Supraglacial ponds regulate runoff from Himalayan debris-covered glaciers

Meltwater and runoff from glaciers in High Mountain Asia is a vital freshwater resource for one fifth of the Earth's population. Between 13% and 36% of the region's glacierized areas exhibit surface debris cover and associated supraglacial ponds whose hydrological buffering roles remain unconstrained. We present a high-resolution meltwater hydrograph from the extensively debris-covered Khumbu Glacier, Nepal, spanning a seven-month period in 2014. Supraglacial ponds and accompanying debris cover modulate proglacial discharge by acting as transient and evolving reservoirs. Diurnally, the supraglacial pond system may store >23% of observed mean daily discharge, with mean recession constants ranging from 31 to 108 hours. Given projections of increased debris-cover and supraglacial pond extent across High Mountain Asia, we conclude that runoff regimes may become progressively buffered by the presence of supraglacial reservoirs. Incorporation of these processes is critical to improve predictions of the region's freshwater resource availability and cascading environmental effects downstream

Field verification of bed-mounted ADV meters

The accuracy of continuous-signal acoustic Doppler velocity (ADV) meters for gauging stream flows is examined, using a case study of nine bed-mounted ?Starflow? meters currently installed at a range of sites in the Pontbren catchment, Wales. The accuracy of the ADV meters was tested, under a range of velocities and depths, by comparing flow estimates with those based on a standard method of measurement with an impeller meter. The accuracy of the ADV meters was found to be poor for very low flows. For higher flows, in five concrete-lined sections, accuracy was reasonable without calibration of the ADV meter (estimates were within 20% of the current-metered flow for 68% of samples) and accuracy was good after calibration (estimates were within 20% of the current-metered flow for 93% of samples). In one natural channel, the performance after calibration was similarly good, while performance was fair to poor for two other natural channels. The predictability of the calibration results, and the reasons for the poor performance, are discussed