Analytical Solutions for Water Infiltration into Unsaturated–Semi-Saturated Soils Under Different Water Content Distributions on the Top Boundary
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Infiltration (HVAC)
The variation rule of soil moisture content and moisture potential gradient in the process of infiltration of unsaturated zone for various precipitations was investigated by means of field test and indoor experiment.It is found that the infiltration process consists of three stages: absorption,passing through and dehydration.The soil moisture content tends to steady if the potential gradient is equal to 1cm H_2O/cm and tends to increase or decrease corresponding to the gradient higher or lower than this critical value.Following the continuous dropping down of groundwater table the influence of unsaturated zone thickness on precipitation infiltration for recharge of groundwater may change.When groundwater table higher than the limited level of groundwater evaporation the increase of unsaturated zone thickness may result in the increase of accumulation of soil moisture deficit and leads to the reduction of infiltration rate and recharged water amount.Whereas,when ground water table lower than the limited level the infiltration rate will maintain a constant in spite of the increase of unsaturated zone thickness.The total recharged groundwater amount is not affected by the thickness of unsaturated zone in unlimited time period,but the recharged rate tends to decrease in a limited period due to the increase of the infiltration path length.
Infiltration (HVAC)
Capillary fringe
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Knowing the soil moisture distribution in the unsaturated zone can improve understanding the water flow through the unsaturated zone and thereby enable the calculation of aquifer recharge, which occurs through precipitation. One part of the Zagreb aquifer recharge occurs through infiltration from precipitation. In order to observe and model infiltration from precipitation through the unsaturated zone, the research polygon was constructed at the Velika Gorica well field, located in the southern part of the Zagreb aquifer, Croatia, where hourly measurements of electric conductivity (EC) and soil moisture content were carried out. EC and soil moisture data are measured by Time Domain Reflectometry (TDR) probes which are placed at different depths in the unsaturated zone. Furthermore, electrical resistivity tomography (ERT) measurements were conducted. Geophysical data, along with moisture and EC data from TDR probes, were used as input data for MoisturEC software, in order to obtain soil moisture distribution along a 2D profile. MoisturEC program offers three options for translating EC data to moisture content data which are all tested in this research. We obtained eight moisture content distributions along the observed profile and concluded that MoisturEC provides reasonable results with input data from geophysical measurements and TDR probe measurements. Soil moisture distribution in the unsaturated zone represents the initial conditions for further unsaturated flow modeling. Understanding the flow in the unsaturated zone enables the quantification of effective infiltration and can improve groundwater management.
Infiltration (HVAC)
Electrical Resistivity Tomography
Reflectometry
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The paper is engaged in a field test of moisture migration in vadose zone under the heterogeneous condition in the Weihe(Shaanxi) flood-plain.The reason why we have chosen the topic is that the evolution of a river may exert serious consequential effects on the groundwater change,the water quality and even the ecological environment along the entire river reach.It is for such purposes,we have dug up some measuring pits as large as 7 m×1 m×2.8 m and taken them as our study profile.For the convenience of observation,we have installed a MP-917 Time Domain Reflectometry(TDR) and a mercury manometer to observe the potential pressure and the moisture content in correspondence with the different properties of lithology and depth respectively.And,then,we have done a five-day infiltration test by using our own-made Bauwer Ooze water meter.Though it is difficult to understand the infiltration mechanism for its complexity with the unsaturated zone being heterogeneous with compacted sandwich structure,the field test is comparatively simple about the moisture migration in vadose zone under heterogeneity.In addition,we have also tested the moisture migration regularity under the heterogeneous condition and the relationship between the infiltration speed and water head height by using the above said Ooze water meter.The results of our study show that,the distribution of moisture content is restricted by the lithology permeability in relation to the vadose zone medium and aeration zone structure.The vadose zone doesn't prove to be easy to get saturated due to the presence of aquitard blocked moisture migration.The infiltration speed,which extends with the thickness of the layer,may help to show its the relation with the height of the water head,because the water infiltrated as unsaturated flow above semipervious layer contributes to the formation of the upper sluggish water volume.And,therefore,in the process of evaluating the water resources formerly,it is not easy to judge exactly the recharge of the river water to the groundwater,for it is necessary to emphasize the role of semipervious layer as the head boundary or the rain type flowing boundary.Thus,it can be seen that the results of our field test can be taken as an exponential support for the problem of disconnection between the river and the groundwater,thus providing a scientific basis for the recoverable resource evaluation and sustainable maintenance of the ecological function of the river water and the surrounding groundwater sources.
Infiltration (HVAC)
Lithology
DNS root zone
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Summary This study shows how to estimate water content of unsaturated sandy soils from ground-penetrating radar (GPR) data acquired during water infiltration experiment. Using the Topp equation, water content can be converted to dielectric permittivity. Afterwards, based on 1D forward modeling method, a GPR synthetic trace is generated. Finally, a trial-and-error match of modeled and observed GPR traces is performed to estimate the optimum set of parameters characterizing the materials composing the soil. According to the comparison of the modeling signal and the real signal, we go back to update the model and water content. Repeating the procedure until the modeling signal fits the real signal very well. We used this procedure to obtain the water content of unsaturated sandy soils. We present the setup experiment carried out for an unsaturated sandy soil. In order to follow the water front progression in depth, we picked up four real measured GPR traces at different injected times and by modeling obtained the water content for each trace.
Ground-Penetrating Radar
Infiltration (HVAC)
SIGNAL (programming language)
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Based on the infiltration experiments of field soils,the main factors which influence the water infiltration features of field soils were analyzed and discussed.The experimental results indicated that the water infiltration features of field soils were influenced by soil moisture,soil structure and soil texture.They have strong influence on infiltration into field soils.Infiltration capacity of field soils decreased while the moisture content increased.The infiltration capacity decreased with soil clay content increasing,where mass percent of clay content of soil grain less than 0.002 millimeter represented soil structures.The infiltration capacity decreased with soil compactness increasing.The result is of practical meaning in determining the field irrigation technical parameters.
Infiltration (HVAC)
Soil texture
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The amount of water that can be stored in soil and actively used by plants, is a key parameter in hydrologic models and is important for crop and pasture production. Often the active soil moisture store is estimated from laboratory measurements of soil properties. An alternative approach, described in this paper, is to estimate the extractable soil moisture capacity from direct measurements of soil moisture content in the field. A time series of soil moisture values, over the depth of the soil, shows the actual changes in water content. The difference between the wettest and driest profiles is an estimate of the dynamic soil moisture store. We have gathered data on extractable soil water capacity for 180 locations over Australia and have compared our values with published results from the Atlas of Australian Soils, derived from profile descriptions and pedotransfer functions. Preliminary results show that data from the Atlas of Australian soils provide a useful lower bound for measured dynamic soil moisture storage, but of the sites examined, 42% had extractable stores greater than two-times the AAS values. This was due to estimates of total soil depth that were underestimated in the AAS results compared to the active depths apparent in the data. These depths were strongly related to vegetation type.
Pedotransfer function
Infiltration (HVAC)
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Infiltration (HVAC)
Pedotransfer function
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The flow condition in the vadose zone was monitored by taking measurements of the electromagnetic properties of the subsoil (electrical conductivity and permittivity) to estimate the spatial distribution of the volumetric water content. A controlled experiment of 4x 1 m 2 of pond infiltration was designed and done in a sandy soil; the time-lapse electrical resistivity tomography (TLERT) was integrated by Time Domain Reflectometry (TDR) electromagnetic monitoring to analyze variations of water content. The results permitted us to estimate the water-content distribution up to a 2 m depth with accurate lateral detail; because of the duration of the experiments (85 days), several rainfall events modified the water contents of the subsoil: however, the combined approach (TDR and TLERT) permitted us to recognize the different water-content conditions in the zone of artificial infiltration. The interpretation of the experiment has been realised combining the geophysical interpretation and the results of a 2-D simulation of the flow in an unsaturated zone using numerical models.
Subsoil
Infiltration (HVAC)
Electrical Resistivity Tomography
Reflectometry
Ground-Penetrating Radar
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Infiltration (HVAC)
Pedotransfer function
Water storage
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