Borehole flowmeters that measure horizontal flow velocity and direction of groundwater flow are being increasingly applied to a wide variety of environmental problems. This study was carried out to evaluate the measurement accuracy of several types of flowmeters in an unconsolidated aquifer simulator. Flowmeter response to hydraulic gradient, aquifer properties, and well‐screen construction was measured during 2003 and 2005 at the U.S. Geological Survey Hydrologic Instrumentation Facility in Bay St. Louis, Mississippi. The flowmeters tested included a commercially available heat‐pulse flowmeter, an acoustic Doppler flowmeter, a scanning colloidal borescope flowmeter, and a fluid‐conductivity logging system. Results of the study indicated that at least one flowmeter was capable of measuring borehole flow velocity and direction in most simulated conditions. The mean error in direction measurements ranged from 15.1° to 23.5° and the directional accuracy of all tested flowmeters improved with increasing hydraulic gradient. The range of Darcy velocities examined in this study ranged 4.3 to 155 ft/d. For many plots comparing the simulated and measured Darcy velocity, the squared correlation coefficient (r2) exceeded 0.92. The accuracy of velocity measurements varied with well construction and velocity magnitude. The use of horizontal flowmeters in environmental studies appears promising but applications may require more than one type of flowmeter to span the range of conditions encountered in the field. Interpreting flowmeter data from field settings may be complicated by geologic heterogeneity, preferential flow, vertical flow, constricted screen openings, and nonoptimal screen orientation.
Shiqmim is a late prehistoric farming village in the Beersheva river valley in Israel's northern Negev desert dating to the late 5th-early 4th millennia B.C. Along with surface architecture, archaeologists discovered a sequence of large subterranean rooms interconnected by narrow tunnels. This discovery, found in the northern Negev, as well as similar subterranean features and dating back to the same period, has created considerable controversy as to the functions of this innovative architecture. To a large extent, this controversy results from conflicting hypotheses based on the small sample of subterranean Negev architectures. A fundamental task in the resolution of these problems is the location and investigation of similar features within this region. This is not a simple task because these subterranean features can be as much as 7 m deep in hard-packed soil and are usually completely filled with fine sediment as a result of depositional forces acting over the 6 millennium since their abandonment. To help quantify the spatial extent of subterranean features at Shiqmim and identify particularly promising locations for excavation, an emerging geophysical method, known as geophysical diffraction tomography, was applied. This method is based on the propagation of acoustic waves and employs the mathematical concepts of optical holography to reconstruct quantitative, high-resolution images of the subsurface environment. Two geophysical imaging field studies were performed at Shiqmim, and the results of these studies indicate that subterranean architecture is much more pervasive at this site than pre-*
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