Calculation of Sediment Yield
To determine the total volume of sediment potentially yielded by recession of the coast,
the DTM was migrated horizontally landwards by a given amount and the volume
between the DTM and the migrated DTM calculated. The amount of migration can be,
for instance, 1 metre, 10 metres or a distance equivalent to 10 years at the present
Determination and Prediction of Sediment Yields
195
difference in the age of the two profiles. In some areas the height of the cliff has
reduced as the cliff has eroded back.
Geological Boundaries
Boundaries between the geological formations on the land area in plan view were
digitised from BGS 1:10,000 geological maps using Microstation. These lines can be
draped onto the DTM in Terrain Analyst.
Erosion Rates
Valentin (1954; 1971) determined the amount of cliff-top recession along the
Holderness Coast by comparison of distances from fixed points depicted on 1:10,560
Ordnance Survey maps published in 1852 and field measurements made in 1952. His
measurements were spaced at approximately 200 metre intervals along the entire coast.
The measurements thus represent average rates of recession averaged over a 100 year
time period. Recession since 1952 may have exceeded 50 metres at some locations. The
grid reference of each measurement given by Valentin represents the intercept between
the cliff-top of 1952 and a line at right angles to it. Each measurement was considered
to represent a value for an orthogonal line from the modern coastline through the grid
references given by Valentin.
Additional orthogonal lines were constructed within Microstation at 10 metre
intervals along the cliff section. These can be assigned values which are intermediate
and in approximate ratio to the values entered from Valentin’s data on either side. By
using the values at this closer spacing, and assuming that the average rate remained
constant with time, a new cliff-top after a given number of years of recession can be
predicted.
Lithological data
Lithological data for each geological formation have been taken from published data
(e.g. Madgett and Catt, 1978) and from field observations. For this study each of the
identified geological formations was given a single average composition. In the future
it is hoped to be able to take account of the lateral variability of the lithological
composition within individual formations by laterally subdividing formations and
assigning different values.
Sea defences
The location of existing sea defences, such as the sea walls, which prevent cliff erosion
at the towns of Withernsea, Hornsea and Bridlington, were digitised in Microstation.
To determine the total volume of sediment potentially yielded by recession of the coast,
the DTM was migrated horizontally landwards by a given amount and the volume
between the DTM and the migrated DTM calculated. The amount of migration can be,
for instance, 1 metre, 10 metres or a distance equivalent to 10 years at the present
Determination and Prediction of Sediment Yields
195
difference in the age of the two profiles. In some areas the height of the cliff has
reduced as the cliff has eroded back.
Geological Boundaries
Boundaries between the geological formations on the land area in plan view were
digitised from BGS 1:10,000 geological maps using Microstation. These lines can be
draped onto the DTM in Terrain Analyst.
Erosion Rates
Valentin (1954; 1971) determined the amount of cliff-top recession along the
Holderness Coast by comparison of distances from fixed points depicted on 1:10,560
Ordnance Survey maps published in 1852 and field measurements made in 1952. His
measurements were spaced at approximately 200 metre intervals along the entire coast.
The measurements thus represent average rates of recession averaged over a 100 year
time period. Recession since 1952 may have exceeded 50 metres at some locations. The
grid reference of each measurement given by Valentin represents the intercept between
the cliff-top of 1952 and a line at right angles to it. Each measurement was considered
to represent a value for an orthogonal line from the modern coastline through the grid
references given by Valentin.
Additional orthogonal lines were constructed within Microstation at 10 metre
intervals along the cliff section. These can be assigned values which are intermediate
and in approximate ratio to the values entered from Valentin’s data on either side. By
using the values at this closer spacing, and assuming that the average rate remained
constant with time, a new cliff-top after a given number of years of recession can be
predicted.
Lithological data
Lithological data for each geological formation have been taken from published data
(e.g. Madgett and Catt, 1978) and from field observations. For this study each of the
identified geological formations was given a single average composition. In the future
it is hoped to be able to take account of the lateral variability of the lithological
composition within individual formations by laterally subdividing formations and
assigning different values.
Sea defences
The location of existing sea defences, such as the sea walls, which prevent cliff erosion
at the towns of Withernsea, Hornsea and Bridlington, were digitised in Microstation.