L. P. Humphries and C. N. Ligdas
174
erosion since changes in bedrock caused by subsidence diminish the role of the beach
as a protective influence on coastal defence. The role of the GIS in this research is not
only to identify spatial patterns and relationships but also to combine, assess and
weight the different factors affecting coastal vulnerability.
Introduction
A long history of coal mining in the Coal Measures seams, underlying the Co. Durham
coastline and extending several hundred meters off-shore, has altered the
geomorphology of the area and left a legacy of despoiled beaches due to the practice of
disposing the colliery spoil directly onto the beaches. At the peak of this activity
(before 1983) over two million tonnes of minestone was disposed annually onto the
beaches.
The three beaches that we chose to examine are Dawdon, Easington and
Horden on the Co. Durham coast of North East England (Fig. 1). All three belong to
the same littoral cell, 1c (Motyka and Brampton, 1993), and they exhibit similar
geological and geomorphological characteristics; cliffed coastline (Magnesian
Limestone cliffs with heavy overburden of boulder clay at the backshore) and sand
beaches containing a high proportion of shales and limestones.
Both the
geomorphology and the geochemistry of the beaches have been largely affected by the
colliery waste. Beaches extend beyond the natural coastline and the sand in most of
them is heavily polluted by coal. Littoral processes are characterised by a moderate
southward drift and tidal currents intensify the southward transport of sand and
colliery waste on the lower beach and on the nearshore sea bed.
Using sedimentary and morphological indices obtained from data collected
between 1991 and 1995, all three beaches have been classified as reflective beaches
(Humphries, 1996) based on the beach stage model by Wright and Short (1983). This
means rather steep beach slopes which are not dissipative of wave action. Cliff
recession in these three beaches seems to proceed at lower rates (0.11 m/yr for
headlands and 0.3 m/yr for cliffs backing the bay) than those observed at beaches north
of Ryhope during the period 1983-1993 (Anon, 1991; Anon, 1993).
Off-shore underground colliery panels have been excavated in roughly 6
seams, ranging from 340 to 465 m depth, over a period of more than 50 years (Table
2). The most recent ones can be seen near the Dawdon area and the northern part of
Easington beach (Fig. 1).
It is probable that subsidence could well have played some part in shaping the
beaches studied here. Calculations conducted by a subsidence engineer from British
Coal have revealed subsidence on the Northumberland coast in the order of one metre
(T. Dixon pers. comm.). On the Co. Durham coastline, the impacts on coastal erosion
of subsidence of this order may have been minimised by the accumulation of colliery
spoil on the beaches.
The aim of this research was to investigate the morphological changes of the
beaches during a 5-year period after the closure of the mines in the area and identify
patterns or anomalies that can be associated to the mining activities and in particular
174
erosion since changes in bedrock caused by subsidence diminish the role of the beach
as a protective influence on coastal defence. The role of the GIS in this research is not
only to identify spatial patterns and relationships but also to combine, assess and
weight the different factors affecting coastal vulnerability.
Introduction
A long history of coal mining in the Coal Measures seams, underlying the Co. Durham
coastline and extending several hundred meters off-shore, has altered the
geomorphology of the area and left a legacy of despoiled beaches due to the practice of
disposing the colliery spoil directly onto the beaches. At the peak of this activity
(before 1983) over two million tonnes of minestone was disposed annually onto the
beaches.
The three beaches that we chose to examine are Dawdon, Easington and
Horden on the Co. Durham coast of North East England (Fig. 1). All three belong to
the same littoral cell, 1c (Motyka and Brampton, 1993), and they exhibit similar
geological and geomorphological characteristics; cliffed coastline (Magnesian
Limestone cliffs with heavy overburden of boulder clay at the backshore) and sand
beaches containing a high proportion of shales and limestones.
Both the
geomorphology and the geochemistry of the beaches have been largely affected by the
colliery waste. Beaches extend beyond the natural coastline and the sand in most of
them is heavily polluted by coal. Littoral processes are characterised by a moderate
southward drift and tidal currents intensify the southward transport of sand and
colliery waste on the lower beach and on the nearshore sea bed.
Using sedimentary and morphological indices obtained from data collected
between 1991 and 1995, all three beaches have been classified as reflective beaches
(Humphries, 1996) based on the beach stage model by Wright and Short (1983). This
means rather steep beach slopes which are not dissipative of wave action. Cliff
recession in these three beaches seems to proceed at lower rates (0.11 m/yr for
headlands and 0.3 m/yr for cliffs backing the bay) than those observed at beaches north
of Ryhope during the period 1983-1993 (Anon, 1991; Anon, 1993).
Off-shore underground colliery panels have been excavated in roughly 6
seams, ranging from 340 to 465 m depth, over a period of more than 50 years (Table
2). The most recent ones can be seen near the Dawdon area and the northern part of
Easington beach (Fig. 1).
It is probable that subsidence could well have played some part in shaping the
beaches studied here. Calculations conducted by a subsidence engineer from British
Coal have revealed subsidence on the Northumberland coast in the order of one metre
(T. Dixon pers. comm.). On the Co. Durham coastline, the impacts on coastal erosion
of subsidence of this order may have been minimised by the accumulation of colliery
spoil on the beaches.
The aim of this research was to investigate the morphological changes of the
beaches during a 5-year period after the closure of the mines in the area and identify
patterns or anomalies that can be associated to the mining activities and in particular