Dispersion of Contaminated Sediment Bed Load

Dispersion of instantaneously released contaminated bed sediments is analyzed within the framework of a Lagrangian probabilistic model. The time and space concentration distributions, with the parameters computed on the basis of the same rate of mass movement and a constant rate of spread, approach Gaussian form asymptotically. A procedure is suggested for deriving approximations to the envelopes of the distribution curves parameterized by either the time or distance. The method is also applicable when the shape factor of the particle step length distribution takes on nonintegral values greater than one. Where the normality approximation is satisfactory, the critical duration for a given degree of pollution varies in direct proportion to the square root of the distance from the source. Graphical results for the critical time limits for the absorption of radiation from contaminated particles for different positions of the subject are also presented.