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Evidence of Change

Planform change can be observed by comparing maps (from different time periods) of the same stretch of river and overlaying them, using a Geographical Information System (GIS). The maps below show Arkle Beck in 1914 and 1980 and once overlaid the pattern of planform change becomes evident and indicates how the gravel bars have changed size and position, indicating transfer of sediments over time.



The Reeth meanders have been the most active area within the recent past, with changing positions of the channel and the extent of gravel bars and the following diagram shows the pattern of movement of the channel over time.

Historical change at Reeth Meanders


Reeth Meanders February 2001

Understanding the history and present river channel change, the supplies of sediment and hydrology can help develop appropriate management options for the catchment and channel.

GeoData Institute undertook a Geomorphological 'Audit' in 2001which looked at the influences on the sediment system of River Swale, Gunnerside Beck and Arkle Beck through interpretation of historic maps and documents, interviews with Environment Agency and National Park Authority staff and contemporary field investigations. This information, held within a Geographical Information System (GIS), allows the river to be categorised into sections according to its physical characteristics and historical influences, as Geomorphological Zones.

Each Geomorphological Zone (GZ) has a description of its predominant sediment characteristics and key influences. Controls on the sediment system in that zone are identified and can be used to determine options for management of bank erosion for example. The appropriate management option is based on the physical characteristics of the area and existing controls on the sediment system. For example, in GZ 3 the reach downstream of the confluence with Straw Beck has actively eroding banks and is a large sediment storage area (see picture).

Active braiding reach downstream of Straw Beck - February 2001

Historically this reach has had a laterally active floodplain (where the channel has meandered across the floodplain) and the channel has widened here to accommodate the sediment that has been deposited. The sediment in the bar is active, as there is no surface vegetation and there is evidence of braiding. The banks are also eroding and adjusting to the sediment accumulation with little stabilising vegetation and are dominated by a gravel toe overlain with a cohesive silty sand layer (another example of banks of this type found downstream of Swinner Gill is shown below).


Eroding bank downstream of Swinner Gill - February 2001

Eroding bank management will depend upon a number of factors. The first decision to make is whether to interfere at all. If action is considered necessary, (i.e. erosion is encroaching on a footpath, road etc.) then appropriate management options will need to be considered. The physical characteristics of these reaches suggest that high stream power (the ability of the river to do work) combined with low bank cohesion has resulted in extensive fluvial erosion of the banks.

To manage these banks effectively vegetation or stone must be used to protect the toe of the bank (which is most sensitive to the erosional forces of the river). Additionally, vegetation should be used to protect the face of the bank where the root matrix will encourage stabilisation. Some of these options are discussed in greater detail in the bank erosion section.

It is through this understanding of the physical controls and influences within Swaledale that effective management solutions can be determined. These solutions should work with the natural processes to maintain as natural a river planform as possible and look upstream for causes of problems or issues rather than always treating the symptoms.

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