Field evidence on major intertidal flat growth initiated by sediment disposals in an estuarine channel
Abstract
Navigation channels in estuaries require deepening and regular maintenance due to the increasing size of vessels. Dredged sediments are generally disposed with the perspective to minimize recirculation to the main channel. More recently, regulations require the creation/restoration of valuable habitats, like intertidal flats and salt marshes. In this contribution, we determine how disposing strategies in channels can influence the eco-morphological development of intertidal habitats.
We consider a case in the Western Scheldt (The Netherlands), a two-channel estuary. Sediment was dredged from the ebb channel that is used for navigation. Already for 20 years, ±1.6 million m3 is disposed annually in the adjacent flood channel, bordered by a fringing tidal flat and salt marsh. We applied a combined approach of data analysis and numerical modelling. We analyzed with yearly transects and single beam data the morphological evolution of the intertidal flat over a time period of 25 years, starting 5 years before the sediment disposals were initiated. To unravel the mechanisms, we combined these observations with hydrodynamic model simulations (Delft3D). The data indicated a transition from erosion towards large accretion rates; in the order of decimeter(s) per year in a time span of 20 successive years. The timing of this transition strongly coincided with the start of the disposals. We identified three general mechanisms driving the accretion of tidal flats by sediment disposals: (1) Locally increased availability of sediment in the channel; (2) Local change in hydrodynamics around disposals; (3) System scale change in hydrodynamics by deepening at the extraction location. The modelling revealed that the local mechanisms (1 and 2) clearly dominated the evolution of the flat. The accretion of the tidal flat is still ongoing with an average rate of 0.1 m/year. At the upper part of the flat, the elevation is now sufficiently high for vegetation to successfully colonize the bare flat. Therefore, our results prove that sediment disposals in channels may be a powerful estuarine management tool to steer eroding tidal flats towards accretion, enhancing salt marsh growth potential and influencing the ecological value of those intertidal flats.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMEP11A..08D
- Keywords:
-
- 0442 Estuarine and nearshore processes;
- BIOGEOSCIENCESDE: 1625 Geomorphology and weathering;
- GLOBAL CHANGEDE: 1641 Sea level change;
- GLOBAL CHANGEDE: 3020 Littoral processes;
- MARINE GEOLOGY AND GEOPHYSICS