the Humber Estuary and the North Sea. History The river was central to establishment of the textile industries in the local area, and flows through the area known as the Yorkshire Heavy Woollen District. Many major mills were constructed along its banks, particularly at Dewsbury and Wakefield, but also in the smaller communities of Brighouse, Hebden Bridge, Sowerby Bridge and Todmorden, as well as along its tributaries: the Hebble at Halifax, and the Colne at Huddersfield. The mills in the Upper Calder Valley specialised in cotton weaving, with some cotton spinning, while those in the lower part of the valley specialised in wool and shoddy. Some of these structures still exist as listed buildings, although the large scale production of yarn and textile has now ceased. The river formed an important transportation system for raw materials and the products of the mills, particularly prior to the development of other infrastructures such as road and railway links to the area. At many places, the river is not navigable because of weirs or the shallow depth, and passage for boats was made by the creation of cuts where boats are able to enter the Calder and Hebble Navigation. Work began to make the Calder navigable above Wakefield in 1758. Wakefield's medieval nine-arched bridge is long, was built in sandstone between 1342 and 1356, and replaced an earlier wooden structure on the site of an ancient ford. The chantry chapel on the bridge was licensed in 1356. At Wakefield, a variety of former mill buildings are currently being redeveloped to create a Waterfront project which will combine residential housing, offices, galleries and public spaces. The Hepworth Wakefield opened in 2011. In the late 1830s and early 1840s, the River Calder was diverted at Kirkthorpe to aid the building of the railway between and . This also straightened out one of the larger curves in the river and was a cheaper option than building bridges to span the river. In 2015 a 100 kW hydro installation and fish pass was completed at Whalley Weir on the River Calder in Whalley. The micro hydroelectric generating plant uses a variable speed Archimedean screw. The weir at Kirkthorpe was adapted in 2017 to be a hydroelectric generating station, with a capacity of 500 kWh. The valley's historic towns and cities have attracted film and television productions. Several films and television series have been filmed in the area,