[1] Detailed bathymetric surveys of the seafloor have enabled the identification and analysis of submarine channels worldwide. Previous authors have remarked on the morphologic similarity of submarine channels and rivers, and have identified a number of similarities and differences in processes of flow and sedimentation. In this study, we compare the width, depth, and slope of 177 submarine channel cross-sections to that of 231 river cross-sections. The results indicate that submarine channels have cross-sectional dimensions that can exceed the dimensions of the largest rivers on earth by an order of magnitude. For rivers and submarine channels with similar width or depth, the slope of submarine channels can be up to two orders of magnitude greater than the slope of rivers. An analysis of trends in driving force vs. channel size suggests that a reasonable estimate of the volumetric sediment concentration of channelized turbidity currents lies in the range C = 0.2% to 0.6%. Bankfull turbidity current velocities are estimated using this range in concentration. Friction coefficients are based on values identified for large rivers and a modified Chezy equation. These velocities are then used in a classic hydraulic geometry analysis of the submarine channels, which shows that submarine channels and rivers follow similar power law trends in width, depth, and velocity as functions of bankfull discharge.Citation: Konsoer, K., J. Zinger, and G. Parker (2013), Bankfull hydraulic geometry of submarine channels created by turbidity currents: Relations between bankfull channel characteristics and formative flow discharge,

In meandering rivers, bend cutoffs have long been recognized as an important mechanism of change in the path of the channel. Meander bend cutoffs can develop by the progressive migration of an elongated bend onto itself, which forms a neck cutoff, or by the erosion of a new channel across the neck of the bend, which is known as a chute cutoff 1 . River cutoffs affect channel navigation 2 , and form meander scars and oxbow lakes in river floodplains 1,3,4 , which are important habitats for riparian ecosystems 5 . The importance of cutoff processes in meander dynamics is well established 1,3,4,6-8 , but the effects of cutoffs on overall sediment flux are poorly characterized. Here we use aerial imagery, global positioning system mapping and measurements of channel bathymetry to estimate the amount of sediment released by two chute cutoffs on the Wabash River in the Midwestern USA. We find that each event triggered the rapid delivery of sediment into the river, at rates that are one to five orders of magnitude larger than those produced by lateral migration of individual bends. We find that much of this material was deposited immediately downstream, at the confluence of the Wabash and Ohio rivers, which led to significant changes in channel morphology. This sedimentation ultimately impeded barge traffic and necessitated extensive dredging.Cutoffs are highly effective geomorphological events 9 that produce long-lasting changes in river morphology, and also strongly influence the three-dimensional sedimentary architecture of floodplains through the subsequent formation and infilling of oxbow lakes 10-12 . A key unresolved problem is the extent to which bend cutoffs perform geomorphic work 9 by rapidly mobilizing floodplain material, thereby contributing to the sediment flux of meandering rivers. Although past investigations have examined channel changes caused by cutoffs and sedimentation rates in oxbow lakes [12][13][14][15] , no previous studies have documented quantitatively the erosional flux of sediment in the early stages of a meander cutoff on a large river. Quantification of erosional sediment influxes is essential for evaluating the influence of episodic erosion by cutoffs on aquatic ecosystems 5 , for determining downstream impacts on river channels and reservoirs (R. G. Jackson, A Depositional Model of Point Bars in the Lower Wabash River unpublished Ph.D. thesis, Univ. Illinois, 269;1975), and for ascertaining how cutoffs contribute to the sediment budgets of large rivers. Over long timescales, sediment budgets associated with cutoffs will be highly asynchronous, with chute cutoffs producing rapid, short-term removal of sediment from the floodplain and subsequent sedimentation within the resultant oxbow lakes leading to long-term sediment storage 12-15 .In this paper, we quantify the erosional flux of floodplain sediment mobilized by two chute cutoff events on a large meander bend on the Wabash River, USA, and show how this flux is one to five orders of magnitude greater than sediment fluxes associated

[1] This paper documents the three-dimensional structure of flow and bed morphology of two developing chute cutoffs on a single meander bend on the lower Wabash River, USA, and relates the flow structure to patterns of morphologic change in the evolving cutoff channels. The upstream end of the cutoff channels is characterized by: (1) a zone of flow velocity reduction/stagnation and bar development in the main channel across from the cutoff entrance, (2) flow separation and bar development along the inner (left) bank of the cutoff channel immediately downstream from the cutoff entrance, and (3) helical motion and outward advection of flow momentum entering the cutoff channel, leading to erosion of the outer (right) bank of the cutoff channel. At the downstream end of the cutoff channels, the major hydrodynamic and morphologic features are: (1) flow stagnation along the bank of the main channel immediately upstream of the cutoff channel mouth, (2) convergence of flows from the cutoff and main channels, (3) helical motion of flow from the cutoff, (4) a zone of reduced velocity along the bank of the main channel immediately downstream from the cutoff channel mouth, and (5) development of a prominent bar complex that penetrates into the main channel and extends from the stagnation zone upstream to downstream of the cutoff mouth. These results provide the basis for a conceptual model of chute-cutoff dynamics in which the upstream and downstream ends of a cutoff channel are treated as a bifurcation and confluence, respectively.

[1] Collecting high-resolution data to quantify the sedimentary architecture within contemporary alluvial channels remains one of the outstanding challenges in fluvial sedimentology. Here, we present data collected using a new geophysical method, the parametric echo sounder (PES), which can meet this challenge. From surveys over a field of sand dunes in the Río Paraná, Argentina, we demonstrate the unique ability of PES to image the subsurface structure within active channels at a decimetric resolution. These data reveal the bounding surfaces between bars and dunes, as well as the foresets and reactivation surfaces within them. This provides quantitative in situ data for recent work that suggests cross-strata preserved by dunes may be more related to flow depths less than the commonly assumed bankfull level. These surveys demonstrate that PES can provide hitherto unobtainable data from alluvial channels and presents significant opportunities for more detailed coupled studies of fluvial processes and their deposits.

No abstract