Catchment Information

The River Calder rises on the Pennine Moors, West of Todmorden and drains an area of 957 km2. It is predominantly an urban catchment flowing through the West Yorkshire conurbation towns of Halifax, Brighouse, Huddersfield, Dewsbury and Wakefield before joining the River Aire at Castleford.

The catchment owes much of its development to the Industrial Revolution, in particular the textile industry, which, along with the chemical industry, is still important to the water management of the catchment today. Due to its industrial base the rivers of the lower catchment suffer from pollution with 25% classed as having poor quality.

The streams of the upper catchment draining the gritstones are so acidic few fish can live in them or the reservoirs they feed. Despite this acidity the catchment is heavily reservoired, with 39 licensed to provide water, after treatment, for public supply. Water supplies within the catchment are supplemented by imported water from Winscar Reservoir at the head of the Don catchment to the south and from the rivers of North Yorkshire.

Because of nearby industry, and the need to move goods around the Calder catchment, there are 68 km of canal and navigable river with the catchment, comprising: the Calder and Hebble and the Aire and Calder Navigations, the Huddersfield Broad and Huddersfield Narrow Canals, and the Rochdale Canal, although today they are mostly used for recreation rather than commerce.

The river and its tributaries flow through steep and relatively narrow valleys which react very quickly to rainfall causing rapid rises in water level. Due to the proximity of development to the river and the constraints of the valley, this increases the risk of flooding. As a result the Environment Agency has an ongoing programme to undertake a series of flood defence schemes designed to protect the community from further flooding.

Topography     

Topography is a word which means 'the shape of the land'. Another word for this is Relief.   

The boundary of the catchment is defined to include all land which contributes surface water to the River Calder and its main tributaries, the rivers Coine and Holme, and all their subsequent tributaries. It also includes those parts of the Calder and Hebble - and the Aire and Calder Navigations, the Rochdale Canal, the Huddersfield Broad and the Huddersfield Narrow Canals which fall within the catchment area.

The Calder catchment is bounded by the Pennine Moors to the west and the River Aire and the Leeds/Bradford conurbation to the north. The Don and Dearne catchments lie to the south.

The Pennine Moors reach heights of the order of 400 to 500 m AOD (Above Ordnance Datum or mean sea level), with the highest points exceeding 580 m AOD at Tooleyshaw Moss on the edge of the catchment.

The waters of the Calder drain east towards its confluence with the River Aire at Castleford, before flowing into the River Ouse and the Humber Estuary. Flowing for just over 86 km the River Calder fails from 400 m AOD where it rises on Healds Moor to below 15 m AOD at its confluence with the River Aire.

Geology

Geology is the study of the formation, structure and chemical composition of the Earth's rocks.

The Calder catchment, because of its relatively small area compared to other Yorkshire catchments, is entirely on Carboniferous rocks of Millstone Grit and Coal Measures as shown on map.

These rocks comprise a sequence of shales and grits, with the grits forming the prominent high moorland areas to the west of Huddersfield and Halifax.

In the Coal Measures the grits are less prominent. There are coal seams that have been extensively mined in the past, although deep coal mining has now moved eastwards and is no longer active within the catchment.

Millstone Grit is often broken by cracks, called joints. It also has gaps between the grains of sand from which it is made. These are called pores. The joints and pores allow water to pass through the rock. Water is stored in the rock. Sandstone also stores water but has less pore space than Millstone Grit. Both of these rocks are said to be permeable. This means that they let water through.

Shale, on the other hand, is impermeable. It does not let water through.

Hydrogeology

Hydrogeology is the study of the movements and stores of water in the Earth's surface rocks.

The gritstone and sandstones of the Millstone Grit and Coal Measures form minor aquifers. Their value is often restricted because they outcrop on hillsides and give
rise to springs. They are also affected by faulting which breaks the continuity of the sandstone horizon.

Borehole yields from Carboniferous rocks are generally low, typically less than 1 tcmd (thousand cubic metres per day), and iron and manganese levels may be high.

The Coal Measures have been extensively pumped in the past for mine de-watering but this has almost ceased in the last few years.

Rainfall and Flow Monitoring

The study of rainfall and flows is called hydrology.

The Environment Agency manages a regional rainfall network which includes 25 rain gauge sites in the Calder catchment. These enable variations in long term average annual rainfall to be calculated. The annual rainfall within the Calder catchment varies markedly, ranging from 1800 mm in the Pennine headwaters to 600 mm at the confluence with the River Aire at Castieford. The reduction in rainfall along the river is particularly pronounced in the upper half of the catchment, with the annual total dropping to 800 mm at the confluence of the Calder and the River Colne near Huddersfield. The rainfall distribution for the catchment is shown on the map.

In addition to the rainfall gauges there is a network of eight river gauging stations, which provide information on river flows and water levels throughout the catchment. The data from these stations is used to produce flow statistics both on a long term and annual timescale.

Ecology

Ecology is the study of plants and animals (including people) and how they link with each other and the environment.

There are few sites of national significance for nature conservation within the Calder catchment, however there are a number of regionally important sites of interest adjacent to the water environment.

In the lower catchment most of the sites of regional or local interest are not associated with the river due to its poor water quality and tend to consist of water bodies and marshes generally isolated from other areas of interest. In the upper catchment woodlands, reservoirs and moorland contribute to the conservation interest. The habitats which have evolved around the canals, mill dams, relics of the catchment's industrial past, also add nature conservation value to the river corridor.

Fisheries

The term fisheries refers to the areas of the river that stock species of fish.

The upper reaches of the Calder catchment, as far downstream as Mytholmroyd, are exclusively trout fisheries. Downstream of Brearley Weir some coarse fish species appear; roach, perch, gudgeon and chub. From Sowerby Bridge downstream, coarse fish predominate, although some trout are present as far down as Elland. Below Elland, a variety of coarse fish species are found including roach, chub, bream, gudgeon, dace, silverbream, perch, ide as well as the occasional grayling, tench, carp or barbel. Downstream of Mirfield coarse fish occur only sporadically close to inputs of clearer water, though the adjoining canal system does support an improving coarse fishery.