to increase beach width for coastal safety or to enhance recreation, e.g., [1]
-called mega feeder nourishments have been proposed as an alternative to more common types of nourishments such as beach and shoreface nourishments [2]
The results of this study on the morphodynamics of the Sand Engine mega feeder nourishment are ordered from general observations to detailed analyses
Summary
Introduction nal affiliationsCoastal nourishments are common practice at many locations around the globe to increase beach width for coastal safety or to enhance recreation, e.g., [1]. Nourishment volumes have increased on many sites, causing an interest and need for new nourishment strategies. In this context, so-called mega feeder nourishments have been proposed as an alternative to more common types of nourishments such as beach and shoreface nourishments [2]. -called mega feeder nourishments have been proposed as an alternative to more common types of nourishments such as beach and shoreface nourishments [2] These beach and shoreface nourishments are expected to mostly enhance beach width inside their initial footprint with limited alongshore spreading. Any sediments transported outside the nourished area are mostly considered a loss [3,4]
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