Geometry and topology of estuary and braided river channel networks automatically extracted from topographic data

Abstract

Automatic and objective extraction of channel networks from topography in systems with multiple interconnected channels, like braided rivers and estuaries, remains a major challenge in hydrology and geomorphology. Representing channelized systems as networks provides a mathematical framework for analyzing transport and geomorphology. In this paper, we introduce a mathematically rigorous methodology and software for extracting channel network topology and geometry from digital elevation models (DEMs) and analyze such channel networks in estuaries and braided rivers. Channels are represented as network links, while channel confluences and bifurcations are represented as network nodes. We analyze and compare DEMs from the field and those generated by numerical modeling. We introduce a metric called the sand function that characterizes the volume of deposited material separating channels to quantify the spatial scale attributed to each link. Scale asymmetry is observed in the majority of links downstream of bifurcations, indicating geometric asymmetry and bifurcation stability. The length of links relative to system size scales with sand function scale to the power of 0.24-0.35, while the number of nodes decreases against system scale and does not exhibit power-law behavior. Link depth distributions indicate that the estuaries studied tend to organize around a deep main channel that exists at the largest scale while braided rivers have channel depths that are more evenly distributed across scales. The methods and results presented establish a benchmark for quantifying the topology and geometry of multi-channel networks from DEMs with an automatic and objective tool.

Predicting Water and Sediment Partitioning in a Delta Channel Network Under Varying Discharge Conditions

“…The availability of new methods for extracting channel networks and geometry from remotely sensed images has increased drastically over the past 5 years (Hiatt et al., 2019; Isikdogan et al., 2017a, 2017b; Schwenk et al., 2019). This offers the ability to monitor and measure morphological changes in rivers and deltas, which is especially useful for sites that are not particularly accessible (e.g., the Arctic region).…”

“…The availability of new methods for extracting channel networks and geometry from remotely sensed images has increased drastically over the past 5 years (Hiatt et al, 2019;Isikdogan et al, 2017aIsikdogan et al, , 2017b; Schwenk…”

Alluvial connectivity in multi‐channel networks in rivers and estuaries

“…On the basis of observations and theory for rivers we expect that, where one of the bifurcated channels is wider and carries more flow than the other, the bed elevation in the smaller channel is higher and the angle with the upstream channel is also higher (Kleinhans et al, 2013). This was already supported by analysis with the striation method, where the smaller bifurcates were often oriented more perpendicular to the main flow direction in an idealised braided river model and an idealised estuary model (Hiatt et al, 2020).…”

“…It is without doubt that flow and sediment fluxes connect the seemingly (partly) disconnected channels. However, neither a simple depth threshold nor a steepest descent method would allow the identification of a network of connected pools as channels from bathymetric data (Hiatt et al, 2020;Kleinhans et al, 2017Kleinhans et al, , 2019Limaye, 2017). In addition to the depth variation elaborated above, water can fill up local minima in the river bed, such that water flows over these minima, causing the river bed to ascend instead of descend.…”

Sediment Connectivity: A Framework for Analyzing Coastal Sediment Transport Pathways

“…Within geomorphology, the use of graph theory for analyzing connectivity has grown in popularity (Heckmann et al., 2015, 2018; Phillips et al., 2015), for applications including sediment delivery in catchments (Cossart et al., 2018; Heckmann & Schwanghart, 2013) and the development of sand bars in rivers (Koohafkan & Gibson, 2018). Graph theory has also been used effectively for studying channel networks in river deltas (Hiatt et al., 2020; Passalacqua, 2017; Tejedor et al., 2015a, 2015b, 2016, 2017) and sea level rise impacts on drainage networks in coastal regions (Poulter et al., 2008). Aggregated morphodynamic models like ASMITA (Lodder et al., 2019; Stive et al., 1998), the reservoir model of Kraus (2000), and BRIE (Nienhuis & Lorenzo‐Trueba, 2019) represent sediment pathways at tidal inlets using a series of reservoirs and the fluxes between them but do not explicitly analyze connectivity in a graph theoretic framework.…”