Subsurface Hydraulic Conductivity Research Articles

Hydrologic Performance of Permeable Pavers and a Dome Concrete Forming System: A Comparative Study

The hydrologic performance of permeable interlocking concrete pavers (PICP) and a dome concrete forming system (DCFS) was quantified and evaluated at a retrofitted residential laneway in Toronto, Ontario. The quantification and evaluation were performed by comparing their monitored performance over 14 months with an adjacent concrete pavement. Their monitored performance was then used to assess their ability to mimic predevelopment hydrologic behavior, estimated through modeling. The PICP and DCFS achieved (1) an average runoff volume reduction of 33% and 85%; (2) an average runoff coefficient of 0.48 and 0.12; and (3) an average peak flow reduction of 43% and 89%, respectively. The outflow duration from the DCFS was extended 4.1 times greater than the inflow duration, indicating its potential to attenuate flashy events. The peak flows produced by the DCFS were delayed by nearly 2.5 h from those occurring on the PICP. Correlation analyses indicated a more significant influence of rainfall depth and intensity on the performance of PICP than that of the DCFS. Compared with predevelopment levels, PICP did not match runoff volumes for smaller events (<10 mm) but produced less runoff for larger events (>30 mm). However, the PICP did not match predevelopment peak flows in 100% of occurrences. The DCFS reduced runoff volumes and peak flows to magnitudes lower than all predevelopment levels. Surface infiltration testing and subsurface hydraulic conductivity estimations indicated that infiltration capability in both systems could be reduced over time. The study demonstrated that the DCFS might need to be prioritized over permeable pavements, especially when installed over low-permeability soils.

Estimation of soil subsurface hydraulic conductivity based on inverse modelling and soil morphology

Soil hydraulic properties play a primary role in water infiltration and movement, and transport of nutrients and contaminants through the soil profile. However, the determination of soil hydraulic properties, especially the hydraulic conductivity at lower depths within the soil profile is very challenging. We investigated the use of inverse modelling based on APSIM (Agricultural Production Simulation Model) to determine likely ranges of the hydraulic conductivity at saturation (Ksat) and field capacity (KDUL) for a slowly permeable subsurface horizon. Simulations were run for the poorly drained Otokia silt loam, in the Otago region of New Zealand. APSIM simulations were set up either according to the site specific soil profile description or based on the national soils database (S-map) pedotransfer functions. Simulated temporal soil moisture data were compared to measurements from a field experiment. Within a sensitivity analysis Ksat values of the subsurface soil were varied from 2.4 to 192 mm/d, and values for KDUL from 0.05 to 1 mm/d. Finally simulations were run over 45 years using three climatic conditions, with annual rainfall amounts of 582, 628 and 730 mm. The effect of varying the hydraulic conductivity of the subsurface fragipan horizon (Cx) on the wetness status of the overlying B2g horizon was determined by calculating the average annual duration of soil moisture above field capacity. These were then used to estimate ranges of the hydraulic conductivity that contributes to a soil being imperfectly or poorly drained. The results highlight the significant influence that KDUL has on the reliability of modelling the hydraulic behaviour of soils with slowly permeable subsoils.

Bridging the gap between numerical solutions of travel time distributions and analytical storage selection functions

AbstractRecent advancements in analytical solutions to quantify water and solute travel time distributions (TTDs) and the related StorAge Selection (SAS) functions synthesize catchment complexity into a simplified, lumped representation. Although these analytical approaches are efficient in application, they require rarely available long‐term and high‐frequency hydrochemical data for parameter estimation. Alternatively, integrated hydrologic models coupled to Lagrangian particle‐tracking approaches can directly simulate age under different catchment geometries and complexity, but at a greater computational expense. Here, we bridge the two approaches, using a physically based model to explore the uncertainty in the estimation of the SAS function shape. In particular, we study the influence of subsurface heterogeneity, interactions between distinct flow domains (i.e., the vadose zone and saturated groundwater), diversity of flow pathways, and recharge rate on the shape of TTDs and the SAS functions. We use an integrated hydrology model, ParFlow, linked with a particle‐tracking model, SLIM, to compute transient residence times (or ages) at every cell in the domain, facilitating a direct characterization of the SAS function. Steady‐state results reveal that the SAS function shape shows a wide range of variation with respect to the variability in the structure of subsurface heterogeneity. Ensembles of spatially correlated realizations of hydraulic conductivity indicate that the SAS functions in the saturated groundwater have an overall weak tendency toward sampling younger ages, whereas the vadose zone gives a strong preference for older ages. We further show that the influence of recharge rate on the TTD is tightly dependent on the variability of subsurface hydraulic conductivity.

An adaptive Gaussian process-based iterative ensemble smoother for data assimilation

Abstract Accurate characterization of subsurface hydraulic conductivity is vital for modeling of subsurface flow and transport. The iterative ensemble smoother (IES) has been proposed to estimate the heterogeneous parameter field. As a Monte Carlo-based method, IES requires a relatively large ensemble size to guarantee its performance. To improve the computational efficiency, we propose an adaptive Gaussian process (GP)-based iterative ensemble smoother (GPIES) in this study. At each iteration, the GP surrogate is adaptively refined by adding a few new base points chosen from the updated parameter realizations. Then the sensitivity information between model parameters and measurements is calculated from a large number of realizations generated by the GP surrogate with virtually no computational cost. Since the original model evaluations are only required for base points, whose number is much smaller than the ensemble size, the computational cost is significantly reduced. The applicability of GPIES in estimating heterogeneous conductivity is evaluated by the saturated and unsaturated flow problems, respectively. Without sacrificing estimation accuracy, GPIES achieves about an order of magnitude of speed-up compared with the standard IES. Although subsurface flow problems are considered in this study, the proposed method can be equally applied to other hydrological models.

Direct Method of Hydraulic Conductivity Structure Identification for Subsurface Transport Modeling

AbstractSolute transport in aquifers is strongly influenced by the spatial distribution of subsurface hydraulic conductivity (K), while limited drilling typically results in lack of data characterizing both the K and the in situ fluid-flow boundary conditions (BC). To characterize such environments, this paper presents an efficient direct inverse method to simultaneously identify an aquifer’s K pattern, values, and flow field. The method ensures fluid-flow continuity using local approximate solutions of the governing flow equation conditioned to limited measurements, while the physics of flow are enforced, making the inverse problem well-posed. A single system of equations is assembled and solved, from which parameters and BC can be simultaneously estimated. For problems with irregular and regular K distributions, inversion is demonstrated for different measurement types, qualities, and quantities. When measurement error is increased, the estimated K pattern is largely insensitive to the error, although t...

Agricultural and forested land use impacts on floodplain shallow groundwater temperature regime

AbstractGiven the importance of groundwater temperature to the biogeochemical health of aquatic ecosystems, a floodplain study was implemented to improve understanding of rural land use impacts on shallow groundwater (SGW) temperature. Study sites included a historic agricultural field (Ag) and bottomland hardwood forest (BHF), each with nine piezometers in an 80 × 80 m grid. Piezometers were equipped with pressure transducers to monitor SGW temperature and level at 30 min intervals during the 2011, 2012, 2013, and 2014 water years. The study is one of the first to utilize long‐term, continuous, automated, in situ monitoring to investigate rural land use impacts on shallow groundwater temperatures. Average SGW temperature during the study period was 11.1 and 11.2 °C at the Ag and BHF sites, respectively. However, temperature range at the Ag site was 72% greater than at the BHF site. Results indicate a greater responsiveness to seasonal climate fluctuations in Ag site SGW temperature related to absence of forest canopy. Patterns of intra‐site groundwater temperature differences at both study sites illustrate the influence of stream–aquifer thermal conduction and occasional baseflow reversals. Considering similar surface soil temperature amplitudes and low average groundwater flow values at both sites, results suggest that contrasting rates of plant water use, groundwater recharge, and subsurface hydraulic conductivity are likely mechanistic causes for the observed SGW temperature differences. Results highlight the long‐term impact of forest removal on subsurface hydrology and groundwater temperature regime. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Using streamlines to simulate stochastic reactive transport in heterogeneous aquifers: Kinetic metal release and transport in CO2 impacted drinking water aquifers

A Lagrangian streamline approach that stochastically represents uncertainty in spatial hydraulic conductivity distribution is coupled to kinetic reactive transport in a heterogeneous 3-D domain. This methodology is designed to efficiently account for uncertainties inherent in subsurface reactive transport while maintaining hydro-geochemical processes. A hypothetical CO2 leak from a geological carbon storage site into an overlying aquifer is used to simulate reactive transport where contamination may occur. Uncertainty in subsurface hydraulic conductivity is accounted for using correlated, Gaussian random fields in a Monte Carlo approach. In this approach 100 realizations of each ensemble were simulated with variances of the natural log of hydraulic conductivity (σ2lnK) of 1, 3.61, and 16. Peak ensemble lead concentrations were found at σ2lnK of 3.61, the middle of the variances simulated. σ2lnK within an aquifer was found to influence chemical residence time, which in turn determined the equilibrium state of the plume along the flow path and at the pumping well thus driving geochemical conditions. However, macrodispersion due to heterogeneous flow paths caused lower contaminant concentrations at the pumping well due to dilution with uncontaminated water. Furthermore, a strong link between σ2lnK and the probability of well-capture was found, suggesting that proper characterization of the σ2lnK within an aquifer will help to quantify the impact of uncertainty on risks of groundwater contamination.

Influences of subsurface heterogeneity and vegetation cover on soil moisture, surface temperature and evapotranspiration at hillslope scales

Physical processes are at the root of determining hydrologic response at all scales. Here, the physical mechanisms linking (1) subsurface heterogeneities to soil moisture and (2) resulting land-surface energy feedbacks to the atmosphere, are examined at the hillslope scale using a fully coupled surface-subsurface-land-surface model, ParFlow. A hillslope with a heterogeneous subsurface and uniform topography was modeled numerically using summer atmospheric conditions and a single precipitation event under controlled boundary conditions in order to isolate the contribution of hydraulic conductivity to land-surface hydrological processes and energy interactions. Patterns of subsurface hydraulic conductivity are shown to govern soil-moisture distribution at the hillslope scale following precipitation. This variability in soil moisture is closely linked to the variability in land-surface energy feedbacks. The role that vegetation plays in subsurface soil moisture and land energy communications is also examined. Results show that hillslope soil moisture variation is first established by patterns in vertical hydraulic conductivity, while later on in the dry-down period, vegetation exerts greater control on the land-surface energy fluxes and controls the rate of hillslope dry down. Furthermore, as compared to bare-soil simulations, grass-cover simulations show an increase in near-surface soil moisture despite water up-take along the rooting depth.

Assessing Ground Water Development Potential Using Landsat Imagery

Seven villages in southeastern Kenya surround Mt. Kasigau and depend on the mountain's cloud forest for their water supply. Five of these villages have regularly experienced water shortages, and all village water supplies were contaminated with Escherichia coli bacteria. There is a need to economically find new sources of fresh ground water. Remote sensing offers a relatively quick and cost-effective way of identifying areas with high potential for ground water development. This study used spectral properties of features on Landsat remote sensing imagery to map linear features, soil types, surface moisture, and vegetation. Linear features represented geologic or geomorphologic features indicating either shallow ground water or areas of increased subsurface hydraulic conductivity. Regarding soil type, black soils were identified as potential indicators of shallow aquifers based on their relatively lower elevation and association with river valleys. A vegetation map was created using unsupervised classification, and three of the resulting vegetation classes were observed to be commonly associated with wet areas and/or ground water discharge. A wetness map, created using tasseled cap analysis, was used to identify all areas of high ground moisture, including those that corresponded to vegetated areas. The linear features, soil type, vegetation, and wetness maps were overlaid to produce a composite that highlighted areas with the highest potential for ground water development. Electrical resistivity surveys confirmed that areas highlighted by the composite image had relatively shallow depths to the water table. Some figures in this paper are available in color in the online version of the paper.

Quantifying the effects of three-dimensional subsurface heterogeneity on Hortonian runoff processes using a coupled numerical, stochastic approach

The impact of three-dimensional subsurface heterogeneity in the saturated hydraulic conductivity on hillslope runoff generated by excess infiltration (so-called Hortonian runoff) is examined. A fully coupled, parallel subsurface–overland flow model is used to simulate runoff from an idealized hillslope. Ensembles of correlated, Gaussian random fields of saturated hydraulic conductivity are used to create uncertainty in spatial structure. A large number of cases are simulated in a parametric manner with the variance of the hydraulic conductivity varied over orders of magnitude. These cases include rainfall rates above, equal and below the geometric mean of the hydraulic conductivity distribution. These cases are also compared to theoretical representations of runoff production based on simple assumptions regarding (1) the rainfall rate and the value of hydraulic conductivity in the surface cell using a spatially-indiscriminant approach; and (2) a percolation-theory type approach to incorporate so-called runon. Simulations to test the ergodicity of hydraulic conductivity on hillslope runoff are also performed. Results show that three-dimensional stochastic representations of the subsurface hydraulic conductivity can create shallow perching, which has an important effect on runoff behavior that is different than previous two-dimensional analyses. The simple theories are shown to be very poor predictors of the fraction of saturated area that might runoff due to excess infiltration. It is also shown that ergodicity is reached only for a large number of integral scales (∼30) and not achieved for cases where the rainfall rate is less than the geometric mean of the saturated hydraulic conductivity.

Runoff and solute mobilization processes in a semiarid headwater catchment

Runoff and solute transport processes contributing to streamflow were determined in a small headwater catchment in the eastern Murray‐Darling Basin of Australia using hydrometric and tracer methods. Streamflow and electrical conductivity were monitored from two gauges draining a portion of the upper catchment area (UCA) and a saline scalded area, respectively. Runoff in the UCA was related to the formation of a seasonally perched aquifer in the near‐surface zone (0–0.4 m). A similar process was responsible for runoff generation in the saline scalded area. However, saturation in the scald area was related to the proximity of groundwater rather than low subsurface hydraulic conductivity. Because of higher antecedent water content, runoff commenced earlier in winter from the scald than did the UCA. Additionally, areal runoff from the scald was far greater than from the UCA. Total runoff from the UCA was higher than the scald (15.7 versus 3.5 mL), but salt export was far lower (0.6 and 5.4 t for the UCA and scald area, respectively) since salinity of the scald runoff was far higher than that from the UCA, indicating the potential impact of saline scalded areas at the catchment scale. End‐member mixing analysis modeling using six solutes indicated that most runoff produced from the scald was “new” (40–71%) despite the proximity of the groundwater surface and the high antecedent moisture levels. This is a reflection of the very low hydraulic conductivity of soils in the study area. Nearly all chloride exported to the stream from the scald emanated from the near‐surface zone (77–87%). Runoff and solute mobilization processes depend upon seasonal saturation occurring in the near‐surface zone during periods of low evaporative demand and generation of saturated overland flow.

Estimation of baseflow residence times in watersheds from the runoff hydrograph recession: method and application in the Neversink watershed, Catskill Mountains, New York

AbstractA method for estimation of mean baseflow residence time in watersheds from hydrograph runoff recession characteristics was developed. Runoff recession characteristics were computed for the period 1993–96 in the 2 km2 Winnisook watershed, Catskill Mountains, southeastern New York, and were used to derive mean values of subsurface hydraulic conductivity and the storage coefficient. These values were then used to estimate the mean baseflow residence time from an expression of the soil contact time, based on watershed soil and topographic characteristics. For comparison, mean baseflow residence times were calculated for the same period of time through the traditional convolution integral approach, which relates rainfall δ18O to δ18O values in streamflow. Our computed mean baseflow residence time was 9 months by both methods. These results indicate that baseflow residence time can be calculated accurately using recession analysis, and the method is less expensive than using environmental and/or artificial tracers. Published in 2002 by John Wiley &amp; Sons, Ltd.

The role of surface water redistribution in an area of patterned vegetation in a semi-arid environment, south-west Niger

The surface hydrology of a semi-arid area of patterned vegetation in south-west Niger is described. In this region alternating bands of vegetation and bare ground aligned along the contours of a gently sloping terrain give rise to a phenomenon known as `brousse tigrée' (tiger bush). At the selected study site the vegetation bands are 10–30 m wide, separated by 50–100-m-wide bands of bare ground. Five species of shrub dominate, Guiera senegalensis, Combretum micranthum, C. nigricans, Acacia ataxacantha and A. macrostachya. Herbaceous vegetation is generally limited to the upslope edges of vegetation bands. A comprehensive field programme was undertaken to investigate the hydrology. Topographic, vegetation and surface feature surveys were carried out in conjunction with the measurement of rainfall, surface and subsurface hydraulic conductivity, particle size and soil moisture content. Four types of vegetation class are recognised, each tending to occupy a constant position relative to the others and to the regional slope. In a downslope direction the classes are: bare ground, grassy open bush, closed bush, bare open bush, bare ground etc. The nature of the ground surface is closely linked to the vegetation class. Over the bare, bare open and grassy open classes various types of surface crust are present with each type of crust tending to occupy a constant position on the regional slope relative to the vegetation class and other crust types. Below closed bush crusts are generally absent. The typical downslope sequence from the downslope boundary of a vegetation band is: structural (sieving) crust→erosion crust→(gravel crust)→sedimentation crust→microphytic sedimentation crust→no crust→sieving crust, etc. It is also shown that these crust types are dynamic and evolve from one to the other as hydrological conditions change. Hydraulic conductivities of surface crusts are low, typically falling within the range 10 −6–10 −7 m s −1. The presence of large expanses of crust over bare regions tends to generate run-off, which moves down the regional slope to be intercepted and pond within and just upslope of vegetated areas. Such run-off concentrates rainfall by a factor of up to 3.7 below vegetated areas. This concentration combined with an absence of crust development in closed bush areas promotes rapid infiltration below and just upslope of vegetation bands. In this way the hydrology of the area operates to ensure that the bulk of the rain which falls is directed as quickly as possible to the areas where it is most needed to support the existing vegetation.

Resolution and uncertainty in hydrologic characterization

Hydrologists have applied inverse techniques to obtain estimates of subsurface permeability and porosity variations and their associated uncertainties. Although inverse methods are now well established in hydrology, important aspects of inverse theory, the analysis of resolution, and the trade‐off between model parameter resolution and model parameter uncertainty have not been utilized. In this paper the concept of model parameter resolution is incorporated into the analysis of hydrological experiments. Model parameter resolution is a measure of the spatial averaging implicit in estimates of a distributed hydrological property such as permeability. There are two important uses of resolution and uncertainty estimates in hydrology. The first use is to plan a hydrologic testing program. Resolution matrices can be developed for proposed well tests in a variety of synthetic media. Then the effectiveness of the test design can be evaluated in terms of model parameter resolution and uncertainty. Secondly, when real data are available and used in an inversion determining the distribution of hydrologic parameters, estimates of model parameter resolution and uncertainty analysis can indicate the reliability of the solution. For synthetic tests in which the hydraulic conductivity varies and porosity does not, it is found that tracer data can provide better spatial resolution of subsurface hydraulic conductivity variations than transient pressure data. Pressure data are most sensitive to hydraulic conductivity variations immediately surrounding the well. Both pressure and tracer data better determine barriers to flow rather than channels to flow. The methodology is applied to a set of transient pressure data gathered at the Grimsel Rock Laboratory of the Swiss National Cooperative for the Storage of Radioactive Waste. In the fracture under study a low hydraulic conductivity region appears to partition the fracture plane into two distinct zones.

Potassium and chloride movement in a forest soil under simulated rainfall

An initial appraisal of the mechanisms involved in reactive solute transport through a weathered soil profile was made by following the movement of potassium and chloride during prolonged leaching on a sprinkle-irrigated native forest plot. The soil was an acid, strongly base-unsaturated red duplex soil with a high surface and subsurface hydraulic conductivity. Water movement was followed by tensiometers located at regular depth intervals to 1.5 m, and soil water samplers with ceramic cups were used to collect soluble potassium and chloride. Some 650 mm of water moved beyond 1.5 m depth in the profile, but chloride did not move beyond 1 m. Nearly all of the potassium was retained in the soil above 0.6 m depth. Although both ions underwent ion exchange, adsorption of potassium was reasonably uniform through the profile, whereas chloride adsorption increased with depth. Immediate ground- and stream-water contamination did not occur under these conditions.