Swaledale Rivers
The River Swale and its tributaries (Gunnerside Beck and Arkle Beck) form a dynamic system moulded by water and sediment. Over 10, 000 years ago a glacier that covered the majority of the Yorkshire Dales shaped the landscape that we see today. As the climate became warmer and the glacier retreated it created a template, which the present river systems have modified. These 'raw' landscapes were subsequently subjected to glacial meltwater floods (like those of the Alps today) and the valley was modified through erosion and deposition, a process that continues today. As the glacier retreated it left valley floor deposits and formed terraces along the valley bottom.

In Swaledale the underlying geology modified the effect of the glacier on the landscape and the form of the channel system. Areas of harder rock at the top of the catchment were more resistant to the erosive powers of the glacier, resulting in the bedrock gorge and waterfalls that are found typically throughout the Yorkshire Dales. In Swaledale (near Keld) Currack Force is one of these waterfalls (seen in the picture below). The erosion in this area resulted in a sequence of rock steps and scour pools, a "step-pool" channel planform.

Currack Force (near Keld) an example of hard rock geology - february 2001

In the middle and lower reaches of the catchment softer rock was eroded more readily by the glacier, leading to the formation of the wider, flat-bottomed valley. The River Swale has subsequently reworked the material in the valley bottoms to create the broad floodplain. This floodplain is particularly wide from Gunnerside Bridge to Marrick Abbey and the photo from just above Grinton Bridge illustrates this wide floodplain over which the river channel has meandered.

Wide, flat bottomed valley upstream of Grinton Bridge - February 2001

During the more recent past the River Swale has been laterally active within the floodplain through a process of meandering [see bank erosion fact sheet]. Evidence from historical maps (dating back over the last 100 years) suggests that the shape of the river is constantly moving and in some areas these changes are quite dramatic.

Sediment and water
Water and sediment interact at a range of scales, over space and time creating the form of the River Swale and its catchment. The following diagram shows a typical pattern of supply, transfer and storage of sediment within Swaledale.

In the upper reaches of the River Swale, Arkle Beck and Gunnerside Beck sediment is supplied to the channel through slope and bank erosion. The drainage network at the top of the Swale is divided into a dense network of small tributaries that supply sediment from the moorland. Sediment is transferred between the channel and its adjacent floodplain in a number of reaches throughout the Swale network and through these processes there is a turnover of sediment and a net transfer downstream. This sediment is routed through transfer reaches (i.e. the wooded reach downstream of Barney Beck) interspersed by supply reaches (i.e. reaches where sediment loss through bank erosion is greater than sediment gain through deposition). The final stages of this process involves long term storage of sediment either in vegetated bar or in the floodplain as found at Reeth Meanders or eventually when the sediment reaches the sea. The sediment that leaves the Swale past Richmond will be deposited, stored and remobilized a number of times before it reaches the mouth of the Humber.

Rates of supply of sediment to the river can be influenced by both natural and/or human induced factors. These factors include changing climate, the changing management within the catchment, agricultural change and in the Swaledale catchment in particular the history of mining. The sequence and coincidences of these factors will influence the patterns of channel change. Some of these factors, and periods of change are illustrated in this table, showing the extent to which factors may occur together, although establishing a causal link may be difficult.

Changes in channel planform and increases in sediment fluxes are linked to increases in moorland gripping, heavy mining activity, changes in landuse practices and changes in flood frequency and magnitude.

Rarely do these factors act in isolation and the greatest changes are most likely when factors increasing supply of sediment (such as heavy mining activity) coincide with increased flood frequencies and magnitudes. Metals within the mining spoil allow us to measure the rates of accumulation of fine sediments within the floodplains downstream and indicate the significance of mining to shaping the river landscape.

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