Geospatial Modeling of the Tombolo Phenomenon in Sopot using Integrated Geodetic and Hydrographic Measurement Methods

Abstract

A tombolo is a narrow belt connecting a mainland with an island lying near to the shore, formed as a result of sand and gravel being deposited by sea currents, most often created as a result of natural phenomena. However, it can also be caused by human activity, as is the case with the Sopot pier—a town located on the southern coast of the Baltic Sea in northern Poland (φ = 54°26’N, λ = 018°33’E). As a result, the seafloor rises constantly and the shoreline moves towards the sea. Moreover, there is the additional disturbing phenomenon consisting of the rising seafloor sand covering over the waterbody’s vegetation and threatening the city's spa character. Removal of the sand to another place has already been undertaken several times. There is a lack of precise geospatial data about the tombolo’s seafloor course, its size and spatial shape caused by only lowering the seafloor in random places, and the ongoing environmental degradation process. This article presents the results of extensive and integrated geodetic and hydrographic measurements, the purpose of which was to make a 3D model of the phenomena developing in Sopot. The measurements will help determine the size and speed of the geospatial changes. Most of the modern geodetic and hydrographic methods were used in the study of these phenomena. For the construction of the land part of geospatial model, the following were used: photos from the photogrammetric flight pass (unmanned aerial vehicle—UAV), laser scanning of the beach and piers, and satellite orthophotomaps for analysis of the coastline changes. In the sea part, bathymetric measurements were carried out with an unmanned surface vehicle (USV).

Using UAV Photogrammetry to Analyse Changes in the Coastal Zone Based on the Sopot Tombolo (Salient) Measurement Project

“…Tombolo (salient) measurement campaigns in Sopot spanned three years. The most important measurements realised with a full range of measurement methods and the use of unmanned systems, took place in November 2018 and November 2019 [ 42 ]. The article covers this two-year period, where measurements were made with a full range of unmanned methods and in accordance with the developed methodology presented in [ 42 ].…”

“…The most important measurements realised with a full range of measurement methods and the use of unmanned systems, took place in November 2018 and November 2019 [ 42 ]. The article covers this two-year period, where measurements were made with a full range of unmanned methods and in accordance with the developed methodology presented in [ 42 ]. The dynamic development of UAV technology during this period resulted in the use of various unmanned platforms equipped with various cameras.…”

“…Coastal currents in this area that displace bottom sediments are responsible for creating links between the mainland and coastal islands or hydro-technical structures. These forms are called salient or tombolo [ 38 , 39 , 40 , 41 , 42 , 43 ]. Tombolo or salient is an accumulative form of coastal relief closely related to the influence of coastal currents.…”

“…Periodic analyses and identification of processes that take place in this area allow for accurate planning of anthropopressure [ 44 ]. For this purpose, we developed and implemented a complementary methodology of evaluation of the phenomena occurring within the littoral area using unmanned platforms [ 42 ].…”

“…The research [ 42 ] presents the genesis of tombolo (salient) formation in Sopot in great detail and describes the methodology of integrated spatial measurements of this phenomenon, and finally, it proves the accuracy of measurement techniques used. This study [ 42 ] uses a unique combination of bathymetric data obtained from a hydrographic motorboat to the 0.6 m isobath, unmanned surface vessel (USV) to the 0.2 m isobath, photogrammetric data obtained from unmanned aerial vehicles (UAVs) and terrestrial laser scanning (TLS), and geodetic data from precision measurements with receivers of global navigation satellite systems (GNSS). This great variety of different sources of spatial information allows one to gain very detailed knowledge about changes taking place in the environment.…”