GPR and aerial imageries to identify the recent historical course of the Obra River and spatial extent of Obrzańskie Lake, altered by hydro-technical works

Abstract

Ground penetrating radar (GPR) measurements have been conducted to retrace the natural course of the Obra River and changes of spatial extent of Obrzańskie Lake (western Poland). The Obra River valley was subjected to intensive anthropogenic transformation. Three artificial canals were constructed here in the beginning of the nineteenth century. The GPR surveys were done using a georadar MALA ProEx equipped with 250 MHz antenna. The measurement was verified by coring and analyses of historical maps, aerial photographs, and satellite images. The research has shown that there are at least three elongated depressions preserved in the modern land surface near the village of Solec, situated in the middle course of the valley. Several structures suggesting functioning of a multi-channel pattern in the past have been detected inside and in the vicinity of the depressions. Filling the channels with silts and peats might have been the effect of flow deceleration caused by the construction of the Obra Canals. Moreover, situation of two of the retraced depressions suggests that the landforms might be the remains of a river bed disappearing in wetlands. Further studies including groundwater flux measurements in the area between the depressions are needed to confirm such hypothesis. Furthermore, the study allowed retracing the spatial extent of Obrzańskie Lake. The sediment structures detected by the GPR measurements and calibrated with coring were interpreted to be the traces of the lake shoreline. The interpretation was supported by the findings inferred from aerial and satellite images. It was shown that Obrzańskie Lake had had at least three islands and had been directly connected with a network of braided channels before the anthropogenic intervention. The spatial extent of the lake was significantly altered by the construction of the North Obra Canal. Disconnecting the lake from the Canal resulted in more than 50 % decrease of the lake surface.

Current uses of ground penetrating radar in groundwater-dependent ecosystems research

“…26% of the total case studies ( Fig. 7b; Table 4) such as (1) water extraction (RI3a) diminishing groundwater transference to natural systems (Endres et al, 2000;Tsoflias et al, 2001;Bevan et al, 2003); (2) point pollution (RI3b) focused mainly on monitoring contamination plumes (Corbeanu et al, 2002;Conant et al, 2004;Talley et al, 2005;Tsoflias and Becker, 2008); (3) civil works (RI3c) modifying groundwater flow of natural courses (Słowik, 2013); (4) agricultural practices (RI3d) altering aquifer recharge rates and mechanisms (Lunt et al, 2005;Lambot et al, 2008); and (5) mining and quarrying practices (RI3e) changing preferential flows (Grandjean and Gourry, 1996) and generating new GDE (Molina-Sánchez et al, 2015). Despite that shallow groundwater propitiated the existence of GDE in most of the case studies, only one study expressly addressed GDE research (Zurek et al, 2015).…”

Transformation of a lowland river from a meandering and multi-channel pattern into an artificial canal: retracing a path of river channel changes (the Middle Obra River, W Poland)

“…1) by means of geophysical (ground-penetrating radar (GPR)) surveys and the analysis of satellite and aerial images. It is a continuation of studies conducted in the Middle Obra valley by Słowik (2011aSłowik ( , 2013. It presents the results of a field research carried out in the area where traces of former river beds were preserved in the modern land surface (Fig.…”

“…1). The canals replaced the natural river course characterized by various patterns (meandering, multi-channel and disappearing in wetlands; Słowik 2011a) and influenced changes of spatial extent of lakes situated in the course of the river (Słowik 2013). According to Dynowska (1972), hydrological regime of the Obra River is temperate with spring floods and groundwater-rainfall water supply.…”

Analysis of fluvial, lacustrine and anthropogenic landforms by means of ground‐penetrating radar (GPR): field experiment

“…c). It represents two wetland depressions (remains of former bays of Obrzańskie Lake; Słowik ) separated by an elevated area composed of fine and medium sands (former lake island).…”