Priory Park lies near the centre of Great Malvern on the sloping ground of the lower parts of the Malvern Hills. It is about 250m from the A449 main road through the town and 35m lower in altitude. This is significant geologically because the road closely follows the great discontinuity between the very hard igneous rock of the high hills and the much weaker, more easily eroded rocks to the east of the boundary. These weaker rocks underlie the built-up parts of the town and the Severn Valley.
On the lower slopes of the Hills and to some distance into the valley, the ground is covered by a layer of rocks and clay from the erosion of the igneous rocks higher up. The erosion and downhill movement occurred mostly in and just after the Ice Age which ended about 8000 years ago. Underlying this layer of rubble is the solid bedrock which is here about 250 million years old and hundreds of metres thick. This ‘Mercia Mudstone’ is impervious to water and is red in colour because it contains compounds of iron. In continuous contact with water it becomes muddy clay.
The thickness of the rubble layer is generally unknown but ranges from zero to tens of metres. It may vary a lot over quite short distances depending on the form of the mudstone bedrock surface underground, even if the ground upper surface is smooth. The thickness may be ascertained if any excavation is deep enough to reach the mudstone. I am not aware of any information of this sort for Priory Park or its vicinity but it may exist in building site records.
There are two apparent water sources in Priory Park. One of them supplies the Swan Pool at its northern end. This outlet is supplied from springs on the Hills (ref.1, page 126) so is irrelevant to the hydrology of the Park. This source was probably installed by the monks.
The second water source feeds the small stream at the south end of the park. While the source and stream could well be just decorative features supplied artificially from a spring on the Hills, this is apparently not the case (ref. 1, page 135). In addition to the stream source, this area of the park occasionally exhibits damp patches and probably receives hill water by way of a natural underground channel. Water sources arising out of the layer of superficial rubble which lies around the Hills are not common but a few occur at locations where the rubble layer is very thin or non-existent (from mapping by the British Geological Survey).
Such channels could have formed at the end of the Ice Age before the rubble and mud became relatively consolidated as they are today. Water running from the hillside swept out mud from its path and flowed at the base of the rubble on the surface of the impermeable bedrock. A mud and rubble layer above the channel formed the ground surface but the channel below was kept clear by the water flow. The channel would form a spring where the rubble layer became very thin and the channel emerged at the surface. Such channels are known to exist in valleys on the Hills and seem likely to occur also on the lower ground.
This idea is strengthened by the occurrence of the Chalybeate Spring in Spa Cottage, just outside the park in Priory Road (ref.1, page 124 and ref. 2, page 152). This spring is first known from a 1744 map. The name refers to the high content of iron compounds in the water, very probably gained from the underground contact with the iron-rich bedrock and confirming the non-artificial nature of the spring.
It is perhaps surprising that such an underground channel has not been disrupted during construction of the large buildings higher on the hill but, for this part of the park there are relatively few such buildings directly above. In addition, in this part of Malvern a band of permeable sandstone rests against the igneous rock of the Hills (roughly along the line of the Worcester Road) and this probably carries some of the hill water to a lower level, beneath the buildings, before it emerges in the suggested underground stream. It is further surprising that the construction of the Swan Pool did not destroy the flow to the Chalybeate Spring but such must be the case.
The park stream and the Chalybeate Spring were initially the headwaters of the Pool Brook which now flows mostly in pipes to the area of the sewage farm before proceeding to near Upton-on-Severn where it joins the River Severn.
Priory Park, like most of Malvern, is on a layer of material eroded from the Hills mostly in the Ice Age. This layer is of unknown thickness but the emergence of ground water in the south of the park indicates that the layer there is quite thin.
- ‘Celebrated Springs of the Malvern Hills’ by Bruce Osborne and Cora Weaver (Phillimore & Co., Andover) 2012
- ‘Aquae Malvernensis’ by Cora Weaver and Bruce Osborne, 1994
By John Payne