Unsaturated Hydraulic Conductivity Variation of Expansive Yazoo Clay with Wet-Dry Cycles

Expansive soils are subjected to shrink-swell behavior with moisture variation in Mississippi, United States. With successive moisture and temperature variations over the seasons, the hydraulic conductivity of expansive soil is subjected to change because of the development of shrinkage cracks, which can be as large as as 1.2 cm wide and 1.5 m deep in the field, affecting the vertical hydraulic conductivity (Kv), whereas the horizontal hydraulic conductivity (Kh) remains fairly constant. The current study intends to investigate the hydraulic conductivity of highly expansive Yazoo clay at different wet-dry cycles. To observe the changes in the hydraulic conductivity with different wet-dry cycles in the laboratory, an instantaneous profile method to measure the permeability was utilized. Compacted Yazoo clay samples at different initial moisture content instrumented with moisture sensors at different depths to monitor changes in the moisture content were investigated. The samples were subjected to one, two, and three numbers (1N, 2N, and 3N) of wetting and drying cycles. For the drying process, testing chambers are kept in a controlled high-temperature booth of about 37°C simulating high summer temperatures in Mississippi. After the end of the wet-dry cycles, the test is performed to investigate the changes in the hydraulic conductivity of soil with the presence of shrinkage cracks. The hydraulic conductivity of highly plastic clay is very low at a fully compacted state and was observed to be (1.0×10-8 cm/s) at the 1N wetting phase. However, with an increment in the wet-dry cycles, the Kv of Yazoo clay increases (3.70×10-4 cm/s) after the sample is exposed to three wet-dry cycles. Even though the changes in the Kv of highly plastic clay define the infiltration behavior, which mostly controls the slope failure and pavement distress, consideration of the climatic loads is ignored in the design phase of the highway embankment and levees. By inclusion of the climatic variation, and evaluating the performance, the design life and resilience of the structures can be significantly increased

Simultaneous identification of contaminant source location, initial contaminant concentration, horizontal and vertical hydraulic conductivity in a three-dimensional coastal aquifer via ensemble Kalman filter

<p>In coastal aquifers, we face the problem of salt water intrusion, which creates a complex flow field. Many of these coastal aquifers are also exposed to contaminants from various sources. In addition, in many cases there is no information about the characteristics of the aquifer. Simultaneous identification of the contaminant source and coastal aquifer characteristics can be a challenging issue. Much work has been done to identify the contaminant source, but in the complex velocity field of coastal aquifer, no one has resolved this issue yet. We want to address that in a three-dimensional artificial coastal aquifer.</p><p>To achieve this goal, we have developed a method in which the contaminant source can be identified and the characteristics of the aquifer can be estimated by using information obtained from observation wells. First, by assuming the input parameters required to simulate the contaminant transfer to the aquifer, this three-dimensional coastal aquifer that is affected by various phenomena such as seawater intrusion, tides, shore slope, rain, discharge and injection wells, is simulated and the time series of the output parameters including head, salinity and contaminant concentration are estimated. In the next step, with the aim of performing inverse modeling, random values ​​are added to the time series of outputs obtained at specific points (points belonging to observation wells) in order to rebuilt the initial conditions of the problem to achieve the desired unknowns (contaminant source and aquifer characteristics). The unknowns estimated in this study are the contaminant source location (x, y, z), the initial contaminant concentration, the horizontal and vertical hydraulic conductivity of the aquifer. SEAWAT model in GMS software environment has been used to solve the equations of flow and contaminant transfer and simulate a three-dimensional coastal aquifer. Next, for reverse modeling, one of the Bayesian Filters subset (ensemble Kalman filter) has been used in the Python programming language environment. Also, to reduce the code run time, the neural network model is designed and trained for the SEAWAT model.</p><p>This method is able to meet the main purpose of the study, namely estimating the value ​​of unknown input parameters, including the contaminant source location, the initial contaminant concentration, the horizontal and vertical hydraulic conductivity of the aquifer. In addition, that makes it possible to achieve a three-dimensional numerical model of the coastal aquifer that can be used as a benchmark to examine more accurately the impact of different phenomena simultaneously. In conclusion, we have developed an algorithm which can be used in the world's coastal aquifers to identify the contaminant source and estimate its characteristics.</p><p> </p><p>Key words: coastal aquifer, seawater intrusion, contaminants, groundwater, flow field, parameter estimation, ensemble kalman filter</p>

New insights into the drainage of inundated ice-wedge polygons using fundamental hydrologic principles

The pathways and timing of drainage from inundated ice-wedge polygon centers in a warming climate have important implications for carbon flushing, advective heat transport, and transitions from carbon dioxide to methane dominated emissions. This research provides intuition on this process by presenting the first in-depth analysis of drainage from a single polygon based on fundamental hydrogeological principles. We use a recently developed analytical solution to provide a baseline for the effects of polygon aspect ratios (radius to thawed depth) and hydraulic conductivity anisotropy (horizontal to vertical hydraulic conductivity) on drainage pathways and temporal depletion of ponded water heights of inundated ice-wedge polygon centers. By varying the polygon aspect ratio, we evaluate the effect of polygon size (width), inter-annual increases in active layer thickness, and seasonal increases in thaw depth on drainage. One of the primary insights from the model is that most inundated ice-wedge polygon drainage occurs along an annular region of the polygon center near the rims. This implies that inundated polygons are most intensely flushed by drainage in an annular region along their horizontal periphery, with implications for transport of nutrients (such as dissolved organic carbon) and advection of heat towards ice wedge tops. The model indicates that polygons with large aspect ratios and high anisotropy will have the most distributed drainage. Polygons with large aspect ratio and low anisotropy will have their drainage most focused near the their periphery and will drain most slowly. Polygons with small aspect ratio and high anisotropy will drain most quickly. Our results, based on idealized scenarios, provide a baseline for further research considering geometric and hydraulic complexities of ice-wedge polygons.

Impact of the Depth of Diaphragm Wall on the Groundwater Drawdown during Foundation Dewatering Considering Anisotropic Permeability of Aquifer

Foundation dewatering combined with a waterproof curtain is widely applied to ensure the safety of the foundation pit in areas with multi-aquifer–aquitard alternative strata. The buried depth of the diaphragm wall can influence the environmental effect due to dewatering obviously. This paper investigates the impact of the buried depth of the diaphragm wall on the groundwater drawdown considering the anisotropic permeability of the dewatering aquifer. Numerical simulation is conducted based on an engineering case. The ratio of penetrating depth of diaphragm wall to thickness of dewatering aquifer (RW) and the ratio of horizontal and vertical hydraulic conductivity of dewatering aquifer (RC) are varied. The relationship between approximate hydraulic gradient (Δi) and RW (or RC) can be fitted by Boltzmann curve (or logarithmic curve). Effective, suggested and control values of RW (or RC) are proposed, of which the suggested value is recommended in practical engineering. The effective, suggested and control value of RW can be calculated by logarithmical equation considering the value of RC.

PERMEABILITY OF COVER DEPOSITS OF CRYSTALLINE ROCKS IN THE SUDETY MOUNTAINS (SW POLAND) BASED ON A FIELD STUDY

Article presents a study on the permeability of weathering covers formed on crystalline rocks, which was conducted in south-western Poland (Sudety Mountains). Evaluation of the infiltration capacity was performed based on field measurements of the vertical hydraulic conductivity carried out by using the Porschet method and the ETC Pask Constant Head Permeameter. During the field investigations conducted in sixteen sites, 28 determinations of the hydraulic conductivity k were made, 16 by the Porschet method and 12 using the ETC Pask Permeameter. Ten sites represent weathering covers of metamorphic rocks (amphibolites, eclogites, mica-schists, crystalline limestones, gneisses) and the next six sites represent covers of igneous rocks (granites). The values of the vertical hydraulic conductivity k determined by the Porschet method ranged between 0.053 and 2.19 m/d, while those obtained using the ETC Pask Permeamet erranged between 0.012 and 0.76 m/d. In the first place, it should be noticed that the results determined during the field investigations conducted according to the Porschet method are generally 3-4 times higher than those obtained using the ETC Pask Permeameter. The results for the vertical hydraulic conductivity allow us to classify weathering sediments of metamorphic and igneous rocks, as semi-permeable to medium permeable rocks. Weathered gneisses were distinctly characterized by the worst capacity to conduct water (semi-permeable) among all types of weathering covers of crystalline rocks. Higher values (0,08-0,8 m/d) of the vertical hydraulic conductivity were found for the weathering covers of the other metamorphic rocks (low permeable). The best conditions to conduct water were found in the weathering covers of granite rocks, which in most cases are classified as medium permeable rocks (more than 0.8 m/d) and exhibit distinctly better permeability coefficients.

PLANTER BOX RAINGARDEN FOR ZINC REMOVAL FROM STORM WATER

Urbanization creates problems for the natural water systems, such as an increase in run-off volume due to the impervious surfaces and a negative impact on groundwater recharge. These changes and exposure to contaminants such as suspended/dissolved solids and heavy metals severely degrade stormwater quality. In Christchurch, heavy metals such as zinc found in run-off, which is mainly sourced from galvanized roofing. The main idea of this research is to solve run-off issues at the source, along with the construction phase. This idea is aligned with the NZ's Unitary Plan to keep rainwater run-off after a new development equal or less than the run-off that occurred before the development. Different methods of treatment for roof run-off were evaluated in this research to propose a sustainable solution followed by an assessment. A multi-layered planter box raingarden was selected since it helps to landscape, improve water quality, and perform as an attenuation device. The research concentrated on maximizing water quality while maintaining a required flowrate. The planter box raingarden performed at a low vertical hydraulic conductivity rate of 164 mm/hr and achieved a high removal rate for heavy metals. The removal rate for dissolved zinc and total zinc was 99.7% and 99.1%, respectively. The results explained that the planter box raingarden performs well as an attenuation device while adsorb and filter contaminants remarkably.

Soil-water physical attributes under different managements systems in the humid tropics in Maranhão

This study was conducted to evaluate the physical properties modifications of an Oxisol under different conditions of use and management. The research was conducted at Fazenda Sítio Novo and in native forest area, respectively in the municipalities of São Benedito do Rio Preto/MA and Chapadinha/MA. The research followed a completely randomized design with 3 treatments and 4 replications, with the following uses and management: no-tillage (PD); conventional planting (CP) and native forest (MN). The following physical properties were analyzed: bulk density, porosity and soil moisture and penetration resistance at depths of 0.0-0.20 m and 0.20-0.40 m. The water properties analyzed were: basic infiltration velocity, total soil water capacity and vertical hydraulic conductivity. The soil presented higher density and low conservation of moisture in PD and PC. Native forest presented higher total porosity and higher conservation of soil moisture. Total soil water capacity was higher in MN (39.89 mm) followed by PC (25.33 mm) and PD (18.84 mm). The uses and management employed in the soils analyzed on the farm reflect the degradation of the physical properties of the soil in relation to native forest.

New insights into the drainage of inundated Arctic polygonal tundra using fundamental hydrologic principles

The pathways and timing of drainage from inundated ice-wedge polygon centers in a warming climate have important implications for carbon flushing, advective heat transport, and transitions from carbon dioxide to methane dominated emissions. This research helps to understand this process by providing the first in-depth analysis of drainage from a single polygon based on fundamental hydrogeological principles. We use a recently developed analytical solution to evaluate the effects of polygon aspect ratios (radius to thawed depth) and hydraulic conductivity anisotropy (horizontal to vertical hydraulic conductivity) on drainage pathways and temporal depletion of ponded water heights of inundated ice-wedge polygon centers. By varying the polygon aspect ratio, we evaluate the effect of polygon size (width), inter-annual increases in active layer thickness, and seasonal increases in thaw depth on drainage. One of the primary insights from the model is that most inundated ice-wedge polygon drainage occurs along an annular region of the polygon center near the rims. This implies that inundated polygons are most intensely flushed by drainage in an annular region along their horizontal periphery, with implications for transport of nutrients (such as dissolved organic carbon) and advection of heat towards ice wedge tops. The model indicates that polygons with large aspect ratios and high anisotropy will have the most distributed drainage. Polygons with large aspect ratio and low anisotropy will have their drainage most focused near the their periphery and will drain most slowly. Polygons with small aspect ratio and high anisotropy will drain most quickly.

Using environmental tracers to characterize groundwater flow in an alpine watershed underlain by sedimentary rock

<p>A growing number of studies indicate that bedrock groundwater is an important component of streamflow in mountain watersheds, yet mountain fractured-rock aquifers remain poorly characterized largely due to a lack of wells. Environmental tracer data from springs and tunnels can provide useful information, but are limited by the fact that spring occurrence is sporadic, and tunnels often disturb the natural groundwater system by acting as deep drains. We present dissolved noble gas, age tracer (<sup>3</sup>H, <sup>3</sup>He/<sup>4</sup>He, and SF<sub>6</sub>), chemistry, and temperature data from two relatively deep (46 and 81 m) boreholes and multiple shallow hand-drilled stream-side piezometers in Redwell Basin, Colorado, USA. The snowmelt-dominated watershed is underlain by sub-horizontally bedded, hydrothermally altered (sulfide-rich) sandstones and shales, and is being studied to better understand hydrogeochemical processes controlling sulfide weathering and metal exports from mineralized mountain headwater catchments. The boreholes were completed with multi-level monitoring wells allowing discrete-depth sampling, and the stream-side piezometers provided integrated samples of groundwater discharge at various points along the stream course. The chemistry of deeper groundwater at depths >10-20 m is markedly different from that of shallow groundwater: pH is 7-8 versus 4-6; specific conductance is 400-600 versus 100-300 μS/cm; and concentrations of multiple metals (e.g., Fe, Zn) are lower by a factor >5. Apparent <sup>3</sup>H/<sup>3</sup>He and SF<sub>6</sub> ages for the shallow groundwater are mainly 5-15 yr, whereas the deeper groundwater is dominantly premodern (>60 yr old) with high terrigenic He concentrations of 4-8 times solubility. Preliminary results from a 2D coupled heat and fluid flow model calibrated with the tracer-based ages and temperature data from the two deep boreholes suggest that active groundwater circulation (Darcy velocities >1 cm/yr) below a depth of 10-20 m is unlikely. This circulation depth is considerably shallower than previously reported depths of generally 100-200 m for mountain watersheds (these being underlain dominantly by crystalline rock), and is probably due to low vertical hydraulic conductivity (K) of the altered sedimentary rocks. Noble gas, age, and chemistry data from the piezometers suggest little to no deep, stream-parallel flow from upper to lower parts of the basin, further supporting relatively shallow active groundwater circulation. The age and chemistry of the piezometer samples also display spatial variations likely attributable to K anisotropy in the bedrock aquifer. The tracer, chemistry, and temperature data thus provide information critical for the development of reliable conceptual and numerical hydrogeochemical models of the watershed.</p>