Understanding of the Hydrologic Connections Between Wide-channel and Adjacent Aquifers Using Numerical and Field Techniques (original) (raw)
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Journal of Hydrology, 2008
The stratification of channel sediments and their vertical hydraulic conductivity (K v ) are important hydrologic information in the analysis of stream-aquifer interactions. This paper describes the use of direct-push technology to generate electrical conductivity (EC) logs and collect continuous sediment cores beneath river channels. The techniques were applied to nine study sites along a 130 km reach of the Platte River in southeast Nebraska. EC logs for the channel surface down to as much as 24 m below the channel surface indicate that the channel sediments in the western part of the reach consist predominantly of sand and gravel; low-K v silt-clay layers occur in the rest of the reach. These silt-clay layers are either interbedded with sand and gravel or occur as a major unit within the channel sediments. As a result, the values of K v , determined from the sediment cores, can vary by four to five orders of magnitude in the same vertical profile of channel sediments at a number of sites. The river channel is not lined by a low-K v layer at the surface. Instead, the K v values for the top part of channel sediments were consistently greater than K v values for sediments in deeper parts. They show a decreasing tendency with the depth. This paper also analyzes the effect of low-K v layers within channel sediments on streamflow depletion induced by groundwater pumping. Simulation results suggest that the effectiveness of low-K v layers on the calculation of streamflow depletion depends on their depth, thickness, vertical permeability, the length along the channel, and the width within the channel, as well as the extension into the aquifer on both sides of the river. A low-K v layer present at the channel surface seems to be the most effective hydrologic feature in reducing the hydrologic connection of stream-aquifer. ª
Water Resources Management, 2010
Streambed vertical hydraulic conductivity (K v) plays an important role in understanding and quantifying the stream-aquifer interactions. While several researchers have discussed the spatial variability of streambed horizontal hydraulic conductivity or K v at one or several close-located sites in a river, they did not develop any statistical distribution analysis of streambed K v at distant sites along a large river. In this paper, the statistical distribution and spatial variation of streambed K v at 18 test sites in a 300-km reach of the Platte River in Nebraska are presented. Insitu permeameter tests using the falling-head method were carried out to calculate the streambed K v values. Fine-grained sediments transported by two tributaries, the Loup River and the Elkhorn River, to the Platte River appear to result in lower streambed K v values downstream of the confluences between the Platte River and the tributaries. The streambed K v values were found to be normally distributed at nearly each test site. When the correlated K v values were eliminated from the grid sampling plots, the remaining independent sub-datasets of streambed K v values were still in normal distribution at each test site. Furthermore, the combined streambed K v values upstream of the first confluence between the Platte River and the Loup River was normally distributed, which may be due to the lack of tributaries in-between and thus streambed sediments were well distributed in this reach and belonged to a single population of hydraulic conductivity values. In contrast, the combined dataset of all measurements conducted downstream of this confluence was no longer in normal distribution, presumably as a result of the mixing of different sediment sources.
Journal of Hydrology, 2008
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j h y d r o l few months of the study. This upstream/downstream difference in K disappeared after the dam collapsed, perhaps in response to re-mobilization of fine sediments or leaf matter that had accumulated in quiet waters ponded on the upstream side of the dam. Temporal variability was significant and followed a variety of different patterns at the 46 measurement locations in the large reach. Temperature data show that variation in streambed and groundwater temperature was not an important cause of the observed temporal variability in K. Measurements of changes in the elevation of the streambed surface suggest erosion and deposition played an important role in causing the observed temporal variability in streambed K (of which the change described above following collapse of the beaver dam was a special case), though other potentially time-varying factors (e.g., gas content, bioturbation, or biofilms in the streambed) were not explicitly addressed and cannot be ruled out as contributors to the temporal variability in streambed K. Temporal variability in streambed K merits additional study as a potentially important control on temporal variability in the magnitudes and spatial patterns of water and solute fluxes between groundwater and surface water. From the data available it seems appropriate to view streambed K as a dynamic attribute, variable in both space and time. ª
Massei et al 2006 Hydrogeology J
Breakthrough tailing has been observed during dye-tracing recovery tests in the Norville aquifer system (chalk), France. Karst-conduit flow and transport parameters were assessed using two different interpretative methods: the linear graphical method and the Chatwin method (implemented in the Qtracer2 program). The linear graphical method was used to model the observed tailing effects, which was explained by a second smaller delayed breakthrough curve. By comparing the results of tracertest interpretation for the two methods, it was possible to relate the area of this second curve to the importance of turbulent flow in spring discharge. The more turbulent the flow, the less important the contribution of the second breakthrough curve and the tailing effect. The observed tailing could possibly be controlled by hydrodynamics to a greater extent than usually expected, the tailing effects Resumen Se ha observado ruptura de colas durante pruebas de recuperación con trazadores de color en el sistema de acuífero carbonatado-arcilloso Norville, Francia. Se evaluaron flujo en conductos kársticos y parámetros de transporte utilizando dos métodos interpretativos distintos: el Método ciente del acuífero lo cual apoyaría la hipótesis de efectos de cola con control hidrodinámico más que difusión en matriz o fisura.
Chinese Science Bulletin, 2010
Determination of streambed hydraulic conductivity is of great importance in the analysis of stream-aquifer interactions and stream ecosystems. In this paper, in situ falling-head standpipe permeameter tests were conducted to determine streambed vertical hydraulic conductivity (K v ) of two connected layers of sediments at 60 test locations from eight sites in the Elkhorn River, Nebraska. Our results show that the K v values for the upper layer of sediments are generally larger than those in their respective lower layer of sediments. The individual K v value for the upper layer of sediments from all test locations of the eight sites range from 2.7 to 104.9 m/d, and the average value is 26.6 m/d. The individual K v value ranges from 0.4 to 73.4 m/d and the average value is 16.1 m/d for the lower layer of sediments. We believe that hyporheic processes can enhance larger streambed K v in the upper layer of sediments. Inflow and outflow through hyporheic zone produce more porous and permeable sediments and further result in an increasing of streambed K v . Moreover, we observe that bioturbation activities can destroy the clogging layer of the exposed sediments and create pore spaces in the sediments, which also further increases streambed K v . streambed vertical hydraulic conductivity, permeameter test, depth of streambed sediment, hyporheic processes, bioturbation Citation: Song J X, Chen X H, Cheng C, et al. Variability of streambed vertical hydraulic conductivity with depth along the Elkhorn River, Nebraska, USA. Chinese Sci Bull, 2010, 55: 992−999,
Determination of the anisotropy of an upper streambed layer in east-central Nebraska, USA
Hydrogeology Journal, 2012
Information on the anisotropy of streambed hydraulic conductivity (K) is a necessity for analyses of water exchange and solute transport in the hyporheic zone. An approach is proposed for the determination of K, developed from existing in-situ permeameter test methods. The approach is based on determination of vertical and horizontal hydraulic conductivity of streambed sediments on-site and eliminates the effects of vertical flow in the hyporheic zone and stream-stage fluctuation, which normally influence in situ permeameter tests. The approach was applied to seven study sites on four tributaries of the Platte River in east-central Nebraska, USA. On-site permeameter tests conducted on about 172 streambed cores for the determination of vertical hydraulic conductivity (K v) and horizontal hydraulic conductivity (K h) at the study sites indicate that the study sites have relatively small anisotropic ratios, ranging from 0.74 to 2.40. The ratios of K h to K v from individual locations within a study site show greater variation than the anisotropic ratios from the mean or median K at each of the study sites.