Sentinel-1 Satellite Radar Images: a New Source of Information on River
Channel Dynamics: Lower Vistula River, Poland.
Abstract
The amount of sediments transported by a river is very difficult to
estimate, however this parameter has an important influence on channel
geometry. It is possible to estimate the bedload transport rate per unit
width of a river channel by measuring bedform profiles’ migration
distance (Δl) in time (Δt) and depth of bedload in motion (hb). Another
method is instrumental measurements using bedload traps and empirical
formulas. Sentinel-1 images at mid latitudes have a temporal resolution
of 2–3 days and spatial resolution of 25 m, which allows them to be
used on large rivers. The research area in this paper is the Lower
Vistula River from km 814 to km 820, where seven alternate sandbars were
selected. The coast lines of the sandbars were delineated on Sentinel-1
images taken during two low flow periods 2018.08.04–09.26 and
2019.07.01–08.31 with similar discharges at low flow phase on the
hydrograph. From water stage observations at the Chełmno and Grudziądz
gauge stations, water elevations were assigned to every coast line of
the alternate sandbars. The centers, volumes and longitudinal profile of
the alternate sandbars were calculated. Average daily movement of the
sandbars in the period 2018.08.04–2019.07.01 was calculated as 0.97
m·day˗1. Similar alternate sandbar movement velocities were obtained
from a study of Sentinel-2 optical satellite images and hydro-acoustic
measurements on the Lower Vistula River. Having the height of the
alternate sandbars and velocity of movement, it was possible to
calculate the rate of the bedload transport as qb = 5 kg·s˗1·m˗1. This
value is similar to results of empirical formulas accepted for use on
large lowland rivers in Poland: Goncarov – 5 kg·s˗1·m˗1, Samov – 3
kg·s˗1·m˗1; Meyer-Peter and Müller – 9 kg·s˗1·m˗1; Skibiński (1976) –
15 kg·s˗1·m˗1. The novelty of this research is showing the use of
Sentinel-1 images for the study of river channel dynamics and
calculation of bedload transport.