GSA Bulletin; January 2008; v. 120; no. 1-2;
p. 127-141; DOI: 10.1130/B26092.1
© 2008 Geological Society of America
Where do floodplains begin? The role of total stream power and longitudinal profile form on floodplain initiation processes
Vikrant Jain
,1,
Kirstie Fryirs
,1 and
Gary Brierley#,2
1 Department of Physical Geography, Division of Environmental and Life Sciences, Macquarie University, North Ryde, NSW, 2109, Australia
2 School of Geography and Environmental Science, University of Auckland, P.O. Box 92019, Auckland, New Zealand
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Figure 1. Downstream changes in river morphology along confined, partly confined, and laterally unconfined valley settings in an idealized system. The transition between the confined and partly confined valley setting marks the floodplain initiation point.
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Figure 2. Location of the upper Hunter catchment. Note the distribution of valley settings and landscape units. Floodplains are absent or occasional along confined valley setting rivers. Floodplain formation begins to occur in the partly confined valley setting where discrete, discontinuous floodplains are formed. Rivers in the laterally unconfined valley setting have continuous floodplains along both channel banks.
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Figure 3. Variation in the catchment-scale bimodal distribution of total stream power for river courses of the upper Hunter. These plots are modeled by varying profile concavity (β) and decay rate (k).
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Figure 4. Surveyed valley-wide cross sections along confined and partly confined rivers on the eastern and western sides of the Hunter-Mooki fault. These cross sections show the transition in valley width and morphology, and depict the formation of distinct floodplain pockets. The partly confined cross sections were surveyed at the first floodplain pocket along each river course.
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Figure 5. Slope–catchment area relationship for different valley settings in the upper Hunter catchment. (A) Catchment-scale average values. (B) Reach scale running average values. The dashed diagonal line marks the fitted criterion of differentiation on the basis of upper Hunter data; the solid diagonal line is from Sklar and Dietrich (1998). The threshold lines at slope values of 0.015 m/m and 0.003 m/m are also marked.
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Figure 6 (continued). Longitudinal profile forms in the upper Hunter catchment. These profiles are divided into a high decay rate curve and low decay rate curve. Where these different curves intercept the longitudinal profile defines the transition zone within which floodplains begin to form in the upper Hunter catchment. The distance range of transition zone is represented by R. Normalized elevation represents the ratio of elevation (H) to the highest elevation in the basin (H0). The numbers on the transition lines mark the location of valley setting transition points and refer to distance downstream along the longitudinal profile.
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Figure 7. Average value and range of total stream power for rivers in different valley settings in the upper Hunter catchment.
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Figure 8. Distribution pattern of total stream power using the smoothing, and first- and second-order theoretical models (see Jain et al., 2006, for details on techniques). The numbers on the transition lines mark the location of valley setting transition points and refer to distance from source. P1 and P2 are the distance from source for the first and second peaks, and T is the distance from source of the intervening trough.
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Copyright © 2008 by Geological Society of America
