Network concepts to describe channel importance and change in multichannel systems: test results for the Jamuna River, Bangladesh

Abstract

Most of the largest rivers on Earth have multiple active channels connected at bifurcations and confluences. At present a method to describe a channel network pattern and changes in the network beyond the simplistic braiding index is unavailable. Our objectives are to test a network approach to understand the character, stability and evolution of a multi‐channel river pattern under natural discharge conditions. We developed a semi‐automatic method to derive a chain‐like directional network from images that represent the multi‐channel river and to connect individual network elements through time. The Jamuna River was taken as an example with a series of Landsat TM and ETM+ images taken at irregular intervals between 1999 and 2004. We quantified the overall importance of individual channels in the entire network using a centrality property. Centrality showed that three reaches can be distinguished along the Jamuna with a different network character: the middle reach has dominantly one important channel, while upstream and downstream there are about two important channels. Temporally, relatively few channels changed dramatically in both low‐flow and high‐flow periods despite the increase of braiding index during a flood. Based on the centrality we calculated a weighted braiding index that represents the number of important channels in the network, which is about two in the Jamuna River and which is larger immediately after floods. We conclude that the network measure centrality provides a novel characterization of river channel networks, highlighting properties and tendencies that have morphological significance. Copyright © 2013 John Wiley & Sons, Ltd.

Assessment of structural sediment connectivity within catchments: insights from graph theory

“…New methodological procedures from graph theory need to be developed, so we propose here a brief description of the state of the art of previous studies in which the influence of a spatial network structure on material or immaterial fluxes has been thoroughly explored using graph theory. Although such studies have focused on geography (Cole and King, 1968;Gleyze, 2008), social networks (Freeman, 1979) or, more recently, ecology (Ludwig et al, 2002;Belisle, 2005), they have developed metrics and discussed concepts particularly relevant to geomorphology: the relationship between connectivity and the total amount of fluxes passing through the system, and the identification of local hotspots where any change may have an impact on the whole system (Marra et al, 2014;FoufoulaGeorgiou, 2014, 2015;Masselink et al, 2017). In such studies, one key requirement is to provide a hierarchy of the influence of nodes within the network.…”

Book of Abstracts NCK days 2017, 15 – 17 March, Royal Netherlands Naval College (KIM) – Den Helder

“…The channel networks of estuaries range significantly in complexity, from single thread straight channels to multi-channel systems that bifurcate and recombine. Analysing estuary channel connectivity can provide insight into estuarine dynamics, as has been done for tributary networks (Rodríguez-Iturbe and Rinaldo, 1997), deltas (Tejedor et al, 2015a,b), and braided rivers (Marra et al, 2014), but no formal analysis of estuary topologic and dynamic connectivity exists. In this study, we extract channel networks for estuaries around the world and apply spectral graph theory (Tejedor et al, 2015a,b) to characterise their topologic and dynamic connectivity.…”

Controllability of Surface Water Networks

“…Typically, a network is represented as a collection of nodes symbolizing junctions, inlets and outlets, and links symbolizing stream paths. Topology-based metrics have been developed to quantitatively analyze and compare surface water networks in three structurally distinct categories: (i) tributary rivers, where the flux converges from several upstream inlets to a single downstream outlet (Bertuzzo et al, 2007;Rodriguez-Iturbe & Rinaldo, 1997), (ii) braided rivers, where a single stream undergoes multiple branching/merging and eventually joins into a single stream (Foufoula-Georgiou & Sapozhnikov, 2001;Howard et al, 1970;Marra et al, 2014;Sapozhnikov & Foufoula-Georgiou, 1996, 1999, and (iii) deltas, where the flux is distributed from a single upstream inlet to several downstream outlets (Edmonds et al, 2011;Passalacqua, 2017;Smart & Moruzzi, 1971;Tejedor et al, 2015aTejedor et al, , 2015b. These studies have significantly advanced our understanding of rivers and streams as networks.…”