Erosion transport-limited

In contrast, under transport-limited conditions, weathering rates are ultimately limited by the formation of soils that are sufficiently thick or impermeable to restrict free access by water to unweathered material. Erosion rates are low, and soils and solid weathering products are cation-deficient. In regions where transport-limited erosion predominates, soils are thick and slopes are slight and convexo-concave (Fig. 6-2b). With time, these... 

Sediment-laden rivers flowing over flat terrain commonly develop extensive floodplains. At times, floodplains coalesce into broad depositional alluvial plains such as the Llanos of South America. The sediments in those deposits weather chemically. Less stable minerals in the sediment are broken down and alluvial soils develop. Eventually, only the most stable minerals such as quartz remain, and the clays are transformed into cation-deficient varieties. Sediment in such rivers, especially the sand, may go through many cycles of deposition, weathering, and erosion before it is transported out of the system. Compositionally, this sediment resembles that derived from transport-limited erosion. Elemental fractionation between the original bedrock and erosion products still occurs because of the permanent burial of some cation-rich material and the uninterrupted transport of much of the fine-grained suspended sediment out of the system (Johnsson etal., 1988 StaUard, 1985,1988). 

The erosion process on slopes can be envisioned as a continuum between the weathering-limited and transport-limited extremes (Carson and Kirkby, 1972 Stallard, 1985,1995a). Erosion is classified as transport limited when the rate of supply of material by weathering exceeds the capacity of transport processes to remove the material. Erosion is weathering limited when the capacity of the transport process exceeds the rate at which material is generated by weath-... 

In contrast, under transport-limited conditions, weathering rates are ultimately limited by the formation of soils that are sufficiently thick or impermeable to restrict free access by water to unweathered material. Erosion rates... 

Table 9-2 Erosion regimes, features, and processes associated with transport-limited and weatherine-limited erosion...

When soil thickness is at the stable value (F), erosion is transport limited. Chemical weathering is also transport limited. This is, however, not because of reaction kinetics instead this limitation is primarily controlled by physical factors, most probably, restricted access of water to the primary minerals. 

In regions where erosion is transport limited, weathering rates are controlled by the supply of reactive fluids to unstable minerals. This is controlled by soil properties, regional base level, and ultimately, sea level. 

Oxygenation treatment also reduces the risk of erosion-corrosion problems and limits iron transport to other parts of the boiler system where fouling could take place. 

Deposition of wax following crystallisation depends on the temperature differential between the bulk crude stream and the pipewall, and the Reynolds number. The larger the temperature differential, the greater the chance of wax deposition since molecular diffusion of dissolved wax to the pipewall intensifies as a result of the increase in wax concentration near the pipewall brought about by the temperature differential. With respect to Reynolds number, maximum wax accumulation is expected in the transition range (Reynolds number between 2000 and 4000). At low (laminar) flew, the net transport of wax to the wall 1s reduced by a relatively thick laminar layer adjacent to the pipewall and during turbulent flow, wax build-up 1s limited by erosion. 

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