Modelling groundwater regime acceptable for the forest survival after the building of the hydro-electric power plant

The reservoir of the future hydro-electric power plant ‘Novo Virje’ plant on Drava river, Croatia, could increase the absolute mean groundwater level in the nearby flood-plain forest. These changes could result in a decline of some forest species, especially the pedunculate oak (Quercus robur L.), which is very sensitive to the groundwater level disturbance. Dendroecological study was undertaken with the objective of finding acceptable groundwater level regime from the perspective of survival of nearby flood-plain forest. The study was spatially intensive (GIS based) and executed in the following steps: (1) building of the model which describes basal area increment of the pedunculate oak as a function of environmental estimators (hydrologic, soil, climatic and tree competition variables); (2) simulation of increment by the model under different groundwater level regimes and comparison of the simulation results with predefined increment minimum; and (3) designing of the envelopes of the acceptable regimes (simulated increment is larger than predefined minimum). These results are the basis for the design of hydro-technical measures aiming at protecting of flood-plain forests after the hydro-electric power plant is built.