Summary:

The article presents the influence of precipitation sewage discharge on the hydrology and chemism of small streams. Catchment areas of small streams such as the Jamna river, the Mleczna river and Murckowski trench located within Upper- Silesian Industrial Area were chosen to be subjects of the research. It has been proved that precipitation sewage discharge to rivers contributes to dynamic changes of water chemism. They are the consequence of both the sewage quality itself and resuspention processes releasing polluted deposits into water. It is due to the downwash of salt used in winter to remove ice from roads. Erosional processes become more intensive as well leading to the transformation of cross-sections of river beds. In case of the Jamna river repeated increase in the area of the river bed cross-section in comparison with the period before intensive urbanisation of the catchment area took place. In case of a small stream – Murckowski trench (Katowice) the lowering of river bed bottom below the outlet of main precipitation sewage pipe reached 1.5m.