The generation ofK indices from digitally recorded magnetic data

TheK index was developed by Bartels and is a measure of geomagnetic activity. The important feature of this index is that it is a measure of solar activity superimposed on the regular daily variation.It is the most used estimate of activity being of particular interest to researchers in ionospheric physics and telecommunications.In response to increased availability of digital data from magnetic observatories and their demand by the scientific community it becomes desireable to check whetherK indices produced from magnetograms plotted from digital data are consistent with those handscaled from La Cour charts.This paper presents results of these comparisons and also reports on several methods tested to produce theK index directly from the digital data.Handscaled indices from digital plots are suitable for producing theK index. Computations using digital data do not reproduceK as defined by Bartels precisely but do provide an equivalent index which is satisfactory for most user and research purposes.     

Anisotropy and depth‐related heterogeneity of hydraulic conductivity in a bog peat. II: modelling the effects on groundwater flow

Anisotropy and heterogeneity of hydraulic conductivity (K) are seldom considered in models of mire hydrology. We investigated the effect of anisotropy and heterogeneity on groundwater flow in bog peat using a steady‐state groundwater model. In five model simulations, four sets of K data were used. The first set comprised measured K values from an anisotropic and heterogeneous bog peat. These data were aggregated to produce the following simplified data sets: an isotropic and heterogeneous distribution of K; an isotropic and homogeneous distribution; and an anisotropic and homogeneous distribution. We demonstrate that, where anisotropy and heterogeneity exist, groundwater flow in bog peat is complex. Fine‐scale variations in K have the potential to influence patterns and rates of groundwater flow. However, for our data at least, it is heterogeneity and not anisotropy that has the greater influence on producing complex patterns of groundwater flow. We also demonstrate that patterns and rates of groundwater flow are simplified and reduced when measured K values are aggregated to create a more uniform distribution of K. For example, when measured K values are aggregated to produce isotropy and homogeneity, the rate of modelled seepage is reduced by 28%. We also show that when measured K values are used, the presence of a drainage ditch can increase seepage through a modelled cross‐section. Our work has implications for the accurate interpretation of hydraulic head data obtained from peat soils, and also the understanding of the effect of drainage ditches on patterns and rates of groundwater flow. Copyright © 2002 John Wiley & Sons, Ltd.     

Radioactive heat production in rocks and its relation to other petrophysical parameters

Summary Radioactive heat productionA is a scalar and isotropic petrophysical property independent of in situ temperature and pressure. Its value is usually expressed in HGU units (1 HGU=10^–13 cal/cm³ sec) and depends on the amounts of uranium, thorium and potassium.A varies with rock type over several orders of magnitude and reflects the geochemical conditions during rock formation (magmatic differentiation, sedimentation or metamorphism).In order to assign realistic thermal parameters to deeper-seated rocks correlations with seismic velocity (which can be determined from the surface) have been looked for. In the range characteristic for crystalline rocks of the crust (5–8 km/sec)A is strongly correlated with density and compressional wave velocityv _p:A decreases with increasingv _p orp. From this relationship it is now possible to estimate heat production values for any particular layer of a crustal section from measured seismic velocities. Contrary to earlier belief there is, as shown by experimental determinations, no correlation between heat productionA and thermal conductivityK in igneous and metamorphic rocks. In sediments however, especially in sand/shale sequences, a correlation betweenK andA is most likely: increasing clay mineral content, characterized by increasingA, causes the decrease ofK in these rocks.Contribution No. 111, Institute of Geophysics, Swiss Federal Institute of Technology, Zurich, Switzerland.     

An intelligent digital magnetic recording system (DIMARS)

The system consists of three magnetic variometers with electrical output signals for theH, D, andZ components, a proton magnetometer for the total field, a data acquisition system, two cassette recorders, an analogue chart recorder, a calendar clock, and a telex. The analogue and digital input data are sampled at 10 sec intervals, averaged over a minute, and recorded on a magnetic tape cassette. The computed hourly and daily mean values and the daily minimum and maximum values are recorded together with the occurrence times on a second cassette, at the operator's request. Rapid run recording of the 10 sec values of each measured component is initiated automatically during magnetic storms.DIMARS incorporates several test functions as ROM test, A/D converter test, recorder test, telexline test and checking the memory content. The test functions can be activated by the equipment keyboard, or via the telex. The telex can also be operated as an output printer.     

The soil hydrologic response to forest regrowth: a case study from southwestern Amazonia

As a large and dynamic land‐use category, tropical secondary forests may affect climate, soils, and hydrology in a manner different from primary forests or agricultural areas. We investigated the saturated hydraulic conductivity K_sat of a Kandiudult under different land uses in Rondonia, Brazil. We measured K_sat at four depths (12·5, 20, 30 and 50 cm) under (a) primary forest, (b) a former banana–cacao plantation (SF1), and (c) an abandoned pasture (SF2). At 12·5 cm, all three land uses differ significantly (α = 0·1), but not at the 20 and 30 cm depths. At 50 cm, K_sat was significantly greater in the former pasture than in other land uses. Lateral subsurface flow is expected during intense rainfall (about 30 times per year) at 30 cm depth in SF1 and at 50 cm depth in the forest, whereas the relatively low permeability at shallow 12·5 cm in the SF2 may result not only in lateral subsurface flow, but also saturation overland flow. For modelling purposes, recovering systems seem to have K_sat values distinct from primary forest at shallow depths, whereas at deeper layers (>20 cm) they may be considered similar to forests. Copyright © 2002 John Wiley & Sons, Ltd.     

Modeling Transient Streaming Potentials in Falling‐Head Permeameter Tests

We present transient streaming potential data collected during falling‐head permeameter tests performed on samples of two sands with different physical and chemical properties. The objective of the work is to estimate hydraulic conductivity (K) and the electrokinetic coupling coefficient (C_l) of the sand samples. A semi‐empirical model based on the falling‐head permeameter flow model and electrokinetic coupling is used to analyze the streaming potential data and to estimate K and C_l. The values of K estimated from head data are used to validate the streaming potential method. Estimates of K from streaming potential data closely match those obtained from the associated head data, with less than 10% deviation. The electrokinetic coupling coefficient was estimated from streaming potential vs. (1) time and (2) head data for both sands. The results indicate that, within limits of experimental error, the values of C_l estimated by the two methods are essentially the same. The results of this work demonstrate that a temporal record of the streaming potential response in falling‐head permeameter tests can be used to estimate both K and C_l. They further indicate the potential for using transient streaming potential data as a proxy for hydraulic head in hydrogeology applications.     

Bootstrap Calibration and Uncertainty Estimation of Downhole NMR Hydraulic Conductivity Estimates in an Unconsolidated Aquifer

Characterization of hydraulic conductivity (K) in aquifers is critical for evaluation, management, and remediation of groundwater resources. While estimates of K have been traditionally obtained using hydraulic tests over discrete intervals in wells, geophysical measurements are emerging as an alternative way to estimate this parameter. Nuclear magnetic resonance (NMR) logging, a technology once largely applied to characterization of deep consolidated rock petroleum reservoirs, is beginning to see use in near‐surface unconsolidated aquifers. Using a well‐known rock physics relationship—the Schlumberger Doll Research (SDR) equation—K and porosity can be estimated from NMR water content and relaxation time. Calibration of SDR parameters is necessary for this transformation because NMR relaxation properties are, in part, a function of magnetic mineralization and pore space geometry, which are locally variable quantities. Here, we present a statistically based method for calibrating SDR parameters that establishes a range for the estimated parameters and simultaneously estimates the uncertainty of the resulting K values. We used co‐located logging NMR and direct K measurements in an unconsolidated fluvial aquifer in Lawrence, Kansas, USA to demonstrate that K can be estimated using logging NMR to a similar level of uncertainty as with traditional direct hydraulic measurements in unconsolidated sediments under field conditions. Results of this study provide a benchmark for future calibrations of NMR to obtain K in unconsolidated sediments and suggest a method for evaluating uncertainty in both K and SDR parameter values.     

The high hydraulic conductivity of three wooded tropical peat swamps in northeast Peru: measurements and implications for hydrological function

The form and functioning of peatlands depend strongly on their hydrological status, but there are few data available on the hydraulic properties of tropical peatlands. In particular, the saturated hydraulic conductivity (K) has not previously been measured in neotropical peatlands. Piezometer slug tests were used to measure K at two depths (50 and 90 cm) in three contrasting forested peatlands in the Peruvian Amazon: Quistococha, San Jorge and Buena Vista. Measured K at 50 cm depth varies between 0.00032 and 0.11 cm s^?1, and at 90 cm, it varies between 0.00027 and 0.057 cm s^?1. Measurements of K taken from different areas of Quistococha showed that spatial heterogeneity accounts for ~20% of the within‐site variance and that depth is a good predictor of K. However, K did not vary significantly with depth at Buena Vista and San Jorge. Statistical analysis showed that ~18% of the variance in the K data can be explained by between‐site differences. Simulations using a simple hydrological model suggest that the relatively high K values could lead to lowering of the water table by >10 cm within ~48 m of the peatland edge for domed peatlands, if subjected to a drought lasting 30 days. However, under current climatic conditions, even with high K, peatlands would be unable to shed the large amount of water entering the system via rainfall through subsurface flow alone. We conclude that most of the water leaves these peatlands via overland flow and/or evapotranspiration. Copyright © 2013 John Wiley & Sons, Ltd.     

The effect of truck traffic and road water content on sediment delivery from unpaved forest roads

A study investigated the effect of truck‐traffic intensity and road water‐content on the quality of runoff water from unsealed forest roads. Three sections of a gravel‐surfaced forest road were instrumented and exposed to low and high levels of truck traffic during wet winter conditions and dry summer conditions between July 2001 and December 2002. Rainfall, runoff, road moisture, and traffic were measured continuously, and suspended and bedload sediments were integrated measurements over 2‐week site‐service intervals. The median suspended sediment concentration from the three road segments under low truck‐traffic conditions (less than nine return truck passes prior to a storm) was 269 mg l^?1, increasing 2·7‐fold to a median of 725 mg l^?1 under high truck‐traffic conditions (greater than or equal to nine return truck passes prior to a storm). These concentrations, and increases due to traffic, are substantially less than most previously reported values. When these data are expressed as modified universal soil loss equation (MUSLE) erodibility values K, accounting for differences in rainfall energy, site characteristics and runoff, high traffic resulted in a road surface that was four times more erodible than the same road under low traffic conditions. Using multiple regression, traffic explained 36% of the variation in MUSLE erodibility, whereas road water content was not significant in the model. There was little difference in the erodibility of the road when trafficked in low water‐content compared with high water‐content conditions (MUSLE K values of 0·0084 versus 0·0080 respectively). This study shows that, for a good quality well‐maintained gravel forest road, the level of truck traffic affects the sediment concentration of water discharging from the road, whereas the water content of the road at the time of that traffic does not (note that traffic is not allowed during runoff events in Victoria). These conclusions are conditional upon the road being adequately maintained so that trafficking does not compromise the lateral drainage of the road profile. Copyright © 2005 John Wiley & Sons, Ltd.     

Eddy diffusion coefficients and the variance of the atmosphere 30–60 km

The results of numerical models or of new observational programs are checked by comparing them with past observations. Also, it is desirable that the eddy diffusion coefficients used in two-dimensional models be derived from the same data set as the circulation statistics which the model outputs are checked against, so that all results refer to the same atmospheric conditions. For the first time, the three components of the eddy diffusion matrix, from 30–60 km, 80°N–10°S are computed, together with the means, variances and covariances of the wind and temperature through the same region using the same data set for 1960–76 and the same handling and analysis methods for all variables. Horizontal diffusivities,K _yy , are obtained from the variance and integral time scale of the meridional wind speed. The present values are generally smaller than past estimates, presumably because temporal variations longer than a month have been removed in this work. Estimates ofK _yz are based on the tentative assumption that the diffusivity is proportional to the slope of isentropic surfaces, and estimates ofK _zz are based on the assumption that small-scale gravity waves are primarily responsible for vertical mixing.     

Attenuation of coda waves in northern Greece

The single scattering model has been applied for the estimation of codaQ values for local earthquakes that occurred in northern Greece during the period 1983–1989 and recorded by the telemetered network of the Geophysical Laboratory of the University of Thessaloniki. CodaQ estimations were made for four frequency bands centered at 1.5 Hz, 3.0 Hz, 6.0 Hz and 12.0 Hz and for the lapse time windows 10–20 sec, 15–30 sec, 20–45 sec, 30–60 sec and 50–100 sec. The codaQ values obtained show a clear frequency dependence of the formQ _c =Q ₀ f ⁿ , whileQ ₀ andn depend on the lapse time window.Q ₀ was found equal to 33 andn equal to 1.01 for the time window of 10 to 20 sec, while for the other windowsQ ₀ increased from 60 to 129, withn being stable, close to 0.75. This lapse time dependence is interpreted as due to a depth dependent attenuation. The high attenuation and the strong frequency dependence found are characteristic of an area with high seismicity, in agreement with studies in other seismic regions.     

Estimation of urban subtropical bahiagrass (Paspalum notatum) evapotranspiration using crop coefficients and the eddy covariance method

Eddy covariance (EC) and micro‐meteorological data were collected from May 2010 to January 2013 from urban, non‐irrigated bahiagrass (Paspalum notatum) in subtropical south Florida. The objectives were to determine monthly crop coefficients (K_c) for non‐irrigated bahiagrass by using EC evapotranspiration (ET) data and the Food and Agriculture Organization 56 Penman–Monteith reference evapotranspiration equation; compare crop ET (ET_c) calculated with new K_c values to ET_c obtained using K_c values available in the literature; and compare results and methodologies for statistical differences. New K_c values ranged from 0.62 to 0.92 and were different from K_c values found in the scientific literature for bahiagrass. Resulting ET_c calculated using literature K_c values were significantly different from EC ET data, whereas ET_c using the new K_c values was not. Specifically, literature K_c values were temporally biased to miscalculate the timing of convergence between potential and actual ET, assuming that our new K_c values calculated with EC methods were most accurate. As a consequence, ET_c calculated using the literature K_c values was either too large or too small. However, one set of literature K_c values from a similar climate and water table depth were closer to our new K_c values, indicating that climate should be considered when selecting urban non‐irrigated K_c from the literature to estimate ET. Results also indicated that more than 1 year of EC ET data was needed when establishing monthly K_c values because of annual variability in factors controlling ET, such as water availability. The new K_c values reported herein could be used as an estimate for urban non‐irrigated bahiagrass within similar climates. Copyright © 2013 John Wiley & Sons, Ltd.     

Processes controlling rapid temperature variations on rock surfaces

In arid environments, thermal oscillations are an important source of rock weathering. Measurements of temperature have been made on the surface of rocks in a desert environment at a sampling interval of 0·375 s, with simultaneous measurements of wind speed, air temperature, and incoming shortwave radiation. Over timescales of hours, the temperature of the rock surface was determined primarily by shortwave radiation and air temperature, while rapid temperature variations, high dT/dt, at intervals of seconds or less, were determined by wind speed. The maximum values of temperature change and time spent above 2°C min^?1 increased at high measurement rates and were much higher than previously reported. The maximum recorded value of dT/dt was 137°C min^?1 and the average percentage time spent above 2°C min^?1 was ～70 ± 13%. Maximum values of dT/dt did not correlate with the maximum values of time spent above 2°C min^?1. Simultaneous measurements of two thermocouples 5·5 cm apart on a single rock surface had similar temperature and dT/dt values, but were not correlated at sampling intervals of less than 10 s. It is suggested that this is resulting from rapid fluctuations due to small spatial and timescale wind effects that are averaged out when data is taken at longer sampling intervals, ～10 s or greater. Published in 2010 by John Wiley & Sons, Ltd.     

Hydraulic Conductivity Calibration of Logging NMR in a Granite Aquifer,Laramie Range,Wyoming

In granite aquifers, fractures can provide both storage volume and conduits for groundwater. Characterization of fracture hydraulic conductivity (K) in such aquifers is important for predicting flow rate and calibrating models. Nuclear magnetic resonance (NMR) well logging is a method to quickly obtain near-borehole hydraulic conductivity (i.e., K_NMR) at high-vertical resolution. On the other hand, FLUTe flexible liner technology can produce a K profile at comparable resolution but requires a fluid driving force between borehole and formation. For three boreholes completed in a fractured granite, we jointly interpreted logging NMR data and FLUTe K estimates to calibrate an empirical equation for translating borehole NMR data to K estimates. For over 90% of the depth intervals investigated from these boreholes, the estimated K_NMR are within one order of magnitude of K_FLUTe. The empirical parameters obtained from calibrating the NMR data suggest that “intermediate diffusion” and/or “slow diffusion” during the NMR relaxation time may occur in the flowing fractures when hydraulic aperture are sufficiently large. For each borehole, “intermediate diffusion” dominates the relaxation time, therefore assuming “fast diffusion” in the interpretation of NMR data from fractured rock may lead to inaccurate K_NMR estimates. We also compare calibrations using inexpensive slug tests that suggest reliable K_NMR estimates for fractured rock may be achieved using limited calibration against borehole hydraulic measurements.     

INVESTIGATION OF INFILTRATION CHARACTERISTICS AND DEBRIS FLOW INITIATION CONDITIONS IN DEBRIS FLOW SOURCE AREAS USING A RAINFALL SIMULATOR

Rainfall was simulated on unconfined plots on regolith in debris flow source areas using a portable simulator. In total, 351 simulations were carried out on steep slopes (27–54°) with rainfall intensities of 28–291 mm/h. From these rainfall simulations the infiltration parameters sorptivity (S) and steady-state infiltration capacity (K) of the regolith, and a threshold for the occurrence of micro-scale mass movements, were obtained. Two evaluation methods were used to obtain the infiltration parameters K and S. The ‘infiltration envelope’ method uses rainfall intensity and time to ponding from multiple tests and fits an infiltration envelope through the data from which K and S can be obtained. The ‘constant runoff’ method uses rainfall intensity and overland flow intensity to calculate K, after which S can be calculated in several ways by using time to ponding. The constant runoff method produced K values of 16.6–128 mm/h, which usually show a log-normal distribution. K values depend on the regolith parent material and rainfall intensity. Using this method, S values are 0.088–0.381 cm/min^1/2. The infiltration envelope method produced K values of 9.8–131 mm/h and S values of 0.14–0.32 cm/min^1/2. It can be argued that both methods overestimate K as well as S, but quantitative relations between measured/calculated and actual values of K and S have not yet been obtained. At high rainfall intensities, typically 100 mm/h or more, micro-scale mass movements sometimes occur. A lower threshold curve for the occurrence of these micro-scale mass movements has been constructed. It is a function of both slope angle and rainfall intensity. The micro-scale mass movements could play an important part in the initiation of debris flows in the study area, possibly by delivering sediment to overland flow. On the very steep slopes, the sediment-rich overland flow can easily mobilize coarse material.     

Accounting for the influence of runoff on event soil erodibilities associated with the EI30 index in RUSLE2

Soil erodibilities (K) associated with the EI₃₀ index vary not only with soil properties but also with soil moisture as it varies in time and space. In Revised Universal Soil Loss Equation Version 2 (RUSLE2), temporal variations in soil erodibility in the USA are calculated using monthly precipitation and temperature as independent variables. K_UM, the soil erodibility factor associated with the Q_REI₃₀ index, varies independently of runoff and the product of K_UM and the runoff ratio for the unit plot (Q_R1) provides an alternative to the temporally varying Ks currently used in predicting storm soil loss in RUSLE2. Comparisons were made between the product of Q_R1 and K_UM and RUSLE2 Ks for representative storms at four locations representing the north to south variation in climate in the USA. Peak erosion associated with the current approach used in RUSLE2 was slightly higher at two locations and slightly lower at the other two locations. One other location, Morris, MN, provided an exception with the peak loss predicted by using the product of Q_R1 and K_UM being 1.7 times that obtained using RUSLE2 Ks. In theory, average annual K_UM values should be better related to soil properties than the average annual values of K frequently used when the average annual values of EI₃₀ are used to predict soil loss. However, work has yet to be performed to determine how K_UM varies directly with soil properties and in space and time. Copyright © 2014 John Wiley & Sons, Ltd.     

Heterogeneous characteristics of streambed saturated hydraulic conductivity of the Touchet River,south eastern Washington,USA

Traditionally a streambed is treated as a layer of uniform thickness and low saturated hydraulic conductivity (K) in surface‐ and ground‐water studies. Recent findings have shown a high level of spatial heterogeneity within a streambed and such heterogeneity directly affects surface‐ and ground‐water exchange and can have ecological implications for biogeochemical transformations, nutrient cycling, organic matter decomposition, and reproduction of gravel spawning fish. In this study a detailed field investigation of K was conducted in two selected sites in Touchet River, a typical salmon spawning stream in arid south eastern Washington, USA. In‐stream slug tests were conducted to determine K following the Bouwer and Rice method. For the upper and lower sites, each 50 m long and 9 m wide and roughly 20 m apart, a sampling grid of 5 m longitudinally and 3 m transversely was used. The slug tests were performed for each horizontal coordinate at 0·3–0·45, 0·6–0·75, 0·9–1·05 and 1·2–1·35 m depth intervals unless a shallower impenetrable obstruction was encountered. Additionally, water levels were measured to obtain vertical hydraulic gradient (VHG) between each two adjacent depth intervals. Results indicated that K ranged over three orders of magnitude at both the upper and lower sites and differed between the two sites. At the upper site, K did not differ significantly among different depth intervals based on nonparametric statistical tests for mean, median, and empirical cumulative distribution, but the spatial pattern of K varied among different depth intervals. At the lower site, K for the 0·3–0·45 m depth interval differed statistically from those at other depth intervals, and no similar spatial pattern was found among different depth intervals. Zones of upward and downward water flow based on VHG also varied among different depth intervals, reflecting the complexities of the water flow regime. Detailed characterization of the streambed as attempted in this study should be helpful in providing information on spatial variations of streambed hydraulic properties as well as surface‐ and ground‐water interaction. Copyright © 2009 John Wiley & Sons, Ltd.     

Feasibility of grain-size analysis methods for determination of vertical hydraulic conductivity of streambeds

Accurate estimation of streambed vertical hydraulic conductivity (K_v) is of great importance in the analysis of water quantity exchange and solute transfer between a stream and its sediments. The paper analyzed the inaccuracy of hydraulic conductivity values of sediments derived from grain-size distribution (K_g), which were determined from eight empirical grain-size methods to represent streambed K_v. In this study, the values of K_v for a streambed were derived using falling-head standpipe permeameter tests conducted at eight study sites in the Elkhorn River, Nebraska, and the tested streambed columns were then collected for grain-size analysis by sieving. These empirical methods were used to calculate the K_g values of the streambed from grain-size distribution data of sediments. Unlike many other studies, this study verifies K_g from grain-size distribution with K_v from permeameter tests on the basis of the same samples of streambed sediments. The K_g values derived from the eight empirical methods were larger than the K_v from permeameter tests; there are five methods that give K_g values of about 3–6 times larger than these K_v. The K_g values from the Kozeny formula followed by the Hazen formula give the largest overestimation error if they are used to represent the K_v of the streambed. The USBR and Shepherd formulas generated K_g values close to K_v, but these K_g values are still larger in general than the K_v values. Moreover, the new values of coefficient C for the empirical formulas were revised so that they can be used to calculate the approximate K_v of a streambed. Among the eight methods, the ratios of the original C values to the average new C range from 1.3 to 5.9. It can be hypothesized that smaller C values must be used in the estimation of K_v for general soil samples if these empirical formulas are used to calculate K_v.     

Evaluating the quality of hydraulic conductivity estimates from piezometer slug tests in peat

Although widely used in wetland hydrological studies, hydraulic conductivity (K) estimates from piezometer slug tests are often of questionable validity. Frequently, this is because insufficient attention is paid to the details of the test procedure. Further, in a potentially heterogeneous and anisotropic medium such as peat, the use of slug tests is prone to error. In this paper we address some of the methodological issues surrounding piezometer slug tests in peat. We compare slug test data with laboratory determinations of vertical and horizontal K obtained using a new method. Piezometers were installed at three depths in a floodplain fen peat in Norfolk, UK. Slug tests were initiated by both slug insertion and slug withdrawal, and repeat tests were conducted to examine the robustness of our K estimates. Most of the tests displayed departures from the log‐linear model of Hvorslev, the form of departure being consistent with compressible soil behaviour. The results suggest that insertion tests gave similar results to those initiated by withdrawal. Repeat testing showed that withdrawal data, in particular, gave highly reproducible normalized responses that were independent of the initial head. Values for K estimated using the slug tests were in the range 1 × 10⁻⁴ to 1·6 × 10⁻³ cm s⁻¹, which is towards the upper end of the range reported for peats generally. Laboratory tests yielded similar values of K to those obtained from the slug tests. Although the laboratory tests showed that the peat was anisotropic, the K values generated by slug testing proved relatively good estimates of both vertical and horizontal K. Copyright © 2005 John Wiley & Sons, Ltd.     

Hydraulic Tomography: 3D Hydraulic Conductivity,Fracture Network,and Connectivity in Mudstone

We present the first demonstration of hydraulic tomography (HT) to estimate the three-dimensional (3D) hydraulic conductivity (K) distribution of a fractured aquifer at high-resolution field scale (HRFS), including the fracture network and connectivity through it. We invert drawdown data collected from packer-isolated borehole intervals during 42 pumping tests in a wellfield at the former Naval Air Warfare Center, West Trenton, New Jersey, in the Newark Basin. Five additional tests were reserved for a quality check of HT results. We used an equivalent porous medium forward model and geostatistical inversion to estimate 3D K at high resolution (K blocks <1 m³), using no strict assumptions about K variability or fracture statistics. The resulting 3D K estimate ranges from approximately 0.1 (highest-K fractures) to approximately 10⁻¹³ m/s (unfractured mudstone). Important estimated features include: (1) a highly fractured zone (HFZ) consisting of a sequence of high-K bedding-plane fractures; (2) a low-K zone that disrupts the HFZ; (3) several secondary fractures of limited extent; and (4) regions of very low-K rock matrix. The 3D K estimate explains complex drawdown behavior observed in the field. Drawdown tracing and particle tracking simulations reveal a 3D fracture network within the estimated K distribution, and connectivity routes through the network. Model fit is best in the shallower part of the wellfield, with high density of observations and tests. The capabilities of HT demonstrated for 3D fractured aquifer characterization at HRFS may support improved in situ remediation for contaminant source zones, and applications in mining, repository assessment, or geotechnical engineering.