Abstract
Floodplains are valuable scenes of water management and nature conservation. A better understanding of their geomorphological characteristic helps to understand the main processes involved. We performed a classification of floodplain forms in a naturally developed area in Hungary using a Digital Terrain Model (DTM) of aerial laser scanning. We derived 60 geomorphometric variables from the DTM and prepared a geomorphological map of 265 forms (crevasse channels, point bars, swales, levees). Random Forest classification was conducted with Recursive Feature Elimination (RFE) on the objects (mean pixel values by forms) and on the pixels of the variables. We also evaluated the classification probabilities (CP), the spatial uncertainties (SU), and the overfitting in the function of the number of the variables. We found that the object-based method had a better performance (95%) than the pixel-based method (78%). RFE helped to identify the most important 13–20 variables, maintaining the high model performance and reducing the overfitting. However, CP and SU were not efficient measures of classification accuracy as they were not in accordance with the class level accuracy metric. Our results help to understand classification results and the specific limits of laser scanned DTMs. This methodology can be useful in geomorphologic mapping.
Highlights
Rivers, through erosion and accumulation processes generate various landforms in their floodplains [1,2,3]
In our previous work [47], we aimed to extract swales and point bars with primary terrain attributes and the Normalized Difference Vegetation Index (NDVI), and we found that the overall accuracy (OA) of the classification of the forms was 71%
We found swales classified as point bars, and a point bar classified as a levee, but the geomorphic characteristics had been well represented in spite of the model errors
Summary
Through erosion and accumulation processes generate various landforms in their floodplains [1,2,3]. Levees, located next to the active or abandoned channels, are the most elevated forms; they can even be a couple of meters higher than the surrounding areas. Due to their position, they may provide the most critical controls on floodplains, determining the distribution of water and sediment [4,5]. Paleo river channels and backswamps belong to the lowest elevation areas of floodplains; they serve as sediment traps and are often marshy areas [12,13,14] All these varied landforms make the surface of the floodplains a complex geomorphic landscape [15,16,17]
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