Winter 2015

Sludge inhibitor increases quality of surface water

The rapid accretion and movement of sludge presents managers of shallow fen pools with a problem. Maintenance is costly; its effect temporary. In addition, sludge has a negative impact on the surface water. That’s why Tauw, together with TenCate Geosynthetics and Hoogheemraadschap Hollands Noorderkwartier, used geosynthetics and TenCate Geotube® to develop the sludge inhibitor.  

The Wormer- en Jisperveld nature area in the Netherlands served as a pilot project. Result: a higher quality of water plus lower maintenance costs. 

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The Wormer- en Jisperveld is one of the most important meadow bird areas in the Netherlands and, with its 2,000 ha, the largest area of contiguous peatland meadows in West Europe. The shallow fen pools in the Wormer- en Jisperveld are turbid, and light barely penetrates to the water bed. Consequently, water plants fail to grow and algae gain the upper hand. The slightest movements in the water set large quantities of sludge in motion. Owing to the sweetening of the system and exposure to oxygen, the peatland ‘burns’. As a result, banks crumble, the bed sinks, and the burnt peatland ends up as sludge in the water. Over time, various measures have been taken to improve the water quality but have produced only limited and temporary results. 

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To cope with this problem, Tauw, together with TenCate Geosynthetics and Hoogheemraadschap Hollands Noorderkwartier, have developed the sludge inhibitor and the dredge spoil buffer (see box). The sludge inhibitor consists of a screen of UV-resistant geotextile that partly emerges above the water and is anchored to the bed with a sand-filled container (TenCate Geotube® technology). The fabric is manufactured by TenCate Geosynthetics in Nijverdal; the non-woven in the plant in Linz (Austria); the material for floats at TenCate in Malaysia. The site in Almelo makes the composite product.
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 In January 2014, the sludge inhibitor was placed in a large fen pool in the Wormer- en Jisperveld − a quick and low-cost operation. In total four elements, each 25 metres, were installed; one was also equipped with a 10-metre-long ‘bird jetty’. Nearly two years have now passed, and in the meantime the wetland watch have come across various protected bird species that have landed on the sludge inhibitor to rest. Furthermore, a remarkable plant community has developed on top of the sludge inhibitor. So water quality, nature, recreation and ease of maintenance come together in this sustainable solution.

geosynthetics baggerbuffer

Based on the sludge inhibitor concept, Tauw, together with TenCate Geosynthetics, have developed the dredge spoil buffer. The dredge spoil buffer offers a robust, sustainable and nature-friendly solution for the remediation of water beds.  The sludge spoil buffer is a retaining structure, consisting of sand- or sludge-filled TenCate Geotube® units and a float. Behind this, the dredged sludge is stored under the water. The whole structure is built on land and transported using pontoons. The dredge spoil buffer can be vegetated or kept just under water level. The water becomes clearer and more tranquil. Flora and fauna are given new chances. 

Blue fabric (Tecawork Blue 65287)