Infiltration of Water into Soil
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Infiltration (HVAC)
Ponding
Infiltrometer
Infiltrometer
Infiltration (HVAC)
Macropore
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Time-to-ponding can be determined quickly and with minimal disturbance to the soil surface by the use of a sprinking infiltrometer developed at Michigan State University (MSU). Solenoid valves controlling each of six nozzles mounted on a horizontal boom approximately 1 m above the ground surface are used to produce constant but selectable water application rates ranging from about 10 to 75 mm/h. Each nozzle delivers water over a 1 m diameter site with a coefficient of uniformity greater than 85%. Water is applied until surface ponding covering an area approximately 25 mm in diameter is observed. Log-log regression analysis is used to model the time-to-ponding (infiltration) curve from which the predicted application rates that would just result in ponding after 60 minutes of irrigation are predicted for various tillage, soil, and machine traffic conditions.
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Stormwater control measures (SCMs) are used to control runoff volume and peak flow rates. Rain gardens are one type of vegetated SCM which can utilize engineered or native media. Hydraulic conductivity, which can be measured in the field or laboratory, is a major design parameter for infiltration SCMs. The double-ring infiltrometer (ASTM D3385) is the most commonly used technique to determine hydraulic conductivity in the field; however, it can be cumbersome because of its considerable size and large water usage. In this study, various infiltration techniques, such as Modified Philip-Dunne, single-ring, and double-ring infiltrometers, were used to determine the hydraulic conductivity at different sites. In addition, the UMS KSAT Benchtop laboratory method was used to find hydraulic conductivity. Preliminary results indicate that the Modified Philip-Dunne provides results similar to the other tests methods.
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Permeameter
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<p>The continuous rain simulator used with very precise dosing enables both simulation of characteristic rainfall as well as accurate determination of infiltration rate and automatic calculation of hydraulic conductivity of soils under natural conditions. As a part of the research of infiltration processes induced by characteristic rainfalls, the effects of stormy rainfalls were verified in the described project stage. Stormy rain with constant intensity was applied by rain simulator in a single ring infiltrometer. Samples were tested in the laboratory (soils and kaolinite) and directly in the field. During rain infiltration was measured ponding time. Theoretical base of the research comes from non-steady state unsuturated vertical infiltration, which process (in one-dimensional flow conditions) can be described by Richard&#180;s equation. Final simplified solution is provided by Philip&#180;s simplified infiltration equtions. Hydraulic conductivity K&#160;was approximated from the analysis of time series of the process of vertical non-steady cumulative infiltration, going after ponding time. Sorptivity S was calculated by the numerical experiment with known values of stormy rain intensity, ponding time and hydraulic conductivity. Compared to traditional methods (single or double ring infiltrometer), soil hydro-physical characteristic (K, S) determined by this method is more reliable, informative and verified by ponding time.</p>
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Ponding
Sorptivity
Infiltration (HVAC)
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Double ring and tension infiltrometer are simple, fast and suitable instruments for determining soil hydraulic conductivity. The effect of land slope on soil properties such as saturated and unsaturated hydraulic conductivities has been reported by various researchers. The aim of this study was to estimate and compare soil hydraulic conductivities at different slope gradients under steady state and transient flow regiones. Field experiments were conducted in a loamy soil with different slope gradients in Gonbad research station, Hamadan, Iran. Soil surface slope gradients, of 0 (level), 10, 20, 30 and 40 degree were selected in this station. For each slope gradient, water infiltration experiments were carried out using a double ring and a tension infiltrometer at tensions of 0, 6, 9 and 15 cm in three replications. Totally 60 infiltration experiments were carried out. In steady state, values of saturated and unsaturated hydraulic conductivities were estimated using Reynolds et al. and Ankeny et al. procedures, respectively. In transient statevalues of the hydraulic conductivity, for different land slopes and water pressure heads, were calculated from the parameter of the second term of Philip's two-term equation, Results indicated that the hydraulic conductivity values for both steady state and transient flow regines were decreased with increasing in tension and slope gradient values. The higher rate of hydraulic conductivity decreases was obtained for lower tensions. In steady and transient state, by increasing in slope gradient from 0 to 40 degrees, decreasing of hydraulic conductivity in 0 tension was 4.1 and 3.7 times more than these in 15 cm tension, respectively. The fitness between the Gardner exponential model and steady state flow procedure was higher than that of transient flow procedure. In all experiments, values of relative difference of hydraulic conductivities were less than 7% that indicated good fitness between the steady state and transient flow procedures.
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Core Ideas The accuracy of the PI method in estimating soil K s was tested by numerical simulations. Estimated K s using two‐ponding‐depth and multiple‐ponding‐depth infiltration were compared. Transient and steady‐state infiltration data for six soils were used to estimate K s . The PI should yield more accurate K s estimates in coarse‐ than fine‐textured soils. The transient method does not solve the K s inaccuracy problems in fine‐textured soils. The single‐ring pressure infiltrometer (PI) method is widely used to determine saturated soil hydraulic conductivity, K s , directly in the field. The original and still most common way to analyze the data makes use of the steady‐state model developed by the Canadian School in the 90s and two (two‐ponding‐depth, TPD, approach) or more (multiple‐ponding‐depth, MPD, approach) depths of ponding. The so‐called Wu method based on a generalized infiltration equation allows analysis of the transient infiltration data collected by establishing a single ponding depth of water on the infiltration surface. This investigation, making use of simulated infiltration runs for initially unsaturated sand to silty clay loam soils, showed that, with a run duration of practical interest (e.g., 2 h), the PI can be expected to yield more accurate estimates of K s in coarse‐textured soils than in fine‐textured soils even if the transient method is used instead of the steady‐state method. Performing a three‐level experiment and analyzing the estimated steady‐state infiltration rates with both the TPD and MPD approaches is a way to predict the reliability of the estimated K s value. The K s accuracy should be acceptable if the two approaches yield similar results. Otherwise, the MPD approach should be expected to yield more accurate K s estimates than the TPD approach. The transient method does not solve the K s inaccuracy problems in fine‐textured soils because obtaining accurate K s data requires that the portion of total infiltration varying linearly with time represent a high percentage of total infiltration, but this percentage is small in fine‐textured soils when the run does not exceed a few hours. This investigation opens some new perspective on the use of infiltration data to make predictions on the expected reliability of the K s calculations with reference to both steady‐state and transient data analysis procedures.
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Infiltrometer
Macropore
Infiltration (HVAC)
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Computer based simulation models which estimate hydraulic properties of soil usually make use of statistical approaches such as multiple regressions that relate hydraulic properties to widely measured soil properties like textural fractions, organic matter content and bulk density. The problem is that hydraulic properties are usually only weakly correlated to these properties, because it is more strongly dependent on the characteristics of larger pores in the soil. The characteristics of macropore in soil can be determined by X-ray tomography. The aim of this study was to evaluate the predictive performance of X-ray CT derived macropore characteristics for hydraulic properties of soil.
Twenty undisturbed soil cores were sampled (6 cm high, 6.5 cm diameter) from a soil pit, with replicate cores taken at different depths from clay soil in Skuterud catchment, Norway. Hydraulic properties’, including saturated hydraulic conductivity, was measured using constant head method and unsaturated hydraulic conductivity was measured using Mini-Disk Infiltrometer. Soil columns were scanned using X-ray CT scan at a voxel resolution of 40 microns. Minimum automatic threshold algorithm method was chosen to segment the images between pore space and soil matrix. The images were analyzed for quantifying the macropore characteristics using ImageJ, SoilJ, BoneJ and GeoDict.
Significant correlations were observed between hydraulic conductivity and most CT derived macropore characteristics. Many of the X-ray CT derived macropore characteristics were interrelated. Best multiple linear equations for predicting the saturated and unsaturated hydraulic conductivity were estimated from macropore characteristics. Among the macropore characteristics critical pore diameter largely contributed to the saturated hydraulic conductivity. Macroporosity and connected macroporosity mainly controlled the unsaturated hydraulic conductivity. Physics-based approaches like percolation models based on critical pore diameter serves better than statistical approaches for decision making in soil and water management.
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Simulation experiment was conducted in soil columns and the effects of rock fragments on soil saturated hydraulic conductivity by disc infiltrometer were analyzed. Results indicate that saturated hydraulic conductivity of soil containing rock fragments can be calculated through nonlinearly regressing steady infiltration rates at different negative water heads. Saturated hydraulic conductivity of soil containing rock fragments is closely correlated to the hydraulic conductivity of soil without rock fragments and the shape coefficient of the rock fragments. And the hydraulic conductivity of soil containing rock fragments decreases exponentially with the increase of rock fragments in the experiment.
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Infiltration (HVAC)
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