Publication Abstract

Sea bed morphology modelling for habitat mapping in Eastern English Channel and Marine ALSF Regional Environment Characterisation (REC) studies.

Sea bed morphology modelling for habitat mapping in Eastern English Channel and Marine ALSF Regional Environment Characterisation (REC) studies.

J.W.C. James, R.A. Coggan*, K.F. Rocks and A.P. Iwanoczko.

http://www.alsf-mepf.org.uk/media/16451/mepf 04-01 bgs xyz final report.pdf

This sea bed morphology study is a complementary project to the Eastern English Channel Marine Habitat Map (EECMHM) study (James et al, 2007) and was commissioned to produce a sea bed morphology model across the whole area i.e. a physical relief map of the sea bed surface in both 2D and 3D (with appropriate software), to improve resolution of current mapping.

A sea bed morphology model has been successfully produced from single beam echo soundings derived from 26 UKHO bathymetric surveys. In total four million points have been modelled. The area covered runs from Selsey Bill to Dungeness, a distance of 128 km, and extends out from the coast to virtually the median line with French waters, a maximum distance of 66 km.

The bathymetric survey soundings have been produced at a variety of line spacing and this means there is a concomitant variability in the resolution of the sea bed morphology model. However, the model produced has provided a continuous well-delineated surface, which has enabled us to meet the objective of improving the original interpretation.

The original interpretation for the Eastern English Channel Marine Habitat Map (EECMHM) divided the study area into five physical regions. These regions are discernable within the model but the coverage and detail of the model has enabled the region boundaries to be modified and improved, based on greater resolution of morphology and bedforms.

In some areas where bedrock has been mapped the model has picked up linear features which have been compared with high resolution multibeam and seismic data collected for the original study and this has enabled us to correlate these linear features with specific geological formations. Some of these features were not apparent in the original interpretation.

The larger sand waves in the Greater Bassurelle Sands are discernable in the model although at a low resolution. An objective of the study was to compare the positions of these larger waves on the model with the same area on high-resolution multibeam corridors. Although not definitive the comparisons are reasonable in a number of areas and inferences can be drawn with regard to sand wave mobility.

The sounding data has also been processed to produce a slope angle model and a rugosity model. Although neither model was complete in the low resolution sounding areas the slope angle model was particularly good at delimiting channel systems, sand waves, scarps and rough bedrock. The rugosity model was disappointing and showed no discernable patterns.

The association between biological sampling points and the sea bed morphology model has provided corroborating evidence that supports the original differentiation of both infaunal biotopes and epifaunal biotope complexes. There are indisputable spatial correlations between certain biotope classes and certain physical features revealed by the model, which has allowed the biotope boundaries to be mapped more precisely and confidently.

The data has reduced the uncertainty associated with the placement of boundaries representing gradual transitions from one biotope to another, and the uncertainty in the spatial extent of areas previously classified as ‘heterogeneous’. It has also provided suitable evidence to support inferences that some of the boundaries of infaunal biotopes and epifaunal biotope complexes are indeed confluent with each other and with distinct morphological features.

Appendix 1 lists Digital Survey Bathymetry (DSB) files of single beam bathymetry, licensed from SeaZone, for the four MALSF REC regions and areas which are to be investigated in the MALSF round of 2008 -2011. Also included in the appendix are geotif images of sea bed morphology models of relevant REC regions or areas derived from the DSB data. These data were compiled by BGS as an addition to the EECMHM work described in this report and was undertaken to enable the DSB data to be available at the commencement of the South Coast, Thames, East Coast and Humber REC studies. The files and models were provided to each REC contractor under licence for further processing and interpretation.

http://www.alsf-mepf.org.uk/media/16451/mepf%2004-01%20bgs%20xyz%20%20final%20report.pdf

J.W.C. James, R.A. Coggan*, K.F. Rocks and A.P. Iwanoczko.

British Geological Survey, Marine Geoscience Programme, Open Report OR/08/016, MEPF ref 04/01 (ext)