Process studies were led there by Malcolm Newson who, after learning to speak Welsh, was chair of the local Parish Council for a while. Malcolm and Kevin Gilman carried out work on the networks of soil pipes in the catchments as well as velocities of overland and channel flow and some early isotope studies Gilman and Newson, The catchments were also the base for a number of PhD studies, including Paul Wolfendon UCW , Brian Knapp Reading who carried out early work on soil pipes in the catchments.
It was also used by visiting undergraduate field trips, including the students from the University of East Angia in the early s who spent a lot of time crawling on their knees over the hillslopes mapping out networks of pipes. Pipe connectivity was also investigated by Malcolm and Kevin, out in the rain, listening for water flowing in near-surface soil pipes while traversing the tops and bottoms of slopes with maps and walkie-talkies.
One of his most important contributions at Plynlimon was the study of the two flood events in and Newson, This event showed that the sequence of events could be important in that the geomorphological effect of the first was mostly on hillslopes, particularly shallow landslides, while that of the second was mostly on channel form, redistributing material from the first event. This initiated a reconsideration of notions of geomorphological effectiveness of hydrological events. Instrumentation of the sites was a challenge.
The gauging stations for the two main catchments were completed in Wye and Severn respectively. Eight additional sites were subsequently gauged on the three major tributaries of each main catchment The streams were steep with heavy sediment load and with the help of Hydraulics Research Station at Wallingford at that time still a government research station high and narrow steep stream flumes were developed to get more accurate estimates of discharge on a number of sub-catchments within both the Severn and the Wye Harrison and Owen, The narrowness of the flumes however has meant that they have limited capacity and they have been by-passed in some more extreme events.
The stage- discharge ratings for the flow gauges were checked by multiple depth current metering and dilution gaugings. Five sub-catchment gauges were built in the early s Cyff, Gwy, Hore, Nant Iago and Tanllwyth , the Hafren flume was completed in and the Upper Hore was instrumented in to act as an experimental control while the forest was clear-felled in the downstream part of the Hore catchment.
The gauge on the Nant Iago which is affected by old mine activities in the subcatchment was discontinued in June In autumn , a new flume was completed to monitor the unforested headwaters of the Hafren. Measuring the input to the water balance was also a challenge since the catchments have sufficient elevation range, aspects and wind speeds. Studies were made of how the wind affected the catch of different types of gauge, relative to a new type of ground level gauge.
In , the pattern of monthly rainfalls was also investigated using 48 monthly gauges in a stratified sample across elevation and aspect. In the Wye, precipitation was estimated from 21 ground level gauges while in the Severn, the measurements were made from a combination of 11 canopy gauges in the forest areas and 7 ground level gauges in the higher upland pasture part of the catchment.
During severe snow periods, information was provided by 9 UK standard height Standard height gauges were also used in place of some of the canopy gauges after forest felling. Scaling up to catchment precipitation was performed using the Thiessen polygon method.
In addition to the storage gauges, sub-daily hourly or less data are available from between 4 and 6 tipping bucket raingauges depending on the time period. In , to lower the costs and the labour involved, the number of storage gauges was reduced from 48 to Interception losses and transpiration were measured, including some large sheet under-canopy collectors, large scale plot lysimeter studies and cut whole tree transpiration measurements by Ian Calder, John Roberts and others. Weather data were measured at a number of sites using Wallingford Automatic Weather stations, and soil moisture using the Wallingford Neutron Probe.
The hydrological instrumentation and having hydrological scientists on site also allowed work to be carried out on runoff processes, sediment sources and transport, and water quality. More recently, the effect of sampling frequency on a large range of water quality variables has been investigated, initially with some storm sampling, then with daily sampling Kirchner et al.
The original aim of the Plynlimon investigation was to determine whether the land use affected the water balance in the catchments.
Thus, the water balance for the catchments has been revisited a number of times see Kirby et al. A number of issues were identified with some of the subcatchment data including an apparent trend in discharge for the Tanllwyth and the effects of old mine workings on the Nant Iago. The excess evapotranspiration determinations of the forest over the grass catchment areas were outside the range of uncertainty, with the difference falling as felling of the trees started to take effect Robinson and Dupeyrat, The Plynlimon catchments had a significant impact on forest policy in the UK after work by Ian Calder and Malcolm Newson extended the implications of the research nationwide.
Gilman, K and Newson, M. Mongraph 1, Geobooks, Norwich. Hudson, K.
ExpeER - PLYNLIMON (UK)
Gilman, and I. Calder, , Land use and water issues in the uplands with reference to the Plynlimon study, Hydrol. Earth Syst. Kirchner, J. Fractal stream chemistry and its implications for contaminant transport in catchments. Nature, , pp. Law, F, , The effect of afforestation upon the yield of water catchment areas, J. Waterworks Ass. Marc, V. The long-term water balance — of upland forestry and grassland at Plynlimon, mid-Wales. Hydrology and Earth System Sciences, 11 1 , pp.
McCulloch, , All our yesterdays: a hydrological retrospective, Hydrol. Neal, C. High-frequency water quality time series in precipitation and streamflow: From fragmentary signals to scientific challenge. Science of the Total Environment, , pp.
Newson, M. Earth Surface Processes, 5 1 , pp. Penman, H. Pereira, J. Nash, and M. Nixon, , A view from the watershed, Hydrol. Robinson, M. Hydrological Processes, 19 6 , pp. Forest and Water Guidelines. A complete bibliography for Plynlimon prior to is given in C. Kirby, C. Neal, H. Turner, and P. Moorhouse, , A bibliography of hydrological, geomorphological, sedimentological, biological and hydrochemical references to the Institute of Hydrology experimental catchment studies in Plynlimon, Hydrol.
Many of these are available on-line via the core. Two special issues on Plynlimon have been produced in Hydrology and Earth System Sciences 1 3 , and 11 1 , Johnson, R. The forest cycle and low river flows: a review of UK and international studies.
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Forest Ecology and Management, 1 , pp. Stott, T. Effects of plantation forest clearfelling on stream temperatures in the Plynlimon experimental catchments, mid-Wales. Hydrology and Earth System Sciences Discussions, 4 1 , pp. Catchment-scale advection and dispersion as a mechanism for fractal scaling in stream tracer concentrations. Journal of hydrology, 1 , pp. Foster, H. A hydrochemical modelling framework for combined assessment of spatial and temporal variability in stream chemistry: application to Plynlimon, Wales. Hydrology and Earth System Sciences Discussions, 5 1 , pp.
Long-term changes in the water quality of rainfall, cloud water and stream water for moorland, forested and clear-felled catchments at Plynlimon, mid-Wales. Hydrology and Earth System Sciences Discussions, 5 3 , pp. Geoscience Communication. Geoscientific Instrumentation, Methods and Data Systems. Geoscientific Model Development. Hydrology and Earth System Sciences. Natural Hazards and Earth System Sciences. Nonlinear Processes in Geophysics. The Cryosphere. Weather and Climate Dynamics.
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Encyclopedia of Geosciences. Journal topic HESS. Author Title Abstract Full text. User ID. Journal metrics Journal metrics IF 4. Volume 11, issue 1. Article Metrics. Volume 11, issue 1 Hydrol.