DOI: 10.5285/86f17d61-141f-4500-9aa5-26a82aef0b33
title: Flow velocity, discharge, and suspended sediment compositions of the Irrawaddy and Salween Rivers, 2017-2019

description: This dataset contains water flow velocity, discharge, and suspended sediment compositions of the Irrawaddy (Ayeyarwady) River at Pyay, Myanmar
and the Salween (Thanlwin) River at Hpa-An, Myanmar. The suspended sediment samples and the hydrological data were collected both during peak monsoon
conditions (August 2017 and August 2018) and peak dry season conditions (February 2018 and May 2019). Water velocity was measured using Acoustic
Doppler Current Profiler (ADCP) while collecting suspended sediment samples at various depths in the river. 

Additional flow velocity data was collected while laterally crossing the river channel from bank to bank, and was used to calculate total river discharge at these sites. The dataset includes suspended sediment concentrations, particulate organic carbon concentrations, and particle size distributions of sediment samples collected at various depths and locations in the two river channels.
description: Flow velocity was measured using an Acoustic Doppler Current Profiler (ADCP) Rio Grande II 1200 kHz (Teledyne Instruments). deployed on a moving boat. The ADCP was attached on a rigid frame close to the bow, in a down-facing orientation, and the transducer submerged at 40-60 cm depth. Data were collected while the boat crossed the river perpendicular to the flow. Boat position during the transect was recorded using an external GPS unit with horizontal accuracy of <5 m. Between 1 and 5 such transects were collected, depending on the site, with total discharge reproducibility typically better than 6%. Additional flow velocity data were collected during suspended sediment sampling in August 2018 and May 2019 while the boat was drifting with the current.

ADCP data were collected and initially processed using WinRiver II software. The data were then exported and further processed using Velocity Mapping Toolbox. Using multiple river cross-sectional transects, a mean cross-section was created for each sampling date, ensuring it was perpendicular to the river channel, and calculating the average stream-wise flow velocity field across the river channel. The data were then additionally processed in MATLAB 2019b, filling data gaps, removing erroneous outlier data, and calculating total discharge. Both the raw flow velocity (WinRiver-exported) data and the processed flow velocity and discharge data are included in this dataset.

Depth profiles of suspended sediments were collected in August 2017, August 2018, and May 2019 at both sites. Only surface sediment samples were collected in February 2018. Sediment samples were collected at various depths using a modified Van Dorn style depth sampler while the boat was drifting with the flow. Samples were transferred into 10 L sterile polyethylene bags, ensuring complete transfer of all sediment particles. The bags were weighed and the samples filtered within 24h using 0.2μm polyethersulfone (PES) membrane and freeze-dried back in the lab. Particle size distributions of dried samples were measured using laser diffractometry. The organic carbon concentration (as weight %) was measured using coupled elemental analysis - isotope ratio mass spectrometry (EA-IRMS) after carbonate removal using liquid HCl.

All methods are described in detail in the supporting documentation.