JBA Consulting
The River Skerne in County Durham currently faces a range of
issues in its upper and middle reaches which contribute to a
Water Framework Directive (WFD) classification of Poor to
Moderate. This is reflected in several ecological failures and
water quality impacts. The project aimed to investigate the
degree of connectivity between groundwater and surface water,
to identify where this may result in gaining or losing flows in the
River Skerne and how this may contribute to ecological and/or
water quality impacts.
One aspect which the study sought to address was any potential
link between poor surface water quality and historic coal mining
activities. Following closure of the last collieries in the South
Durham Coalfield groundwater levels have risen in the
abandoned mine workings and the overlying Magnesian
Limestone Aquifer. Upward flow of mine water from the
abandoned mine workings has been thought to affect water
quality in the River Skerne, as it is underlain by the Magnesian
Limestone and there are reaches where groundwater from the
aquifer discharges into the Skerne.
Challenge
Assessing the Impact of Historic Coal Mining on Surface Water Quality
Location: County Durham
Solution
Our investigation commenced with a detailed review of a wide range of
background information including previous hydrogeological reports,
mine abandonment plans and water level and chemistry data. This
data was used to develop a good understanding of the Skerne
catchment and historic mining activities which had taken place in the
South Durham Coalfield. More specifically, historic mining activities in
the area to the south of the Butterknowle Fault, which acts to separate
the local mining block from other areas of the coalfield where mine
water levels are currently managed through pumping by the Coal
Authority.
We developed a conceptual hydrogeological model to define distinct
river reach types and the following tasks were subsequently
undertaken:
- Detailed review of high-resolution geological mapping data to identify
the thickness of superficial deposits overlying the aquifer and
determining depths to groundwater along the river.
- Flow gauging across the catchment targeting areas of
geological/hydrogeological changes where it was thought that
groundwater was discharging into the river.
Client: Environment Agency
Skerne catchment showing the WFD-defined sub-catchments which
form the study area
Conceptual understanding of Skerne river reaches