Hafren SMART Watershed

Continuous high-frequency monitoring is ongoing at the Hafren watershed in the headwaters of the River Severn at Plynlimon mountain, Wales.

The Plynlimon experimental watersheds have been maintained since the 1960s by CEH for the long-term study of streamflow, chemical fluxes and climate at an upland site. The watersheds are found within the headwaters of the River Severn and the River Wye in the Cambrian Mountains, 300-700 m above sea level, and cover a combined area or 19.25 km2. They are SoilTrEC /Critical Zone Observatory watersheds.

Lancaster University research into the use of SMART sensors for very high-frequency (1-5 minute) monitoring of hydrometric, water quality and climatic variables in the Hafren watershed at Plynlimon began in late 2014 and is ongoing, This has yielded novel hydrochemical data spanning over a year, and is suitable for SMART modelling approaches.

In 2013 the Hafren and Gwy watersheds at Plynlimon were temporarily instrumented by CEH Bangor, in partnership with Lancaster University, with SMART water quality sensors as part of the NERC-funded Diversity in Upland Rivers for Ecosystem Service Sustainability (DURESS) project. 

Location of the site can be found on our interactive map.

CEH monitoring infrastructure at the Lower Hafren flume at Plynlimon. Stilling well now equipped with SMART sensors for water quality, measuring at 1-minute sampling intervals.

Hafren site details

Coordinates: N 52° 28′ 31.2″, W 003° 42′ 17.9″   

Area: 360 ha (Upper Hafren 120 ha)

Land Cover: Coniferous plantation (Sitka Spruce dominant)

Geology: Lower Palaeozoic slate, mudstone, greywacke and sandstone.

Soils: Predominantly stagnopodzols, but acidic peat, acid brown earths and stagnogleys also occur.

Mean Annual Precip: 2600 mm/yr at Carreg Wen

SMART sensors: Campbell Scientific CR1000 with temperature, water level, electrical conductivity and pH sensors (1-min monitoring).

Hobo RX3000 (telemetry) with water level and rainfall (5-min monitoring).

Solinst rain and level loggers (2-min monitoring).

SMART models: n/a

Landowner: Natural Resources Wales

Infrastructure: CEH (contact Dave Norris)

Raingauge with Solinst datalogger at Carreg Wen weather station

Example pertinent publications from the Hafren watershed

Benettin P, Kirchner, JW, Rinaldo A, and Botter, G, 2015. Modeling chloride transport using travel-time distributions at Plynlimon, Wales, Water Resources Research, 51, 3259-3276. view online

Halliday, SJ, Skeffington RA, Wade AJ, Neal C, Reynolds B, Norris D, and Kirchner, JW, Upland streamwater nitrate dynamics across decadal to sub-daily timescales: a case study of Plynlimon, Wales, Biogeosciences, 10, 8013-8038. view online.

Kirchner, JW and Neal, C. 2013. Universal fractal scaling in stream chemistry and its implications for solute transport and water quality trend detection. PNAS, 110: 12213-12218. view online.

Neal C, Reynolds B, Kirchner J, Rowland P, Norris D, Sleep D, Lawlor A, Woods C, Thacker S, Guyatt H, Vincent C, Lehto K, Grant S, Williams J, Neal M, Wickham H, Harman S and Armstrong, L. 2013. High-frequency precipitation and stream water quality time series from Plynlimon, Wales: an openly accessible data resource spanning the periodic table. Hydrological Processes, 27: 2531-2539. view online

Halliday SJ, Wade AJ, Skeffington RA, Neal C, Reynolds B, Rowland P, Neal M, Norris D. 2012. An analysis of long-term trends, seasonality and short-term dynamics in water quality data from Plynlimon, Wales. Science of the Total Environment, 434: 186–200. view online.

Neal C, Reynolds B, Norris D, Kirchner JW, Neal M, Rowland P, Wickham H, Harman S, Armstrong L, Sleep D, Lawlor A, Woods C,Williams B, Fry M, Newton G, Wright D. 2011. Three decades of water quality measurements from the Upper Severn experimental catchments at Plynlimon, Wales: an openly accessible data resource for research, modelling, environmental management and education. Hydrological Processes, 25: 3818–3830. view online.

Godsey SE, Aas W, Clair TA, de Wit HA, Fernandez IJ, Kahl JS, Malcolm IA, Neal C, Neal M, Nelson SJ, Norton SA, Palucis MC,Skjelkvåle BL, Soulsby C, Tetzlaff D, and Kirchner JW. 2010. Generality of fractal 1/f scaling in catchment tracer time series, and its implications for catchment travel time distributions. Hydrological Processes, 24: 1660–1671. view online.

Neal C, Robinson M, Reynolds B, Neal M, Rowland P, Grant S, Norris D, Williams B, Sleep D, Lawlor A. 2010. Hydrology and water quality of the headwaters of the River Severn: stream acidity recovery and interactions with plantation forestry under an improving pollution climate. Science of the Total Environment, 408: 5035–5051. view online.

Kirchner JW, Feng XH, Neal C, Robson AJ. 2004. The fine structure of water-quality dynamics: the (high-frequency) wave of the future.Hydrological Processes, 18: 1353–1359. view online.

Neal C, Wilkinson J, Neal M, Harrow M, Wickham H, Hill L, Morfitt C. 1997. The hydrochemistry of the River Severn, Plynlimon, Wales. Hydrology and Earth System Sciences, 1: 583–617. view online.

Our Infrastructure and Sensor Deployment

The following images give an insight into the Lancaster University  infrastructure and sensor system set up at the Hafren watershed:

Hobo RX3000 telemetry logger deployed alongside CEH Upper Hafren flume. Measuring rainfall (via tripod mounted raingauge) and streamflow (in stilling well) at 5-min sampling intervals.

Interior of CEH Lower Hafren flume hut, containing a stilling well. This has been equipped with Lancaster University’s mobile pH unit and batteries. The pH unit consists of a Campbell Scientific CR1000 datalogger and associated sensors, and measures pH and other water quality variables at 1-minute sampling frequency. Also shown is an S::CAN system (i::scan and con::cube) which was temporarily deployed for testing at this site.

Water quality box (identical to those deployed at Llyn Brianne) temporarily deployed at the Hafren watershed by CEH in conjunction with Lancaster University as part of the DURESS project.

Exterior of CEH flume hut at the Lower Hafren flume. Stilling well used for high-frequency water quality is located furthest left beneath the flume hut.


The datasets for the Hafren watershed include:

Lower Hafren:

November 2014 – present: stream temperature, electrical conductivity, pH (1-min sampling interval).

November 2014 – present: streamflow (2-min sampling interval)

Upper Hafren:

May 2015 – present: rainfall, streamflow (5-min sampling interval).

Carreg Wen:

November 2014 – present: rainfall (1-min sampling interval).

Please contact us if you are interested in using our datasets.

Example 1-min sampled rainfall and H+ (derived from pH) time-series through three contiguous storms in December 2014. Presented at AGU Fall Meeting, December 2015.