River Derwent, Yorkshire

The Derwent is a river in Yorkshire in the north of England.

It flows from Fylingdales Moor in the North York Moors National Park, east then southwards as far as its confluence with the River Hertford then westwards through the Vale of Pickering, south through Kirkham Gorge and the Vale of York, joining the River Ouse at Barmby on the Marsh. The confluence is unusual in that the Derwent converges on the Ouse at a shallow angle in an upstream direction.

The river used to flow further east, its old course entering the Ouse east of Howden.

The River Derwent catchment area includes the Upper Derwent, River Rye, River Hertford, Bielby Beck and Pocklington Canal and their tributaries. It covers an area of 2,057 square kilometres and includes the towns of Stamford Bridge, Malton, Pickering, Helmsley, Filey and Scarborough. The area is bounded by the Cleveland Hills, North York Moors and Hambleton Hills to the north, the Yorkshire Wolds and the coast to the east, the Vale of York to the west and the River Ouse and Humber Estuary to the south. The area around the river is primarily rural in nature with grazing moorland in the upland areas and a variety of agricultural uses at lower levels. There are large areas of designated conservation sites throughout the area. There are two titles named after the River Derwent in the British peerage, Viscount FitzAlan of Derwent which is extinct and Baron Derwent.

Uses

The river is used for water abstraction, leisure and sporting activities and effluent disposal, and also has several important nature reserves. It is the subject of conflicting interests.

Water abstracted from the Derwent supplies towns and cities such as Hull, Leeds, York and Scarborough. The river water is of generally good quality with BOD levels remaining below 2 mg/L all year round. It is typical of northern British rivers in that it exhibits acid flushes at peak times of rainfall (during the winter months).

There are also several effluent sites scattered along this river at Malton, Stamford Bridge, Elvington, Wheldrake and Bubwith.

As of 2023 the River Derwent is only navigable by small powered craft between East Cottingwith Lock and Barmby Barrage. Upstream of East Cottingwith/Thorganby are the remains of the stanchions of an old bridge which are a choke point for drifting fallen trees, which prevent access. Additionally the locks at Elvington/Sutton on Derwent are silted and not accessible to river users.

Geology

thumb|left|The geology of Yorkshire including the River Derwent catchment area

At its source on the North York Moors the River Derwent and its tributaries run over Corallian Limestone from the Jurassic period. Downstream of Stamford Bridge the catchment area is mainly of Sherwood Sandstone from the Triassic period. To the east this sandstone dips under Mercia Mudstone, also of the Triassic period.

Some of the underlying rocks are major aquifers and provide a valuable source for water supply in the area. The major aquifers are the Corallian limestone, chalk and Sherwood sandstone. The Corallian Limestone outcrops on the hills surrounding the Vale of Pickering and is made up of a series of limestones and sandstones. This aquifer is unconfined in parts and gets water from the River Rye and River Derwent through swallow holes. During the Ice Age these outlets were blocked by a tongue of ice which extended down the North Sea basin carrying with it large amounts of glacial detritus. As the ice melted the detritus was deposited to form the Wykeham moraine and permanently blocked the eastern exits of the watercourse. Water from the melting ice and the North York Moors formed a lake in the Vale of Pickering which expanded and deepened until eventually the water escaped by overflowing at the lowest point at Kirkham. The water cut a gorge through the Howardian Hills as it drained away southwards, breaching the Escrick moraine just east of Wheldrake, and joining the Humber glacial lake. After collecting the waters of the Jugger Howe Beck, Black Beck and Troutdale Beck it flows south through the Forge Valley to East and West Ayton. From there it continues across lower ground to where it is joined by the River Hertford. The Sea Cut, a man made channel, connects the Derwent to the North Sea near Scarborough to alleviate flooding in the lower reaches of the Derwent, downstream of the Cut. This management area is about 127 km<sup>2</sup> and largely rural with no major settlements. Corallian limestone lies beneath this area. The landscape is upland moors in the upper reaches with lower lying flatter land near Hackness. The river flows through the narrow Forge Valley and several designated natural conservation sites. Water is retained behind a weir at West Ayton and there are sink holes in the river bed where river water is lost to underlying aquifers, so that in drought years the river below the weir may run dry. There are no wastewater treatment works. The ecology and fisheries have a very high sensitivity to changes in water flow.

Barmby Barrage

Water from the tidal River Ouse is prevented from entering the Derwent by means of a barrage at Barmby on the Marsh.

Natural history

The main river, its tributaries and adjacent wetlands are significant for nature conservation, ecology and landscape. The area contains a wide diversity of habitats and a number of designated sites.

Special Protection Areas provide protection to birds, their nests, eggs and habitats. (SPAs)
Special Areas of Conservation contribute to biodiversity by maintaining and restoring habitats and species other than birds. (SACs)
Ramsar Sites are wetlands of international importance designated under the Ramsar Convention
Sites of Special Scientific Interest (SSSIs)

{| class="wikitable"

! SSSIs

! SACs

! SPAs

! Ramsar sites

| River Derwent, Derwent Ings, Breighton Meadows, Skipwith Common, Melbourne and Thornton Ings, Pocklington Canal, Newton Mask, Kirkham Park and Riverside, Jeffrey Bog, Ellers Wood and Sand Dale, Raincliffe Woods and Forge Valley.

| River Derwent, Skipwith Common, Lower Derwent Valley, Ellers Wood and Sand Dale, North York Moors.

| Lower Derwent Valley, North York Moors.

|Lower Derwent Valley

History

The unusual upstream-facing outfall of the Derwent is man-made. It is believed to have been cut during the Roman occupation of Britain to reduce the distance between the Derwent mouth and the Roman legionary headquarters at York by 9 miles. The first navigation weir, also believed to be of Roman origin, was a flash weir built near Wheldrake to raise the level of the river upstream and regulate its flow downstream.

It has been suggested that the name "Derwent" is related to that of Deira, one of the post-Roman kingdoms that later became Northumbria. a derivation also found in the Latin name for Malton, .

During the reign of King John (1199–1216) a water mill on the Derwent at Wheldrake was given to the monks of Fountains Abbey, and later in the 13th century a weir is known to have existed at the same place.

By 1462 when the Lord Mayor of York was authorised to "correct and amend defects" of the Derwent "from the Ouse as far as the town and bridge of Sutton upon Derwent" the river must have been navigable at least to Sutton. A corn mill existed at Sutton upon Derwent by 1597. It was rebuilt in 1836 and continued in use until 1960. There are other water mill sites at Stamford Bridge, Buttercrambe, Howsham, Kirkham and Malton.

Settlements

thumb|right|250px|[[Fylingdales moor]]

thumbLangdale End
Broxa
West Ayton
East Ayton
Yedingham
Old Malton
Malton
Norton-on-Derwent
Low Hutton
Kirkham
Crambe
Howsham
Scrayingham
Buttercrambe
Stamford Bridge
Gate Helmsley
Low Catton
Kexby
Elvington
Sutton upon Derwent
West Cottingwith
Thorganby
Ellerton
Aughton
Bubwith
Breighton
Wressle
Barmby on the Marsh