A hyporheic zone is the region underneath or near the streambed that has interaction with groundwater and surface water. It serves many functions including exchange of water, nutrients and organic matter. Hydraulic parameters such as permeability and hydraulic gradient across streambeds control the water flow in the hyporheic zone. The accuracy of measurements of those parameters is important for learning and interpreting the hyporheic zone properties. The first part of this study will focus on the air compressibility effect on the Bouwer and Rice (B&R) seepage meter. The second part of the study will focus on the process of baseflow to a stream with a low hydraulic conductivity thin layer streambed. The third part of the study will focus on the bank storage effect in unsaturated and saturated zone with a streambed. A correction is obtained for calculating the seepage flux rate that includes consideration of air compressibility inside the manometer of a Bouwer and Rice seepage meter. The result shows that the effect of air compressibility in the manometer increases with the volume of air in the manometer. The correction of this study will work as a quantitative tool to determine if air compressibility can be neglected or not for a Bouwer and Rice seepage meter test. For the baseflow to a stream process, a low hydraulic conductivity thin layer streambed is considered along with an unsaturated-saturated coupled model. The hydraulic head in unsaturated and saturated zones are analytically derived. The integration of lateral seepage flux across both unsaturated and saturated zones are calculated afterwards. The study suggests that streambed affects the total discharge rate into the stream at early and late times in quite different manners, where the total discharge rate includes the horizontal discharge rates of both saturated and unsaturated zones. The peak of total discharge rate which occurs in early time is lowered and the baseflow decay process is prolonged when there is a streambed. In slope recession hydrograph analysis, the streambed affects early time slope and has little impact on late time slope. This results in an underestimation of hydraulic conductivity, specific yield and saturated aquifer thickness if the streambed effect is not considered in the analysis. Bank storage effect in unsaturated and saturated zone can be influenced by the streambed. A lower streambed hydraulic conductance value will lead to a lower peak value of the flux exchange rate between the aquifer and the stream. The total bank storage volume will also be lower if the streambed hydraulic conductance is lower. The bank storage releasing time is slightly shorter in the unsaturated zone than that in the saturated zone, which means that bank storage is released faster in the unsaturated zone than that in the saturated zone. The distribution of bank storage between saturated and unsaturated zones can be influenced by a thin layer of streambed and the unsaturated zone properties.
ETD Chair
Zhan, Hongbin Holder of Endowed Dudley J. Hughes '51 Chair in Geology and Geophysics
