Techniques for Estimation of Inflow and Outflow Rates In Streambed

Water exchange occurs at the stream-sediment interface. Seepage meters are considered cost-effective devices for determination of the water flux in streambed. However, researchers have identified some problems in use of seepage meters in streams. This paper describes an alternative method for measuring the water flux in streambed. First, a bottomless tube is pressed into streambed and an in-situ sediment column of streambed is created inside the tube; hydraulic gradient between the two ends of the sediment column is determined. Secondly, the vertical hydraulic conductivity of the sediment column is determined using falling-head permeameter test in the river. Given the hydraulic gradient and vertical hydraulic conductivity of the streambed, Darcy's law is used to calculate the specific discharge. This approach was applied to the Elkhorn River and its tributaries in northeastern Nebraska. The results suggest that the magnitude of the vertical flux varied largely within a short distance. Furthermore, the flux can change directions from downward to upward between two spots only several meters apart. This spatial pattern of variation probably represents the complexity of inflow and outflow within the hyporheic zone, not the regional ambient flow system. In this study, a thermal infrared camera was also used to detect the discharge locations of groundwater in the streambed. After hydraulic gradient and vertical hydraulic conductivity were estimated from the groundwater spring, the groundwater discharge rate was calculated.