The Relationship between Suspended Solid Loads and Dissolved Material during Floods of Various Origin in Catchments of Different Use

The paper presents the results of stationary, detailed studies on the variability of the mutual share of two fluvial loads, i.e., suspended solids and dissolved material during floods caused by rainstorm, continuous rainfalls and snowmelt in selected rivers (Silnica, Sufraganiec) draining small catchments in central Poland, including two characterized by a high level of urbanization. Irrespective of the origin of the flood, the share of suspended solids load did not exceed 80% in urbanized catchments, in suburban catchments—44%, and in forest catchments—32%. In the former, the gradient of the increase in the share of suspended solids and concentration time in the first phase of the flood was several times higher than in the other catchments. It was proved that statistically significant relationships exist between the share of sealed surfaces (roads, car parks, roofs, etc.) in the total catchment area and the average share of suspended solids, both in the rising and falling phase of the flood wave, regardless of their origin. Similar relationships were documented by analyzing: the density of the drainage network (storm sewers, roads, etc.)—the share of suspension. The obtained results have an interesting cognitive aspect and in practice are used for the development of hydrotechnical documentation related to water management in the city.