Possibilities for the use of drone data in geomorphological analysis of river deltas, based on the delta of Jeziorsko Reservoir

Abstract

The annual lowering of the water level in Jeziorsko Lake in autumn and spring provides an opportunity to observe interesting changes related to bottom morphology and riverbed evolution, especially in the unstabilized northern part of the delta. This is the period when about 50% of the bottom is exposed. During this period, it is possible to observe and analyse changes shaped by water currents. The aim of this study is to prove the usefulness of carrying out photogrammetric flights using drones to analyse the evolution of deltas of water reservoirs. The muddy and boggy wetland of the exposed bottom of Jeziorsko Lake poses a problem for ground surveys, so unmanned aerial vehicles were used to conduct the research. The surveys produced four orthophotos at intervals ranging from a few days to several months in succession, thus depicting the exposed section of the unstabilized delta. Initial observations of the photogrammetric imaging revealed variability of morphological forms of the bottom of Jeziorsko Lake, which is visible in overlapping parts of the imaging. In particular, a dynamic evolution of riverbeds draws attention. Changes in their positions reached up to about 1.5 m in two days. Other observations include changes in water level, increased overgrowing of exposed fragments of the bottom by vegetation in the period from the end of April. The study also revealed increased anthropogenic activity, which may lead to degradation of the frequented area, especially where lowering of the water level revealed