Properties of minor aquifers within the Thames Basin

Map showing the distribution of minor aquifers outcrop in the Thames Basin

In addition to the principle aquifers of the Thames Basin, several minor aquifers are present.

These aquifers are not significant in terms of water resources but they are locally important and may support unique ecological habitats.

The minor aquifers of the Thames Basin are shown on the hydrostratigraphy table.

Additional information about some of the more well-known minor aquifers is provided below.




Corallian Group

Section of Corallian Group exposed in a quarry

The Corallian Group forms a south-west to north-east trending limestone ridge between Swindon in the south-west and Aylesbury in the north-east.

The Corallian deposits form a multi-layered minor aquifer with a highly variable lithology comprising limestones, sandstones and mudstones.

Aquifer porosity and borehole yields are also highly variable. The contrast in permeability resulting from the varied lithology gives rise to considerable spring flow and perched water tables.

Groundwater from the Corallian in the Thames Basin supports unique and ecologically important habitats such as saline springs in the Ock valley and calcareous fen near Marcham.

Upper Greensand Formation

Sand and gravel-pit in the Cotswold Water Park

The Upper Greensand Formation is comprised of both poorly consolidated and cemented sands and is separated from the Lower Greensand Formation by the Gault Clay.

The Upper Greensand Formation is frequently in hydraulic continuity with the overlying Chalk aquifer and the two units behave as one.

Springs which issue from the base of the Upper Greensand are thought to derive from Chalk groundwater regionally.

There are places within the Thames Basin however where marls at the base of the Lower Chalk keep the Chalk and the Upper Greensand separate.

River terrace deposits

There is an extensive covering of river terrace deposits within the Thames Basin associated with the River Thames itself and the rivers Kennet, Ock and Lee.

The large number of sand and gravel quarries within the Thames Valley is a reflection of the economic importance of these deposits to the aggregate industry.

The river terrace deposits are also of hydrogeological importance; with high porosity and high permeability the sand and gravel deposits provide a large storage volume within flood plains.

The distribution of this storage has a particular bearing on river flow characteristics and bank storage with implications for drought and flood resilience and river-aquifer nutrient exchange.

BGS projects about minor aquifers in the Thames Basin


Contact Stephanie Bricker for further information