Temporal variability of the selected flood parameters in the Biebrza River valley
Annals of Warsaw University of Life Sciences, Land Reclamation
Temporal variability of the selected fl ood parameters in the Biebrza River valley. The paper presents the application of the hydrodynamic one-dimensional model of river fl ow based on St Venant equations for calculation of annual fl oods characteristics in the Lower Biebrza River Basin situated in the Northeast of Poland. This model was combined with the Digital Elevation Model (DEM) for determining of area of fl ooding, its mean depth and fl ood volume. The model was calibrated using
... ated using measurements of fl ood extent and verifi ed comparing calculated fl ood extent to satellite images. The water level values calculated with the numerical model of fl ood-fl ow for cross--sections were next used to determine the digital model of the fl oodwater table in the valley. Then, inundation extent maps and water depth maps were calculated for whole area of the valley by overlaying the DEM and water table layers. This procedure, fl ood simulations with the hydrodynamic model and GIS analysis for determinations of inundation extent, was repeated for each day of the analyzed period of 1966-2000. A set of each year maximum calculated areas of fl ooding with related mean water depths and fl ood volumes was created and it was submitted to the trend analysis in order to determine possible change tendencies. Statistical analysis of three above described time series of annual fl ood characteristics was conducted with the use of moving average technique and linear regression method. Moving averages were calculate in two variants: with time step of 5 years and of 10 years. Next, linear trends were calculated by linear regression method. The results indicate that the developed hydrodynamic model of river fl ow combined with the DEM was useful for the calculation of annual maximum fl oods in the Lower Biebrza Valley and their parameters. Analysis of calculated fl ood parameters variability within the analyzed time period of 1961-2000 show decreasing trends for investigated area. This means that results of climate changes are perceptible in investigated area and they form serious danger to riparian wetlands.