Is it time to eliminate field surveys from hydromorphological assessments of rivers?—Comparison between a field survey and a remote sensing approach

Abstract

With growing accessibility to remote sensing (RS) data, field surveys (FS) are no longer the only tool for obtaining information on river hydromorphology. The current study addresses the question of comparability between RS- and FS-based assessments of large river hydromorphological (HM) characteristics, using the Slovenian hydromorphological assessment method as a comparison tool. The applied RS approach was based on manual digitalization and free-available RS imagery, while FS were conducted using the River habitat survey. FS and RS data were obtained for 73 sites, covering a broad gradient of large river conditions, from nearly natural to severely modified. To account for natural diversity, sites were grouped into simple and complex channel sites. Furthermore, the RS approach was tested for its ability to trace changes in HM conditions along the river continuum (1,144 sites) and to detect factors of major HM change. Our research showed that FS- and RS-based approaches can give very similar outcomes in large river HM assessment, especially when assessing general HM conditions, as the high correlations of the final indices of the Slovenian hydromorphological assessment method illustrate. Stronger relationships were recognized for simple compared to complex channel sites. The applied RS approach proved its viability in tracing habitat conditions along the river continuum, exposing hydro-dams and urbanization as the main drivers of habitat change. Overall, our findings support a stronger integration of RS into HM assessments, although caution is recommended when applied on complex systems. In order to capture the whole HM diversity of large rivers, FS are still needed.