Plynlimon experimental catchments, Wales UK

Location of the Plynlimon catchments, Wales, UK

Catchment size

• Wye: 10.6 km²
• Severn: 8.7 km²

Climate

Humid climate, with annual average precipitation of about 2650 mm.

Geology

The generalised pattern is of parent materials, which are similar throughout the catchments (Palaeozoic grits, mudstones and shales, or drifts composed of them) and therefore soil differentiation is mainly dependent on drainage. Thus the impeded drainage of the plateaux and wider interfluves have led to the accumulation of organic deposits - blanket peat - whilst the more freely draining slope soils are podzolized. In the valey bottoms, drainage is also impeded and there occurs a complex of peat and gleyed mnineral soils, the balance of which at any site is the result of local topography. Whilst the two catchmnents are almost identical in soil types, the lower parts of steeper slopes in the Wye are mantled by a free-draining brown earth; steeper slopes in the Severn have skeletal soils or patchy podzols.

Topography

The landscape of Plynlimon is dominated by rolling hills dissected by steep valleys. The altitudinal range is from 319 m ODN in the Severn and 341 m in the Wye up to 738 m. In terms of slopes, the Severn is locally steeper than the Wye catchment. Both catchments have limited development of valley flat areas associated with hort alluvial reaches. Most reaches are confined within valley side slopes. Most streams are flowing over bed rock, sometimes with a shallow covering of river sediments. The irregularities in the profiles are typical of British upland channels. The steps often coincide with resistant bands of rock Such rock controls are apparent in both catchments. Although there are slope angles greater than 25° which are local to the lower parts of the Wye catchment the vast majority of slopes in both catchments are in the range 0° to 15°. The major differences between the two catchments concern the degree to which the extensive Tertiary plateaux of Plynlimon are crossed by their tributary streams.

Vegetation/Land use

The Wye catchment is 98.8% grassland, while in the Severn forestry is dominant, covering 67.5% of the catchment.

Context of investigation

• Ecological Processes & Resilience
• Environmental Monitoring & Observation
• Soil
• Sustainable Land Management
• Water Resources

Measurements/Equipment

• Climate station
• Suspended sediments
• Solute transport
• Soil moisture
• Ecological Processes & Resilience
• Sustainable Land Management
• Water Resources

Links to project webpages

• Plynlimon: a critical zone observatory, CEH

other Links

• Plynlimon in wikipedi
• Plynlimon at theHistory of Hydrology Wiki

References

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• Benettin, P., van Breuekelen, B.M., 2017. Decomposing the Bulk Electrical Conductivity of Streamflow To Recover Individual Solute Concentrations at High Frequency. Environmental Science and Technology Letters, 4(12), 518-522, DOI: 10.1021/acs.estlett.7b00472.
• Beven, K.J., Kirkby, M.J., Schofield, N., Tagg, A.F., 1984. Testing a physically-based flood forecasting model (TOPMODEL) for three U.K: catchments. Journal of Hydrology, 69, 119-143.
• Beven, K.J., 1979. On the Generalized Kinematic Routing Method. Water Resources Research, 15(5), 1238-1242.
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• Francis, I.S., Taylor, J.A. 1989. The effect of forestry drainage operations on upland sediment yields: a study of two peat-covered catchments. Earth Surface Processes and Landforms, 14(1), 73-83, DOI: 10.1002/esp.3290140107.
• Francis, I.S. 1987. Blanket peat erosion in mid- Wales: two catchment studies. Unpublished Ph.D. thesis, University of Wales.
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