Stochastic Theory Of Bed Load Transport

Bedload transport is an major part of sediment transport in nature, and essential forevolution of river morpholody, flash flood and dambreak flood. Aiming to predict themean bedload transport rate, the conventional bedload transport theories lack of detailsof bedload motion and fail to represent the large fluctuations in bedload transportprocess. However, the state-of-art mechanical theories, such as macroscopic two-phaseflow model, kinetics model or microscopic discrete element model, have too manypresumptions to describe various bedload transport processes.In this study, the Markovian birth-death model, including the process of discretemass exchange, is used to develop a general stochastic theory of bedload transport,which is expected to cover the multiple temporal-spatial scales’ behavior of bedloadtransport. The Markovian birth-death model consider not only the discreteness ofbedload particle but also pursue the characteristic of the particle system i.e. the numberof moving particle. After the Markovian birth-death model is combined with theLangevin equation of an individual particle, the general stochastic theory is able topresent the mechanical behavior over a broad range of spatial scales. The present thesisincludes the following contents.(1)The theoretical and experimental study on the bimodal characteristics of PDF ofthe stop time between two emigration particles；(2)The three-regime relation between variance of bedload transport flux and itssampling time scales；(3)Development of multi-cell model of the Markovian birth-death model and itsapplication on the study of the spatial behavior of bedload transport；(4)Theoretical combination of the Markovian birth-death model and Langevinequation of an individual particle and the description of PDF of bedload transportrate(rolling regime) over a broad range of spatial scales.