Effects of lateral confinement in natural and leveed reaches of a gravel‐bed river: Snake River, Wyoming, USA

• Published in: Earth surface processes and landforms Vol. 42; no. 13; pp. 2119 - 2138
• Main Authors: Leonard, Christina, Legleiter, Carl, Overstreet, Brandon
• Format: Journal Article
• Language: English
• Published: Bognor Regis Wiley Subscription Services, Inc 01.10.2017
• Subjects: Anthropogenic changes; Anthropogenic factors; Bank erosion; Banks (topography); Bars; Bathymetry; Braiding; Capacity; Channel erosion; Confining; Digital Elevation Models; Elevation; Erosion; Gravel; Levees; Lidar; Mobility; Morphology; Ratios; regulated river; Remote sensing; Remote sensing techniques; Rivers; Sediment; Sediment transport; Sensing techniques; Slope; Snake River; Spatial variations; Statistical analysis; Terraces; Topography; Topography (geology); Tracers; Transport; Tributaries; Width; United States > US; Wyoming; Snake River
• ISSN: 0197-9337; 1096-9837
• DOI: 10.1002/esp.4157

This study examined the effects of natural and anthropogenic changes in confining margin width by applying remote sensing techniques – fusing LiDAR topography with image‐derived bathymetry – over a large spatial extent: 58 km of the Snake River, Wyoming, USA. Fused digital elevation models from 2007 and 2012 were differenced to quantify changes in the volume of stored sediment, develop morphological sediment budgets, and infer spatial gradients in bed material transport. Our study spanned two similar reaches that were subject to different controls on confining margin width: natural terraces versus artificial levees. Channel planform in reaches with similar slope and confining margin width differed depending on whether the margins were natural or anthropogenic. The effects of tributaries also differed between the two reaches. Generally, the natural reach featured greater confining margin widths and was depositional, whereas artificial lateral constriction in the leveed reach produced a sediment budget that was closer to balanced. Although our remote sensing methods provided topographic data over a large area, net volumetric changes were not statistically significant due to the uncertainty associated with bed elevation estimates. We therefore focused on along‐channel spatial differences in bed material transport rather than absolute volumes of sediment. To complement indirect estimates of sediment transport derived by morphological sediment budgeting, we collected field data on bed mobility through a tracer study. Surface and subsurface grain size measurements were combined with bed mobility observations to calculate armoring and dimensionless sediment transport ratios, which indicated that sediment supply exceeded transport capacity in the natural reach and vice versa in the leveed reach. We hypothesize that constriction by levees induced an initial phase of incision and bed armoring. Because levees prevented bank erosion, the channel excavated sediment by migrating rapidly across the restricted braidplain and eroding bars and islands. Copyright © 2017 John Wiley & Sons, Ltd.