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Mirnserklif is located along the Frisian IJsselmeer coast, east of the city of Stavoren in the northern parts of the Netherlands. It is connected to the nature area ‘Mokkebank’ which is managed by the nature protection association ‘It Fryske Gea’.

In 1993, four undefended (e.g. not protected by any artificial structure) sand bars were constructed. In total, 120,000 m3 sand was replaced. The height of the sand bars varied from 0,20m +NAP to 0,20m –NAP. The main goal of the project was to create foraging, resting and nesting habitat for birds dependant on reed and marshes by extension of the marshland.

As this project has been executed some decades ago, the case Mirnserklif serves as a historical case from which lessons can be learned.

    General Project Description

     

    Title: Mirnserklif
    Location: IJsselmeer area, the Netherlands. Southeast of the city of Stavoren, at the same level as the village ‘Mirns’
    Date: 1993- 1994
    Companies: Rijkswaterstaat, It Fryske Gea, Natuurmonumenten
    Costs: € 316,000
    Abstract: Four undefended sand bars were constructed at Mirnserklif in 1993 to develop marshland and create foraging, resting and nesting habitat for a variety of birds.
    Topics: Sand nourishment, terrestrial habitat, birds, erosion, sedimentation, rising water level

    View pilot location in a larger map.

    Information on other historic pilots can be found in: Workummerbuitenwaard and It Soal.

    Planning and Design

    The project Mirnserklif was executed in 1993 and 1994 as a joint project between the Directorate-General Rijkswaterstaat of the Ministry of Transport, Public Works and Water Management and the nature protection organisations It Fryske Gea and Natuurmonumenten. Mirnserklif was an experiment aimed at the creation of new bird habitat via four sand banks. They should lead to more depth variation and more coastal and terrestrial habitat. Thus the foraging, nesting and resting area for various bird species would be expanded.

    Construction

     

    In 1993, four emerging sand banks were built along the Frisian IJsselmeer coast. Their orginal height varied between NAP + 0,20 m and NAP - 0,20 m. In total, 120,000 m3 of sand was deposited in the area (see adjacent figure).

    Project delivery

    Over a four-year period, the sand bars were flattened and lost height. The three westernmost ones, the highest and the least dynamic, moved as expected in northern direction towards the coast. The lowest and most exposed easternmost bank totally disappeared in 2007; its sand has most probably been transported eastwards. One of the reasons for the disappearance of the easternmost sand bank is the almost constant water level in the IJsselmeer; a relatively large part of the wave activity due to the predominantly southwesterly winds is therefore concentrated on a small part of the outer profile of the bank, thus causing concentrated erosion.

    The experiment at the Mirnserklif was perceived as quite successful. This is partly due to the specific properties of this location, in a sheltered area close to the mainland. This is important for the local transport and sedimentation in between the sand banks and for the development of the coast and new reedland.

    Operation and Maintenance

    Recent images show that the two westernmost banks have merged with the shore and only one remains offshore. In the meantime the first (peninsular) and second bank still emerge. At these locations vegetation succession takes place by lack of morphodynamics and a relative quiet environment. In the lee of the banks sedimentation takes place and shoreline vegetation and marshland have developed. The initial expectation of the project was that the sand bars at Mirnserklif would not have to be defended by any artificial structure. This is only partly true: the Mirnserklif project positively contributes to Natura2000 and EU WFD goals for the area, but this effect is gradually decaying and maintenance nourishments seem to be needed in order to restore the optimal situation.

    Results related to morphology

    The created sandbanks are influenced by erosion and sedimentation processes as a result of the natural dynamics in the area. They slowly move towards the coast and lose height. Most of the sand is deposited in the shallow zone landward of the banks. The first bank has merged with the coast, thus has become a peninsula. As the sheltering effect of the banks decreases, regional morphological processes become stronger and the system gradually returns to a stable state without banks, but with a sediment-rich foreshore and a more diverse habitat.

    This shows that in the present situation (small-scale undefended sand nourishments) local dynamics and sediment transport lead to temporary sedimentation and a more diverse habitat. Mirnserklif is an example of how sacrificial shoreline nourishments can be successful in low-dynamic conditions in terms of waves and currents.

    Effects of rising water level on morphology

    As the mean water level of the IJsselmeer has been stable since the creation of the islands at Mirnserklif, the project provides no insight into the morphological effects of a slowly rising water level. It seems reasonable, however, to expect that – by lack of significant bank-building mechanisms - the nourished banks will get submerged, wave action will increase and the vulnerable shores and habitats will be less protected and bound to get submerged.

    If the rate of lake level rise remains small, the rising water level it will prevent vegetation succession on the banks, which is actually desirable. When combined with a more natural water level variation, this can lead to the development of desired vegetation (Natura 2000 regulations define exactly which species must be protected). In that case, a more flexible management of the water level may well enable the Mirnserklif to grow along with a gradually rising water level in the IJsselmeer.

    Results related to ecology

    In the first year after construction, the sand banks contributed greatly to the natural values and flora and fauna diversity at Mirnserklif. Vegetation mapping carried out in 1996 at the Mirnserklif showed that there was a special vegetation composition, with amongst others  Rumex maritimus  and  Chenopodium rubrum . On the peninsula dry and wet pioneer vegetation, helophytes and different types of sedge vegetation developed. As the 3rd and 4th island got submerged, terrestrial vegetation disappeared here. In 1998, some very rare breeding pairs of the little gull ( Larus minutus ) were observed. Also a significant increase in numbers of black ternscommon terns and gulls was observed. In relation to the EU Water Framework Directive there is a positive effect on macrophytes and fish species.

    The current natural value in the area, however, is lower than the initially intended. Some banks are permanently submerged, some are attached to the mainland and possibly influenced by succession. The peninsula is less suitable for breeding birds as the whole area is now accessible by beasts of prey. In order to keep the Natura 2000 objectives (namely island with pioneer vegetation) maintenance nourishments would be needed.

    Effects of rising water level on ecology

    More water level variation leading to temporary flooding of the bank reduce succession. As a result, artificial maintenance of the vegetation is not necessary. needed as a result. Erosion and other morphodynamic processes, however, will influence and displace the banks. In case of permanent submergence the terrestrial habitat will disappear, like in the case of the third and the fourth bank. Higher mean water levels will reduce the occurrence of shore plants. An increase in wave activity onshore behind the isles maylead to erosion and regional levelling. Higher mean water levels are likely to shift the movement of the shore zone inland.

    Lessons Learned

    • From the fact that in four years’ time three out of the four sandbanks created by the nourishment had moved shorewards and the fourth one had disappeared we can learn that the water and sediment dynamics in the area determine whether or not such artificial sandbanks remain in place. At low-dynamic locations, the banks may create new habitats and only lose some sand to the immediate vicinity. In a more dynamic situation, the sediment can be spread over larger areas and a bank can disappear entirely.
    • The fact that two out of four sandbanks at the Mirnserklif still exist shows that in sheltered circumstances with a wide shallow zone artificial structures to maintain such banks are not needed. Yet, after a couple of years maintenance nourishments are needed in order to keep the sandbanks in shape and maintain their nature value.
    • Sand nourishments like the one on Mirnserklif temporarily allow for a terrestrial habitat with pioneer vegetation on their top. In the longer run, they contribute to sedimentation in the coastal zone on local and regional scales and enable water,- marsh- and shoreline vegetation to develop.
    • These lessons have been taken into account in the design of the Sand Engine IJsselmeer coast.

    References

    Literature

    1. Bak A., W.M. Liefveld, H.A.M. Prinsen & F. van Vliet (2007). Evaluatie Natuurontwikkelingsprojecten IJsselmeergebied. Bureau Waardenburg bv in opdracht van Rijkswaterstaat IJsselmeergebied (in Dutch).
    2. Groot, A., Lenselink, G., Vlieger, B. de & Janssen, S. (2010). Morfologische, ecologische en governance principes voor ecodynamisch ontwerpen: Toegespitst op de 'Bouwen met Natuur' pilots Friese IJsselmeerkust (in Dutch).
    3. Lauwaars, S. & M. Platteeuw (1999). Een groene riem onder het natte hart: evaluatie van natuurontwikkelingsprojecten in het IJsselmeergebied. Ministerie van Verkeer en Waterstaat: Lelystad (in Dutch).

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