upper reaches of the river are located just to the west of the Yorkshire Wolds, a large aquifer composed of chalk, from which springs emerge to supply much of the base flow of the waterway. This flow is supplemented by a large number of surface drainage ditches, which were cut to improve the land for agriculture. As a result, flows in the river vary significantly depending on the amount of rainfall. The Black Dike and Black Beck tributaries augment the flows in the upper reaches. Further downstream, the river flows over several soil types including Loam, Sand and Alluvium. There are over of drainage ditches that feed into the river, but few natural tributaries. Much of the upper river has been heavily modified over the centuries, and the water can become brown in colour, due to the presence of ferrous oxides in the subsoil over which the river flows. Any disturbance of this compound which results in its exposure to air, such as during weed cutting, results in it changing to ferric oxide, which is insoluble, and causes the discolouration. This can be particularly noticeable near Major Bridge. History The river has been variously known as the Foona, the Fulnath when the Commission of Sewers reported in 1323, the Foonah in a poem about the witches of Wallingfen, the Foulney when a survey of the drainage of the area was conducted in 1664, and the Foulness more recently. It is the main source of natural drainage in the Vale of York, an area to the west of the Yorkshire Wolds, the southern part of which was known as Houghdenshire when John Leland conducted his survey of England in the 16th century, and Howdenshire subsequently. Most of the Vale of York is less than above ordnance datum, with the main exception being Holme-on-Spalding-Moor, which rises to . At its southern edge, the area borders the Humber, which has a tidal range of . The river valley has been populated since Palaeolithic times with many artefacts from that age being unearthed by archeologists. Remains from Mesolithic, Neolithic, Bronze Age, Iron Age and Roman times have also been found by various digs in the area. Much of the area was marshland at the time, interspersed with deposits of sand and gravel, which provided locations for the prehistoric settlements. Areas which have been particularly productive for prehistoric finds are near the river between Hasholme