Anabranching reaches juxtaposed with lowland meandering rivers in the
midwestern United States: morphological characteristics and power
regimes
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.