What is a Catchment?
The River Lark Catchment consists of all the named and unnamed waterbodies that flow into the River Lark, together with the landscapes which ‘catch’ their waters, and feed them with underground springs. The Lark depends on groundwater, both from the underlying chalk aquifer, and, in some parts of the catchment, from 'perched' water buried in the clay deposits overlaying the chalk.
A river catchment, sometimes known as a drainage basin, is an area of land from which all water flows into a single river system. It comprises the geographical area that surrounds a river and its tributaries - the land, hills, lakes, ponds and ditches - but also the uses to which that land and those waterbodies are put: arable or animal agriculture; industrial or urban; open country or woodland. When precipitation, such as rain or snow, falls within the catchment, it will eventually end up in the river system either by running over the ground or being absorbed into the ground, and later released.
In this image of the Great Ouse catchment, the Lark catchment, including the catchments of its tributary streams, is shown in red.The Lark Catchment, which covers 650km2 of Suffolk and Cambridgeshire, is thus a sub-catchment of the much larger Great Ouse catchment which covers much of Eastern England.
In order to understand the river, it is essential to understand how the catchment functions, and the network of land uses that make it up. For example, pesticides that are sprayed onto a field of crops may end up in the river, either directly by running overland or through field drainage. Silt entering the river by erosion in one part of the catchment, may be transported down the river to cause problems downstream. The construction of a concrete car park may reduce the infiltration of water into the ground and therefore impact groundwater levels. Concrete impediments to river flows such as weirs, culverts, and staunches may cause puddling of the river, and a lack of dissolved oxygen which is a danger to aquatic life. For all these reasons, the River Lark Catchment Partnership is committed to improving the environment of not just the river itself, but the whole catchment.