Methodology:

The borehole was created on 1st May 2018 with a hot water drill. At a depth of 334 m, deepening of the borehole halted and the drill stem was gritty when brought back to the surface: it was concluded that a connection was made to the bed at this point.

Annual displacement of the borehole top (2021-2024): 42 m/yr, with components N +25 m/yr, E -34 m/yr.

Data collection:

Temperature was measured using Honeywell UNI-curve 192-502-LET-AOI negative temperature coefficient thermistors.

Electrical conductivity was measured by inverting the resistance measured across two brass-rod electrodes (5 mm diameter, ~11 mm long, 11 mm separation). AC excitation voltage was used to cancel polarisation.

Suspended sediment concentration was measured using turbidity sensors based on a photo diode to measure the backscatter of infrared light emitted by an infrared light-emitting diode. Based on that of Orwin & Smart (2005).

Water pressure was measured using a GEOKON 4500SH (range 5 MPa), vibrating wire piezometer, connected to a Campbell Scientific CR1000 datalogger via a CS AVW200 vibrating-wire interface.

Data quality:

Detailed methodology of suspended sediment concentration, water pressure and electrical conductivity measurements is given in Doyle et al. (2018). Detailed methodology of thermistor measurements, including accuracy estimation, is given in Miles et al. (2018).

Turbidity sensors were calibrated in the laboratory using fine (grain size <63 um) glacial sediment at concentrations from 0 (distilled water) to 6 g l-1. Calibration limitations are detailed in Doyle et al. (2018), but regardless, we expect SSCs between 3 - 20 g l-1 to fall within the full-scale range of the sensors.

Water pressure sensors were calibrated by the manufacturer to an accuracy of +/- 0.1 % F.S. corresponding to +/- 5 kPa (+/- 0.5 m head).

Electrical conductivity sensors were calibrated in sodium chloride solutions against a laboratory EC probe between 0 - 200 uS cm-1, giving an accuracy of ~5 %. More details are given in Doyle et al. (2018).

Thermistors are accurate to 0.4 deg C as supplied. This was improved to +/- 0.05 deg C by calibration in an ice bath. See Doyle et al. (2018) and Miles et al. (2018) for more information.