The thesis deals with the first flush phenomenon. Given are the definitions of the first flush, the method
for defining the event mean concentration and the procedure of defining mass first flush ratio, which
gives us the quantity of the mass of emitted pollutants, as a function of the storm progress indicated by
the normalized runoff volume. The second part describes programme SWMM (Storm Water
Management Model). The third part represents the results of measurements which took place at Vič in
Ljubljana. The analysis took place in all seasons and it contained twenty parameters. The fourth part
shows results of measurements on the stormwater overflow in Črnomelj and the influence of overflow
water on the quality of the Dobličica river. I used the results for calibration of the model in SWMM.
With that model, I simulated the oscillation of the pollutants over time. I defined the mass of wash-off
pollutants in the rainfall event of 21 November 2015 in which there were 20 millimetres of rainfall after
20 droughty days. With the results of simulation, I determined the event mean concentration and the
amount of mass emission in relation to cumulative flow volume. It was found that if the stormwater
overflow and stormwater holding tank worked correctly, pollution would be reduced by 70%. I also used
the calibrated model in simulating the rainfall event with duration of 30 minutes and one-year return
period. Simulation was set with 20-day and 50-day dry period.