The Flood Risk Assessment in cities as an element of a Flood Risk Management: A CASE STUdY of Krakow, Poland

Urbanization comes with a variety of environmental problems for both the local and downstream ecosystems. The loss in permeable surfaces reduces the infiltration into soil; the introduction of artificial drainage alters or replaces natural pathways. Soil sealing-related impervious surfaces inflict the risks of augmented runoff and lower infiltration rate. The aim of the work was to assess the risk of flood in urban area on the example of Krakow. Krakow is a city located in the highland climate region of Poland and has high impervious cover. The analysis was performed for watersheds that are main tributaries to the Vistula river.

Flood risk assessment was carried out for maximum flows with a probability of exceeding 1%. Because almost all of analyzed watersheds are ungauged, the peak discharges and flood hydrograph were calculated based on rainfall-runoff model based on Nash cascade of linear reservoirs, according to the guidelines recommended by Association of Polish Hydrologists . To determine the flood areas and wave movement, a one-dimensional model was used, based on the Saint-Venant equations. 

The analyses showed that in the Krakow agglomeration, there are 45 areas where flood hazard is identified, of which 39 are located on the tributaries of the Vistula and 6 - within the range of the direct influence of the Vistula River. The main problems of flood risk are linked to the following causes: 1) backwater effect occurs in the tributaries to the Vistula , 2) The limited capacity of the rivers - fig. 1, 3) obstruction of culverts or bridges, which influences the capacity of the rivers - fig. 2.

Fig. 1.  The flood area in the Struga Rusiecka stream as a result of too small bed capacity

Fig. 2. The flood area in the Drwinka river as a result of a culvert obstruction