Since 1993 a hydrological study has been carried out by the Forest Research Institute in the Kampinos National Park with a view to recognize the role of water in the processes of forest site formation. Ground water dynamics in a wet coniferous forest site is characterized based on the equation of water balance in the soil. Two study catchments have been identified and within those a network of forest plots instruments have been installed for measuring water cycle parameters. The observation network includes: 112 wells, for simultaneously measuring the ground water dynamics, distributed throughout the catchments under study in the National Park; instrumentation installed in two plots in a wet coniferous forest site for continuous monitoring of changes in balance elements within the Lasica River catchment; a pluviograph for measuring bulk precipitation installed at the climate station at Granica. The measurements are used to validate the dynamic model of water cycling. The approach is to examine which changes in the ground water storage are defined as a result of summation of water balance components of the plant community under study, i.e., the effective precipitation is measured as input, while downward flow and evapotranspiration losses are determined from the model. In order to determine changes in retention resulting from lateral inflow and outflow in the ground, a new validated model based on the hydraulic theory of filtration will be applied. The model takes advantage of a method which consists of dividing the infiltration space into calculation blocks. The following hypotheses are presented which helped formulate the model: 1) the ground water table underlying forest cover undergoes annual cyclic changes; 2) evapotranspiration on wet forest sites is inversely proportional to the depth of ground water occurrence; and 3) downward flow is directly proportional to the height of the ground water table. The first hypothesis has been proven in this case study.
Key words: water balance, ground water, wet forest site, model of water cycling.
Correspondence: Robert Jedra, Forest Research Institute, Division of Water Management, 3 Bitwy Warszawsk1920 r. Street, 00973 Warszawa, Poland