Text S2: Field collection and data processing of Acoustic
Doppler Current Profiler (ADCP) supraglacial river discharge
measurements
Over the period 5-13 July 2016, a total 847 ADCP transects were acquired
at a fixed cross-section (location 67.0499°N, -49. 0180°W) in the
main-stem Rio Behar supraglacial river, using field methods based onSmith et al. (2017) (Figures S1-S4 ). Of these 847
transects, 677 later passed rigorous quality-assurance screening and
were used to compute 174 in situ supraglacial river discharge estimates
(Tables S1-S2; Figure S5 ). The 174 measurements were acquired
between 13:00:09 UTC on 5 July 2016 and 10:37:57 UTC on 13 July 2016. Of
these measurements, 168 were collected consecutively every hour starting
11:34:50 UTC on 6 July 2016 and
ending 10:37:57 UTC on 13 July 2016. These 168 consecutive hourly
measurements (1 full week) are the moulin input dataset analyzed in this
study. The additional 6 discharge measurements collected intermittently
on 5/6 July 2013 are excluded from our analysis because they do not
fully capture the diurnal cycle, but are included in the archival
dataset.
All surveys were conducted using a SonTek River Surveyor® M9 ADCP
mounted on a SonTek HydroBoard II and a moving-boat survey type. To
complete each survey, the M9 system was towed, in-transect, back and
forth across the Rio Behar Channel, using a custom bank-operated
cableway that enabled single-side tensioning and operation
(Figures S1-S4 ). Between 3-9 individual hydrographic profiles
or transects of channel cross-section, wetted perimeter, and flow
velocity were collected during each measurement hour, yielding a total
of 847 transects acquired over the field experiment study period
(Tables S1-S2, Additional Supporting Information
Datasets S1-S3 )
ADCP data were later processed into high-quality discharge retrievals
using the following quality assurance (QA) and quality control (QC)
workflow. This QA/QC workflow is similar to that described inSmith et al. (2017) and consists of the following:
- Open all ADCP output files for a given hour in River Surveyor Live
(RSL) software and manually check/edit system settings. For all files,
the Transducer depth was set to 0.1 m, the magnetic declination was
set at -29, GPS reference was set to GGA, and the depth reference was
set to Vertical Beam (VB) (rather than Bottom Track, BT).
- Instrument performance was also validated in RSL. Our system quality
checks include: ensuring system power or voltage >9.5,
GPS quality >= 3, Horizontal Dilution of Precision (HDOP)
<= 2, the track reference was >0. Quality
checks were initially conducted manually, and were later automated
using Matlab.
- The edge or bank data for each measurement were manually inspected to
confirm that the ADCP was receiving velocity and depth data near the
profile edges. Profiles with no edge data (for either or both edges)
were discarded from the final hourly discharge estimate.
- The depth data for each profile were inspected by comparing both the
VB and BT data series and determining which depth reference was higher
quality (i.e. had fewer outliers and less dropout). If both VB and BT
were of equal quality, VB was selected as the depth reference. If VB
had substantial dropout or anomalies, BT was selected. If either VB or
BT had data dropout whereas the other depth reference contained data,
composite tracks were selected such that RSL fills gaps in depth data
series. Each profile was manually ranked on a scale from 0 to 3, where
0 or 1 indicates a poor or unusable transect due to insufficient depth
data, 2 indicates a profile with minimal outliers and dropout, and 3
indicates a profile with no outliers or dropout. Profiles ranked as 0
or 1 were discarded from the final hourly discharge estimates, unless
all transects in a given measurement hour were ranked as 0 or 1. In
this instance, all transects were kept unless certain transects had
notable more outliers or data dropout than other transects, in which
case lower quality transects were removed from the final hourly
discharge estimate.
- Velocity vectors and the signal-to-noise ratio were also inspected
manually. Velocity vectors were ranked on a scale of 1 to 3, where 1
indicates minimal perpendicular vectors, substantial drift, or no
data, 2 indicates vectors with moderate drift and some vector
crossover, and 3 indicates minimal to no drift or crossover. Profiles
with a ranking of 1 were discarded from the final hourly discharge
estimate.
- All QA/QC’d data files were exported from River Surveyor Live as
Matlab files. Both original ADCP data files (.riv or .rivr) readable
in River Surveyor Live (which can be freely downloaded from the
SonTek/Xylem website after registering with an email address) and
output to Matlab files are available via Additional Supporting
Information Dataset S3 .
- Following manual/automated QA/QC checks, resultant ADCP data and
associated variable descriptions were summarized for each measurement
hour. These summary data are presented in Tables S1-S2 ; and
in as Additional Supporting Information in Excel spreadsheet
(Dataset S1 ) and .txt (Dataset S2 ) formats.