Case study:Nigg Bay Managed Realignment Scheme

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Location: 57° 44' 11", -4° 0' 1"
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Project overview

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Status Complete
Project web site http://www.rspb.org.uk/reserves/guide/n/niggbay/index.asp
Themes Habitat and biodiversity
Country Scotland
Main contact forename Susanne
Main contact surname Armstrong
Main contact user ID
Contact organisation ABPmer
Contact organisation web site
Partner organisations RSPB, SEPA
Parent multi-site project
This is a parent project
encompassing the following
projects
No
Project picture

Project summary

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Promoted by the RSPB and the Scottish Environmental Protection Agency with the aim of creating important habitats for wildlife at Meddat, while also reducing maintenance requirements for the existing and failing defences.

This was the first planned realignment in Scotland and involved making two 20m-wide breaches in existing sea defences to allow the top of the tide to flood a 25ha field. This field was the last area of Nigg Bay to be land claimed (in the 1950s) and a secondary sea wall was already in place; this needed repairing and raising to a 1 in 50 year standard in advance of tidal inundation. The soils adjacent to the wall were suitable for use to build up the wall where required (on average by 10-20cm, over a length of 860m). The site was prepared by culverting drains which linked to adjacent fields, topping and grazing to reduce the amount of terrestrial vegetation, and the removal of trees. No internal earthworks were needed to create a creek system as a relict creek was still present. Approximately 2/3 of field is inundated at spring high water.

The site is owned and managed by the Royal Society for the Protection of Birds (RSPB), and forms part of its wider Nigg Bay reserve. This reserve incorporates extensive areas of mudflat, saltmarsh and wet grassland (RSPB website, 2011).

https://www.therrc.co.uk/sites/default/files/projects/48_niggbay.pdf

Monitoring surveys and results

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A range of monitoring studies were undertaken to describe ecological development of site (i.e. surveys of overwintering waterbirds, benthic invertebrates, vegetation and sedimentation/erosion patterns) as well as impacts to saltmarsh habitats and benthic invertebrate communities outside the breached area.

A PhD study investigating sediment characteristics and invertebrate colonisation reported the following results from monitoring the site during the first three winters post implementation (with the caveat that the realignment sampling points were higher in the tidal frame than those on the reference intertidal flats) (Crowther, 2007):

(1) The particle size of the sediments in Nigg Bay realignment site was significantly smaller than that of the (fronting) reference intertidal flats (mostly silts compared to mostly fine sands) – this was attributed to the sheltered environment and limited wave exposure within the site.

(2) The organic matter content of the sediments on the reference intertidal flats was less than 1%, whereas within the site, it was 46.6% in the first winter, and 27.2% in the second. The author highlighted that ‘organic matter is usually associated with fine grained sediments (…), so the sediments in [the site] are likely to have provided a large surface area for colonisation by micro-algae’. Furthermore, the higher organic content during the first winter was described as ‘not surprising given the large quantity of vegetation that had been killed following the re-establishment of tidal conditions’. A significant positive relationship with elevation in the tidal frame was found for the percentage organic matter in the sediments during the second winter. The author theorised that such high organic matter content of the sediments ‘may have caused hypoxic conditions due to the increased biological oxygen demand of the sediments’, however oxygen content was not measured (and the presence of hypoxia hence not determined).

(3) The following four invertebrate species were found to be most abundant within the site three years after the re-establishment of tidal conditions: Corophium volutator, Hediste diversicolor, Hydrobia ulvae and Macoma balthica. All of these were also noted as colonists in the first year, and also found to be the most abundant species on the adjacent reference marshes. The presence of M. balthica during the 1st winter was considered unusual, as it is usually considered to be relatively immobile. It was theorised that this could have resulted, at least in part, from wind or wave-driven immigration. The presence of C. volutator and H. diversicolor was (amongst others) attributed to the high organic content of the sediments. Intertidal invertebrate densities within the site were generally lower than the reference intertidal flats; which was mostly related to the higher elevations of the realignment site.s well as impacts to saltmarsh habitats and benthic invertebrate communities outside the breached area.

Lessons learnt

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By 2005 the area had developed into three distinct zones:

(i) an upper zone, which is rarely inundated and retains terrestrial grassland;

(ii) an intermediate zone, which has been colonised by salt marsh species; and

(iii) a lower zone, which experiences regular inundation and in which terrestrial grassland has been replaced by fine sediments. Nineteen species of waders and wildfowl were recorded using the site during winter 2004/05, the commonest of which were redshank (RSPB, 2005).


Image gallery


Sea aster in bloom; view across site towards one of the breaches (Taken by: K. Chisolm, RSPB, 2007)
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Catchment and subcatchment



Site

Name Cromarty Firth, Highland Region
WFD water body codes
WFD (national) typology Intertidal
WFD water body name Cromarty Firth
Pre-project morphology
Reference morphology
Desired post project morphology Estuary (tidal)
Heavily modified water body No
National/international site designation
Local/regional site designations
Protected species present Yes
Invasive species present No
Species of interest Wading birds (e.g. Lapwing), wigeon, oyster catchers, pintail
Dominant hydrology Estuary
Dominant substrate Estuarine mud
River corridor land use Arable;
Average bankfull channel width category
Average bankfull channel width (m)
Average bankfull channel depth category
Average bankfull channel depth (m)
Mean discharge category
Mean annual discharge (m3/s)
Average channel gradient category
Average channel gradient
Average unit stream power (W/m2)


Project background

Reach length directly affected (m)
Project started 2001/03/01
Works started
Works completed
Project completed 2004/03/01
Total cost category
Total cost (k€) £47k
"£" is not declared as a valid unit of measurement for this property.
Benefit to cost ratio
Funding sources Heritage Lottery Fund (HLF), Scottish Natural Heritage, Scottish Environment Protection Agency, Miss EMP Scott Will Trust

Cost for project phases

Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname
Investigation and design
Stakeholder engagement and communication
Works and works supervision
Post-project management and maintenance
Monitoring

Supplementary funding information

Land purchased by RSPB in 2001, project part funded by HLF, SNH and SEPA grants as well as a legacy from Miss EMP Scott Will Trust. Excluding staff costs and land purchase, the whole scheme cost £53,840 to complete. Of this, £22,400 were spent on the design and impact study; £2,100 on strengthening existing landward defences; £1,470 on culvert blocking and breach digging; £1,100 on tree removal from the sea wall; £8,450 on fencing to retain stock on site; £1,350 on topping; £8,500 on surveys and monitoring; £1,400 on a video, £600 on the launch event; and £110 on the FEPA licence. In terms of staff cost, the RSPB estimated that for the duration of the project (March 2001 – March 2003), total staff time was equivalent to 70-75% of one full time employee (Chisholm et al., 2004).



Reasons for river restoration

Mitigation of a pressure Flood and coastal erosion protection
Hydromorphology
Biology
Physico-chemical
Other reasons for the project


Measures

Structural measures
Bank/bed modifications
Floodplain / River corridor
Planform / Channel pattern
Other Salt marsh and mudflat restoration
Non-structural measures
Management interventions
Social measures (incl. engagement)
Other


Monitoring

Hydromorphological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative
Substrate conditions No Yes Yes No No

Biological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative
Invertebrates No Yes Yes No No
Macrophytes No Yes Yes No No

Physico-chemical quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Any other monitoring, e.g. social, economic

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative


Monitoring documents



Additional documents and videos


Additional links and references

Link Description
http://www.rspb.org.uk/reserves/guide/n/niggbay/index.asp RSPB reserve website

Supplementary Information

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  • Chisholm, K., Kindleysides, D., Cowie, N., 2004. Identifying, developing and implementing coastal realignment projects in Scotland; Lessons learned from Nigg Bay, Cromarty Firth. RSPB,Inverness.
  • Crowther, A., 2007. The restoration of intertidal habitats for non-breeding waterbirds through breached managed realignment. Thesis submitted for the degree of Doctor of Philosophy, The University of Stirling.
  • Nottage, A., Robertson, P., 2005. The saltmarsh creation handbook: a project manager's guide to the creation of saltmarsh and intertidal mudflat. RSPB, Sandy, 128p.
  • The Royal Society for the Protection of Birds (RSPB), 2005. RSPB’s involvement in intertidal habitat creation projects. RSPB, Sandy, 7p.