Saltmarsh restoration

Abstract

A dredging apparatus comprises a dredge box supported on skids. The dredge box has an open forward end with solid side walls, and a rearward end. A winch is adapted to pull the dredge box across an es

Description

Description This disclosure relates to a method and apparatus for saltmarsh restoration. Saltmarsh habitats are incredibly important ecosystems that play vital roles in coastal environments. Saltmarshes serve as breeding and nursery grounds for a variety of marine species, including fish, crustaceans, and shellfish. Many commercially important fish species, such as sea bass and shrimp, rely on these habitats during their early life stages. They are crucial for migratory birds, providing feeding grounds during migration and nesting sites for numerous bird species. Saltmarshes are especially important for wading birds and waterfowl. Saltmarshes act as natural buffers, absorbing wave energy and reducing the impact of storm surges and coastal erosion. This helps protect coastal communities and infrastructure from flooding and storm damage. They trap and stabilize sediments, which helps in maintaining and building up the coastline, preventing land loss and contributing to the overall stability of the coastal ecosystem. Saltmarshes are highly efficient at capturing and storing carbon dioxide (CO2) from the atmosphere, a process known as carbon sequestration. They store "blue carbon" in their vegetation and sediments, helping to mitigate the effects of climate change by reducing the amount of CO2 in the atmosphere. Saltmarshes act as natural filters, trapping pollutants, nutrients (such as nitrogen and phosphorus), and sediments from runoff before they reach open waters. This process improves water quality, reduces algal blooms, and helps maintain healthy marine environments. They also help in breaking down organic matter and detoxifying harmful substances, contributing to the overall health of coastal waters. Saltmarshes offer opportunities for recreation, such as bird watching, fishing, and kayaking, which can be significant sources of revenue for local communities. These habitats are valuable for scientific research and education, providing insights into coastal ecology, climate change, and natural resource management. Saltmarshes are dynamic environments that can adapt to rising sea levels by accumulating sediment and migrating inland. This makes them important for longterm coastal resilience to climate change. In summary, saltmarshes are vital for maintaining biodiversity, protecting coastlines, improving water quality, and supporting both local economies and global climate regulation efforts. Preserving and restoring these habitats would be important for sustaining the health of our coastal ecosystems. The decline of saltmarsh habitats in the United Kingdom is a significant environmental concern, with multiple factors contributing to the loss and degradation of these vital ecosystems. The expansion of coastal cities, towns, and infrastructure, such as roads and sea defences, has led to the direct loss of saltmarsh areas. Coastal development often encroaches on these habitats, leading to habitat fragmentation and destruction. Historically, many saltmarshes in the United Kingdom were reclaimed for agriculture, industry, and urban development. This practice has significantly reduced the extent of saltmarsh habitats. As sea levels rise due to climate change, saltmarshes are caught between advancing seas and fixed coastal defences, such as sea walls. This "coastal squeeze" prevents the natural inland migration of saltmarshes, leading to their erosion and loss. Dams, regular dredging (of ports, docks, harbours and marinas), and other human activities have altered the natural flow of sediments to coastal areas, reducing the ability of saltmarshes to accumulate sediment and keep pace with rising sea levels. Dumping of the dredging sediments offshore denies the local estuarial cell, the “sediment engine” (natural concentrations of moving sediments) switching off the natural processes of accretion and accumulation that sustain saltmarshes. Excessive nutrients from agricultural runoff, particularly nitrogen and phosphorus, can lead to eutrophication, causing harmful algal blooms which can “blind” the saltmarsh (denying sunlight) and alter the ecological balance of saltmarshes. Contaminants from industrial activities can degrade the quality of saltmarsh habitats, harming the species that rely on them. The introduction of invasive plant and animal species can outcompete native saltmarsh flora and fauna, leading to changes in habitat structure and function. More frequent and intense storms, driven by climate change, can lead to accelerated erosion and damage to saltmarshes. Small changes in temperature and salinity can alter the composition of saltmarsh plant communities, potentially leading to a decline in native species. The decline of saltmarshes results in the loss of critical habitats for numerous species, including birds, fish, and invertebrates, leading to declines in biodiversity. As natural buffers against storm surges and coastal erosion are lost, coastal communities become more vulnerable to flooding and other climate-related impacts. The degradation of saltmarshes reduces their capacity to sequester carbon, potentially leading to increased carbon dioxide levels in the atmosphere and exacerbating climate change. The loss of saltmarshes means a reduction in their natural filtering capacity, leading to poorer water quality in coastal areas. Managed realignment involves breaching sea defences or allowing tidal waters to flood previously reclaimed land, creating new saltmarsh habitats. Projects like the Medmerry Managed Realignment Scheme in Sussex have successfully created new saltmarsh areas by flooding farmland inland of the ageing coastal defences. Restoration projects often involve planting native saltmarsh vegetation and adding sediments to raise land levels, helping to restore degraded saltmarshes. It is important to protect existing saltmarshes from further degradation and supports their conservation. The United Kingdom government has implemented various policies, including the National Planning Policy Framework (NPPF), to protect coastal habitats, including saltmarshes, from development pressures. Increasing public awareness about the importance of saltmarshes and involving local communities in conservation efforts are crucial for the long-term protection of these habitats. The decline of saltmarsh habitats in the United Kingdom is a complex issue driven by both natural and human-induced factors. However, through a combination of restoration efforts, managed realignment, and protective legislation, there are opportunities to halt and even reverse the decline of these crucial ecosystems. Preservation of saltmarshes is essential not only for biodiversity but also for coastal resilience and climate change mitigation. The present invention has arisen from Land and Water Services Ltd’s investment in technologies aimed to help restore this vital environment. Depleted saltmarsh will naturally recolonize if suitable sediments are placed at the correct height above Mean High Water Springs (MHWS). We have developed technology to assist the transport and placing of previously dredged materials to the target height. Target heights vary according to location, coastal morphology and tidal, gradient and wind exposure factors. As we explain below, our technology allows dredged materials to be deposited close to the restoration location (inaugural deposition of sediments is by others, and at such time as suits the dredging and environmental permits and consents), and our apparatus is proposed for collecting the dumped sediments and skid them across the intertidal mudflats and failed saltmarsh and deposit them in the location for suitable reuse and reclamation. We explain below how a skid is formed of a scoop (dredge box) that has enclosed sides and a tailgate, the tailgate is closed when skidding to collect and carry the sediments to the restoration area (from the dumping area) and open when returning to the dumping area to collect the next scoop of material. In accordance with a first aspect of the present disclosure there is provided a dredging apparatus comprising a dredge box supported on skids; the dredge box having an open forward end with solid side walls, and a rearward end; and a winch adapted to pull the dredge box across an estuarine environment for saltmarsh restoration; the dredge box having a tailgate and being adapted to excavate silt and to re-distribute it on to existing saltmarsh areas to restore them or on to intended saltmarsh areas; the dredge box having an open base; and the tailgate having a planing blade adapted to open on the tailgate on back runs and to be closed on forward runs at a selected depth that enables it to plane material under it on to areas of saltmarsh, or intended saltmarsh. Preferred arrangements have one or more of the following features: The tailgate is provided with an operating mechanism comprising a lever arm extending vertically above the remainder of the dredge box. Those parts of the side walls which would be downstream of the tailgate during planing use of the planing blade are formed as an open framework. It will be seen from the present disclosure that dredging apparatus may comprise a dredge box, and a winch adapted to pull the dredge box across an estuarine environment for saltmarsh restoration. The dredge box has a tailgate adapted to excavate near-shore dumped silt and to re-distribute it on to existing saltmarsh areas without damaging growing saltmarsh or on to intended saltmarsh areas; the dredge box having an open base, the tailgate having a planing blade, designed to open on back runs and to be closed on forward runs at a selected depth that enables it to plane material under it on to areas of saltmarsh, or intended saltmarsh areas, without damaging the said areas. Suitably, the dredge box is pulled from deeper water up onto saltmarsh restoration sites by a twin wire winch (preferably mounted to a hydraulic excavator). The dredge or drag box tailgate is arranged to open on back runs but is pulled shut on forward runs to trap silts and soils for passage across the saltmarsh without damaging the saltmarsh. The depth of the tailgate is suitably fixed, and the tailgate pivots from the top. Preferably, the planing blade on the tailgate can be adjusted. The preferred twin wire winch allows the loaded drag box to be pulled towards the winch and equally away from the winch when the load is deposited. The winch wire suitably travels through a pulley which is anchored beyond the collection / excavation point (typically to a spud pontoon) so that the drag box can be winched empty (with the tail gate open / up) back out over the collection / excavation point ready for a second cycle and so on. In a second and alternative aspect of this disclosure, a dredging method employs a dredge box with an open base pulled by a winch across an estuarine environment for saltmarsh restoration; the dredge box using a tailgate to excavate near shore dumped silt and to re-distribute it on to saltmarsh areas without damaging growing saltmarsh; the dredge box tailgate having a planing blade that is opened on back runs and is closed on forward runs at a depth selected to enable it to plane material under it on to areas of growing saltmarsh without damaging the saltmarsh. Reference should be made to the accompanying drawings, by way of example only, for further details of a preferred embodiment of dredge box for saltmarsh restoration, in which: Fig. 1 is a somewhat schematic side elevational view, with parts omitted for clarity, of an embodiment of dredging apparatus adapted to be drawn across a portion of estuarine territory growing or intending to support and encourage growth of saltmarsh to improve it; Fig. 2 is an enlarged side elevational view of a tailgate of the dredging apparatus of Fig. 1 with a planing blade deployed; Fig. 3 is a view similar to Fig. 2 of the apparatus shown in Fig 2 without the planing blade deployed; Fig. 4 shows a perspective view of the dredge box, tailgate and tailgate; Fig. 5 shows a side elevational view of a preferred embodiment of dredging apparatus; Fig. 6 shows a front elevational view of a spreader beam illustrated in Fig. 5; and Fig. 7 shows an elevational view of the dredge box shown in Fig. 5 as seen along the plane VII-VII in Fig. 5. An embodiment of dredging apparatus, is somewhat schematically shown in Figs. 1 to 4 of the accompanying drawings. It comprises a dredge box 1 adapted to be drawn by a winch (not shown) and connecting rope or chains, schematically indicated at 2 cooperating with fairleads 3, to pull the dredge box 1 supported on skids 4 across an estuarine environment for saltmarsh improvement. The skids 4 are preferably replaceable by skids of different width. The dredge box 1 mounts a tailgate 5 pivotally supported at 6 on the dredge box 1 and adapted to excavate near-shore dumped silt and to re-distribute it on to existing saltmarsh areas. The illustrated apparatus achieves this, without significant saltmarsh damage, encourages growth of saltmarsh in existing areas, and encourages growth of saltmarsh in new or intended saltmarsh areas. The tailgate 5 achieves this by having a planing or plough blade 7 pivotally supported at 8 to the tailgate 5 which is adapted to open on back runs (as show in Fig. 3) and to be closed in Fig. 2 on forward runs, at a selected depth that enables it to plane material under it on to areas of saltmarsh, or on to intended saltmarsh areas, without damaging the said areas. In use, the tailgate 5 is pulled shut, and its planing blade 7 closed on forward runs without damaging the saltmarsh. The depth at which the planing blade 7 opens is chosen so that it depends, when closed, below the dredge box 1, as shown in Fig.l, and so that the dredge box 1 and its planing plough blade 7 will plane over the saltmarsh to avoid the dredge box 1 damaging it. Haul-in and return ropes or chains 9, schematically indicated in Fig. 1, but also shown in Fig. 5, are attached to the tailgate 5. The tailgate 5 is pivotally supported at 10 to a tailgate carrying frame 11 supported by the dredge box 1 so that the accessible volume of the dredge box capacity for receiving dredged material to the left in Fig.l can be adjusted. Front fairleads 12 are suitably adjusted to allow the available capacity of the dredge box 1 to the left of the tailgate 5 in Fig. 1 to be changed. As can be seen from Fig. 4, the rear end of the dredge box 1 is formed as a simple open framework 13, with the tailgate 5 supported on the framework 13 mounted on skids 4. The front end of the dredge box 1 has solid side walls 14. Figs. 5 to 7 show a presently preferred embodiment of the dredging apparatus. Like reference numerals are used for features similar to those of the embodiment of Figs. 1 to 4. Preceding the dredge box 1 in the direction of forward travel over a saltmarsh is a spreader beam 15. A twin wire hydraulic winch is associated with twin haul-in chains 9 coupling pivotal supports 8 associated with the tailgate 5 with respective legs 16 of the spreader 15 that make contact with the saltmarsh surface. Accordingly, the dredge box 1 is provided with a twin wire winch for the twin haul-in chains 9 adapted to pull the dredge box 1 from deeper water up onto a saltmarsh restoration site. The spreader beam 15 accordingly has the effect of reducing drag back of planed saltmarsh material on return pulls of the dredge box 1 over the saltmarsh. The pitch of the dredge box runs can accordingly be adjustable by adjusting the length of front haul of the haul-in chains or ropes, here coupled between the tailgate 5 and spreader beam 15. The tailgate 5 is provided with a vertically extending operating arm 17, the distal end 18 of which is coupled to a driven pulleys-and-belt operating system 19. This aids faster and higher opening of the tailgate 5, which increases productivity with less effort and reduces back pulling forces.

Claims

1. A dredging apparatus comprising a dredge box supported on skids; the dredge box having an open forward end with solid side walls, and a rearward end; and a winch adapted to pull the dredge box across an estuarine environment for saltmarsh restoration; the dredge box having a tailgate and being adapted to excavate silt and to re-distribute it on to existing saltmarsh areas to restore them or on to intended saltmarsh areas; the dredge box having an open base; and the tailgate having a planing blade adapted to open on the tailgate on back runs and to be closed on forward runs at a selected depth that enables it to plane material under it on to areas of saltmarsh, or intended saltmarsh.

2. A dredging apparatus according to Claim 1, wherein the dredge box is provided with a twin wire winch adapted to pull the dredge box from deeper water up onto a saltmarsh restoration site.

3. A dredging apparatus according to Claim 1 or Claim 2, wherein the tailgate is provided with an operating mechanism comprising a lever arm extending vertically above the remainder of the dredge box.

4. A dredging apparatus according to any preceding Claim, wherein those parts of the side walls which would be downstream of the tailgate during planing use of the planing blade are formed as an open framework.

5. A dredging method employing dredging apparatus incorporating a dredge box with skids and an open base pulled by a winch across an estuarine environment for saltmarsh restoration; the dredge box being provided with a tailgate and serving to excavate near shore dumped silt and to re-distribute it on to saltmarsh areas; the dredge box tailgate having a planing blade that is opened on the otherwise closed tailgate during back runs and is closed on forward runs at a depth selected to enable it to plane material under the tailgate on to areas of growing saltmarsh.

6. A dredging method according to Claim 5, wherein pulling the dredge box across a saltmarsh by a winch and using a spreader beam reduces drag during return pulls, and use of a lever arm and pulley system controls tailgate movement.5 7. A dredging method according to Claim 5 or Claim 6, wherein a twin wire winch is used to pull the dredge box from deeper water on to restoration sites.A

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