Detail on Pole Transects
Detail on Pole Transects
Incorporating the canes used to mark the locations of the plates, extra canes were subsequently added closer to the bank and closer to the low tide mark to create a full transect covering the intertidal zone. They were spaced at 3m intervals.
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A suitable site for a benchmark was then chosen. This tended to be on something immovable such as a piece of pavement or concrete platform. A hole was drilled and a screw and washer glued permanently into place. At most locations, there is also an Environment Agency benchmark already in existence for which the 3D national grid coordinates are already known. This will be combined into the survey to give the coordinates for the new benchmark.
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The first time the total station was set up over the benchmark, a prism was taken out onto the mudflat and the cane locations were surveyed. This gives us the hypotenuse for use in later elevation change trigonometrical calculations. It also allows a 3D picture of the mudflat surface to be created in a GIS.
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On a bi-monthly basis, the total station is set up over the benchmark. The intersection of the accretion poles and the mudflat surface is recorded as an angle from the station. A reduction in the angle shows accretion and an increase in the angle shows erosion.
These pages maintained by Martin Wingfield This section last updated 20/MAY/2003