Here you will learn about the impacts expected from climate change by the 2050s on groundwater and mine water.
The regional assessment provides an overview of the main issues associated with groundwater resources and mine water outbreak under climate change in the Yorkshire and Humber region. There are some generic risks, such as subsidence, which are assessed primarily at the regional level, along with moderately high-risk, large scale processes, such as groundwater-fed surface flooding from the Chalk aquifer and saline intrusion. Some of the uncertainties associated with the effects of climate change on these factors are also considered. The sub-regional assessment then highlights some key patterns and locations at risk of climate change impacts in more detail. Specific local matters are addressed in the relevant Local Area reports. The principal mine locations across the region are shown below.
Description
Groundwater:
Groundwaters in hydraulic continuity with the surface waters of the Yorkshire and Humber region occur in a range of strata, predominantly:
- Quaternary sands and gravels (near to river channels, in localised pockets scattered throughout the region).
- Coal Measures strata (a cyclic sequence of coal seams interbedded with sandstones, siltstones and mudstones) of Upper Carboniferous age covering much of West Yorkshire and South Yorkshire.
- sandstones of the Millstone Grit Group (of Carboniferous age) primarily in the Pennines in the north of the region and in West Yorkshire
- sandstones and limestones of Lower Carboniferous age within the Yorkshire Dales.
- Magnesian Limestone (dolostones) of Permian age (in a narrow band in the central part of the region).
- the Triassic Sherwood Sandstone aquifer in the centre of the region.
- the Corallian Group and the Ravenscar Group of sandstones and limestones (of Jurassic age) in the north east of the region.
- the Chalk of East Yorkshire and Humberside.
With the exception of the Chalk aquifer in East Yorkshire, which has been the subject of a number of hydrogeological investigations (Elliot et al. 1998, 2001; Salmon et al. 1996; Finch et al. 2007), there is relatively little information available in the open literature on groundwater conditions in most of these strata. Although significant research has been undertaken, leading to the development of conceptual models of all major aquifers, data pertaining to groundwater conditions are sparse in the open literature. The Chalk is an important regional aquifer which has been exploited since the end of the 19th Century, principally to provide water supply to the City of Hull. The Sherwood Sandstone is another principal aquifer which provides part of the water supply to several towns and cities in the region, including Leeds and Doncaster. In the north east of the region, the Corallian Group principal aquifer has also been extensively developed for water supply (Reeves et al. 1978; Carey and Chadha 1998). The Magnesian Limestone is also a principal aquifer and although a major resource further north, in Durham, it is less heavily exploited in Yorkshire and has only been extensively investigated in the area from the River Aire to the River Wharfe (Aldrick 1978). Elsewhere, minor aquifers within the Carboniferous Limestone, Millstone Grit and Coal Measures strata provide domestic, industrial and agricultural water supplies.
Groundwater Resource:
Natural groundwater flows in the Region are important in relation to spring discharges, with many rivers and streams deriving their water from groundwater spring flow. This has important implications for the localised support they offer to ecosystems, such as salmonid spawning habitats. The regional groundwater resources used for domestic, industrial and agricultural supply could feasibly be susceptible to long term reduction, with a lowering of groundwater levels induced by lower recharge rates. Lower recharge may well occur due to reduced annual average rainfall. In addition, the greater concentration of rainfall in intense events is likely to result in an increased ratio of runoff to recharge, leading to further reductions in recharge rates. Nationwide assessments of climate change induced changes to recharge suggest a 5 to 15% reduction overall by the 2020s, but these figures are highly uncertain (UKWIR 2003). Additionally, increasing demand for water abstraction during hotter summers, at the very times of lowest river flow and greatest ecological vulnerability, may lead to further pressures on already strained groundwater resources (Wilby et al. 2006). Overall, it is estimated that the total annual river flow in England and Wales could drop by as much as 10 to15% as a result of lower summer and autumn river flows with a corresponding delay to the start of the recharge season which could affect groundwater storage (Environment Agency 2008). Coastal aquifers may also be subject to increased saline intrusion with sea level rise coupled with lower groundwater levels inducing the migration of saline water further inland.
Groundwater-fed Surface Flooding:
There is at least some possibility that the larger aquifers in the region (especially the Chalk and to a lesser extent the Jurassic and Magnesian Limestones) could give rise to groundwater-fed surface floods under changed climate conditions in the future, as has previously been experienced in Chalk catchments in southern England and northern France (cf Younger 2007, pp 180 - 181). Increased winter rainfall could lead to higher recharge rates and, as a result, increased groundwater levels, with an enhanced risk of flooding in rivers with a strong baseflow component. The Chalk is particularly vulnerable to groundwater-fed surface flooding due to the complexity of its hydraulic properties, with flow through both the matrix and fractures, and its low storage capacity (Finch et al. 2007). Although it should be acknowledged that the Chalk in Yorkshire and Lincolnshire has a low incidence of groundwater-fed surface flood events compared to the Chalk aquifer to the south, increased winter rainfall and higher recharge rates could increase the risk of such flooding. The Jurassic limestones are in close continuity with surface water and show a rapid response to rainfall so could also be vulnerable to groundwater-fed surface flooding. The Triassic sandstones in the region are considered to be less vulnerable to groundwater-fed surface flooding.
Subsidence:
Land subsidence could be locally triggered by lowering of groundwater below historic levels under drought conditions, in those parts of the region where groundwater occurs in partly karstified strata (which includes the limestones of the Yorkshire Dales and to a lesser degree the Magnesian Limestone). Lowering of groundwater levels can remove buoyant support from the roofs of caverns, and / or provide inflow gradients towards caverns entraining overlying sediment, leading to the localised development of sinkholes.
Slope Stability / Spoil Heap Collapse:
Near-channel groundwater is conceptually important in relation to slope stability, particularly where the valley sides are steep. Equally, where spoil associated with former mining is deposited in steep-sided valleys there may be an increased risk of slumping with rapid rises in near-channel groundwater expected with increased frequency of intense rainfall events.
Mine Water:
There are numerous mine water discharges throughout the Yorkshire region. Discharges associated with abandoned coal mines are present along the outcrop of Coal Measures in the west of South Yorkshire and southerly areas of West Yorkshire.
Discharges associated with former metal mining (principally lead & zinc mines) occur across the Yorkshire Dales in the headwaters of the Rivers Swale, Ure, Nidd and Wharfe.
Mine Water Outbreak:
Mine water discharges from abandoned coal mines could be potentially vulnerable to structural instability as a result of intense rainfall events leading to collapse of shallow, near-surface workings and breakout of large volumes of mine water. Rapidly rising groundwater levels prompted by multi-day rainfall events may assist in providing conditions conducive to breakout. There are several examples of this happening in recent years within the region and similar examples from outside the region. Wherever there is a mine water discharge, there could be scope for plugging of adit discharges (with iron-rich precipitates, sediments or larger debris) and subsequent outbreak that could be prompted by intense rainfall events. There remains a large degree of uncertainty as to the precise locations at risk of outbreak, the causal mechanisms in each case and thus prediction remains speculative. Outbreaks do however typically occur at, or in the vicinity of existing discharges (particularly where groundwater rebound is completed in areas of historic mining in areas of Coal Measures outcrop), hence the overview of important mine water discharges provided in the County level summaries. A nationwide Defra-funded study (undertaken by Newcastle University in partnership with The Coal Authority and Atkins) is currently collating and assessing the information on mine water outbreak risk from abandoned non-coal mines such as those in the Yorkshire Dales.
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© Copyright Steve Morgan for Yorkshire Futures, 2008 |
Impacts
Impacts due to declining groundwater levels and increased drought on water resources:
Although abstractions from the Yorkshire Chalk are equivalent to only 7% of the total recharge the aquifer receives (Elliot et al. 1998), the long-term sustainability of the Chalk aquifer has recently been questioned. These concerns relate to the drying up of a number of springs, particularly in the south of the region, mainly due to sustained groundwater abstraction. Indeed, groundwater abstraction has long been considered to be in a state of hydrological imbalance in this southern zone (Elliot et al. 1998). It should be noted, however, that hydrographs produced by the Environment Agency do not support the view of a recent decline in groundwater levels with the loss of springs attributable to the installation of public water supply boreholes in the early 1900’s. Since many rivers and streams derive their water from Chalk groundwater spring flow, reductions in groundwater levels induced by climate change could also have important implications for river flow, particularly in summer. In addition, declining groundwater levels and the loss of spring flow in Chalk catchments could impact salmonid spawning grounds with a reduction in the amount of flow across the hyporheic zone. The Corallian Limestone aquifer in the north east of the region is in close continuity with the River Derwent, which has been seen to lose almost its entire flow to the aquifer during drought, via swallowholes (Carey and Chadha 1998). Local springs and becks are also fed by groundwater discharge from the aquifer. Some potentially sensitive wetlands are also reliant on groundwater flows, examples being the calcareous marsh communities of Millington Wood and Pastures SSSI in the chalk of the Yorkshire Wolds near Pocklington and the spring-fed flush of North Newbald Becksies, a nature reserve south east of Pocklington. A reduction in recharge rate could lead to lower groundwater levels and a decline in river levels which may threaten these resources. A possible risk to groundwater resources due to declining groundwater levels and increased drought is therefore considered in areas underlain by the Chalk and Corallian Limestone aquifers. In the absence of increased artificial abstraction from the other principal regional aquifers (the Magnesian Limestone and the Sherwood Sandstone in the centre of the region), it is unlikely that a change of climate on its own will substantially decrease the groundwater resource or outflows to wetlands and other ecologically sensitive features. The higher storage capacity of these aquifers gives them a buffering effect which is the reason that groundwaters, in general, are likely to be relatively robust in the face of climate change compared with surface water. Overall impacts on groundwater resources in areas not underlain by the Chalk and Corallian Limestone aquifers are considered small.
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© Peter Roworth / Natural England |
Impacts due to groundwater-fed surface floods:
The unprecedented high rainfall during the summer of 2007 led to concerns of possible groundwater-fed surface flooding from the Chalk aquifer of Yorkshire and Lincolnshire over the winter of 2007/08 even with average winter rainfall (Finch et al. 2007). The subsequent dry autumn relieved such fears but increased winter rainfall and higher short-term recharge rates associated with climate change means there is a possible risk of groundwater-fed surface floods from the Chalk aquifer in the region. Such floods have previously been observed in Chalk catchments in southern England and northern France (Younger 2007) but the underlying geological conditions in Yorkshire make flooding less likely. The Corallian Limestone is typically in continuity with surface water and shows a rapid response to rainfall. Therefore, there is also a possible risk of groundwater-fed surface floods from the Corallian Limestone aquifer in the region. The Sherwood Sandstone aquifer is not considered to be at risk from groundwater-fed surface flooding since it is slower responding than the Chalk and Corallian Limestone aquifers. Similarly, on the basis of current conceptual models of groundwater-derived surface flooding, the unsaturated zone drainage behaviour of the Magnesian Limestone aquifer is such that it is unlikely to support the kind of supra- water table storage processes which are considered responsible for the sudden rise in the water table over a wide area which is necessary to generate this type of flood (cf Younger 2007, pp 180 – 181). In terms of impacts due to temporary increases in groundwater head in the Sherwood Sandstone and Magnesian Limestone aquifers, risks of groundwater-fed surface flooding are considered negligible in these areas.
Impacts due to rising sea levels prompting saline intrusion:
In fractured aquifers, such as the Chalk, saline intrusion can be rapid along individual fractures and extend inland for considerable distances. Historical over-abstraction of the Chalk in the Hull area has induced saline intrusion from the Humber Estuary. The usable body of fresh groundwater is limited by the presence of saline water, although much of the saline water in the aquifer is considered to be natural in origin, being relict features of past saline water ingress during ancient higher sea level stands (Elliot et al. 2001). The problem has been overcome along the south bank of the Humber Estuary by using groundwater and surface water in conjunction, with each source used at different times of the year according to its availability. A management strategy is also in place to constrain groundwater abstraction licences during periods of drought. The results of salinity surveys suggest that the saline front is at least stable if not retreating towards the Humber shore. Given these results and the current management of the resource, saline intrusion impacts are considered negligible at current abstraction rates.
Impacts due to declining groundwater levels on subsidence:
Increasing subsidence risk during drought is not considered an important risk in relation to the Permian aquifer in the centre of the region, though analogy with similar systems elsewhere (e.g. Younger 2007, pp 178 – 180) suggests that localised instances cannot be ruled out in the more extensively-karstified, higher topographic relief circulation systems in the Carboniferous Limestones of the Yorkshire Dales. However, most of the vulnerable zones are in sparsely populated areas and therefore likely to not be of severe impact.
Impacts due to temporary increases in groundwater head in close proximity to stream / river banks:
Slope stability has previously been found to be sensitive to localised increases in groundwater head where local sand and gravel lenses within the Quaternary deposits discharge groundwater to the surface on steep ground. It is likely that the incidence of this process will increase in the event of periods of intense rainfall, given the localised nature of recharge to these lenses and the possibility for saturation from above adding to that already arising from below. Therefore, localised exacerbation of natural slope failure processes cannot be ruled out under future climate scenarios. All spoil heaps (and the few former tailings / finings ponds) in close proximity to inhabited areas in the Region have long since been stabilised by local authority reclamation programmes implemented with great care in the 1970s and 1980s, in the wake of the Aberfan disaster in South Wales (Oct 21 1966). Risks associated with these spoil heaps are therefore considered vanishingly small, at least as long as current inspection and maintenance regimes are sustained. Some risks relate to relatively remote localities across the orefields of the Yorkshire Pennines where exposed spoil lies on steep valley sides. However, given the lack of documented examples of spoil heap failure in the areas (to the authors knowledge), and the sparse population in these areas, the risk of spoil heap slumping must be viewed as moderately low given the timescales (decades to centuries) in which much of the spoil has been in place in these upland locations. An associated mining-related contamination problem that could be affected by climate change is the distribution of sediment-bound contaminants in heavily mined river basins. There has been extensive assessment of the processes of delivery, re-working and deposition of contaminated fluvial sediments from source mining areas (and associated mineral processing sites) down through river basins (e.g. Macklin et al. 1997; 2006). Large areas of floodplain in the Swale and wider Ouse basin are contaminated with high concentrations of lead (amongst other metals) from mining-age sediments (although whether such contamination causes any major impacts on grazing cattle is unclear). Whether climate change will have a derogatory impact (e.g. through increasing delivery of contaminated sediments from spoil heaps or greater re-working of previously deposited metal-rich fluvial sediments) or play a potentially beneficial role (e.g. through greater delivery of uncontaminated sediments to dilute the instream contamination) is also unclear.
Mine water outbreak:
Recent examples of coal mine water outbreak in the region have occurred at Sheephouse Wood (near Stocksbridge, South Yorkshire) and Jackson Bridge (near Holmfirth, South Yorkshire). While outburst of mine water can be prompted by hydrogeological phenomenon such as adit plugging or workings collapse (which appeared to be the case at Sheephouse Wood), outbreak events have been recorded at Jackson Bridge and similar sites outside of the region following intense multi-day rainfall events. Given the predictions for increased frequency of multi-day rainfall events there is a chance that there will be a slight increase in the number of mine water outbreak events from those currently occurring.
These outbreaks have the potential to cause damage to infrastructure (pictured) and significant pollution to recipient water courses. The most likely locations for these are at discharges from shallower workings, for example where Coal Measures strata were worked near the ground surface in South Yorkshire from south of Sheffield up to Wakefield . Here, mine water flow rates can be more variable and workings are more susceptible to ingress of surface waters, which is conducive to breakout.
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Outbreak of coal mine water at Sheephouse Wood on the 28th February 2002 showing impact on A616 [Photo courtesy of IMC Consulting Engineers] |
Widespread pumping operations are being undertaken in the region by the Coal Authority to prevent upward migration of contaminated mine waters to the surface and overlying Permian strata (sandstone) to the east of the outcrop (and for operational deep-mining purposes at Maltby by Hargreaves). Coal Authority pumping operations are planned to be expanded in some parts of the region, while existing pumping schemes may require greater capacity. For example the combined pumping operations at Caphouse (at the National Coal Mining Museum south-west of Wakefield) and Wooley (south of Wakefield) limit upward migration and potential outbreak of coal mine water in the south of West Yorkshire. Increased pumping capacity has been required at Caphouse in recent years (with a reduction of required pumping rate at Wooley) due to changes in groundwater circulation in large interconnected mine voids (thought to be due to some underground collapse in the workings: i.e. not connected to climate change). This has however been exacerbated by the flashiness of the Coal Measures near Caphouse on the outcrop which leads to a larger volume of poor quality groundwater requiring pumping and treatment (through chemical dosing) prior to surface discharge, particularly after intense, multi-day rainfall episodes. Increased flows at this location and incidence of extreme rainfall events could therefore lead to a greater cost burden for treatment in future years.
Information on outbreak risk for metal mine discharges in the Yorkshire Dales is sparse, however an identified yet unquantified risk of outbreak is suspected by local Environment Agency staff for some of the metal mining areas in the headwaters of the rivers Nidd, Wharfe and Swale. The worked mineral veins are associated with karstified Carboniferous limestone which has been documented to be susceptible to ingress of surface waters and subsequent breakout on occasions in the adjacent north–east region (e.g. Rispey mine and Bolt’s Burn Level on the Rookhope Burn in Weardale, County Durham).
| North Yorkshire | West Yorkshire | Humber | South Yorkshire |
Description
Important groundwater units within North Yorkshire include:
- Quaternary sands and gravels are locally important in sustaining ecologically significant flows to rivers and wetlands.
- The Corallian Limestone aquifer is of importance for abstractions and of significance for sustaining river baseflows.
- The Sherwood Sandstone is an important aquifer for public, agricultural and industrial water supplies.
- The Magnesian Limestone supports some domestic and agricultural water supplies.
- The Carboniferous limestones and sandstones of the Yorkshire Dales support localised abstractions and are of importance for sustaining river baseflows.
- The Millstone Grit supports localised abstractions in the west of the County.
- The Ravenscar group (Jurassic sandstones and limestones) in the east of the County supports some isolated groundwater abstractions.
Major mine water discharges in North Yorkshire are associated with metal mine drainage from the Yorkshire Pennine Lead-Zinc Orefield (principally into the headwaters of the Rivers Swale, Nidd and Wharfe). In the River Swale the main mine pollution issues are in the Barney Brook, Hard Level Gill, Gunnerside Gill and Arkengarthdale subcatchments. In the River Nidd and tributaries (Ashfold Side Gill) mining-related pollution is associated with the former lead mines of Properous & Providence, Murrayfield, Scarhouse, Cockhill / Gillfiel and Greenhow Gill. In Upper Wharfedale, former lead mines are located at Grassington, Hebden Moor and Gill Heads which drain into the Hebden Beck, Fir Beck and Blands Beck.
The principal vulnerabilities are related to:
- The groundwater resource (namely the Sherwood Sandstone and Corallian Limestone) should recharge rates be reduced under climate change. This could have implications for groundwater abstractions and flows to wetlands.
- Subsidence exacerbated by drought conditions and slope stability compromised by increased intense rainfall events.
- Metal mine water outbreak from increased multi-day rainfall events.
- Increased slumping of metal-rich spoil heaps or re-working of mining-age fluvial sediments may lead to greater fluxes of metal contaminants emanating from headwater areas.
Impacts
The Sherwood Sandstone aquifer is unlikely to be impacted over coming decades by climate change impacts at current abstraction rates since it has a high storage capacity. The Corallian Limestone aquifer, on the other hand, is in continuity with the River Derwent which is a key factor in controlling the groundwater regime and in maintaining a water balance for the aquifer. Although the rate of leakage varies seasonally, in dry periods the entire river can be lost to the aquifer. This leakage is equivalent, on average, to over 90% of the abstraction from the aquifer (Carey and Chadha 1998). Clearly, declining groundwater levels and increased drought could exacerbate this problem and pose a possible risk to the resource. In addition, the bulk of groundwater discharge from the aquifer takes place via spring flow. A reduction in groundwater levels could therefore also impact on ecological flows.
There is at least a possibility that subsidence could be exacerbated by lowering of groundwater head under drought conditions particularly in karstified limestones of the Yorkshire Dales, although this area is sparsely populated so the risk is considered to be negligible. Lowering of groundwater levels can remove buoyant support from the roofs of caverns, and / or provide inflow gradients towards caverns entraining overlying sediment, leading to the localised development of sinkholes in gypsum terrains. Subsidence associated with dissolution of gypsiferous strata (within the Permian Magnesian Limestone) has been documented in and around the city of Ripon (Cooper 1986). While lowering of groundwater head can promote subsidence, high rates of groundwater flow can increase the rate of gypsum dissolution. A documented example of high water flow resulting in almost complete dissolution of gypsum, and subsequent subsidence, is at Snape Mires, near Bedale.
Mine water outbreak from shallow unstable workings could be intensified by increased frequency of multi-day rainfall events. Local EA staff consider there to be an identified but unquantified generic risk of outbreak in the Swale, Nidd and Wharfe headwaters. These areas are however sparsely populated and impacts would relate primarily to pollution episodes. Given these are likely to occur during high flow events the dilution effects should limit instream concentrations and the principal concern would relate to the fate of sediment-bound contaminants in the river basin.
Should there be an increase in contaminant flux from headwater areas, there would likely be increased deposition of sediment-bound contaminants in downstream floodplain areas. This could potentially be of impact on biota and land use (e.g. grazing cattle).
Description
Important groundwater units within West Yorkshire include:
- Quaternary sands and gravels which are locally important in relation to slope stability.
- Coal Measures strata – of very localised importance for industrial abstractions.
- The Permian Magnesian Limestone supports some industrial abstractions
- The Millstone Grit provides public water supply at several locations in the west of the County
Major mine water discharges in West Yorkshire are associated with drainage from Carboniferous Coal Measures in the west and south of the county. Major discharges that are ranked amongst the top 100 on the Coal Authority’s national priority list for remediation occur along the Coal Measures outcrop at Clough Foot and Craggs Moor on the far western margin of the county on the Pennine Lower Coal Measures outcrop and at Alexandra Drift, Shopley Dyke and Jackson Bridge to the south of the county on the Pennine Middle Coal Measures outcrop.
The principal vulnerabilities are related to:
- Groundwater resources (namely the Permian aquifer and Millstone Grit) being compromised by reduced recharge.
- Slope failure being exacerbated by increased intense rainfall events.
- Coal mine water outbreak from increased multi-day rainfall events.
- Increased pumping burden due to heightened risk of ingress into workings
Impacts
Water levels in the Permian aquifer and Millstone Grit are unlikely to be compromised by slight reductions in recharge at current abstraction rates.
There is at least a chance of slope failure being exacerbated by rapid rise in groundwater head in sands and gravels. Locations for this are likely to be along deeply incised valleys.
Mine water outbreak from shallow unstable workings could be intensified by increased frequency of multi-day rainfall events. The Jackson Bridge discharge near Holmfirth in the Jackson Bridge Dyke catchment has experienced several such blow-out events in the past decade. These have caused a short term release of large volumes of metal contaminants (principally iron and manganese). Similar coal mine water discharges on the outcrop may be susceptible to adit plugging and rapid ingress of water conducive to breakout. The latter process could be exacerbated by the weather patterns predicted under climate change.
Pumping and treatment costs for the Coal Authority at the Caphouse pumping station may increase due to: (1) the trend in increased pumping requirement at the Caphouse part of the Caphouse-Wooley pumping system that is occurring irrespective of climate change; and (2) the susceptibility of the Caphouse system to ingress after heavy rainfall, which may well be exacerbated by increased incidence of multi-day rainfall events.
Description
Important groundwater units in the Humber area include:
- The Chalk aquifer is an important regional aquifer and supports many public water supply abstractions as well as supporting industrial and agricultural supplies
- Quaternary sands and gravels are locally important in relation to groundwater-surface water interaction.
- The Triassic Sherwood Sandstone aquifer supports numerous industrial and agricultural abstractions.
The principal vulnerabilities are related to:
- Groundwater resources (namely the Chalk aquifer) being compromised by reduced recharge.
- Groundwater-fed surface flooding from the Chalk aquifer.
- Saline intrusion into the Chalk aquifer
Impacts
The Chalk aquifer is an important regional aquifer but concerns have recently been made over its long-term sustainability. While many major Chalk-fed artesian springs still flow in the northern half of the region, particularly around Great Driffield with winter discharges of as much as 1m3/s acting as the source of the River Hull, over the last century most of the springs between Beverley and Hull have dried up, mainly due to sustained groundwater abstraction at Cottingham since the 1930s (Elliot et al. 1998). Indeed, in this southern zone groundwater abstraction has long been considered to be in a state of hydrological imbalance, as evidenced by Arnell and Delaney (2006) who noted that water resources availability in summer is at risk due to the unsustainable or unacceptable abstraction regime south of the Humber. It should be noted, however, that hydrographs produced by the Environment Agency do not support the view of a recent decline in groundwater levels with the loss of springs attributable to the installation of public water supply boreholes in the early 1900’s. The Chalk is particularly susceptible to changes in groundwater levels since it is a high transmissivity and low storage aquifer. Since many rivers and streams derive their water from Chalk groundwater spring flow (85% of the headwaters of the River Hull derive their water from the Chalk groundwater spring flow), reductions in groundwater levels induced by climate change will not only threaten the groundwater resource but could also have important implications for river flow, particularly in summer. The chalk aquifer also supports some potentially sensitive flush and wetland habitat which could be threatened by reduced groundwater outflows. Examples of these include the calcareous marsh communities of Millington Wood and Pastures SSSI in the chalk of the Yorkshire Wolds near Pocklington and the spring-fed flush of North Newbald Becksies, a nature reserve south east of Pocklington.
In the absence of increased artificial abstraction from the Sherwood Sandstone aquifer, it is unlikely that a change of climate on its own will substantially decrease the groundwater resource or outflows to ecologically sensitive features. The Sherwood Sandstone has a higher storage capacity than the Chalk so is less susceptible to changes in groundwater levels. Additionally, the Sherwood Sandstone is confined by the Mercia Mudstone Group in much of the Humber Region so is likely to be less sensitive to potential slight falls in recharge and increased drought periods.
The Chalk in Yorkshire and Lincolnshire has a low incidence of groundwater-fed surface flood events compared to the Chalk aquifer to the south but nevertheless the high rainfall during the summer of 2007 led to concerns of possible groundwater-fed surface flooding (Finch et al. 2007). Although the subsequent dry autumn allowed groundwater levels to recover, the potential for future flooding given the predicted increased winter rainfall induced by climate change poses a possible risk. A similar event occurred during the UK floods of 2000 / 2001 when groundwater replenishment exceeded 300% of the long-term average in Yorkshire (Marsh and Dale 2002). Groundwater levels in the Chalk rose by some 17.3m compared to a mean annual range of 8.7m. The East Yorkshire Chalk is potentially vulnerable to groundwater-fed surface flooding due to the complexity of its hydraulic properties, particularly dual permeability through the matrix and fractures and its low storage capacity.
Historical over-abstraction of the Chalk aquifer in the Hull area has contributed to the intrusion of saline water from the Humber estuary. Moderately saline or brackish waters are also associated with the area around Flamborough Head in the north of the region, a small pocket around Meaux Abbey, the area around Atwick and a broad area towards Spurn Head, as well as to the south of the Humber estuary in the area around Grimsby. Further reductions in groundwater level and increased drought could exacerbate this problem, although during a period of extreme regional groundwater fluctuation from August 1976 to April 1977, following drought, exceptionally low groundwater levels (over 10m below sea level) were observed in the Hull area but this did not induce further saline intrusion on a large scale suggesting that only a limited hydraulic conductivity now exists between the estuary and the Chalk aquifer (Elliot et al. 1998). A later salinity survey (1986) suggested that the saline front is at least stable if not retreating towards the Humber shore. Under the Environment Agency’s Catchment Abstraction Management Strategy (CAMS), abstraction licences in the Hull and Grimsby areas are constrained under drought conditions to manage saline intrusion and to help minimise environmental impacts at low flows. This has seen a reduction in the salinity levels in these areas. Given the current management of the problem, saline intrusion impacts to the Chalk aquifer are considered negligible at current abstraction rates.
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Description
Important groundwater units within South Yorkshire include:
- The Sherwood Sandstone aquifer is an important resource for public water supply, particularly in the Doncaster area
- Carboniferous Coal Measures strata are of localised importance for abstractions.
- The Permian Magnesian Limestone supports several industrial and agricultural abstractions
- Quaternary sands and gravels are locally important in relation to slope stability and groundwater-surface water interaction.
- The Millstone Grit in the west of the County supports some localised industrial abstractions
Major mine water discharges in South Yorkshire are associated with drainage from Carboniferous Coal Measures in the western areas of the county from south of Sheffield, stretching to the north along the outcrop to Barnsley. Major discharges that are ranked amongst the top 100 on the Coal Authority’s national priority list for remediation occur at Silkstone (near Barnsley), Bullhouse and Cranberry Holes Dyke (both near Langsett), Sheephouse Wood (near Stocksbridge), Claywheels Lane, Loxley Bottom (both north east Sheffield) and Limb Brook (south of Sheffield).
The principal vulnerabilities are related to:
- Groundwater resources (namely the Sherwood Sandstone aquifer) being compromised by reduced recharge.
- Slope failure being exacerbated by increased intense rainfall events.
- Coal mine water outbreak from increased multi-day rainfall events.
Impacts
Water levels in the Sherwood Sandstone aquifer are unlikely to be compromised by slight reductions in recharge at current abstraction rates since the aquifer has a high storage capacity.
There is at least a chance of slope failure being exacerbated by rapid rise in groundwater head in sands and gravels.
Mine water outbreak from shallow unstable workings could be intensified by increased frequency of multi-day rainfall events. The Sheephouse Wood discharge near Stocksbridge provides one of the best examples of such mine water outbreak events in the UK. In February 2002, a sudden outburst of contaminated water occurred from Sheephouse Wood into the Little Don River, presumably the result of water building up behind a temporary blockage in the adit, and resulted in a section of the A616 being destroyed, and then temporarily closed for repairs. Similar mine water discharges on the Coal Measures outcrop in the county may be at heightened risk of outbreak under climate change.
