Zmienność współczynnika filtracji w strefie hyporeicznej w świetle badań laboratoryjnych

Abstract

Variability of the hydraulic conductivity in the hyporheic zone in the light of laboratory research.A b s t r a c t. The interaction between surface water and groundwater throughout the hyporheic zone determines the diurnal water level vfluctuations in springs, streams and lakes. The previous studies have listed evapotranspiration, variability of hydraulic conductivity in the hyporheic zone, melting and freeze-thawing processes, thermal expansion and water viscosity among the factors responsible for the water level diurnal fluctuations. The aim of the research was to investigate the variability of hydraulic conductivity in the hyporheic zone and its impact on the diurnal fluctuations of the water level. Experimental series were performed in laboratory conditions using seepage columns. Four types of sand sediments, with a hydraulic conductivity ranging from 6×10−6 to 5×10−4 m/s, were tested. The obtained values of hydraulic conductivity appeared to depend on the sand grain size, temperature, the direction of the hydraulic gradient, and the fluidization of the sediment (flowing sand). In all tests, higher hydraulic conductivity values were observed when water was set to flow in the direction opposite to gravity (flow up) rather than downward (flow down). In the sediments, which have not reached the state of fluidization, with anincrease of the hydraulic gradient, values of hydraulic conductivity were two times higher during flow up than in the case of flow down. In the case of sediments being fluidized, the obtained values of hydraulic conductivity were roughly 3 times higher. The initiation of the fluidization process has been observed at the hydraulic gradient close to one. The results of laboratory experiments allow for a better understandingof the factors that have impact on diurnal fluctuations of the water level, especially when seepage of groundwater is present. Fluidization of the hyporheic zone after precipitation or thawing events may inhibit diurnal fluctuations.