For the purposes of planning the protection against and control of water pollution in streams, on the basis of theoretic and numeric analyses of the problem, a methodology has been worked out for defining incidental pollution spread in open streams, which is generally applicable to non-stationary releases and spread of pollution in a stream. It covers the problem of longitudinal dispersion in natural streams in its totality. Attention has been paid to dissoluble or suspended non-depositable polluting substances. Presented are the required field, laboratory and numeric investigations. By the basic program DISPER a numeric model has been developed and the program INCH) made. The programs for calculation of dispersion coefficient have been made and successfully applied: D (commonly measured values of the flow) and RUTINGD (data on the stream tracing). The programs had been previously checked, assuming simple calculation cases and using the existing data on tracing in the river Miljacka. For further checking and applicability of the methodology, measuring data have been used, obtained for a selected stretch of the river Vrbas for a length of 31,897m. For prediction of possible incidental pollution spreading, assumed was an unpredicted release of a constant quantity of untreated waste cyanide water during 1600s. On the basis of the data from one tracing reach of the river Vrbas, it has been shown that by numeric calculation it is possible to obtain excellent concordance of the measured and numeric curve. Therefore, it is necessary to use corresponding hydraulic-hydrologic data, and importantly, to define reliable values of dispersion coefficients.

A chronological and critical review is made of existing methods for predicting coefficients and the area of the longitudinal turbulent dispersion, which were chosen by their importance and applicability to open natural streams. For natural mountain streams, a suitable method for calculating dispersion coefficient on the basis of flow parameters is accepted. A new method is proposed for determining characteristic mixing lengths l’\ds\dr for nonuniform winding streams. There is a description of investigations carried out in a mountain, expressly nonuniform flow, which were used to check the given assumptions.