Search Results (2)

A comprehensive hydrogeological, geophysical, and hydrochemical investigation was conducted in southeastern Hitchcock County, Nebraska, within the Driftwood Creek alluvial aquifer. This study assessed groundwater contamination stemming from the surface disposal of saline wastes from oilfield activities. A contaminated area, initially identified through regional groundwater sampling, was examined in detail. Monitoring wells were installed, and groundwater and soil samples were collected for chemical analysis. Surface electrical resistivity surveys were also performed to delineate contamination patterns. The findings revealed that the groundwater contamination originated from the leaching of residual evaporative salts through the vadose zone, beneath an abandoned emergency-evaporation brine storage pit. Data from down-hole specific conductance logs, water quality analyses, and computer-generated interpretations of surface electrical resistivity indicated that contaminant migration was primarily influenced by gravity, bedrock topography, and the local hydraulic gradient. An initial surface electrical resistivity profile survey was conducted to optimize the placement of monitoring wells and soil sampling sites within the vadose zone. Following well installation, a contaminant source with complex brine contamination patterns was detected within the shallow aquifer. Vertical electrical soundings were then carried out as the final investigative step. The data from these soundings, combined with test hole records, water level measurements, brine contaminant distribution, and soil analyses, were refined through a computer program employing the method of steepest descent. By incorporating known layer thicknesses and resistivities as constraints, this approach minimized the common issue of non-unique electrical sounding interpretations, providing information on the distribution of brine contaminants within the alluvial aquifer. Full article

The quantification of driftwood deposition in rivers is important for understanding the total budget of driftwood at the watershed scale; however, it remains unclear how such driftwood storage in rivers contributes to the overall system because of the difficulties in undertaking field measurements. Herein, we perform numerical simulations of driftwood deposition within an idealized river reach with a sand-bed, to describe the role of large-scale bedforms, more specifically, alternate bars, multiple bars, and braiding, in driftwood storage in rivers. The numerical model we propose here is a coupling model involving a Lagrangian-type driftwood model and an Eulerian two-dimensional morphodynamic model for simulating large-scale bedforms (i.e., bars and braiding). The results show that the channel with a braiding pattern provides a wide area with enhanced capacity for deposition of driftwood, characterized by exposed mid-channel or in-channel bars, leading to high driftwood storage. The alternate bar is also a large bedform representing a sediment depositional element in rivers; however, because of the narrow exposed bar area and its downstream-migrating feature during floods, the alternate bars seem to contribute less to driftwood deposition in rivers. This suggests that the role of multiple bars and braiding is critically important for the driftwood deposition in rivers. Full article