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Saltmarsh Management Manual |  |
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Surveying & Monitoring |
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Measuring Change |
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| Satellites • Other remote sensing techniques • Saltmarsh morphology • Vegetation • Species specific studies Saltmarsh morphology Three key morphological attributes of saltmarshes provide a means of detailing both the existing nature of the habitat and the development of new habitat (e.g. as a result of managed realignment). These are:
The extent, creek attributes and surface elevations (although the latter to +/- 0.1m only) of saltmarsh may be measured using remotely sensed data. Aerial reconnaissance, currently undertaken by the Environment Agency and local authorities in eastern and southern England, is a suitable technique for quantifying the extent of habitat and changes in habitat areas. Aerial survey has several advantages over other methodologies, including the existence of long-term archives for many areas. It is also a well established technique and offers the ability to determine surface elevations. Other methods, including CASI (Compact Airborne Spectral Imaging) and LIDAR, offer individual advantages but not the range offered by aerial survey (where CASI will show vegetation cover but does not provide information on levels). The Environment Agency has in the recent past employed a five year rolling programme of aerial survey of coastal areas, with subsequent analysis of the photographs (although coverage may be variable in the future).
Aerial photos (particularly with forward motion compensation) may also be used to determine topography using photogrammetric techniques, although the level accuracy is only suitable for long-term changes or large magnitudes of change (suggested at over 0.1m vertically). Surface elevations of saltmarshes are more accurately surveyed using conventional ground survey techniques and these are currently measured within programmes such as the first Regional Strategic Monitoring Programme established by the Environment Agency’s Anglian Region in 1990. This programme includes profiles, extending across saltmarshes where they occur. The programme covers both the open coast (bi-annually) and estuaries landward of the Coast Protection Act (1949) Schedule IV boundaries (on a five-year rolling programme). Within estuaries, bathymetric surveys (which may be undertaken by the Harbour Authority or the Environment Agency) usually incorporate the ‘shoreline topography’. The resolution of bathymetric data is not comparable with the ground survey but does provide an indication of the whole estuary and how the system might be changing. The combination of different methods of survey, monitoring or surveillance should be undertaken with great care and understanding of the differences in accuracy, resolution and the assumptions made. |
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