SOME GREEN INFRASTRUCTURE DEVELOPMENT SCENARIOS AND
THEIR INFLUENCE ON CERTAIN CONDITIONS OF URBAN FLOW
FORMATION. CASE STUDY OF REVUCA CITY, SLOVAKIA

With the development of cities, modeling the flow of water in urban conditions becomes an increasingly necessary task. A preliminary assessment of the prospects of different scenarios of green infrastructure development is the goal of this work. To fulfill the task, the current land cover of the city and its changes under various scenarios were analyzed from a hydrological point of view. Such an assessment is necessary both in the context of the development of specific cities, and as a data preparation for further detailed modelling.

The object of this study is the inner city of Revuca, south-eastern part of the Banská Bystrica Region, Slovakia. The city lies mostly on a flat alluvial cone; the topography includes moderately cutted highlands in the central part, and mountains on its edge. Soils are deeply antropogenically transformed, represented mainly by fluvial cultisems on the floodplains and by various subtypes of cambisoles, with medium and high water permeability. Their hydrological type was predefined as intermediate between C and D.

The type of land cover and its imperviousness are among the key factors that determine the course of water flow formation processes. As an integral, digital indicator was used Curve number number (CN). It is a function of hydrologic soil group (HSG), cover type, treatment, hydrologic condition, antecedent runoff condition and impervious area in the catchment. CN vary from 0 to 100, where a CN equal to 100 means that all the precipitation turned to surface runoff and no infiltration occurred, CN of 0 means that all precipitation infiltrated, so there was no runoff. Curve numbers were determined using official tables, data from other similar cities, maps of land use categories, using photos and satellite images. The percentage of impermeable areas was calculated also separately. For detailed analysis, the city was divided into 447 subcatchments according to how water enters the stormwater network. Averaging across catchments is done using QGIS.

Current conditions and possible changes under three development scenarios were assessed. Sequential scenarios include: replacing the roofs of the largest buildings with green roofs (scenario 1), plus replacing of the paved areas (not the roads) with permeable pavements (scenario 2) and plus the significant improvement of the vegetation condition in areas with bare soil (scenario 3). These scenarios describe changes in approximately 21% of the studied area. Each subsequent stage changes about a third of this number, while bare soil accounts for the largest area. At the same time, the same percentage of the city is occupied by green zones and grass plots, and almost 23 percent are occupied by households.

It was determined that in the inner city of Revuca, the average CN in current conditions is 88.8, more than 38.7% of the territory is impervious. Considered changes allow reducing average CN to 85.8, while the percentage of water impervious surface decreased by almost a third, to 27.8%. The changes are much more significant in central and industrial districts, which can contribute to reducing the load on the drainage network.

The next steps are to refine the data on land cover and the corresponding CN, add other scenarios and model the change in the flood passage scenarios according to each of them.

Keywords: Green infrastructure, land cover, Curve Number method, GIS