Hydrological observation and modelling relationship for the determination of water budget in Lusatian post-mining landscape

The hydrological observation network in a small, sparsely vegetated watershed within the post-mining landscape includes measurements of meteorological quantities (precipitation, temperature, global radiation, humidity, wind speed), of water level in a swale by pressure transducers, and of soil water by TDR-probes, tensiometers and a seepage gravity lysimeter. The field observations resulted in a modelling concept, where modules for actual evapotranspiration, soil water movement and surface runoff were specified and coupled with each other.The results of measurements and modelling for a 2 years observation period revealed a predominant relation of the distribution of hydraulic properties on hummocks and erosion channels, formed by runoff and erosion. On hummocks both processes are intensified by the water repellency of the tertiary sandy overburden, which seems to be related to wetting–drying-cycles of the dump substrate. During periods of hydrophobic conditions, surface runoff is increased from the hummocks and most groundwater recharge occurs within the erosion channels.Under consideration of the wetting–drying-cycles, the components of the water balance were obtained from daily precipitation values by a simplified storage approach version of the model in acceptable quality compared to the results of the detailed model version. In this version surface runoff occurs only under water repellent substrate conditions.To analyse the variability of water balance components for a real fluctuation of weather conditions, a 30-year meteorological record was considered. The precipitation in the investigated catchment (corrected for errors of wind, for wetting of the collector and for loss of evaporation from the collector) of 628 mm per year is divided into the evapotranspiration of 325 mm per year, groundwater recharge of 303 mm per year for 30-year average climatic conditions.