Disclaimer:
The authors are solely responsible for the content of this report. Material included herein does not represent the opinion of the European Community, and the European Community is not responsible for any use that might be made of it.
Back to overview measures
Overall, the monitoring has found an accretionary trend over the survey period between 2007 and 2011, with an average difference between 2007 and 2011 of +14cm. The degree of accretion was found to have decreased over time. The main change in elevation took place in the initial year following the breach, with typical elevations increasing by between 0 and 50cm between 2006 and 2007.
The change in elevation in subsequent years has decreased, although increases of up to 40cm have still been observed at some locations across the site between the 2009 and 2011 surveys. Over the survey period, the majority of change in elevation (accretion) has occurred in lowest (seaward) parts of the site, which were around 1.5 to 1.75mODN in 2007 - with changes in elevation of the order of 10-40cm.
Erosion was initially noted in the creeks, and continually towards the rear of the site within the created saline lagoons. The latter should, however, be viewed with a degree of caution as the presence of standing water can reduce the accuracy of the LiDAR data. The higher elevations (above ca. 2.75mODN) have barely, or not at all, been subject to a net gain in elevation.
Saltmarsh vegetation has generally established in areas above 2.5 to 3mODN (2.5mODN is approximately 50cm above the MHWN level). Most of the mudflat areas below 2mODN remain unvegetated.
Species diversity has also been fairly consistent over the years monitored to date and average abundance has increased rapidly and, although variable, is still continuing to increase four years post inundation of this site.
The monitoring has shown that invertebrates have colonised this new sediment. In 2009, between 571 and 15,429 specimens were found per m² (belonging to between 2 and 6 species). The abundance, diversity and biomass of species in the mudflat have been increasing since the realignment has been implemented, and are now similar to the fronting, pre-existing, mudflat sites; in fact, average abundance within the samples collected in 2008 was greater than the fronting mudflats.
Back to top
Welwick
Table of content
- 1. Measure description
- 1a. Description of the issue and measure
- 1b. Monitoring
- 1c. Monitoring results
- 2. Execution of main effectiveness criteria
- 2a. Effectiveness according to development targets of measure
- 2b. Impact on ecosystem services
- 2c. Degree of synergistic effects and conflicts according to uses
- 3. Additional evaluation criteria in view of EU environmental law
- 3a. Degree of synergistic effects and conflicts according to WFD aims
- 3b. Degree of synergistic effects according to Natura 2000 aims
- 4. Crux of the matter
Monitoring results
Accretion
The monitoring programme includes Laser/LiDAR topography surveys to determine accretion and erosion on site. The Laser surveys were undertaken for the baseline surveys. The survey was repeated in March 2007, June 2008, April 2009 and June 2011 using LiDAR and comparisons between the resulting elevation models have since been made. The comparison of these datasets required careful interpretation due to the differing accuracies of the two techniques.Overall, the monitoring has found an accretionary trend over the survey period between 2007 and 2011, with an average difference between 2007 and 2011 of +14cm. The degree of accretion was found to have decreased over time. The main change in elevation took place in the initial year following the breach, with typical elevations increasing by between 0 and 50cm between 2006 and 2007.
The change in elevation in subsequent years has decreased, although increases of up to 40cm have still been observed at some locations across the site between the 2009 and 2011 surveys. Over the survey period, the majority of change in elevation (accretion) has occurred in lowest (seaward) parts of the site, which were around 1.5 to 1.75mODN in 2007 - with changes in elevation of the order of 10-40cm.
Erosion was initially noted in the creeks, and continually towards the rear of the site within the created saline lagoons. The latter should, however, be viewed with a degree of caution as the presence of standing water can reduce the accuracy of the LiDAR data. The higher elevations (above ca. 2.75mODN) have barely, or not at all, been subject to a net gain in elevation.
Saltmarsh vegetation has generally established in areas above 2.5 to 3mODN (2.5mODN is approximately 50cm above the MHWN level). Most of the mudflat areas below 2mODN remain unvegetated.
Vegetation
At Welwick, saltmarsh colonised the site very rapidly, covering some 28ha within two years of the site being inundated. The extent of saltmarsh has also continued to increase since this time, although the rate of expansion has decreased as time has elapsed.Species diversity has also been fairly consistent over the years monitored to date and average abundance has increased rapidly and, although variable, is still continuing to increase four years post inundation of this site.
Bird Usage
Breeding birds have been specifically monitored at Welwick and the number of species of breeding bird observed has been consistent across the five year monitoring period, with a five year average of 27 species (range 23 to 33). Total numbers observed have also remained consistent.Invertebrates
The invertebrate usage of the saline lagoons at Welwick, have been monitored annually since 2006 when the site was first inundated. None of the species recorded are specialists of saline lagoons (as listed by Bamber et al., 2001) and there is little indication that the pools are developing a lagoonal fauna. It is considered likely that pools on the developing saltmarsh are probably too exposed to tidal flooding to support anything other than a typical low-marsh invertebrate fauna. It was also noted that the pools were completely dry during low tides in June 2011, so conditions are probably too unstable to support a diverse invertebrate community. It has been agreed that the monitoring of saline lagoons will continue beyond the originally planned five year review period.The monitoring has shown that invertebrates have colonised this new sediment. In 2009, between 571 and 15,429 specimens were found per m² (belonging to between 2 and 6 species). The abundance, diversity and biomass of species in the mudflat have been increasing since the realignment has been implemented, and are now similar to the fronting, pre-existing, mudflat sites; in fact, average abundance within the samples collected in 2008 was greater than the fronting mudflats.