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Understanding Dredging

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Low-Flow Sediment Removal and Beneficial Use of Sediments, Experiences from the Life Sure Project

€ 20,-

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Presented during:

WODCON XXIII - Dredging is changing - The Practice. The Science. The Business.

Authors:

R.T. Foks


Abstract

"Introduction The LIFE SURE project's location is the Malmfjärden bay situated in the city of Kalmar in the South of Sweden. The project has developed an innovative way to remove soft sediments from shallow water bodies without causing resuspension of sediments. The project's solution runs autonomous, has a low, and possible CO2-neutral, energy consumption and can be implemented in other regions and projects. The LIFE SURE solutions can inspire those who work on sediment removal in protected areas, storm water basins or in combination with a water body restoration. Besides developing and testing a low impact sediment removal and dewatering solution, LIFE SURE has also tested several beneficial uses of the sediments, once removed from the waterbed. Background Stormwater runoff from built-up environments, agriculture and forestry cause leakage of nutrients, heavy metals and other contaminating substances to our water bodies. These substances then accumulate in the sediments of the recipients, lakes, and bays. Malmfjärden bay is an example of such a water body at risk. It is a shallow (max 1-2 meters depth) and semi-enclosed brackish bay, covering an area of circa 1 km2. The hydrology of Malmfjärden bay is determined by its connections to the Baltic Sea and stormwater runoff from the surrounding urban area. A balanced ecosystem in the Baltic Sea is of key importance to Kalmar as a city, as it provides necessary services such as transportation, a tourist destination and attractive living and recreation environments. Unbalances in the ecosystems of the coastal environments cause problems such as oxygen depletion, algae bloom, fish death and bad smells. The deteriorating state of the water quality and ecosystem in the coastal areas have been engaging politicians and inhabitants for many years. Previous mitigating actions in this shallow bay, such as conventional dredging, only made things worse, causing turbulence and disturbing the living conditions for predator fish and plants. Kalmar Municipality and the Linnaeus University combined their ambitions and applied for a LIFE project that would find a solution for restoring shallow marine environments using a low-flow sediment uptake solution. Meantime, the project also studies and develops new applications for the beneficial use of the sediments once removed from the bay, thus contributing to a more circular economy. Low-flow sediment uptake and dewatering LIFE SURE has developed and demonstrated a sediment uptake solution that can remove sediment without negative effects on the fragile shallow water body. The LIFE SURE´s solution is a low-flow dredging robot that carefully removes sediments from the bottom of the bay while slowly and autonomously moving through a designated area. As conventional dredging solutions focus on removing sediments within a short period of time, putting pressure on both the marine environment and the dewatering capacity, LIFE SURE has looked in the opposite direction. By using a low-flow sediment uptake solution to remove soft sediments from shallow waters, the turbulence is kept to a minimum and fish and birds are not affected by the operation. The low-flow of incoming sediments also allows for a semi-passive dewatering of the sediments, thus saving on energy and investments. The dewatering process in LIFE SURE is done using geotextiles and an automated polymer feed. All processes are continuously being monitored and evaluated by the project's researchers at Linnaeus University, thus giving the project important feedback. The sediment removal and dewatering can be done continuously, day and night, and most of the year (except wintertime here in Sweden). The"

Keywords: low-flow, beneficial use, turbidity, energy use, automatic

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