Catchment Area

The catchment area (also refered to as the drainage basin) is the area from which water flows into the River Calder. Its eastern limit is the point at which the river joins the River Aire. Westward water collects from high moorland and is channeled through a network of streams into the major tributaries of the Calder. The river falls from 400 metres AOD on Healds Moor to below 15m AOD at its confluence with the Aire.

The Calder catchment (957 sq km) is relatively small compared to other Yorkshire rivers. It is almost entirely over Carboniferous rocks of Millstone Grit and the Coal Measures.

Key terms associated with the idea of a catchment area are:

Watershed - the high point surrounding the catchment area.
Tributaries - the smaller streams and rivers feeding larger ones.
Confluence - the point at which two rivers join.
Aquifer - rocks containing water
Water table - the level at which water is stored in the aquifers.
Channel - the hollow in which the river water flows.
Runoff - the flow of water either across the surface or in rivers.
Discharge - the volume of water passing a particular point.