Assessment and beneficial use of the material from seabed dredging operations

Being a peninsula, surrounded three sides by sea, Turkey obviously has considerable amount of shorelines. Turkey geographically provides a connection between the two continents Europe and Asia significantly effecting both its economical and social state and development. In 2014, Turkey conducted a maritime routed foreign trade by aproxiamtely 58% for import and 55% for exports, making a total of 283.25 million tonnes of freight. Global increase in marine transportation brings heavy ship traffic as well as larger ship sizes. Dredging operations are essential, since the country has a very significant portion of its transportation via the sea, which emphasizes the continuous maintenance of the navigation waterways by dredging operations. As high as 14 million m3 (according to DLH of Turkey) of dredged material is extracted between 2000&2009; which is usually dumped at the sea, other than the fairly small amount that is disposed upland. As the continuous dredging activities are crucial for the maintenance of the main ports and harbours of Turkey, high amounts of dredged material are to be extracted continuously. Thus, sustainable management of this material is very important. Disposal at sea has been the primary practiced solution to this day. The present study aims to guide the decision-makers concerning the dredging operations and the disposal of the material, in alternative ways to use it beneficially. This involves naming the processes in characterization of the material for certain usability options; as well as providing some of the best practices around the globe as example. Primarily, this study suggests that, DM is not a waste product, but a valuable sediment material resource, provided it is applied properly in a beneficial way. This type of approach can make innovative practices for DM management and result in potentially less environmental impact due to avoidance of sea dumping; as well as reduced costs because of the potential possibility to re-use a material extracted from the site itself as resource. Recently, there has been an increasing research for the beneficial usage of DM. Also the practice of management gains larger application grounds internationally. The range of beneficial usage options are also widening. This will undoubtedly result in several positive outcomes, such as the reduction of disposed material, negative impacts on environment, savings on project costs. The traditional way of managing the DM, which is basically dumping it at the sea or inland landfills, fails to satisfy the increasing trend of environmental awareness, which brings along a more and more restrictive legislation. For compliance, alternative management applications, namely beneficial usage options of the DM is presented; such as usage in civil engineering, manufacture or agriculture. However, re-using of this material is possible only if it satisfies the echonomical, technical and environmental criteria. At present, the solutions proposed are not adequate for every type of sediment, and sometimes relatively expensive, better research and management approaches are going to lead to using significant amounts of DM beneficially in time. A wide range of beneficial uses of DM have been practiced; these may generally be categorised as: Engineering uses: Involves beneficially using DM typically as an alternative to land based resources (for example quarry aggregate) and is common in many engineering projects, e.g. land reclamation, beach nourishment and coastal protection works. Suitable DM can be used as an alternative barrier material to traditional natural clays which act as a capping layer for municipal waste landfills; it may be applied as a daily, intermediate or as a final permanent capping layer. The purpose of this semi-permeable layer is to control nuisances (e.g. flies, birds, rodents), minimise escape of odours and landfill gas, and reduce the infiltration of rainfall and/or lateral egress of leachate. Placing clean dredged material in shallow water in the form of shore-parallel subaqueous berms benefits the nearshore zone by providing material to the littoral system and reducing wave action landward of the berm. DM has been applied in coastal protection works internationally in a variety of different ways and has often involved the direct use on-site of DM generated locally as a construction material. It has commonly been used in the core of rubble mound breakwaters (typically sand) or potentially on the outer layers of breakwaters where the appropriate rock grading is available. In such cases the DM produced (rock or otherwise) must meet the specific design requirements of the particular coastal structure. 2. Environmental Enhancement: Involves using DM as a resource with the potential for environmental enhancement when managed in a sustainable manner, e.g. habitat creation or sediment cell maintenance. DM has been widely used to establish new wetland areas, to nourish and enhance existing habitats or to provide stability to eroding wetlands. A wetland is land that is covered intermittently, either seasonally or due to tidal or water table changes. Tidal variation, for example, causes the soil to reach saturation regularly, forming a combination of terrestrial and aquatic characteristics with unique aquatic organisms. Sediment cell maintenance, also known as sustainable sediment relocation involves the placement of DM in tidal estuary systems potentially reducing the erosion of tidal mudflats, banks and saltmarshes and also potentially improving both shallow sub-tidal and intertidal habitats. It typically applies to maintenance dredging projects where sediment contaminant levels are typically very low or entirely absent. This approach may be considered to combine traditional disposal with modern soft engineering practice to enhance the local ecosystem and reduce potential negative impacts from dredging activities. Both uncontaminated and contaminated material containing metal and organic contaminants (within regulatory limits) can be stabilised using cementitious materials (e.g. alkaline activated coal ash) to form low permeability cementitious fill for abandoned mine and quarry reclamation, with potentially significant environmental benefits 3. Agricultural and Product uses: Suitable DM may be used to form useful products or in the agricultural sector once the appropriate physical, chemical and biological properties comply with the appropriate industry standards, e.g. manufactured topsoil, landfill cover or production of ceramics/bricks/concrete. The basic raw materials for concrete production are cement, aggregate/sand and water. Coarse sandy DM has been used to supplement the aggregate component of concrete. Fine grained DM has recently been proposed as a fine granular corrector in partial substitution of raw sand. Coarse and fine DM can be used in different aspects of road construction, including both as a structural material and as a general fill for the construction of road embankments and roadworks. Landfill liners are designed and constructed to create a barrier between the landfill waste and the ambient natural environment and to redirect the leachate to a collection and treatment facility. Traditional landfill liner materials include compacted clays, bentonite enriched soils and flexible synthetic membranes. Several research studies have investigated the use of DM combined with a stabilising material as an alternative or supplementary material to these traditional systems. DM may be directly used as topsoil material depending on its properties and the presence of organic material in the DM. However the use of engineered manufactured topsoil (MS) allows the use of DM combined with recycled organic waste material to produce a manufactured topsoil that can improve soil growth characteristics. Dredge sediment has been used as a raw material for brick production. Suitable fine-grained DM can be used as a substitute for sand and/or natural clay (depending on the specific DM characteristics) to produce bricks and ceramics without the need for any alteration in the standard manufacturing process. Contaminated DM may also be used, as the process of manufacturing bricks involves the thermal immobilization of contaminants in the stabilised finished product. As can be seen, in many cases, dredged material is far from a waste to be disposed. It is, on the contrary, a valuable resource if it is realized, planned and managed correctly towards beneficial use. This can only be achieved with proper coordination between all the involved parties. Although varying in suitability, there is a significant amount of beneficial usage options for dredged material.