Abstract
Tidal flats are valuable habitats for different plants and animals. However, the total area of tidal flats is decreasing worldwide caused by various problems like sea level rise, subsidence by gas extraction and erosion initiated by manmade constructions. Nourishing tidal flats might be a promising solution, but the impact both on the physical processes and the ecological system are unknown.
This article describes the lessons learnt from a pilot nourishment executed at the Galgeplaat tidal flat in 2008 (Eastern Scheldt, The Netherlands) with a total volume of 130,000 m3 over a total area of 150,000 m2. The hypothesis is that as a result of the natural dynamics, i.e., the combined effect of currents and waves, the nourishment will gradually spread out and heighten the flat. To become a valuable habitat, the nourished area has to recolonise after the nourishment has buried all benthic fauna. To optimise nourishment strategies in the future with respect to shape, size and frequency, both the recolonisation of benthic fauna as well as the physical processes are monitored, modelled and analysed. After two years, only minor morphological changes of the nourishment are observed. Some redistribution of sediment occurred, but the overall change in sediment volume is approximately only 2%.
The nourishment killed all benthic macrofauna when buried. The recovery started directly after the nourishment was put in place. On the nourishment the recolonisation of the benthic macrofauna was very patchy, with some sites having a relatively rich fauna, whereas at other sites hardly any macrofauna was observed. The latter are mainly situated on the higher parts of the nourishment, where sediments dry out more during low tide compared to lower sites on the nourishment. The shape and nourishing method appear to be important factors influencing benthic recolonisation. Model results confirm the (small) morphodynamic changes and reveal the influence of currents and locally generated waves on the degradation of the flats. Combining the monitoring and modelling results shows that the biogeomorphological interactions (morphological changes driving recolonisation and vice versa) play a role and should be taken into account to come to successful nourishment strategies for tidal flats.
This article was first published in the Proceedings of the CEDA Dredging Days, Rotterdam, November 2011 and is reproduced with slight revisions with permission. Bas Borsje was the lead author and received the IADC Young Authors award for his work. Other contributing authors are Katherine Cronin and Harriette Holzhauer of Deltares, Isel de Mesel and Tom Ysebaert of IMARES – Institute for Marine Resources & Ecosystem Studies and Anneke Hibma of Van Oord, all of whom are also members of the Ecoshape | Building with Nature team.
The work was carried out as part of the innovation programme “Building with Nature”, which is funded from several sources including the Subsidieregeling Innovatieketen Water (SIW, Staatscourant nrs 953 and 17009) sponsored by the Dutch Ministry of Transport, Public Works and Water Management and partner contributions of the participants to the Foundation EcoShape. The programme receives co-funding from the European Fund for Regional Development EFRO and the Municipality of Dordrecht. The monitoring programme of the Galgeplaat is established by the Dutch Ministry of Transport, Public Works and Water Management. The field measurements are carried out by the Dutch Ministry of Transport, Public Works and Water Management. Previous model work was carried out under the ANT (Autonome Neerwaardse Trend) Oosterschelde study commissioned by the Dutch Ministry of Transport, Public Works and Water Management.
This article describes the lessons learnt from a pilot nourishment executed at the Galgeplaat tidal flat in 2008 (Eastern Scheldt, The Netherlands) with a total volume of 130,000 m3 over a total area of 150,000 m2. The hypothesis is that as a result of the natural dynamics, i.e., the combined effect of currents and waves, the nourishment will gradually spread out and heighten the flat. To become a valuable habitat, the nourished area has to recolonise after the nourishment has buried all benthic fauna. To optimise nourishment strategies in the future with respect to shape, size and frequency, both the recolonisation of benthic fauna as well as the physical processes are monitored, modelled and analysed. After two years, only minor morphological changes of the nourishment are observed. Some redistribution of sediment occurred, but the overall change in sediment volume is approximately only 2%.
The nourishment killed all benthic macrofauna when buried. The recovery started directly after the nourishment was put in place. On the nourishment the recolonisation of the benthic macrofauna was very patchy, with some sites having a relatively rich fauna, whereas at other sites hardly any macrofauna was observed. The latter are mainly situated on the higher parts of the nourishment, where sediments dry out more during low tide compared to lower sites on the nourishment. The shape and nourishing method appear to be important factors influencing benthic recolonisation. Model results confirm the (small) morphodynamic changes and reveal the influence of currents and locally generated waves on the degradation of the flats. Combining the monitoring and modelling results shows that the biogeomorphological interactions (morphological changes driving recolonisation and vice versa) play a role and should be taken into account to come to successful nourishment strategies for tidal flats.
This article was first published in the Proceedings of the CEDA Dredging Days, Rotterdam, November 2011 and is reproduced with slight revisions with permission. Bas Borsje was the lead author and received the IADC Young Authors award for his work. Other contributing authors are Katherine Cronin and Harriette Holzhauer of Deltares, Isel de Mesel and Tom Ysebaert of IMARES – Institute for Marine Resources & Ecosystem Studies and Anneke Hibma of Van Oord, all of whom are also members of the Ecoshape | Building with Nature team.
The work was carried out as part of the innovation programme “Building with Nature”, which is funded from several sources including the Subsidieregeling Innovatieketen Water (SIW, Staatscourant nrs 953 and 17009) sponsored by the Dutch Ministry of Transport, Public Works and Water Management and partner contributions of the participants to the Foundation EcoShape. The programme receives co-funding from the European Fund for Regional Development EFRO and the Municipality of Dordrecht. The monitoring programme of the Galgeplaat is established by the Dutch Ministry of Transport, Public Works and Water Management. The field measurements are carried out by the Dutch Ministry of Transport, Public Works and Water Management. Previous model work was carried out under the ANT (Autonome Neerwaardse Trend) Oosterschelde study commissioned by the Dutch Ministry of Transport, Public Works and Water Management.
| Original language | English |
|---|---|
| Pages (from-to) | 3-12 |
| Journal | Terra et aqua |
| Volume | 126 |
| Publication status | Published - 2012 |