Formulative Influences on the Landscape
Physical Influences
Geology and Landform
A deep chalk bed laid down in the Cretaceous period forms the basic underlying geology of the Test Valley Borough. The Upper Chalk, the youngest of this chalk series, dominates the northern and central part of the Borough. In the north, accompanying the Upper Chalk, limited areas of Middle Chalk are found flanking the valley sides contributing to the more pronounced landform found to the north which includes high chalk ridges dissected by steeply sloping predominantly dry valleys and escarpments. These distinctive dry valleys were formed as part of a river system that evolved immediately after the Ice Ages, when the chalk would have been frozen at a depth and thus impermeable leading to streams of meltwater from the ice sheets. In contrast the central area of the Borough has a gentler undulating landform, although there are a number of small chalk hills and scarps which form distinctive features, such as Quarley Hill, Isle of White Hill and Danebury Hill with scarps at Broughton Down and Ashley Down.
Across this chalk area are localized deposits of Clay with flints, laid down during the interglacial period. The most extensive areas of Clay with flints occur to the south east and south west of Andover, at Ashley Downs and south of Upton to the north of Andover.
Towards the south of the Borough, the chalk stratum dips towards the sea and becomes buried beneath younger deposits of sands, gravels and clays. To the north, these include the deep bands of the Reading Beds and London Clay which due to their comparatively soft sedimentary character have formed a low-lying landform of small hills, ridges and valleys. Further to the south, the landform becomes flatter with the clays and clayer sands of the Bracklesham Beds and the Bagshot Sands which form the flat plateau of the New Forest. Broad bands of alluvium and valley gravels mark the river valleys and extensive area of plateau gravel overlie the sands and clays to the east and west of the Test Valley and Romsey. Other superficial deposits include localised pockets of Brickearth, a river terrace deposit found around Romsey.
Drainage and Hydrology
The River Test is the dominant river system of the Borough, starting east of Overton in the adjacent Borough of Basingstoke and Dean, flowing along a flat valley bottom as a series of braiding streams before forming the head of the Solent at Southampton. Over the central area, the Test River is joined by a number of tributary rivers and streams, principally the Dun, Dever, Anton and Wallop Brook. Winterbournes are a feature of this river system, formed when the water table is high and subsequently running above ground as small streams within the winter months. Towards the south of Michelmersh and Newtown, where, the underlying geology is more permeable, a drainage pattern of surface streams, which include Tanners Brook and the River Blackwater, has evolved feeding into the River Test.
Soils and Agriculture
Soils on the chalk tend to be well drained and calcareous and are typically brown earths on the higher ground to the north and brown rendzinas across the more gentle chalk plain to the south. These soils are good quality Grade 3, with a small number of very localized pockets of Grade 2. Due to their good quality, these soils are intensively farmed, with a range of crops resulting in large open fields. However relief and soil depth are limiting factors with the shallower soils found on the scarp slopes less suitable for cultivation and often wooded, or colonized by scrub or under permanent pasture and used for sheep grazing.
The more complex geology of the southern area of the Borough gives rise to a more mixed pattern of soils and agriculture land value. This area is dominated by stagnogley soils, which comprise seasonally waterlogged fine or coarse loamy soils over clay. These soils support a mix of pasture and arable crops and are classified within this area as mainly Grade 3. However the poor drainage has created further areas which are less productive and are mostly under woodland or wet lowland heath vegetation.
Brown earth soils, which are better quality, are found on the deposits of gravel along the river valleys. This has created soils of agriculture land quality of Grade 2 to the south and north of Romsey within the River Test Valley.
The river valleys are dominated by peaty calcareous mineral soils with high ground water levels. This has resulted in the valley bottoms being mainly under permanent grassland and used for rough grazing with a small amount for arable. These areas of grassland also support semi natural fen, wetland and grassland habitats. At the southern most end of the Test Valley, the valley floor is occupied by alluvial soils that are silty and peaty in character and have been drained to produce a more productive land suitable for cereals and other arable or vegetable crops.