Abstract
The stream length-gradient (SL) index is widely used in geomorphological studies aimed at detecting knickzones, which are extensive along-stream deviations from the typical concave-up shape assumed for stream longitudinal profiles at steady-state conditions. In particular, SL was practical for identifying anomalous gradients along bedrock stream channels in mountainous catchments. This work presents the GIS toolbox SLiX designed to extract values of the SL index, starting from Digital Elevation Models (DEMs). SLiX is also suitable for the spatial analysis of the SL values, allowing for the identification of landscape portions where anomalous high values of SL occur and, consequently, those catchment sectors where stream channels show peaks in the erosional dynamic. The SLiX main outputs are (i) point shapefiles containing, among stream channels attributes, the extracted values of SL along the stream network analyzed, and (ii) SL anomaly maps in GeoTIFF format, computed through the Hotspot and Cluster Analysis (HCA), that permit the detection of the catchment sectors where the major SL anomalies occur and consequently the principal knickzones. The application of the proposed tool within an experimental catchment located in the Northern Apennines of Italy demonstrated the proper functionality and the potential of its use for different geomorphological and environmental studies. The accurate and cost-effective detection of anomalous changes in stream gradient ensured by SLiX is of great interest and can be useful for studies aimed at unravelling the Earth processes responsible of their formation (e.g., active hillslope processes, such as landslides directly interacting with the streambed, presence of geological structures, and meander cut-off). The applications of SLiX have clear implications for preliminary analyses, at a regional scale in different morpho-climatic contexts, for the hydrological management of river basins and/or to prevent geological hazards related to the fluvial erosional dynamics.
Highlights
The landscape evolution, due to the opposing actions of active tectonic uplift and subsidence, as well as erosion and sedimentation processes, implies steady changes of Earth surface topography [1]
The geomorphometry of stream longitudinal profiles has been helpful so far for modeling the evolution of erosional landscapes [2] and reference therein] and, in particular, for better understanding the role of different superimposed factors, such as those derived from active tectonics and climate change [3]
The knickzones identified through the stream length-gradient (SL) point map (Figure 7a) and better interpreted by means of the SL-Hotspot and Cluster Analysis (HCA) approach (Figure 7b) have been verified through aerial photo interpretation, visual inspection of Google® Earth satellite imagery and, by means of detailed observations directly on the field
Summary
The landscape evolution, due to the opposing actions of active tectonic uplift and subsidence, as well as erosion and sedimentation processes, implies steady changes of Earth surface topography [1]. Troiani et al (2017) [8] proposed a new mapping method of SL, applicable at both small catchment and regional scale, based on the Getis–Ord statistic (i.e., SL-HCA maps), useful for identifying and fine-tuning the interpretation of wide stream reaches affected by anomalous high gradients (i.e., knickzones). It is fundamental to ensure the extraction of a “real” channels network, including only the landscape portions experiencing fluvial process [17,18] This can be ensured by determining an appropriate value for the channel initiation in terms of the contributing area, which can be selected detecting the critical threshold separating slope and fluvial process domains in the relationship between drainage area and slope [16,17,18]
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