River Dee

The River Dee (Welsh: Afon Dyfrdwy) flows 110 miles from it's source to Hilbre Island. Travelling through Wales and England and also forming part of the international border between them, the river rises in Snowdonia, flows north via Chester and discharges into an estuary between Wales and The Wirral. The lower reaches of the river are unusual in that comparatively little water occupies so large a basin. One theory of a contributory factor to the large basin is that once the River Mersey and/or the River Severn flowed into the Dee. A more recent theory, however, is that the estuary was not formed by water, but by ice being pushed southwards by the pressure of an icecap over the Irish Sea. The total catchment area of the River Dee up to Chester Weir is 1,816.8 square kilometres (701.5 sq mi). The average rainfall over the catchment is estimated to be 640 millimetres (25 in) yielding an average flow of 37 m³/s.

The Dee is one of the most regulated rivers in Europe, it supplies more water for public supply than the whole of the English Lake District and two-thirds of the river water is abstracted before the River Dee reaches the weir at Chester. The natural flow of the River Dee during most summers is insufficient to sustain this rate of abstraction, so a series of reservoirs have been constructed to store excess water available in wintertime and release it back into the River Dee during drier months. This system of low-flow regulation was used by Thomas Telford at the beginning of the 19th Century in order to guarantee a supply of water to the Ellesmere Canal. Telford constructed sluices at the outlet of Bala Lake to control the flow of the Dee downstream so that there was always sufficient water to supply the canal where it started at Horseshoe Falls.



The history of the Dee has many interwoven layers. There is the geological record, from the Ordovician rocks at its source to the modern deposits in the estuary. There is a historical record starting with it's use as a trade route in pre-Roman times. A path of myth which places the young Arthur at it's source. And an industrial tale bringing gold, stone, wool and water downstream as the railways and canals crept ever upstream towards it's head. We make no apology for mashing-up these strands for the Dee is a river to be explored in its many moods on many levels.

We have divided the story of the river and its journey from source to sea into three parts:

Upper Reaches


From the source of the river at springs on the slopes of "Black Hill" Dduallt above Llanuwchllyn in the mountains of Snowdonia, through Wales, to its emergence from the Vale of Llangollen; here the young river flows swiftly and the majority of erosion takes place, cutting relatively narrow, steep-sided, "V"-shaped valleys, often with interlocking spurs.

Here, Victorian geologists fought out their battles to trace the history of rocks through time and a young Charles Darwin made his first explorations of the deep past.

Middle Reaches
Through England and the Welsh borders to Chester; the "middle aged" river slows down and the valley becomes broader. Both erosion and deposition of material takes place, leading to the formation of meanders and occasional changes of course which have in cases left pockets of England "stranded" on the Welsh side of the River Dee.

Lower Reaches
Back in Wales, below Chester to Hilbre Islands and the sea; the river is now in "old-age" and while there is little erosion a lot of material is deposited. In the case of the River Dee this deposition has had a significant impact on the economic development of Chester, effectively turning a major port into a relatively quiet backwater. The estuary is important for birdlife and has been designated both as a "Site of Special Scientific Interest" and under the "Ramsar Convention" on "Wetlands of International Importance", especially as waterfowl habitats.

The River Dee begins near the remains of a spectacular volcano, erupting from the "Isles of Avalon" over 450 million years ago and ends at the haunting Hilbre Islands.

Sources and Links

 * River Dee Geology;
 * The Dee Regulation Scheme - a system of flow balancing and quality management along the River Dee managed by a consortium of the three largest water companies;
 * Dee Valley Water - the area of supply covers 831 square kilometres in North East Wales and the North West of England;