Case study:Noard-Fryslân Bûtendyks Managed Realignment Scheme
Project overview
| Status | Complete |
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| Project web site | |
| Themes | Habitat and biodiversity |
| Country | Netherlands |
| Main contact forename | Susanne |
| Main contact surname | Armstrong |
| Main contact user ID | |
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| This is a parent project encompassing the following projects |
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Project summary
In order to implement this scheme, and buy the majority of the Noard-Fryslân Bûtendyks summer polder complex, the NGO It Fryske Gea obtained funding from the EU LIFE nature programme(some €4.5million), and match (and additional) funding from the Dutch Directorate-General for Public Works and Water Management, the Dutch Ministry of Agriculture, Nature and Food Quality and the Province of Friesland. WWF and It Fryske Gea raised €0.5million. The Dutch Ministry of Agriculture, Nature and Food Quality handled the land purchase. The objective was to transform a summer polder into a grazable saltmarsh – a semi-natural landscape with high vegetation diversity and as many (natural salt marsh) plant and animal species as possible. Most of the summer polder complex is to be realigned in stages over the 50 years or so (300ha are still in private hands, as the farmer did not want to sell). It Fryske Gea has decided on this staged approach as the summer polder complex is an important feeding ground for geese, and as a realigned polder takes a few years to develop goose-preferred vegetation; this approach will ensure relatively small amounts of feeding grounds are temporarily unavailable at any one time. The next stage, which will be implemented over the next 5 years, will amount to some 200ha (personal communication).
Monitoring surveys and results
An intensive monitoring programme investigated a range of factors, including salinsation, sedimentation, creek development, vegetation and birds (van Duin et al., 2007).
Van Duin et al. (2007) concluded that to date, the realignment had been successful, although the site was obviously still evolving. They attributed the relatively rapid success of the scheme to a number of (environmental and management) boundary conditions having been fulfilled at the same time – namely its appropriate position in the tidal frame, sediment availability, tidal exchange, drainage, closeness to target plant species, and grazing management.
Salinisation: The report firstly concluded that salinisation of the upper soil layer had been slower than expected. By the end of the monitoring period, salinity was still 30% below that of the reference saltmarsh (with increases most pronounced in the first year; plateauing in the third or following years after ‘de-polderisation’). No increased saline influence could be measured in the adjoining summer polder (in some parts fresh water influence actually increased).
Accretion: Sediment accretion in the (higher) easterly part of the restoration site was greater than in the westerly part; average accretion at elevations above 1.5mNAP was 6mm/year and 14.8mm/year below, i.e. rates were higher at the lower levels. Whether this was solely due to the lower elevation or whether it was caused by other factors (e.g. a greater transport of sediment from the saltmarsh due to creek shape) was not clear. No evidence was found that the sediment accretion in the restoration site had been at the cost of adjacent saltmarshes. On the basis of the site’s elevation, it was expected that saltmarsh vegetation would develop throughout the entire site. There were some localised issues with stagnated drainage resulting in infilling of the creeks or cessation of the connection with the excavated creek systems. The excavated, over-dimensioned, creeks had become shorter and shallower (due to sediment accretion), and some of the silted up sections had become colonised by pioneer species. The accretion rates were approximately 38% lower where grazing occurred as compared to non-grazed reference areas. Other noted effects of grazing were that it led to higher biodiversity, the colonisation of sea couch (Elytrigia atherica); to a slightly drier, more compact and saline upper soil layer; and lastly to slight positive effects on chloride concentrations in the soil.
Vegetation: Halophytes quickly settled in the lower parts of the polder (~0.3m above MHT), whilst in the higher parts (~0.6m above MHT) changes were more gradual. In lower lying parts, salt marsh has developed well, dominated by Suaeda maritima and Salicornia europea. These pioneer species are slowly being replaced by more grassy vegetation (Puccinellia maritima).
Brent Geese: Autumnal geese grazing has to date been significantly lower than on existing salt marshes. In the first season following the realignment, there was however a substantial increase. The expectation is that through an increase of grassy vegetation in the polder, the number will slowly increase. The use of the farm land behind the main dike by geese stayed low, although there was a slight increase in brent geese, in line with an overall population increase (farmers had expressed fears that geese would be displaced and start grazing on their crops, due to generally lower grazing densities on saltmarshes when compared with summer polders (NB: summer polder would be classed as coastal grazing marsh in the UK)). No significant change in the breeding bird populations was observed.
Lessons learnt
Image gallery
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Catchment and subcatchment
Site
Project background
Cost for project phases
Supplementary funding informationThe Noorderleech realignment cost some €600,000 in total – €2,000 of which were spent on permits, and €20,000 on plan production. It Fryske Gea alone spent at least 5,000 man-hours on implementing the scheme.
Reasons for river restoration
Measures
MonitoringHydromorphological quality elements
Biological quality elements
Physico-chemical quality elements
Any other monitoring, e.g. social, economic
Monitoring documents
Additional documents and videos
Additional links and references
Supplementary InformationEdit Supplementary Information
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