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This report describes an experiment to make a completely non-contact open-channel discharge measurement. A van-mounted, pulsed doppler (10GHz) radar collected surface-velocity data across the 183-m wide Skagit River, Washington at a USGS streamgaging station using Bragg scattering from short waves produced by turbulent boils on the surface of the river. Surface velocities were converted to mean velocities for 25 sub-sections by assuming a normal open-channel velocity profile (surface velocity times 0.85). Channel cross-sectional area was measured using a 100 MHz ground-penetrating radar antenna suspended from a cableway car over the river. Seven acoustic doppler current profiler discharge measurements and a conventional current-meter discharge measurement were also made. Three non-contact discharge measurements completed in about a 1-hour period were within 1% of the gaging station rating curve discharge values. With further refinements, it is thought that open-channel flow can be measured reliably by non-contact methods.

An integrated suite of advanced geophysical logging methods was used to characterize the geology and hydrology of three boreholes completed in fractured-sedimentary bedrock in Ventura County, California. The geophysical methods included caliper, gamma, electromagnetic induction, borehole deviation, optical and acoustic televiewer, borehole radar, fluid resistivity, temperature, and electromagnetic flowmeter. The geophysical logging 1) provided insights useful for the overall geohydrologic characterization of the bedrock and 2) enhanced the value of information collected by other methods from the boreholes including core-sample analysis, multiple-level monitoring, and packer testing. The logged boreholes, which have open intervals of 100 to 200 feet, penetrate a sequence of interbedded sandstone and mudstone with bedding striking 220 to 250 degrees and dipping 15 to 40 degrees to the northwest. Fractures intersected by the boreholes include fractures parallel to bedding and fractures with variable strike that dip moderately to steeply. Two to three flow zones were detected in each borehole. The flow zones consist of bedding-parallel or steeply dipping fractures or a combination of bedding-parallel fractures and moderately to steeply dipping fractures. About 75 to more than 90 percent of the measured flow under pumped conditions was produced by only one of the flow zones in each borehole.

This paper presents a cross-hole radar attenuation tomography method based on analysis of the down-shift in the spectrum centroid frequency, and spectral broadening of the received radar signals. The method uses a parameter that combines centroid frequency down shift and variance increase for the projection function to construct the tomography algorithm. In comparison with other methods for estimating attenuation, the frequency down shift method is relatively insensitive to the effects of geometric spreading, antenna coupling, antenna radiation pattern, and instrument response, but the method requires the data to be broad-band so the frequency shift is easily measured. This method is well suited for difference tomography when electrically conductive tracers are used. The method was tested using cross-hole radar data acquired before and during a saline tracer injection experiment at the U.S. Geological Survey’s Fractured Rock Research Site at Mirror Lake, in Grafton County, New Hampshire. The attenuationdifference tomogram clearly outlines the location of the saline tracer within the tomography plane.

Haddam Meadows State Park in Haddam, Connecticut, serves as a test site for the Branch of Geophysical Support of the USGS in Connecticut. At this site, various geophysical techniques are tested for detection of structures that could influence dense non-aqueous phase liquids (DNAPL) migration. DNAPLs sink through the water column until they reach an impermeable boundary. The geology of Haddam Meadows consists of Ordovician metamorphic bedrock, approximately 43 m deep, overlain by glaciofluvial and alluvial deposits. If no aquitards exist above bedrock, any DNAPLs present at this location should collect in topographic lows in the bedrock. A 3-D seismic dataset was collected at the site to determine the feasibility of using this methodology to constrain bedrock topography. Data were recorded from an evenly spaced shot grid along five parallel receiver lines. Although acquisition was rapid (two days), the offset, azimuth, and full-fold ranges of the dataset are restricted by the nonoptimized shot-receiver pattern, limiting our ability to examine bedrock structure. Data are reduced and interpreted using conventional oil-exploration methods. Two prominent reflections are observed. Both of these tie to a vertical seismic profile (VSP) dataset collected in the same area. The upper reflector corresponds to the refusal depth of the well from which the VSP was acquired. This reflector can be interpreted as either the top of fractured bedrock or the top of an overlying till layer. On the basis of previous refraction studies, we prefer the former interpretation. The lower reflector shows less topographic relief and is approximately 61 m deep. It is distinguished by larger amplitudes and is spatially more continuous. We interpret this reflection as originating from the top of competent bedrock. Amplitude anomalies along each reflection are examined. We interpret the observed amplitude anomalies as being indicative of mineralogic changes within the bedrock, which could be related to remineralization of open fractures or to the presence of pegmatites. Compared to drilling shallow test wells or acquiring less costly geophysical datasets, 3-D seismic surveys at this site have limited economic viability. Investigations that might be deemed suitable for the application of 3-D near-surface seismic include those that (1) contain aquicludes of sufficient thickness, lateral extent, and velocity contrast to be resolved by seismic methods, (2) have targets that are relatively deep (>15 m), (3) display significant spatial variability in target depth, target properties, or target continuity, and (4) require the use of noninvasive methods.