Determination and Prediction of Sediment Yields
193
have focused on the loss of farmland and cliff-top property caused by retreat of the
cliffs that have led to calls for construction of coastal defences. Construction of ‘hard’
engineered defences will inevitably lead to a reduction in sediment yield from coastal
recession, with consequent, but largely unknown, impacts elsewhere. Although there
are many published estimates of sediment yield for the Holderness coast (e.g. Redman,
1869; Pickwell, 1878; Dossor, 1955; Valentin, 1971) these are based on coastal length
and assumptions of average cliff height, cliff recession rate and cliff composition.
Consequently estimates have varied by up to an order of magnitude. This paper
describes work currently in progress to improve on the quantification of sediment yield
by using digital photogrammetry and GIS data analysis techniques. The establishment
of a sediment budget is regarded as one of the key information needs for sustainable
planning and management(Department of the Environment, 1995).
The work was carried out at the British Geological Survey (BGS) as part of
the NERC Land-Ocean Interaction Study (LOIS).
The Holderness GIS
The method used in the study involved the creation of a DTM using digital
photogrammetry derived from scanned vertical aerial photographs and combined with
other datasets in a GIS environment.
The project was carried out using a suite of Intergraph software packages. The
initial photogrammetry was undertaken using Intergraph ImageStation. The DTM
derived from the photogrammetry was transferred to a Windows NT workstation and
manipulated using Intergraph Terrain Modeler. Terrain Modeler is a specialized
package developed for analysis, manipulation, modification and graphical display of
elevation modelling data and is built on Microstation, which is a computer-aided
drawing package.
The datasets can be summarised as follows.
3D DTM-from aerial photography
Colour aerial photography at 1:6000 scale was acquired by the NERC aircraft during lowtide conditions (around 10:15 am) on 14 April 1995 along the Holderness coastline. At this
scale, the photographs generally covered 75% land, 5-10% beach and the remainder sea. In
order to use the photographs photogrammetrically, a GPS ground control survey was
commissioned to provide 80 points for forty photographs. These were generally chosen to
occur within the triple overlap areas of adjoining stereomodels. The accuracy specified for
the GPS ground control was better than ±0.1 m in Easting, Northing and Height. The
actual mean transformed coordinates of the 11 stations produced root mean square error
(RMSE) values of E=0.033 m, N=0.020 m and H=0.004 m. Colour diapositives were made
from the negatives and scanned at a resolution of 20 microns to produce 3 band, red-greenblue digital images, each measuring 432 Mb in size. The images were subsequently
compressed using the JPEG method and six overviews added to each, resulting in a final
colour image size of about 132 Mb.
193
have focused on the loss of farmland and cliff-top property caused by retreat of the
cliffs that have led to calls for construction of coastal defences. Construction of ‘hard’
engineered defences will inevitably lead to a reduction in sediment yield from coastal
recession, with consequent, but largely unknown, impacts elsewhere. Although there
are many published estimates of sediment yield for the Holderness coast (e.g. Redman,
1869; Pickwell, 1878; Dossor, 1955; Valentin, 1971) these are based on coastal length
and assumptions of average cliff height, cliff recession rate and cliff composition.
Consequently estimates have varied by up to an order of magnitude. This paper
describes work currently in progress to improve on the quantification of sediment yield
by using digital photogrammetry and GIS data analysis techniques. The establishment
of a sediment budget is regarded as one of the key information needs for sustainable
planning and management(Department of the Environment, 1995).
The work was carried out at the British Geological Survey (BGS) as part of
the NERC Land-Ocean Interaction Study (LOIS).
The Holderness GIS
The method used in the study involved the creation of a DTM using digital
photogrammetry derived from scanned vertical aerial photographs and combined with
other datasets in a GIS environment.
The project was carried out using a suite of Intergraph software packages. The
initial photogrammetry was undertaken using Intergraph ImageStation. The DTM
derived from the photogrammetry was transferred to a Windows NT workstation and
manipulated using Intergraph Terrain Modeler. Terrain Modeler is a specialized
package developed for analysis, manipulation, modification and graphical display of
elevation modelling data and is built on Microstation, which is a computer-aided
drawing package.
The datasets can be summarised as follows.
3D DTM-from aerial photography
Colour aerial photography at 1:6000 scale was acquired by the NERC aircraft during lowtide conditions (around 10:15 am) on 14 April 1995 along the Holderness coastline. At this
scale, the photographs generally covered 75% land, 5-10% beach and the remainder sea. In
order to use the photographs photogrammetrically, a GPS ground control survey was
commissioned to provide 80 points for forty photographs. These were generally chosen to
occur within the triple overlap areas of adjoining stereomodels. The accuracy specified for
the GPS ground control was better than ±0.1 m in Easting, Northing and Height. The
actual mean transformed coordinates of the 11 stations produced root mean square error
(RMSE) values of E=0.033 m, N=0.020 m and H=0.004 m. Colour diapositives were made
from the negatives and scanned at a resolution of 20 microns to produce 3 band, red-greenblue digital images, each measuring 432 Mb in size. The images were subsequently
compressed using the JPEG method and six overviews added to each, resulting in a final
colour image size of about 132 Mb.