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.
Keywords: Lower Vistula River, alternate sandbars, Sentinel-1
radar satellite images