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River restoration schemes that utilise natural processes need to be monitored post-implementation to inform adaptive management, to assess their success at delivering sustained ecological improvements and to contribute to the design of other schemes. All three of these monitoring objectives require an understanding of the geomorphic mechanisms that cause channel adjustment and how they shape the mosaic of geomorphic units that make up physical habitat. In the last decade repeat, high-resolution topographic surveys of river restoration schemes have become commonplace through the application of a range of geomatics technologies including echo-sounders, laser scanners and Structure from Motion photogrammetry. Such datasets offer opportunities to map geomorphic change and geomorphic unit evolution to quantitatively analyse the relative roles of different processes in generating physical habitat. Here, we present results from an investigation into the morphodynamics of the Whit Beck river restoration scheme, implemented by the West Cumbria Rivers Trust, UK. We use repeat Digital Elevation Models (DEMs) to quantify patterns of erosion and deposition using the Geomorphic Change Detection (GCD) toolbox and to map geomorphic units, using the Geomorphic Unit Tool (GUT). The segmentation of maps of erosion and deposition with maps of geomorphic units quantifies physical habitat transitions. The resulting analysis indicates the different mechanisms of adjustment that generate physical habitat throughout the restoration scheme and how they are linked to different initial conditions.

Bedrock rivers exert a critical control over landscape evolution, yet little is known about the sediment transport processes that affect their incision. We present theoretical analyses and field data that demonstrate how grain entrainment, translation and deposition are affected by the degree of sediment cover in a bedrock channel. Theoretical considerations of grain entrainment mechanics and sediment continuity each demonstrate that areas of exposed bedrock and thin sediment depths cause sediment transport to be size-independent, albeit excluding extreme grain sizes. We report gravel and cobble magnetic tracer data from three rivers with contrasting sediment cover: the bedrock River Calder (20 % cover), the bedrock South Fork Eel River (80 %) and the alluvial Allt Dubhaig (100 %). These datasets show that: 1) transport distances in the River Calder are controlled by sediment patch location, whereas in the other rivers transport distances are described by gamma distributions representing local dispersion; 2) River Calder transport distances are size-independent across all recorded shear stresses, whereas the other rivers display size-selectivity; 3) River Calder tracers are entrained at a dimensionless shear stress of 0.038, which is relatively low compared to alluvial rivers; and, 4) virtual grain velocities in the River Calder are higher than in a comparable reach of the Allt Dubhaig. These contrasts result from differences in the thicknesses and spatial distribution of sediment in the three rivers, and support the theoretical analysis. Sediment processes in bedrock rivers systematically vary along a continuum between bedrock and alluvial end members.

The Irrawaddy (Ayeyarwady) River of Myanmar is ranked as having the fifth-largest suspended load and the fourth-highest total dissolved load of the world's rivers, and the combined Irrawaddy and Salween ( Thanlwin) system is regarded as contributing 20% of the total flux of material from the Himalayan-Tibetan orogen. The estimates for the Irrawaddy are taken from published quotations of a nineteenth-century data set, and there are no available published data for the Myanmar reaches of the Salween. Apart from our own field studies in 2005 and 2006, no recent research documenting the sediment load of these important large rivers has been conducted, although their contribution to biogeochemical cycles and ocean geochemistry is clearly significant. We present a reanalysis of the Irrawaddy data from the original 550-page report of Gordon covering 10 yr of discharge ( 1869-1879) and 1 yr of sediment concentration measurements ( 1877-1878). We describe Gordon's methodologies, evaluate his measurements and calculations and the adjustments he made to his data set, and present our revised interpretation of nineteenth-century discharge and sediment load with an estimate of uncertainty. The 10-yr average of annual suspended sediment load currently cited in the literature is assessed as being underestimated by 27% on the basis of our sediment rating curve of the nineteenth-century data. On the basis of our sampling of suspended load, the nineteenth-century concentrations are interpreted to be missing about 18% of their total mass, which is the proportion of sediment recovered by a 0.45-mm filter. The new annual Irrawaddy suspended sediment load is MT. Our revised estimate of the annual sediment load 364 +/- 60 from the Irrawaddy-Salween system for the nineteenth century ( 600 MT) represents more than half the present-day Ganges-Brahmaputra flux to the Indian Ocean. Since major Chinese rivers have reduced their load due to damming, the Irrawaddy is likely the third-largest contributor of sediment load in the world. Publisher PDF