土壤潛移是一種擾流嗎?

本文透過批判性的文獻回顧來重塑一個埋論架構，使得我們得以藉此來判斷那些相對緩慢的沉積物搬運，例如潛移，一是否可以被視爲擾流。在這個理論架構下，潛移被視爲總是流動速度緩慢的特殊顆粒流，而我們在野外和實驗室中都觀測到這樣一種緩慢、高密度的顆粒流會展現明顯的速度震盪。本文爲緩慢擾流提出一個修正的雷諾係數，標誌爲Re'。現階段，它的理論基礎仍有猜測成份。對於沒有擾動的層流而言，修正的雷諾係數值和傳統的雷諾係數值一致。而修正的雷諾係數值更爲優越的地方在於它可以被用來確認緩慢擾流，並且可以將不同類型的流體放在相同的理論架構下來判識。

關鍵字

擾流；顆粒流；潛移；蘭式方程式；雷諾係數

並列摘要

Based upon a critical review, the target of this paper is to reshape a theoretical framework under which one may justify if relative slow sediment transport processes, such as soil creep. a turbulent flow or not. Under this theoretical viewpoint, soil creep is treated as a special granular flow whose velocity is always slow, and such a slow and dense granular flow shows significant velocity fluctuation that can be observed in both field measurement and laboratory experiment. For describing slow turbulent, a compatible modified Reynolds number, Re', is proposed with some conjectures. For laminar flow without any significant velocity fluctuation, Re' gives the same value as the conventional Reynolds number, Re', does. However. Re' manage to recognise the slow turbulent granular flow, meanwhile keeps different kinds of flux flow under the same framework of justification. Taking for an example. Re is equal to 500 for a river with 0.5-cm•sec^(-1) flow velocity, 10-cm flow depth, and a water temperature of 20℃ (i.e., ν=0.01 cm^2•secj^(-1) while Re' is equal to 3500 which is in the transitional range close toward the turbulent flow in fluid dynamic literatures. Applying Re' to soil creep having annual speed of 1 mm with an average speed fluctuation about 90% of the annual speed, the diffusion coefficient (i.e., viscosity in such a case) is then about 0.81 mm^2 year^(-1). If the characteristic length (L) is defined as the wavelength of a terracette (about 1.2 meter). then Re' gives '2681', while the conventional Re gives only '1481'. Notice that L is chosen as 1.2 meter, and implies that the constant creeping speed can be realised only over a distance of 1.2 meter, or equivalently we can have constant creeping rate under the measurement duration of 1,200 years.