PREDICTING THE MIGRATION OF DISSOLVED TOXIC-SUBSTANCES FROM CATCHMENTS BY A COLLECTIVE MODEL

In the present paper a collective model for predicting the migration o f dissolved toxic substances through drainage areas is described. The model has been validated using data for Cs-137 and Sr-90 concentration s in water of some European contaminated rivers following the atmosphe ric fall-out from the accident at the Chernobyl power plant. It has be en demonstrated that the migration rate lambda (s(-1)) of a dissolved toxic substance from a catchment may be evaluated by the following app roximate formula: lambda=(c In tf d)lt, where t is the time from a pul se deposition event and the coefficients c and d depend on the charact eristics of the substance. It has been shown that the mathematical for m of the transfer function (flux of dissolved substance at time t foll owing a single pulse deposition of a pollutant onto the catchment) of a toxic substance from a drainage area is very simple. Moreover, the v alues of the transfer function parameters are slightly variable despit e the large range of characteristics of the catchments here examined. Indeed, the statistical aggregation of competing migration processes c an lead to 'stable' collective behaviours that are less variable than each single process. (C) 1998 Elsevier Science B.V. All rights reserve d.