A multi-sensor approach to continuous monitoring of a glacier outflow channel: Virkisá River, SE Iceland

Continuous monitoring of meltwater river flows provides valuable data in understanding glacier response to changing climatic conditions. Where glacial catchment runoff converges into a single channel, continuous flow measurement enables total catchment outflow to be quantified, comprising total melt of snow and ice, plus rainfall-derived runoff. However, in practice, the derivation of continuous flow data is often constrained by practical considerations – such as ice affecting the continuous monitoring of water levels and frequently shifting channel features. A multi-sensor approach has been adopted in monitoring the Virkisá River, SE Iceland, to attempt to address these challenges. A road bridge is used as the gauging site, given the otherwise braided nature of the channel, and the structure of the bridge as a robust monitoring platform. Water level sensors have been installed in the centre and margin of the river channel, to generate independent measurements of water level. Water temperature is recorded by one of the sensors, and contributes to the quality assurance of the water level time series. The site is calibrated by periodic flow gaugings obtained either by wading or, in higher flows, by bridge gaugings. A water-surface velocity sensor facilitates a continuous, independent and indirect check on the calibration. This permits the detection of any rating shifts which may occur between infrequent site visits. Finally, two cameras provide visual information on conditions, allowing assessments of the presence or absence of ice, evidence of control changes, and unexpectedly detecting the temporary diversion of the channel while bridge maintenance was undertaken. In the first 3 years of operation, the resultant flow record after quality control is 83% complete, yielding a catchment-average annual runoff of 5.7 m. The multi-sensor approach has proved successful in generating reliable data and allowing new insights into the melt behaviour of the glacier, and surface water/groundwater interactions in the adjacent sandur.