Royal HaskoningDHV conducted the program NMIJ (‘Natuurlijker Markermeer IJmeer’) with the purpose to advise the government on measures to obtain a durable robust ecological situation in the second largest fresh water lake in the Netherlands. One of the field experiments that was conducted as part of the program was the construction of a wetland area, built up of soft sediments (mud) dredged from the original lake bed. This pilot proofed that wetland construction with very soft sediment is possible and can contribute to a better ecological quality of the lake.
Measures are needed to improve the ecological quality of lake Marken-IJ
The present ecological situation of the second largest lake in the Netherlands is poor due to poor water quality, a high silt concentration in the water and lack of natural banks. Different kinds of improvements are necessary to obtain a more durable and robust ecological situation in the lake the system. These are:
- creation of zones with clear water along the coast of Noord-Holland;
- creation of smooth transitions from clear to turbid water (gradient in turbidity);
- creation of smooth transitions from land to water;
- nature development on both sides of the dykes around the lake with connections between them.
Research program with field experiments to advise government on feasible measures
Royal HaskoningDHV conducted the research program (NMIJ) (‘Natuurlijker Markermeer IJmeer’) to advise the government on feasible measures to obtain a durable robust ecological situation in the lake. Part of this program are nine field experiments, monitoring of existing situations and desk and model studies of mud dynamics and ecology.
The largest experiment is a wetland pilot of circa 10 ha. This wetland was built up with a 4-meter layer of soft sediments (mud), dredged from the original lake bed. The soft sediments were kept in place by a fringe of geotubes filled with sand. During several years the ecological, morphological and geotechnical development of the wetland area was monitored.
Pilot proofs that wetland construction with very soft sediments is possible and can contribute to a better ecological quality of the lake
The wetland experiment showed that it is possible to design and build a new wetland with very soft sediments. Already after two years the dry parts of the wetland were completely covered with vegetation and the surrounding lake area was experiencing lower suspended sediment concentrations.