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Anabranching reaches juxtaposed with lowland meandering rivers in the midwestern United States: morphological characteristics and power regimes
  • Tanya Shukla,
  • bruce rhoads
Tanya Shukla
university of illinois

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bruce rhoads
university of illinois
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Abstract

Geomorphic heterogeneity is a primary characteristic of real rivers. An important, yet overlooked aspect of geomorphic heterogeneity of rivers in intensively managed agricultural landscapes of the midwestern United States is spatial variability in channel planform. In particular, these otherwise meandering rivers often contain anabranching reaches characterized by multiple channels separated by stable, vegetated islands. Morphologically, these anabranching reaches appear to differ from anabranching forms previously reported in the literature in terms of island shape and bifurcation angle (Figure). This research quantitatively characterizes the morphological characteristics of anabranching reaches within meandering river systems based on number of channels, island shape and size, bifurcation angles, and cross-sectional geometry across the channel belt. A combination of high-resolution imagery and LiDAR elevation data is used to construct a three-dimensional classification scheme (planform + bed profile) to better characterize anabranching river types. Although differences in planform types have been explained as a function of stream power, which represents the energy of a river to perform geomorphic work, the environmental domain of anabranching rivers has yet to be defined precisely, especially in relation to other planform types. Plotting of anabranching and meandering reaches on slope-discharge plots reveals that both types of reaches generally have similar power regimes – a finding consistent with the notion that the development of anabranching in these systems probably occurs through top-down (floodplain incision) rather than bottom-up (bar growth into islands) mechanisms. The study is a first attempt at characterizing juxtaposed anabranching-meandering systems and provides the basis for further process-oriented fieldwork exploring the role of natural versus human-induced processes on the formation and evolution of mixed planform river characteristics in intensively managed agricultural landscapes.