Project part-financed by the European Union (European Regional Development Fund)

The Interreg IVB North Sea Region Programme

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Chowder Ness

Crux of the matter

The “crux of the matter“ refers to the basic, central or critical point of an issue. For example, in this context, the main issues relating to the development and progression of the specific measure detailed within this FAS Repost represent the crux of the matter.

Overall there has been an accretionary trend throughout most of the site, with an average difference between 2007 and 2011 of +43cm. The majority of this change took place over the first two years following the breach of the site, however the 2011 survey has also seen an increase in elevation since the 2009 survey.

Between 2007 and 2011 elevations have generally increased by between 10 and 100cm, with maximum height differences in excess of 100cm observed in a few locations.

It should be noted that an apparent error can be observed between the 2007 and 2011 data which shows areas of (non-existent) erosion along the floodbank. Errors appear to occur where vegetation is or has been present. Although vegetation differences should have been filtered out of the LiDAR data it is clear that the accuracy of these measurements may have been affected. However, it is assumed that the overall trends within the data sets are accurate.

Areas of highest accretion between 2009 and 2011 are observed in limited areas in the north-east and south-west corners of the site, although these results need to be reviewed in the context of the accuracy of the LiDAR which is approximately ±25cm. Again these areas coincide with sites of saltmarsh growth and although this should have been filtered out of the LiDAR this may still affect the accuracy of these measurements. Accretion values between 2009 and 2011 throughout the rest of the site ranged from 10 to 60cm.

The lowest accretion rates are thought to be characterised by:
  • A wide connection to the estuary (essentially a very wide breach);
  • Exposure to significant fetch from the predominant wind direction; and
  • Relatively high flows due to its proximity to the main Humber navigation channel and the Humber Bridge (the latter constriction causing higher flows).
It is notable that the lower accretion rates at Chowder Ness occur, despite its location near to the estuary turbidity maximum, which might otherwise have been expected to generate higher accretion rates. Generally, accretion at saltmarsh elevations has been much lower, in the order of a few cm at most over 5 years.

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