Discrimination of alluvial and mixed bedrock–alluvial multichannel river networks

Abstract

This paper explores the use of planview morphological metrics to quantitatively describe and distinguish mixed bedrock-alluvial multichannel networks from alluvial multichannel networks. The geometries of the channel planforms of two bedrock-constrained networks (Mekong and Orange rivers) are compared with the classic alluvial anastomosed Upper Columbia River and the wandering Ganga River. Widely recognized indices utilized include: channel link count and channel sinuosity, with additional emphasis being given to the less common metrics: network bifurcation angles and island shape characteristics (i.e. aspect ratio, compactness, roundness and convexity). Link count data, with one notable exception, conform to theoretical expectations. Bifurcation angles for all four multichannel rivers are significantly greater than angles reported for braiding rivers. Island convexity clearly discriminates the two alluvial rivers from the two bedrock-influenced rivers. The width of the macrochannel, in which each network develops, has a positive influence on the number of channel links and is further related to channel slope variations which, in turn, are influenced by terrain structure revealed using trend-surface analysis. The geometry of multichannel networks are often laterally constrained such that the values of channel bifurcation angles and link sinuosity values reduce as the network intensifies and channel links are shortened. These latter observations go some way to explain the oft-noted relatively 'straight' links seen within multichannel networks which are a necessary adjustment to space-filling constraints placed on a network.

The morphometric variation of islands in the middle and lower Yangtze River: A variational analytical explanation

“…4 that for different islands, the paired values of water and sediment proportions are very different, leading to island length-to-width ratios varying in a considerable range. This demonstrates that there are many streamlined morphologies even for river islands of a triangular shape, consistent with the finding of Meshkova and Carling (2013) and Latrubesse (2015). While this study highlights the role of an adjustment in channel slope, it needs to point out that in the development of river islands of a triangular shape, channel slope adjustment is not the sole factor.…”

“…Hence, streamlining implies an adjustment of island morphology to the hydrology such that minimal stream energy loss occurs (Zanoni et al, 2008). When more observations are gathered together, however, Meshkova and Carling (2013) demonstrated that the length of river islands shows a degree of nonlinear proportionality with width in many environments, with the length-to-width ratios of all islands varying in a wide range of 1.2 to 8. Hence they argued that length-to-width ratios varying between 3 and 4 are only the ideal cases for river islands.…”

Bar dynamics and bifurcation evolution in a modelled braided sand‐bed river

“…The use of such metrics and ratios is comparable to e.g. Meshkova and Carling [2013]. Furthermore, we computed 2D maps of lateral water surface gradient to determine its influence on bifurcation evolution after detrending water surface by the initial longitudinal bed slope.…”

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

“…As an alternative to such braiding indices, detailed maps of pixel-based changes can be produced from remote sensing images, but this neither characterizes the spatial relations of a pattern nor reduces the spatial data to a set of relations or characteristics. Meshkova and Carling (2013) and Passalacqua et al (2013) defined several quantitative and objective spatial statistics for island size and shape that are useful for single time slices but ignore linkage and changes through time. Time-dependent statistics of characteristics such as channel abandonment are also useful (Klaassen et al, 1993) but ignore the spatial relations in networks.…”