Hydrological interactions between unregulated river and its floodplain :field study of the Lužnice River floodplain

Abstract

This paper presents preliminary results of an assessment of the groundwater - surface water (GW-SW) interaction processes of the Lužnice River floodplain during a selected time period, comprising high and low stream flow. It analyses various events that reflect the spatial and temporal variations in water flows to and from the floodplain. Hydrological exchange processes in the floodplain of a groundwater - surface water system are studied on the basis of an experimental site. The chosen study area comprises a c. 10 km long section of the Lužnice River floodplain, located in the south part of the Czech Republic. Water stages in Lužnice River were continuously measured with limnimeters installed upstream, downstream and in the middle of the floodplain length. Five boreholes were drilled along a transect perpendicular to the river to monitor the water table fluctuation in the floodplain. Water level variations of a wetland pool, located at the floodplain left margin in the transect were also continuously recorded. The results indicate that observed groundwater levels are closely associated with the river flows and the assessed reach was gaining most of the time. Downstream flood wave attenuation was not observed during the period of the highest flows due to the large lateral subsurface inflow contribution.