The Test & Itchen Catchment


Overview

The Test & Itchen catchment drains approximately 1,760 square kilometres of land, in the county of Hampshire, with both rivers rising from springs on the chalk downs at their respective sources near Ashe and Hinton Ampner, before flowing through predominantly rural parts of the county, until they reach a shared estuary in Southampton Water.

Geology and soils

The geology of the catchment is dominated by chalk which covers 80% to 90% of the catchment, and comprises large, mostly unconfined, aquifers that provide the majority of flow to both rivers, as well as providing drinking water for the catchment and the surrounding area. The chalk downland in the upper catchment is covered mainly by shallow, well-drained, calcareous, flinty and silty soils.

In contrast, in the lower parts of the catchment, the Rivers Dun, Blackwater, and Lower Test, and the Bow Lake, and Lower Itchen, flow over tertiary clay geology where soils are more prone to structural degradation.

Land use

The Test and Itchen is a largely rural catchment and the majority of land, approximately 1,100 sq km or 62%, is used for farming.

The main agricultural activity, accounting for 80% of agricultural land, is arable farming and includes the production of wheat, barley, oats and oil seed rape. There are also a number of mixed farming and livestock enterprises, most of which are concentrated in the lower catchment and the river valleys.

The river valleys are also home to the watercress industry, which relies on plentiful supplies of high quality spring water for its watercress growing operations.

Population

The main centres of population within the catchment are Southampton, Andover, Winchester, Eastleigh and Romsey. The catchment population is approximately 725,000 (2011 Census) with the highest population densities in Southampton, which creates significant pressure on water resources and increased levels of pollution entering the Southampton Water.

Environment and landscape features

In terms of both landscape and biodiversity, the catchment contains a number of sites of local, national and international importance, with a diverse range of habitats supporting a rich variety of species.

To the east, a substantial part of the upper Itchen catchment is included in the South Downs National Park and similarly, most of the Bourne Rivulet catchment and part of the upper Test catchment is within the North Wessex Downs Area of Outstanding Natural Beauty (AONB). The river valleys themselves also attract a number of statutory designations that reflect the importance of their unique chalk river systems and the diversity of species they support. Significant portions of each of the Test and Itchen Rivers are designated as a Site of Special Scientific Interest (SSSI), as well as large swathes of the floodplain. In addition, the River Itchen is also designated as a Special Area of Conservation (SAC) under the EC Habitats Directive, recognising the international importance of chalk river habitat and the species it supports.

The current configuration of the river is the result of re-engineering for land drainage, water mills, water meadows and navigation over a long period of time. These functions have long gone, as has the associated income that paid for the maintenance of the complex river system, which is now semi-derelict in parts.

There are many relict weirs and control structures along the river and several reaches where the already modest gradient was removed to maintain a head of water to power waterwheels or to spill water into the meadows. These man-made features are part of our industrial and agricultural heritage but can be in conflict with aspirations for a fast-flowing, silt-free river.

Please visit the Test & Itchen Catchment Partnership website to find out more.

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