1. Developments in Seabed Mapping
Jon Evans
I’m going to give a brief talk and update about our habitat mapping program and recent progress we have made.
Shows some examples of the areas we have mapped and reported on this year
Brief overview of how the maps are created and what data is required
How the various data types help identify certain habitats and sediment types
Future uses
Developments in Seabed Mapping

2. Swath bathymetry data extent
Red– bathy data commission by the monitoring program – and meets the IHO order 1a swath bathy
Blue– Areas mapped
Habitat mapping data extent

3. Anthropogenic Features
Seabed Mapping
Bathymetry
Backscatter
Ground Truthing
Seabed Habitats:
Basic
Anthropogenic Features
Substrate Type
How they are created.
Firstly we need high quality multibeam bathymetry data – IHO order 1a – if the bathy data meets this standard and has 100% coverage we can use this and the backscatter data that is collected simultaneously and combine this with a variety of ground truthing data.
Backscatter – secondary, but improving with technology
Sediment sampling part of spec and other groundtruthing from divers, IFCAS, wildlige trust etc
Using this data a number of features and maps can be created including….
Seabed Habitats:
Detailed

4. Example of bathymetry data

5. GROUNDTRUTHING
Examples of groundtruthing – very important when trying to set boundaries etc

6. Hillshade – Creates a shaded relief from a raster layer
Hillshade – Creates a shaded relief from a raster layer. a hillshade layer was derived which is a form of artificial sun-illumination which helps to enhance depth changes and features in the bathymetry dataset.
Slope – Identifies different levels of slope gradient. This layer helps distinguish those areas of the seabed that have a steep gradient or sharp changes in slope, and those areas which are relatively flat.
Got some examples of where these types of data are useful to back each other up

7. Beachy Head, East Sussex
Extensive rock platform
Also where ground truthing points are useful to help set boundaries
Different sediment types can be defined

8. Seaford, East Sussex
Underlying bedrock can be clearly identified using the backscatter layer

9. Beachy Head, East Sussex
Extensive rock platform and rocky ridges
Geology continues offshore
Steep drop off

10. Chichester Harbour Entrance
Narrow, deep channel cutting though shallow sediment

11. Anthropogenic features – Shoreham Harbour, West Sussex

12. EUNIS Level 3 marine habitat classifications
Rock
Rock and thin Sediment
Sediment
High energy
littoral rock
Moderate
energy
littoral
rock
Low energy
and thin
Littoral
mud
sand
mixed
sediment
coarse
infralittoral
rock and
thin Sediment
Sublittoral
circalittoral
Aim from these data types is to create a habitat map and a substrate map
Using these various layer the bathymetry is initially divided into areas of rock, rock and thin sediment and sediment. Once we are confident in these boundaries we use the MLWS to split the littoral and sublittoral areas apart and also create an boundary between circalittoal and infralittoral boundaries. Often far more complex than a singular depth contour, can change spatially and temporally but one has to be chosen. It is chosen based on sechhi disks depths and also video/ photography / diver data if available. The boundary denotes the change from where habitats are dominated by light.
European nature information system
We also separate areas in high, low, medium energy using wind and tide data.
In the classifications, ‘Rock’ collectively refers to bedrock, stable and artificial substrata (concrete, wood, metal). Mobile cobbles and pebbles with gravel and coarse sand are collectively referred to as ‘Coarse Sediment’. ‘Mixed Sediment’ consists of mixtures of gravel, sand and mud which may contain stones and shells.
The littoral zone lies landward of Mean Low Water Springs (MLWS) with the sublittoral zone seaward of MLWS. For areas of ‘Rock” or ‘Rock and thin Sediment’ the sublittoral zone is split into the infralittoral zone and the circalittoral zone based upon site specific biological parameters ‘Rock and thin Sediment’ is applied to areas with some thickness of surficial sediment through which the underlying bedrock geology is discernible in the bathymetry.
JNCC/CEFAS modified EUNIS classification added ‘Rock and thin Sediment’ category

13. Images courtesy of SCOPAC

14. Physical substrate Rock & hard substrates Sediments Bedrock Boulder
Cobble
Sediment
Coarse
Sediments
Sand
Mud
Mixed

15. Images courtesy of SCOPAC

16. Substrate map
Habitat map
Exposure & tidal stream data
Bedform orientation
Slope & aspect of bedrock
Geology
Ground-truthing
Backscatter
Bathymetry

17. Images courtesy of Sussex IFCA

18. Images courtesy of Sussex IFCA

19. Conclusion
Swath bathymetry, backscatter and ground-truthing essential.
Improved understanding of:
nearshore habitats, geology, seafloor topography
wave environment
sediment dynamics
Informs sediment transport, marine conservation and marine planning.
Cuckmere Haven, East Sussex