the river spen, known colloquially as spen beck, is a river in the county of west yorkshire, england and is a tributary of the river calder. it rises north of cleckheaton, runs through liversedge and flows into the river calder, west yorkshire south of dewsbury at ravensthorpe. the average rainfall for the river valley is between 600–1000mm per annum. combined with the steep narrow river channel, this makes the spen susceptible to regular flooding.