An experimental study of flow, bedload transport and bed topography under conditions of erosion and deposition and comparison with theoretical models

Abstract

The nature of flow, sediment transport and bed texture and topography was studied in a laboratory flume using a mixed size-density sediment under equilibrium and non-equilibrium (aggradational, degradational) conditions and compared with theoretical models. During each experiment, water depth, bed and water surface elevation, flow velocity, bed shear stress, bedload transport and bed state were continuously monitored. Equilibrium, uniform flow was established with a discharge of about 0.05 m3 s ~ ', a flow depth of about 0-01 m, a flow velocity of about 0-81-0.88 m s *Present address: Department of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK. 1 1 7 118 S. J. Bennett and J. S. Bridgeand non-equilibrium flow conditions, total and fractional bedload transport rates and changes in bed topography and texture very well.

Landscape disequilibrium on 1000–10,000 year scales Marsyandi River, Nepal, central Himalaya

“…Deposits, such as the Higher Terrace, are preserved when sediment supply exceeds a river's carrying capacity. This excess sediment could have caused the channel to steepen to a new energy slope (Soni et al, 1980;Bennett and Bridge, 1995;Tucker, 1996;Alves and Cardoso, 1999).…”

“…Delta, where Early Holocene deposition rates are at least double the Late Holocene rates (Goodbred and Kuehl, 2000). Such doubling of sediment flux is likely to cause both aggradation and river-bed steepening (Bennett and Bridge, 1995).…”

The c. AD 1315 syn‐eruption and AD 1904 post‐eruption breakout floods from Lake Tarawera, Haroharo caldera, North Island, New Zealand

“…Flow divergence across the wider valley, and a consequent reduction in flow velocity, caused deposition of coarse, dense sediment from traction deposits. The poorly defined horizontal bedding and vague downstream dipping fabric of the coarser clasts characteristic of the bar (and other bars in this study, comprising stratified bouldery gravel lithofacies, Table 1) reflects deposition on the surface of the bar and shallow downstream dipping bar face (Miall 1977;Rust 1978;Bennett & Bridge 1995b), rather than sediment avalanching down the face of the bar to create foreset bedding characteristic of channelled scablandbars (Baker 1973).…”

Numerical Modelling of Alluvial Deposits: Recent Developments

“…MIDAS considers widthaveraged flow and sediment transport in straight channels, and therefore cannot predict the flow and sediment transport associated with point bars and braid bars. Vogel et al (1992), Bennett & Bridge (1995a), and Robinson et al (2001) used MIDAS to predict conditions of erosion and deposition in various flumes and modern rivers. Under erosional conditions, the model predicted well the temporal and spatial variation in sediment transport rate, grain-size distributions of the bed, armour layer, and eroded sediment, and the amount of erosion.…”