Hydraulic Property Data Research Articles

Hydrologic‐based modelling of burn depth potentials in degraded peat soils

AbstractPeatland drainage may degrade system resilience to high intensity, soil‐consuming fires. Peat soil fires are unique in that they can smoulder vertically through the soil column, with a multitude of consequences including large carbon emissions, altered hydrology, and dramatic shifts in vegetation communities. In this work we developed and verified a new method to model peat burn depths with readily available water level and peat hydraulic property data at the Great Dismal Swamp National Wildlife Refuge (VA and NC, USA). To model peat burn depths across 11 sites in the Great Dismal Swamp National Wildlife Refuge we combined water table time series data and soil moisture release curves, developed at multiple depths, with moisture‐to‐ignition thresholds. A subset of the results from this empirical modelling approach of peat burn depth severity were compared against those made using a mechanistic model of soil moisture, HYDRUS 1‐D. By comparing modelled burn depth potentials between these two approaches for a range of peats, we confirmed that our simpler, water table‐based approach had similar performance to HYDRUS 1‐D in drained and degraded peats, like those found in the Great Dismal Swamp National Wildlife Refuge. A comparative analysis of modelled burn depths across our study site found that water table position and peat water holding capacity were the key governing controls on burn depth potential. Our findings suggest that drainage weakens both short‐ and long‐term controls on peat burn depths by reducing soil moisture and by decreasing peat water holding capacity. This new approach offers land managers with an additional tool for assessing risk while offering insight into the drivers of peatland wildfire severity.

Study on heat extraction characteristics in a rock fracture for the application of enhanced geothermal systems

Enhanced geothermal systems (EGS) technologies aim to extract geothermal energy from hot dry rock (HDR). Heat extraction performance is of great importance for thermal efficiency and life cycle of EGS. It is intuitively considered that EGS reservoir modeling should be established based on accurate measured data of thermal and hydraulic properties of rock matrix and fluid, such as thermal conductivity, heat capacity and fracture permeability, however, which are time-consuming to obtain in some projects. This paper aims to clarify the influence of these parameters on heat extraction performance, which can provide basis for reservoir model simplification during preparation process of engineering scheme. Numerical simulations were carried out based on a rough fracture of granite rock at core scale, which has been validated by amount of experiments. First, the differences between simulation results and the previous experiment results were presented and analyzed, for variations of heat extraction rate per flow rate. Compared with the method with constant flow rate, the compensating method with various flow rate greatly increased the heat extraction rate and postpone thermal breakthrough time. Therefore, a simplified method was proposed in this paper to optimize the flow rate or predict the heat extraction rate when EGS operation with various flow rates. The method are applicable for geothermal reservoir management for efficient and stable heat extraction. Finally, the effects of properties of rock mass and fracture were studied. The production temperature and heat extraction rate were larger with larger thermal conductivity and heat capacity. It was found that the maximum influence on heat extraction rate were less than 20% and 10% within the common value ranges of thermal conductivity and heat capacity, respectively. There were almost no differences in the heat transfer process in fractures with different fracture permeabilities. It can be concluded that the prediction error of heat extraction performance is tolerable for engineering reservoir simulations, even without precise experimental test for thermal and hydraulic properties variations with temperature or pressure.

Post Audit of Simulated Groundwater Flow to a Short-Lived (2019 to 2020) Crater Lake at Kīlauea Volcano.

About 14.5months after the 2018 eruption and summit collapse of Kīlauea Volcano, Hawai'i, liquid water started accumulating in the deepened summit crater, forming a lake that attained 51 m depth before rapidly boiling off on December 20, 2020, when an eruption from the crater wall poured lava into the lake. Modeling the growth of the crater lake at Kīlauea summit is important for assessing the potential for explosive volcanism. Our current understanding of the past 2500 years of eruptive activity at Kīlauea suggests a slight dominance of explosive behavior over effusive. The deepened summit crater and presence of the crater lake in 2019 raised renewed concerns about explosive activity. Groundwater models using hydraulic-property data from a nearby drillhole successfully forecast the timing and rate of lake filling. Here we compare the groundwater-model predictions with observational data through the demise of the crater lake, examine the implications for local water-table configuration, consider the potential role of evaporation and recharge (neglected in previous models), and briefly discuss the energetics of the rapid boil-off. This post audit of groundwater-flow models of Kīlauea summit shows that simple models can sometimes be used effectively to simulate complex settings such as volcanoes.

Parameterization of two‐dimensional approaches in HYDRUS‐2D: Part 1. Simulating water flow dynamics at the field scale

AbstractParameterization of theeffective properties as input in hydrogeological models for simulating water flow is a time consuming and costly process, and it is characterized by high uncertainty because of the spatial variability of soil properties. Integrating visible−near‐infrared spectroscopy (vis−NIRS) models and a developed pedotransfer function, a hydrogeological tool was suggested by Varvaris et al. in 2019 for estimating the hydraulic properties used in an equilibrium approach. In the current study, the proposed concept was further expanded for assisting on a rapid and inexpensive parameterization of effective parameters in nonequilibrium models. In our approach, the soil‐water retention curves for the wet and hyper‐dry ends were predicted using existing vis−NIRS calibration models for obtaining the parameters for the Campbell retention model and the Campbell and Shiozawa model, respectively. The HYDRUS‐2D software package was used to simulate tile drainage discharge in a loamy structured field using as initial input hydraulic parameters the output from the suggested concept. The estimated parameters were validated based on measured hydraulic properties in the laboratory. Two‐dimensional models incorporating nonequilibrium flow were used to evaluate the ability of each approach to predict the tile drainage discharge: a single‐porosity with modified van Genuchten function, a dual‐porosity model, and a dual‐permeability model. All approaches gave a fairly good fit to the hydrograph features for both calibration and validation datasets with dual‐porosity to present the highest predictive ability. Finally, the suggested initial parameterization concept proved its potential to be used as an alternative for covering the absence of measured data of soil hydraulic properties.

Simple functions for describing soil water retention and the unsaturated hydraulic conductivity from saturation to complete dryness

Many applications require accurate soil hydraulic functions that can describe the dynamics of water in variably saturated systems from full saturation to complete dryness. Current functions considering zero water content at the dry end involve the summation of capillary and adsorption functions. This study proposes relatively simple yet complete soil hydraulic functions from full saturation to oven dryness that can be incorporated into existing models. The proposed water retention model is constructed by scaling the saturation function of Fredlund and Xing (1994) to describe capillary and adsorptive water retention as well as zero water content at oven dryness. To describe the hydraulic conductivity due to capillary and film flow, the model of Wang et al. (2018) is used. We further incorporated hysteresis in the water retention function of Wang et al. (2018). Testing on 241 hydraulic property data sets covering a wide range of soil textures from sands to clays, shows good agreement with laboratory observations, especially for coarse-textured soils. The proposed model accounts for the following processes: hysteretic capillary and adsorptive water retention, hysteretic hydraulic conductivity as a function of pressure head, non-hysteretic hydraulic conductivity as a function of water content, the effects of entrapped air, and closed scanning curves. This paper successfully derives the parameters of the main wetting curve from the main drying curve. Using the proposed functions for soil water flow modelling should lead to improved dynamic flow predictions, especially for drying soil conditions.

Wood allocation trade-offs between fiber wall, fiber lumen, and axial parenchyma drive drought resistance in neotropical trees.

Functional relationships between wood density and measures of xylem hydraulic safety and efficiency are ambiguous, especially in wet tropical forests. In this meta‐analysis, we move beyond wood density per se and identify relationships between xylem allocated to fibers, parenchyma, and vessels and measures of hydraulic safety and efficiency. We analyzed published data of xylem traits, hydraulic properties and measures of drought resistance from neotropical tree species retrieved from 346 sources. We found that xylem volume allocation to fiber walls increases embolism resistance, but at the expense of specific conductivity and sapwood capacitance. Xylem volume investment in fiber lumen increases capacitance, while investment in axial parenchyma is associated with higher specific conductivity. Dominant tree taxa from wet forests prioritize xylem allocation to axial parenchyma at the expense of fiber walls, resulting in a low embolism resistance for a given wood density and a high vulnerability to drought‐induced mortality. We conclude that strong trade‐offs between xylem allocation to fiber walls, fiber lumen, and axial parenchyma drive drought resistance in neotropical trees. Moreover, the benefits of xylem allocation to axial parenchyma in wet tropical trees might not outweigh the consequential low embolism resistance under more frequent and severe droughts in a changing climate.

Simulations of freshwater lens recharge and salt/freshwater interfaces using the HYDRUS and SWI2 packages for MODFLOW

Abstract The paper presents an evaluation of the combined use of the HYDRUS and SWI2 packages for MODFLOW as a potential tool for modeling recharge in coastal aquifers subject to saltwater intrusion. The HYDRUS package for MODFLOW solves numerically the one-dimensional form of the Richards equation describing water flow in variablysaturated media. The code computes groundwater recharge to or capillary rise from the groundwater table while considering weather, vegetation, and soil hydraulic property data. The SWI2 package represents in a simplified way variable-density flow associated with saltwater intrusion in coastal aquifers. Combining these two packages within the MODFLOW framework provides a more accurate description of vadose zone processes in subsurface systems with shallow aquifers, which strongly depend upon infiltration. The two packages were applied to a two-dimensional problem of recharge of a freshwater lens in a sandy peninsula, which is a typical geomorphologic form along the Baltic and the North Sea coasts, among other places. Results highlighted the sensitivity of calculated recharge rates to the temporal resolution of weather data. Using daily values of precipitation and potential evapotranspiration produced average recharge rates more than 20% larger than those obtained with weekly or monthly averaged weather data, leading to different trends in the evolution of freshwater-saltwater interfaces. Root water uptake significantly influenced both the recharge rate and the position of the freshwater-saltwater interface. The results were less sensitive to changes in soil hydraulic parameters, which in our study were found to affect average yearly recharge rates by up to 13%.

Unsaturated zone flow and solute transport modelling with MIKE SHE: model test and parameter sensitivity analysis using lysimeter data

This study presents the test of the widely used model MIKE SHE at the lysimeter in Wagna in Southern Styria (Austria). At the lysimeter comprehensive data of vegetation, i.e., cultivation types, and soil hydraulic properties are available to parameterise the model. The aim of the study is to test the water movement and solute transport simulation in the unsaturated zone and the evapotranspiration module by a comparison with measured recharge rates at the lysimeter bottom and measured soil water contents and soil tensions in different depths. For the unsaturated zone calculation, the Richards equation and the Van Genuchten–Mualem approach is used. With the parameterised model the solute transport module is tested against data of a tracer experiment (Bromide). The water content simulation in the different soil depths yielded good results. However, particularly in the gravel zone (below 70 cm) the strong recharge dynamics and at the same time also strong water content dynamics can hardly be reproduced by one individual soil physical parameter set. Two different sets were identified and the corresponding soil water retention functions are located at the opposite ends of the relatively large range obtained by the measurements in this zone. Also, the saturated hydraulic conductivity had to be increased by an order of magnitude to accurately represent the recharge dynamics. The test of the solute transport simulation showed generally very good results. However, the early rapid rise of the measured concentrations could not be reproduced with either parameter set. The discrepancies found in the study indicate a complex pore system in the gravel zone consisting of different flow paths (e.g., system of matrix flow and macro-pore flow) activated at different soil moisture conditions, which cannot be fully represented by the used approach. However, the parameter study herein highlights the main parameters to be altered in a calibration procedure at point scale. The paper includes also a step from point to regional scale. For comparison test calculations with data, which are usually available on regional scale, showed good results for the 5-year average balance (−7 % compared to measurements) but rather large deviations from the measurements at shorter time scales.

Using categorical soil structure information to improve soil water retention estimates of tropical delta soils

Models of soil water and solute transport require input data of soil hydraulic properties (e.g. soil water retention and hydraulic conductivity curves). Lack of such data, especially in tropical delta regions, has usually been the main constraint for the application of simulation models. Direct field or laboratory measurement of soil water retention is costly, laborious and time-consuming; therefore, indirect estimation from other easily measured soil properties has received great interest. However, indirect estimates are often unreliable. In this study, we hypothesise that including basic descriptive information of soil structure such as aspect of presence or absence of pedality can improve the prediction of the soil water retention characteristic (SWRC). Stepwise multiple linear regression was used to develop point pedotransfer functions (PTFs) to estimate soil water retention at eight pressure potentials (e.g. –1, –3, –6, –10, –20, –34, –100, –1500 kPa). Soil structural information was exploited as a preliminary grouping criterion to test our hypothesis. Soil samples were taken from 160 horizons distributed along the Mekong Delta, Vietnam. The results reveal that SWRC of tropical Mekong Delta soils could be satisfactorily estimated by typical predictors of PTFs (e.g. soil texture, organic carbon content and bulk density). Moreover, incorporating soil structure in developing PTFs did improve the prediction accuracy of SWRC, especially in the wet moisture range. Plastic limit was found to be a promising predictor for SWRC-PTFs of soils having a given degree of structural development.

Complementary techniques to assess physical properties of a fine soil irrigated with saline water

Water flow and solute transport numerical modeling is strongly limited due to the lack and difficulty in obtaining hydraulic property data in saline soils. A comparison of different techniques for physical characterization of soil structure is carried out in this study aiming to emphasize the complementarities and the synergy of the different approaches and their suitability for soils affected by salinization. In situ measurements of hydraulic conductivity (HC) by tension disc infiltrometer, water retention (WR) characteristics and pore size distribution by image analysis on undisturbed soil samples and aggregates stability have been measured in lab on a light clay soil of an experimental field undergone to two extreme irrigation treatments, NS (not-saline water, ECw = 0.9 dS m−1) and S (saline water with 1% of NaCl; ECw = 15 dS m−1). Following, the replicates have been denoted with the under script 1 and 2. The results show: a strong reduction of the index of aggregate stability in water, equals to 37 and 34% for NS1 and NS2, respectively, against the values of 18.9% for S1 and 18.5% for S2, respectively. The water retention curves of the S soils, for all the pressure heads investigated, are above those measured on not-saline soils. The image analysis has showed a larger quantity of pores (>36 μm) on the not-saline soils with respect to the saline ones. The total porosity (>36 μm) was 21.8% for NS2 and 11.9% for S1. This porosity reduction (9.9%) was spread over the entire ranges of pores with the greatest reduction in pore classes lying in the size range between 700 and 2,000 μm. The unsaturated hydraulic conductivity of the not-salines samples shows higher values respect to those of the saline samples. All the techniques applied showed converging results and provided a specific contribution towards the demonstration of a process of clogging of macropores under saline condition. Furthermore, the direct measurement of the pore changes provided by soil image analysis allowed a detailed interpretation of the mechanisms behind soil pore-structure worsening due to salinity. Combined use of the tension disc infiltrometer and image analysis methods showed the highest potential to overcome difficulties in hydraulic characterization close to saturation in salinized horizons.

Data of hydraulic properties of North East and North Central German soils

Abstract. The paper presents a data base of soil physical and hydrological properties of North East and North Central German soils. Included are measured data of the soil water retention curve and the unsaturated hydraulic conductivity function. Information on geo-reference, soil type and horizon are given. Soil hydraulic functions were measured with the evaporation method. The applied measurement technique is described and information to actual innovations and advanced technology is given. Additional soil physical data like particle size distribution, dry bulk density, organic matter content and other variables are presented. The data base includes original measurement results of 278 organic and of 497 mineral soil samples from 103 sites. The mineral soils cover a wide range of texture classes and dry bulk densities. The organic soils and samples represent different states of decomposition and mineralization. Furthermore hydraulic functions are included of soils anthropogenically altered by deep plough sand covering measures.

Uncertainty in the determination of soil hydraulic parameters and its influence on the performance of two hydrological models of different complexity

Abstract. Data of soil hydraulic properties forms often a limiting factor in unsaturated zone modelling, especially at the larger scales. Investigations for the hydraulic characterization of soils are time-consuming and costly, and the accuracy of the results obtained by the different methodologies is still debated. However, we may wonder how the uncertainty in soil hydraulic parameters relates to the uncertainty of the selected modelling approach. We performed an intensive monitoring study during the cropping season of a 10 ha maize field in Northern Italy. The data were used to: i) compare different methods for determining soil hydraulic parameters and ii) evaluate the effect of the uncertainty in these parameters on different variables (i.e. evapotranspiration, average water content in the root zone, flux at the bottom boundary of the root zone) simulated by two hydrological models of different complexity: SWAP, a widely used model of soil moisture dynamics in unsaturated soils based on Richards equation, and ALHyMUS, a conceptual model of the same dynamics based on a reservoir cascade scheme. We employed five direct and indirect methods to determine soil hydraulic parameters for each horizon of the experimental profile. Two methods were based on a parameter optimization of: a) laboratory measured retention and hydraulic conductivity data and b) field measured retention and hydraulic conductivity data. The remaining three methods were based on the application of widely used Pedo-Transfer Functions: c) Rawls and Brakensiek, d) HYPRES, and e) ROSETTA. Simulations were performed using meteorological, irrigation and crop data measured at the experimental site during the period June – October 2006. Results showed a wide range of soil hydraulic parameter values generated with the different methods, especially for the saturated hydraulic conductivity Ksat and the shape parameter α of the van Genuchten curve. This is reflected in a variability of the modeling results which is, as expected, different for each model and each variable analysed. The variability of the simulated water content in the root zone and of the bottom flux for different soil hydraulic parameter sets is found to be often larger than the difference between modeling results of the two models using the same soil hydraulic parameter set. Also we found that a good agreement in simulated soil moisture patterns may occur even if evapotranspiration and percolation fluxes are significantly different. Therefore multiple output variables should be considered to test the performances of methods and models.

High‐quality unsaturated zone hydraulic property data for hydrologic applications

In hydrologic studies, especially those using dynamic unsaturated zone moisture modeling, calculations based on property transfer models informed by hydraulic property databases are often used in lieu of measured data from the site of interest. Reliance on database‐informed predicted values has become increasingly common with the use of neural networks. High‐quality data are needed for databases used in this way and for theoretical and property transfer model development and testing. Hydraulic properties predicted on the basis of existing databases may be adequate in some applications but not others. An obvious problem occurs when the available database has few or no data for samples that are closely related to the medium of interest. The data set presented in this paper includes saturated and unsaturated hydraulic conductivity, water retention, particle‐size distributions, and bulk properties. All samples are minimally disturbed, all measurements were performed using the same state of the art techniques and the environments represented are diverse.

Variability of soil physical and hydraulic properties at the Mojave Global Change Facility, Nevada: Implications for water budget and evapotranspiration

The purposes of this study, conducted at the Mojave Global Change Facility in Nevada, USA, were to examine whether, and to what extent, spatial structure in soil physical properties would manifest as similar spatial structure in hydraulic properties and in spatial differences of evapotranspiration (ET) predictions. Soil samples were collected from 0 to 5 and 5 to 10 cm depths at each of 96 test plots. Hydraulic properties were estimated using textural properties and bulk density in the pedotransfer function method and then examined for spatial structure using variogram analysis. Results show a fining of texture at both depths in the northeast (downslope) quadrant, which led to higher water-holding capacity. Weak spatial structure was observed for most properties (ranges ∼75 m). Hydraulic property data were then used as input to a one-dimensional numerical model (HYDRUS-1D) applied at each of the 96 sites for 159 days. Four different shrub cover percentages (0, 10, 20, and 30%) were used. The results showed a predominant soil evaporation-dominated water balance in the northeast quadrant of the site, regardless of plant cover. Elsewhere, plant transpiration was more dominant as percent cover decreased. Results revealed the important role that soil hydraulic properties play in near-surface water balance.

Upscaling Schemes and Relationships for the Gardner and van Genuchten Hydraulic Functions for Heterogeneous Soils

Upscaled soil hydraulic properties are needed for many large‐scale hydrologic applications such as regional and global climate studies and investigations of land–atmosphere interactions. Many larger scale subsurface flow and contaminant transport studies also require upscaled hydraulic property estimates. The objectives of this study were to develop a methodology for upscaling hydraulic property functions using a p‐norm approach, to examine how p‐norm values differ for two commonly used soil hydraulic property models (the Gardner and van Genuchten functions), and to investigate the relative sensitivities of p‐norms and the effective hydraulic parameters to the degree of soil heterogeneity (expressed in terms of variances and auto‐correlation lengths of the hydraulic parameters) and other environmental conditions. The p‐norm approach expresses upscaling schemes such that it reduces their sensitivity to uncertainties (heterogeneities) in site conditions. The upscaling schemes are obtained as the result of two new criteria proposed to upscale soil hydraulic properties in this study—one preserving the ensemble vertical moisture flux across the land–atmosphere boundary, and a second preserving the ensemble soil surface moisture content. The effective soil hydraulic parameters of a heterogeneous soil formation are then derived by conceptualizing the formation as an equivalent homogeneous medium that satisfies the upscaling criteria. Upscaling relationships between the Gardner and van Genuchten models can then also be established for steady‐state vertical flow using the statistical structures of the hydraulic parameters of these two models as estimated from field measurements. The upscaling scheme is demonstrated using hydraulic property data collected at 84 locations across a site in the Mojave Desert. Our results show that the p‐norms generally vary less in magnitude than the effective parameters when the variances of the hydraulic parameters increase. We also show that, in general, p‐norm values are better defined for the van Genuchten model than the Gardner model. Hydraulic parameter auto correlations, as defined by correlation lengths, were found to have little impact in relating the upscaling schemes (p‐norm values) for the two hydraulic property models, but correlation between the hydraulic parameters within the hydraulic property models can significantly affect p‐norm relationships.

English

The accurate determination of saturated and unsaturated hydraulic properties of mine waste and cover material is critical for predicting long-term drainage behavior and closure performance. The rock fragments typically found in mine waste and borrow materials complicate laboratory hydraulic property measurements. Many hydraulic testing laboratories address this issue by removing all material greater than 4.75 mm in diameter, repacking the remaining fine-earth sample in small diameter cores, and “correcting” the resulting measurements for the gravel content using published correction factors. In order to evaluate several of the aforementioned gravel correction and hydraulic property prediction methods, a laboratory experiment was designed to test various well-graded gravelly materials. An alluvial material sample was used to fabricate eight soils with various particle size distributions. The primary sample matrix for all testing was chosen to be the fine-earth fraction, less than 4.75 mm in diameter. Additional soil materials were then fabricated in which either part of the fine-earth fraction was removed, or gravel material ranging from 4.75 mm to 19 mm diameter was added. Test results show that saturated hydraulic conductivity (Ksat) decreased with up to 30% gravel content but increased by orders of magnitude at higher gravel contents. Moisture retention characteristic (MRC) data showed that the air entry value decreased with increasing gravel contents, although the amount of retained water only slightly decreased as gravel content increased. Depending on how the MRC data is interpreted, the predicted unsaturated hydraulic conductivities either showed increasing hydraulic conductivity as gravel contents increased, or the values converge. The measured hydraulic property data could not be accurately predicted using published correction factors, or by other prediction methods that use particle size distribution data. Consequently, removing the gravel fraction could result in significant error in the prediction of mine waste drainage behavior and the performance of cover systems. It is recommended that published correction factors not be used unless the sample is similar in gradation and bulk density to the soils tested by the published method. .

The transferability of Australian pedotransfer functions for predicting water retention characteristics of French soils

AbstractA French data set was used to evaluate how well two widely used analytical functions describe measured soil water characteristic (SWC) data. Both the van Genuchten (sigmoidal) and Campbell (power‐law) equations gave good descriptions of the data (mean R2 of 98.1 and 97.1% respectively). Methods of predicting SWC data were also evaluated. When a power‐law equation was parameterised using just two measured SWC points and bulk density (the ‘two‐point’ method), a very good SWC prediction was obtained for the French data (mean R2 of 94.8%). An empirical equation for prediction of the SWC was also assessed using the French data set. This method was developed using multiple regression analysis from Australian soil data and requires soil texture and bulk density as input. The predictions (mean R2 of 85.2%) lacked accuracy and precision in comparison with the two‐point method but the empirical approach uses more readily available input data. The accuracy of prediction from both methods was similar to that observed previously for Australian data sets. The empirical approach developed from Australian soil data has reasonable applicability to French soils. The approach of assuming a power‐law model and empirically predicting slope and air entry potential is shown to have merit. A strategy for achieving adequate coverage of soil hydraulic property data for France is suggested incorporating hydraulic prediction methods such as those evaluated here.

Vadose Zone Clays and Water Content beneath Wet and Dry Canyons of the Pajarito Plateau, New Mexico

Clay mineralogy in the vadose zone at Los Alamos National Laboratory (LANL), situated on the Pajarito Plateau of northern New Mexico, differs significantly beneath wet and dry canyons. Drainage across LANL is generally from west to east and feeds into the Rio Grande along the eastern margin of the plateau. Canyons with headwaters in the Sierra de los Valles west of the plateau support more flow and are wetter than canyons with headwaters on the plateau. Los Alamos Canyon, one of the wetter canyons, has extensive clay alteration to depths >30 m in the subcanyon vadose zone. Mortandad Canyon, one of the drier canyons, has less clay alteration. Hydraulic property data for the Otowi Member of the Bandelier Tuff, one of the most widespread lithologies of the plateau, indicate that zones of high clay abundance have hydraulic transmissivities (Ksat) one to two orders of magnitude lower than less altered tuff (∼10−4 vs. 10−2 to 10−3 cm/s). Occurrences of halloysite, and perhaps kaolinite, indicate zones where the water/rock ratio is or has been high within the vadose zone. Gravimetric water content data collected at 110°C from vadose zone rocks with low to moderate clay content provide water abundance data for matrix flow calculations. These data may be in error by up to ∼5 to 16% because some of the water measured is actually held in clay interlayers rather than in pore spaces; such errors are minor but should be considered in the use of gravimetric moisture data. The use of electrical methods to explore for vadose wet zones is valid on the Pajarito Plateau as long as the results are treated broadly, with the understanding that some intervals of high conductivity are not entirely related to either movable water content or clay abundance.

Measurement of hydraulic properties in deep lake sediments using a tethered pore pressure probe: Applications in the Hamilton Harbour, western Lake Ontario

Estimates of groundwater seepage flux in lake bottom sediments require knowledge of the hydraulic gradient at the sediment‐surface water interface and the hydraulic conductivity of the lake‐bottom materials. In deep waters, in situ measurement of these parameters can be accomplished through the use of piezometer probes lowered and monitored remotely from a surface vessel. In this research work a new tethered piezometer probe was developed and tested for use in collecting hydraulic property data in deep‐lake bottom sediments. The probe uses a variable‐reluctance transducer to measure the differential sediment pore pressure between two ports spaced 100 cm apart. The dissipation of pore pressure transients that develop during rapid emplacement of the probe were extrapolated in time to estimate equilibrium hydraulic gradients. In addition, various data analysis techniques were evaluated for determining sediment hydraulic conductivity and specific storage through interpretation of the pore‐pressure dissipation data. The probe was used to estimate groundwater seepage in the bottom sediments of the Hamilton Harbour, at the western end of Lake Ontario. Upward gradients were measured at nine locations within the harbor ranging from 0.010 to 0.425 and a downward gradient of −0.015 was recorded at one site along the harbor's eastern boundary. Hydraulic conductivities determined from pore‐pressure dissipation over time ranged from 6.9 × 10−9to 4.8 × 10−7 m/s. Specific storage values ranged from 0.08 to 0.19 m−1. Calculated average linear seepage velocities ranged from 4.3 × 10−8 to −8.5 × 10−9 m/s. The groundwater contribution to the harbor through the deeper, fine‐grained sediments was estimated to be 9.1 × 10−2 m3/s, or 2.9 × 106 m3/yr. This represents approximately 1.0% of the harbor basin's total volume, 15% of precipitation's contribution, 1.2% of the contribution of surface inflows (excluding the Burlington ship canal) and 0.22% of the total surface outflow passing through the Burlington shipping canal, which connects the harbor to Lake Ontario.