FLOODS AND FLOOD RISK MAPPING IN THE UPPER DNISTER RIVER VALLEY

I. Kovalchuk, A. Mykhnovych

Ivan Franko National University of Lviv, Ukraine

admin@ukrmap.com.ua

In the last decades the human activity in the mountain part of the Dnister river basin causes activization of extreme floods development. Traditionally the main measures of flood protection in the Upper Dnister catchment was earth embankment, channels, sluices and pumping stations building. Most of dikes have many imperfections.

The problems of flood development, flood protection management and hydrological regime analysis of the Upper Dnister have been investigated within the joint German-Ukrainian research project “Transformation processes in the Dnister region (Western Ukraine)” (1997 – 2004). The main objectives of our research was hydrological regime transformations analysis as well as modelling of flood development and zones flooded during floods of different probability (10, 25, 50 and 1000 years). For this purpose:

▪ hydrological data base (daily discharge and water levels, precipitation) was elaborated;

▪ the data bases containing morphometric parameters of river valley and river bed, morphometry and present state of embankments have been created;

▪ the present technical state of embankments as well as risk of their breaking and overflooding was evaluated;

▪ flood modelling applying GIS technologies is carried out;

▪ GIS-models were verified by comparing them with maps showed real flooded areas created in the upper Dnister river valley.

The floods and flood risk mapping were realized applying ArcView and ARC/INFO GIS software and also GIS-integrated software for hydrological modelling like HEC-RAS.

As the result of investigations the large-scale GIS-model of flooded zones has been created. The dynamic GIS-model of flood development for different probability has been created. Overlaying of created models on the map of land use the risk of economical damages has been evaluated.

Other part of our investigations in the Dnister catchment is assessment of riverbed processes and their impact on a flood risk due to threat of embankments destroying by erosion processes as well as of sediments accumulation.

Assessment of scales, intensity and trends of river beds vertical deformations was based on the set of cross-sections and longitudinal profiles as well as water level–discharges relation curves created for different periods of time.

For investigated catchments trends, scale and average intensity of deformation for period 8 – 32 years have been calculated. Obtained results have shown that mountain and pre-mountain catchments are characterized by highest potential of hydro-geomorphologic processes and intensity of their development. Erosion dominates within the larger part of Dnister catchment.