Abstract
Fluvial avulsion is an important process in the dynamics of the riverscapes and plays a key role in the drainage network evolution in lowland areas, also influencing past and present social processes and economic activities. Crevasse splays represent significant geomorphological features for understanding the fluvial morphodynamics in lowland areas dominated by avulsion processes. Within wide floodplains characterized by very low elevation ranges, the detection and accurate mapping of crevasse splay morphology and features, such as crevasse channels, levees, and deposit, can be very challenging considering floodplain extension, anthropic impact on the natural channels network, logistic difficulties, and in some cases, climate conditions that prevent field work. This research aims at improving the detection and mapping of crevasse splays in lowland areas through the combination of different remote sensing techniques based on optical multispectral imagery and topographic data derived from satellite earth observation missions. The Lower Mesopotamia Plain (LMP) offers a unique opportunity to study the avulsion processes because it presents numerous examples of crevasse splays, characterized by different sizes and states of activity. Furthermore, in this area, a strong correlation exists between the formation and development of crevasse splays and the expansion of agriculture and early societies since the Early Holocene. Different supervised classification (SC) methods of Landsat 8 satellite images have been tested together with topographic analysis of the microrelief, carried out based on two different 1-arcsec DEMs (AW3D30 and GDEM2). The results of this study demonstrate that the combination of multispectral imagery analysis and topographic analysis of the microrelief is useful for discerning different crevasse elements, distinguishing between active and relict landforms. The methodological approach proved helpful for improving the mapping of erosional and depositional landforms generated by the avulsion process and, in the study area, provided the best results for the active landforms.
Highlights
The fluvial avulsion represents a periodic process in the morphoevolution of the floodplains and consists of an abrupt shift of the whole channel belt from one location to another, favouring the formation of a new watercourse [1,2,3,4,5,6]
Results obtained in the study area are summarized
The first section reports the results derived from the preliminary inspection and the topographic analysis carried out exploiting the elevation datasets
Summary
The fluvial avulsion represents a periodic process in the morphoevolution of the floodplains and consists of an abrupt shift of the whole channel belt from one location to another, favouring the formation of a new watercourse [1,2,3,4,5,6] This process mainly occurs during flood events and requires the bed of the new course being topographically lower than the old channel belt [4,6]. Finer and thinner deposits occur in the middle and distal sectors, where cross-laminated sand (essentially climbing-ripples strata) with load structures pass downcurrent to structureless finer sand and silt deposits, and to the floodbasin mudstone [4,6,18,20] These deposits are vertically organized, forming coarsening to fining upward successions that reflect the increase and the decrease of flood energy during deposition
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