Impact of the City on the Rapid Increase in the Runoff and Transport of Suspended and Dissolved Solids During Rainfall—The Example of the Silnica River (Kielce, Poland)

Abstract

Urbanisation changes the water cycle and affects the parameters of transported, suspended and dissolved matter, especially in small river catchments. This paper presents the reasons why river runoff and fluvial transport rapidly increase during rainfall-induced summer floods in the stretch of the Silnica River that flows through the centre of Kielce, a city with a population of 200,000. Examples of implemented hydrotechnical solutions that aim to reduce the height of flood waves and eliminate water accumulation are also presented. The 18.05 km long Silnica River drains a catchment area of 49.4 km2. It flows through areas of varied land use, which have determined the location of five hydrometric stations (outlets) at different sub-catchments: Dabrowa(forest), Piaski (suburbia) and Jesionowa (includes a reservoir), as well as Pakosz and Bialogon (largely impervious areas in the city centre). Specific runoff, suspended and dissolved solids concentration and the specific load of these two types of fluvial transport were determined. It was found that the maximum specific runoff in the outlets of urban sub-catchments was significantly higher during floods than those of the sub-catchments upstream of the city centre; the suspended solids concentration was several times higher, and the suspended solids load was approximately 200 times higher. Recognition of the basic parameters of rainfall-induced flood waves, as well as the dynamics and size of fluvial transport at the hydrometric stations, especially at the outlets of sub-catchments with a large proportion of impervious area (approximately 30%), has become the basis for the development and implementation of modernisation projects and the construction of hydrotechnical facilities and devices in the river channel in the centre of Kielce.