Bedrock channel adjustment to tectonic forcing: Implications for predicting river incision rates

Abstract

We present detailed data of channel morphology for a river undergoing a transient response to active normal faulting where excellent constraints exist on spatial and temporal variations in fault slip rates. We show that traditional hydraulic scaling laws break down in this situation, and that channel widths become decoupled from drainage area upstream of the fault. Unit stream powers are ~4 times higher than those predicted by current scaling paradigms and imply that incision rates for rivers responding to active tectonics may be signifi cantly higher than those heretofore modeled. The loss of hydraulic scaling cannot be explained by increasing channel roughness and is an intrinsic response to tectonic forcing. We show that channel aspect ratio is a strongly nonlinear function of local slope and demonstrate that fault-induced adjustment of channel geometries has reset hillslope gradients. The results give new insight into how rivers maintain their course in the face of tectonic uplift and illustrate the fi rst-order control the fl uvial system exerts on the locus and magnitude of sediment supply to basins.

Natural experiments in landscape evolution

“…Purely transport-limited behavior can be ruled out, given the shape of the long profiles (compare Figures 4 and 1). Stream morphology data also reveal the importance of dynamic adjustment in channel width (Whittaker et al, 2007a;Attal et al, 2008). The Central Apennines example illustrates the value of natural experiments in transient response for teasing out key elements of geomorphic behavior and discriminating between alternative models.…”

“…For instance, some authors have found that a combination of field surveys and photogrammetric 10 m to 30 m resolution DEMs were sufficient (if not ideal) for studying stream incision (e.g. Snyder et al, 2000;Duvall et al, 2004;Whittaker et al, 2007a;Attal et al, 2008), while other applications require meter-to sub-meter, true-ground (not canopy) data of the sort that can be obtained with airborne or ground-based LiDAR (e.g. Roering et al, 1999;Roering, 2008).…”

“…Another approach is to focus on landscape evolution on time scales much longer than a glacial-interglacial cycle. For example, the central Apennines rivers analyzed by Whittaker et al (2007aWhittaker et al ( , 2007bWhittaker et al ( , 2008 and modeled by Attal et al (2008) and Cowie et al (2006Cowie et al ( , 2008 involve transient response extending over about 18 marine oxygen isotope stages. A model calibrated to such a case might therefore be said to represent a weighted average of glacial and interglacial conditions, though understanding the nature of such averaging, and the relative importance of cold versus warm phases, deserves further research.…”

“…Pazzaglia et al, 1998;Hancock et al, 1998) are just a few examples. Regardless of the method, it is critical to know either the time at which the landscape had a particular configuration (like the reconstructed post-glacial topography in Figure 3b), or the rate of baselevel motion over a known period of time (as in Snyder et al, 2000, Whittaker et al, 2007a, 2007b, or ideally both. In a nutshell, data should be available to answer at least one of the following questions: At what point in the past did the landscape have a different configuration that can be reconstructed from preserved remnants?…”

The SPACE 1.0 model: a Landlab component for 2-D calculation of sediment transport, bedrock erosion, and landscape evolution

“…sure for channel width in which width scales as the square root of water discharge (e.g., Leopold and Maddock, 1953;Wohl and David, 2008), it may be desirable for some applications to add dynamic channel width adjustments to the model, as previous work has suggested that width trades off with slope in transient channels (e.g., Finnegan et al, 2005;Turowski et al, 2006;Wobus et al, 2006;Whittaker et al, 2007;Attal et al, 2008;Lague, 2010;Yanites and Tucker, 2010). One option for incorporating dynamic width is to calculate or approximate shear-stress distributions across channel cross sections (e.g., Kean and Smith, 2004;Wobus et al, 2006Wobus et al, , 2008Turowski et al, 2009).…”