A Systematic, Automated Approach for River Segmentation Tested on the Magdalena River (Colombia) and the Baker River (Chile)

Abstract

This paper proposes a systematic procedure to identify river reaches from a geomorphic point of view. Their identification traditionally relies on a subjective synthesis of multi-dimensional information (e.g., changes of slope, changes of width of valley bottom). We point out that some of the attributes adopted to describe geomorphic characters of a river (in particular sinuosity and confinement) depend on the length of reaches, while these latter are not yet identified; this is a source of ambiguity and introduces, at least conceptually, an unpleasant, implicit, iterative procedure. We introduce a new method which avoids this difficulty. Furthermore, it is simple, objective, and explicitly defined, and as such, it is automatable. The method requires to define and determine a set of intensive attributes, i.e., attributes that are independent of the segment length. The reaches are then identified by the intersection of the segmentations induced by such attributes. We applied the proposed procedure in two case studies, the Magdalena River (Colombia) and the Baker River (Chile), and investigated whether the adoption of the traditional approach for the definition of reaches would lead to a different result. We conclude that there would be no detectable differences. As such, the method can be considered an improvement in geomorphic river characterization.

A Computer Aided Approach for River Styles—Inspired Characterization of Large Basins: A Structured Procedure and Support Tools

“…We can honestly say that the proposed systematic procedure and set of computer-aided tools (the ToolBox, some of whose tools we presented herein) do provide a significant benefit. An objective and systematic identification of reaches (addressed in Nardini et al, [18]), a reliable (although perhaps somehow cumbersome) confinement procedure, the reductionist-holistic tools, and the automatic, GIS based, grouping tool (not described in detail here: see Table A1 of Appendix A) provide all together a substantial support.…”

“…A synthesis of the Magdalena case study is available in Nardini et al [17], where we show the essential outputs obtainable by applying the procedure described herein; details can be found in [16,17]. We warmly suggest that this paper be read together with the case study (and also with Nardini et al [18] when it be published) because they are indeed highly complementary. From a methodological point of view, Nardini et al [17] present the essential contents of a River Styles characterization-classification exercise, while here we present the organized collection of technical steps involved.…”

“…(b) Identifying objectively the (variable length) reaches according to the spatial intersection of only the set of intensive-type attributes of the Procedural Tree (i.e., those not depending on the extension of the length of the considered segment) and assessing all the extensive-type attributes as spatial statistics over such reaches. This idea is further explained in [16][17][18]. (c) Relying on a spatial database (called "skeleton") obtained by segmenting the valley bottom in sub-segments along its axis, and determining a value for each relevant attribute in each sub-segment.…”

Width undulation drives flow convergence routing in five flashy ephemeral river types across a dry summer subtropical region

“…Variability is present in many key factors, such as sediment facies, aquatic and riparian vegetation, large bed elements (including wood, boulder and bedrock features), and topography. One‐meter resolution topo‐bathymetric digital elevation models (DEMs) are increasingly available and utilized in fluvial geomorphology (Piegay et al, 2015) to describe topography (Notebaert et al, 2009; Scown et al, 2015), segment rivers (Nardini et al, 2020), model two‐dimensional (2D) hydraulics (Milan & Schwendel, 2021; Pasternack, 2011; Tonina et al, 2020), classify and map landforms (Cavalli et al, 2008; Clubb et al, 2017), document sedimentary dynamics (Baartman et al, 2013), identify periodic width (W) and detrended bed elevation (Zd) undulations (Brown & Pasternack, 2017; Duffin et al, 2021), and evaluate topography for specific hydro‐morphodynamic mechanisms (Pasternack et al, 2018a, 2018b; Pasternack et al, 2021).…”

Statistically derived morphological signatures of large river channels extracted from topo‐bathymetric LiDAR data

“…Other contributions integrate parameters extracted from cross‐sections or digital elevation models (DEMs) such as width, depth, flow velocity to achieve the identification of coherent reaches from morphological and dynamical perspectives (Gonzalez & Pasternack, 2015). Furthermore, by studying the covariance of physical river properties, one can identify coherent MUs (Pasternack, Gore, & Wiener, 2021) and even delimit them automatically (Nardini et al, 2020). Hydraulic numerical modelling is another way to segment rivers into MUs (Farò et al, 2018; Farò et al, 2022; Jowett & Duncan, 2012; Wyrick, Senter, & Pasternack, 2014), but this requires significant efforts and data for the model calibration.…”