BGS karst report series : J1 karst in the Jurassic Limestone Corallian Group of Northern England

Maurice, L.; Mathewson, E.; Farrant, A.R.. 2022 BGS karst report series : J1 karst in the Jurassic Limestone Corallian Group of Northern England. Nottingham, UK, British Geological Survey, 72pp. (OR/22/009) (Unpublished)

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This report documents the evidence for karst and rapid groundwater flow in the Jurassic Corallian limestones of Northern England. It is part of the BGS karst report series on those karst aquifers in England in which cave development is limited – principally the Upper Cretaceous Chalk and the Jurassic and Permian limestones. This area represents something of an anomaly in the Jurassic limestones as there is evidence of extensive cave development. The series is the main output of the NERC funded Knowledge Exchange fellowship “Karst knowledge exchange to improve protection of groundwater resources”. The term “karst” applies to rocks that are soluble. In classic karst there are extensive caves and large scale surface karst landforms such as dolines, shafts, stream/river sinks, and springs. In the past, the Chalk and the Jurassic and Permian limestones of England were not considered karstic because they have limited cave development, and because karst features are usually small and have not been well documented. These reports provide data and information on karst in each area. Karst data are compiled from the British Geological Survey databases on karst, springs, and transmissivity; reports and peer reviewed papers; from geological mapping; and through knowledge exchange with the Environment Agency, universities, water companies, consultants and cavers. This report shows that the Jurassic Corallian limestones of Northern England are highly karstic. Although cave development is not as extensive as in the Carboniferous limestones of the Yorkshire Dales, the discovery of the Excalibur Pot cave system in the North York Moors in 2007 demonstrated that large and extensive caves can form in the Corallian limestones. This cave system is now more than 3.8 km long, and there are several other karstic caves recorded in the J1 Jurassic limestone area. There are many large river sinks, with eight major rivers that lose water as they cross the Corallian outcrop. The Forge Valley swallow holes on the River Derwent are particularly substantial, providing point recharge of more than 375 l.s-1. There are several hundred springs recorded in the area, but there is little information on their discharge. At least 15 have very substantial flows, many of them more than 100 l.s-1. There are no records of dolines or dissolution pipes in the area, although some surface depressions above known caves are thought to be karst dolines. Records of karst features are not well developed in this area, and it is recommended that further work be done to develop improved karst datasets. Most tracer testing studies in the area have focused on the Forge Valley swallow holes, and consequently this karst system is very well characterised, with tests demonstrating rapid groundwater flows to multiple outlets spread over a wide area to the south and west of the swallow holes (Foley et al., 2012). Groundwater velocities based on time to peak concentration ranged from 18 to 13000 m/day over distances of between 18 and 7250 m. These tests demonstrate that borehole abstractions in the area have a high degree of connectivity with the main karst systems fed by swallow holes. The groundwater supply Source Protection Zones (SPZs) in this area have been modified, with the development of a bespoke approach to SPZ delineation reflecting the highly karstic nature of the aquifer, and the results of the tracer tests from the Forge Valley swallow holes. In areas away from the River Derwent there has not been much tracer testing. Tests have been conducted to investigate the Excalibur Pot cave system fed by stream sinks on the Hutton Beck, proving velocities of thousands of metres per day; and tracer tests from boreholes have demonstrated rapid flows of hundreds of metres per day to springs at Brompton and Keld Head. Hydrogeological studies in the area provide further evidence of karst and demonstrate that the karst impacts on boreholes. Transmissivity is variable, but there are some sites with very high transmissivities and/or yields indicating connectivity with extensive karstic networks. Borehole logging studies have demonstrated that flows to boreholes are via a small number of high yielding karstic fissures. Overall, there is clear evidence of karstic systems in the Jurassic limestones in this area, which are comparable to those in highly karstic aquifers, with a high proportion of rapid recharge at some groundwater outlets. Consideration of karst is important for all aspects of hydrogeology and aquifer management in this area. Further work is recommended to develop better karst datasets and investigate local karstic networks.

Item Type: Publication - Report
Funders/Sponsors: British Geological Survey
Additional Information. Not used in RCUK Gateway to Research.: This item has been internally reviewed, but not externally peer-reviewed.
Additional Keywords: GroundwaterBGS, Groundwater
Date made live: 16 Sep 2022 13:08 +0 (UTC)

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