Science and research

UK Upland Waters Monitoring Network

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UK UWMN Sites

picture of Afon Gwy (c) Ewan Shilland

Afon Gwy

The Afon Gwy was introduced into the Monitoring Network in 1991 as a replacement site for the Nant y Gronwen, for which access permission had been withdrawn by the landowner.

Catchment Characteristics

The Afon Gwy lies to the east of Plynlimon in central Wales and forms part of the headwater system of the River Wye. The catchment area is 389 ha and rises from 380 m at the sampling station to a maximum altitude of 730 m. Catchment soils are dominated by peats and stagnopodsols. The underlying geology is Lower Palaeozoic mudstones, shales and grits of the Gwestyn and Van formations, overlain in places by locally-derived glacial drift. The catchment consists of moorland grasses, notably Molinia and Nardus, with Eriophorum and the moss Racomitrium on areas of wetter land and Pteridium on the lower slopes. The majority of this grassland supports rough grazing for sheep and in summer, on the lower land, cattle. The local area is crossed with tracks used for rally testing, one of which passes through the southern edge of the catchment.

More than half of the western side of the catchment falls within a SSSI and the stream itself forms the headwater part of the River Wye/Afon Gwy SSSI and SAC.

The area receives annual rainfall of c. 2600 mm.

Site Characteristics

The altitude range is from 440 m to 700 m in the headwaters. The channel section utilised for biological sampling is 3-4 m wide and comprises a series of bedrock ledges, falls and boulder strewn riffles.

Associated Networks

Next to the biological sampling stretch is situated a bulk precipitation collector for the UK Eutrophying and Acidifying atmospheric Pollutants (UKEAP) network, data from which are available here.

Page last modified: 3rd February, 2016