The use of airborne laser scanning in the assessment of groundwater flow conditions in floodplain deposits

The design of geological structure models of contemporary river valleys is largely based on geomorphological analysis. Since the individual valley bottom landforms constituting a record of the evolution of the river system are often characterised by a certain nature of the lithological profile, this analysis can also be useful for determining the variation of filtration conditions in the alluvial layer. The possibilities of landform identification have increased in recent years, mainly due to the dissemination of airborne laser scanning. The paper presents the results of hydrogeological studies conducted using the numerical terrain model along a section of the Middle Vistula River valley near Magnuszew. In this area, flood flows transformed the arrangement of alluvial layers by filling strings of oxbow lakes, reducing the thickness of loamy alluvial soils, as well as by forming extensive sandy alluvial fans. Deep erosion fissures (crevasses), which are the result of concentrated flood flows, were filled and buried during subsequent swellings by loose alluvia of channel facies. Identification of the diversity of the geological structure of floodplain, conducted based on airborne laser scanning imaging, allowed the creation of a conceptual model of hydrogeological conditions, which takes into account the effects of land-forming activity of flood waters. This model subsequently became the basis for the construction and calibration of the mathematical water filtration model. Detailed identification of the geological structure with the use of remote sensing methods also allowed indication and characterisation of intensified filtration areas in the substrate of flood banks and other flood protection structures. Such phenomena are a threat to their stability