Quantification of wetting front movement under the influence of surface topography

Soil Research ◽  
2018 ◽  
Vol 56 (4) ◽  
pp. 382
Author(s):  
Xuefeng Chu ◽  
Xinhua Jia ◽  
Yang Liu
Keyword(s):  
Surface Topography ◽  
Soil Water ◽  
Overland Flow ◽  
Unsaturated Flow ◽  
Soil Surface ◽  
Transport Processes ◽  
Soil Conditions ◽  
Wetting Front ◽  
Dimensional Flow ◽  
Front Movement

Soil surface topography affects fundamental hydrologic processes, such as infiltration and soil water percolation. Topographic variations potentially alter both the magnitude and directions of unsaturated flow. The objective of this study is to evaluate the effects of surface topography on wetting front moving patterns under different rainfall and soil conditions through combined experimental and numerical modelling studies. Specifically, laboratory-scale infiltration and unsaturated flow experiments and HYDRUS-2D modelling were conducted for different topographic surfaces, rainfall intensities, and soil types. The simulated and observed wetting front distributions were compared and evaluated. Two different stages were observed: topography-dominated two-dimensional flow and uniform one-dimensional flow. A uniformly distributed wetting front was eventually achieved although soil surfaces had dissimilar topographic characteristics. However, the timing or duration to reach such a uniform flat wetting front varied, mainly depending on surface topography, rainfall characteristics, and soil hydraulic properties. The findings from this study are important to better understand the mechanism of topography-controlled unsaturated flow, wetting front movement, and overland flow generation, and to further improve modelling of soil water flow and transport processes under such complex conditions across different scales.

scholarly journals Laboratory Experiments on the Effect of Microtopography on Soil-Water Movement: Spatial Variability in Wetting Front Movement

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
Leif Sande ◽  
Xuefeng Chu
Keyword(s):  
Soil Water ◽  
Smooth Surface ◽  
Laboratory Experiments ◽  
Unsaturated Flow ◽  
Water Movement ◽  
Experimental Studies ◽  
Soil Profiles ◽  
Wetting Front ◽  
Front Movement ◽  
Soil Water Movement

The effect of microtopography on soil-water movement is a topic of interest for a range of disciplines, with experimental studies investigating the relationship between the two lacking. Laboratory experiments were conducted by simulating rainfall across packed soil surfaces to investigate the effect of microtopography on wetting front movement within experimental soil profiles. In small soil box experiments, the observed wetting fronts for soil profiles showed considerably deeper movement beneath a smooth surface than depressions for 12–60 min rainfalls. For large soil box experiments, the wetting front reached moisture sensors installed at 5 and 10 cm depths and corresponding to various rough and smooth surface features at significantly different times, with movement being most rapid beneath the smooth surface. Wetting front movement was “quicker” beneath surface peaks than depressions for the rough surface as attributed to 2D/3D unsaturated flow. This study provides valuable experimentally based insight into the effect of microtopography on soil-water movement.

scholarly journals Spatial variability and temporal stability of water storage in a cultivated tropical soil

Bragantia ◽  
2010 ◽  
Vol 69 (suppl) ◽  
pp. 153-162 ◽  
Author(s):  
Antonio Carlos Andrade Gonçalves ◽  
Marcos Antonio Trintinalha ◽  
Marcos Vinicius Folegatti ◽  
Roberto Rezende ◽  
Cássio Antonio Tormena
Keyword(s):  
Water Content ◽  
Soil Water ◽  
High Efficiency ◽  
Temporal Stability ◽  
Water Storage ◽  
Soil Surface ◽  
Soil Water Storage ◽  
Soil Conditions ◽  
Content Uniformity ◽  
Water Application

Irrigated agricultural fields usually show variable crop water demand. If water application is done to match this spatially variable demand, the water use efficiency can be substantially improved. Soil water management by irrigation has been one of the most important factors to increase crop yield. To look for the economic viability of the process, the use of several inputs, particularly water, should be done with high efficiency levels. Historically, irrigation uniformity has been evaluated above the soil surface, in which applied water was the only factor to be taken into account. However, the crop will respond to soil water content uniformity, which can differ from the uniformity of water application. To evaluate temporal stability of spatial pattern of soil water storage (SWS), this work was done on a Brazilian clayed soil. Volumetric water content from soil surface to 0,30m depth, was measured by TDR in 80 points regularly spaced (3 x 3 m) on an experimental area cultivated with bean crop, irrigated by conventional sprinkling. The evaluations were done immediately before and after a water application by irrigation. Experimental semivariograms made from values obtained in the field showed that SWS distribution was spatially structured and strongly stable in time, being regulated mainly by intrinsic factors of the soil. In addition, obtained results showed that water application uniformity did not influence the spatial distribution pattern of SWS in these soil conditions.

Redistribution of water following precipitation on previously dry sandy soils

Soil Research ◽  
1975 ◽  
Vol 13 (1) ◽  
pp. 13 ◽  
Author(s):  
BA Carbon
Keyword(s):  
Soil Water ◽  
Seedling Emergence ◽  
Soil Water Potential ◽  
Sandy Soils ◽  
Soil Surface ◽  
Field Capacity ◽  
Wetting Front ◽  
Applied Water ◽  
Dry Soil ◽  
The Relationship

Theoretical and experimental evidence is provided to show that the redistribution of a given amount of water some days after infiltration into a previously dry soil can be predicted, provided that the relationship between soil water potential and soil water content is known. The capillary potential at the wetting front during infiltration into the dry soil is also required. In sandy soils an increase in amount of applied water leads to a decrease in the soil moisture content at the soil surface. This change in 'field capacity' as a function of applied water is shown to strongly influence seedling emergence.

The role of soil water repellency in overland flow generation in pine and eucalypt forest stands in coastal Portugal

Soil Research ◽  
2005 ◽  
Vol 43 (3) ◽  
pp. 337 ◽  
Author(s):  
J. J. Keizer ◽  
C. O. A. Coelho ◽  
R. A. Shakesby ◽  
C. S. P. Domingues ◽  
M. C. Malvar ◽  
...  
Keyword(s):  
Soil Water ◽  
Overland Flow ◽  
Slope Angle ◽  
Soil Surface ◽  
Water Repellency ◽  
Rainfall Simulation ◽  
Soil Water Repellency ◽  
Infiltration Capacity ◽  
Eucalypt Forest ◽  
Flow Generation

Soil water repellency is now known to occur in diverse soils in various parts of the world. One of the possible adverse effects of soil water repellency is that it can reduce infiltration capacity and hence, on sloping terrain, enhance overland flow and soil erosion. The main aim of the present work is to assess the effects of soil water repellency on surface runoff production in the inner coastal dune areas of central Portugal. This was done for a pine and a eucalypt forest stand and, within each stand, for 2 slopes with contrasting aspect and somewhat different slope angles. Overland flow was measured for 4 pairs of unbounded plots of about 5 m2 at fortnightly intervals from February to October 2001. Over the same period, soil water repellency at and immediately below the soil surface was measured next to the plots at monthly intervals. The runoff–repellency relationship was also studied by carrying out rainfall simulation experiments on 0.24-m2 plots and associated repellency measurements. The effect of soil water repellency was most clearly demonstrated by statistically significant higher runoff coefficients under strong-to-extremely than under none-to-slightly hydrophobic conditions immediately below the soil surface. Such a difference in runoff over the measurement period was, however, restricted to 2 unbounded plots, both of which were located on the eucalypt slope with a southerly aspect and the greater slope angle. At the scale of these plots, the increase in runoff coefficient due to soil water repellency is moderate, when integrated over the entire period of strong–extremely repellent conditions, but can be quite substantial for individual 2-weekly periods. With respect to the observed differences in runoff between plots, be it plots on the same slope or not, it has proved difficult to distinguish the effect of soil water repellency from that of other factors likely to affect overland flow generation.

scholarly journals A free boundary problem describing the saturated-unsaturated flow in a porous medium

2004 ◽  
Vol 2004 (9) ◽  
pp. 729-755 ◽  
Author(s):  
Gabriela Marinoschi
Keyword(s):  
Free Boundary ◽  
Boundary Conditions ◽  
Unsaturated Flow ◽  
Soil Surface ◽  
Water Infiltration ◽  
Richards Equation ◽  
Multivalued Operator ◽  
Wetting Front ◽  
Pressure Form ◽  
A Free Boundary Problem

This paper presents a functional approach to a nonlinear model describing the complete physical process of water infiltration into an unsaturated soil, including the saturation occurrence and the advance of the wetting front. The model introduced in this paper involves a multivalued operator covering the simultaneous saturated and unsaturated flow behaviors and enhances the study of the displacement of the free boundary between these two flow regimes. The model resides in Richards' equation written in pressure form with an initial condition and boundary conditions which in this work express the inflow due to the rain on the soil surface on the one hand, and characterize a certain permeability corresponding to the underground boundary, on the other hand. Existence, uniqueness, and regularity results for the transformed model in diffusive form, that is, for the moisture of the soil, and the existence of the weak solution for the pressure form are proved in the 3D case. The main part of the paper focuses on the existence of the free boundary between the saturated and unsaturated parts of the soil, and this is proved, in the 1D case, for certain stronger assumptions on the initial data and boundary conditions.

scholarly journals Impact of soil conditions on hydrology and water quality for a brown clay in the north-eastern cereal zone of Australia

Soil Research ◽  
2009 ◽  
Vol 47 (4) ◽  
pp. 389 ◽  
Author(s):  
D. M. Freebairn ◽  
G. H. Wockner ◽  
N. A. Hamilton ◽  
P. Rowland
Keyword(s):  
Water Quality ◽  
Soil Water ◽  
Suspended Sediment ◽  
Management Practices ◽  
Soil Surface ◽  
Management Tool ◽  
Soil Conditions ◽  
Water Runoff ◽  
Arid Environments ◽  
Functional Relationships

Hydrology and water quality impacts of alternative land management practices are poorly quantified for semi-arid environments in the northern Australia cropping zone, yet wide-scale changes in tillage practices and land use were being recommended based on experience from other environments. The objective of this study was to explore changes in soil profile and catchment hydrology and water quality associated with different soil surface conditions created by different tillage and grazing practices. Soil water, runoff, and suspended sediment concentrations were monitored on 4 contour bay catchments over an 18-year period. Soil conditions were described by soil moisture, soil cover, and surface roughness in order to explore functional relationships between management, hydrology, and water quality. The site was chosen to represent the drier margins of cropping in southern Queensland where clay soils with high water-holding capacity, in conjunction with fallowing to store water for later crop growth, are an essential risk management tool. Accumulation of soil water in fallows was inefficient, with fallow efficiencies ranging from –7 to 40% due to high evaporation and runoff losses. Runoff amount was determined by soil water content, which was strongly influenced by antecedent rainfall, water use, and evaporation patterns. Surface cover and roughness had subtle influences on runoff, and a greater effect on suspended sediment concentration. Runoff and suspended sediment losses were considerably lower under pasture than cropping. A participative approach between farmers and scientists was demonstrated to be an efficient method to carry out an extensive and long-term catchment study at a remote location. This study provides benchmark data for future hydrologic and water quality investigations.

A field study of phosphorus mobilisation from commercial fertilisers

Soil Research ◽  
2004 ◽  
Vol 42 (3) ◽  
pp. 313 ◽  
Author(s):  
D. Nash ◽  
M. Hannah ◽  
L. Clemow ◽  
D. Halliwell ◽  
B. Webb ◽  
...  
Keyword(s):  
Overland Flow ◽  
Soil Surface ◽  
Wetting Front ◽  
Single Superphosphate ◽  
Agricultural Catchments ◽  
Sampling Position ◽  
Eastern Australia ◽  
Before And After ◽  
Fertiliser Application ◽  
Flow Study

Fertilisers contribute to phosphorus (P) exported from agricultural catchments in south-eastern Australia. Phosphorus concentrations were initially measured in overland flow caused by rainfall after broadcasting either single superphosphate [SSP, Ca(H2PO4)2] or diammonium phosphate [DAP, (NH4)2HPO4] blends to pastures. In addition, P concentrations in overland flow were measured at intervals down border irrigation bay before and after fertiliser application. The period between fertiliser application and irrigation varied from 1 to 10 days.For the rainfall-induced overland flow, total dissolved P (TDP) concentrations were higher where DAP rather than SSP had been applied. For the irrigation study, sampling position behind the wetting front, irrigation pre and post fertiliser application, and irrigation number post fertiliser application explained 49.7, 20.5, and 15.2% of the total sum of squares, respectively. TDP concentrations were highest in the wetting front and diminished with distance behind the wetting front. For the irrigation before, and 2 irrigations following, fertiliser application, concentrations in the wetting front were 2.3, 17.6, and 6.5 mg TDP/L, respectively. In general, wetting front concentrations were c. 4 times the mean concentrations for the bays. As most P is exported when the wetting front enters the drainage network, sampling behind the wetting front would appear to underestimate P exports. The TDP concentration decreased as the time between fertiliser application and irrigation increased but the effects were variable between farms and fertilisers. Contrary to the rainfall induced overland flow study, in the irrigation study higher TDP concentrations were measured where SSP rather than DAP had been applied. This finding is explained in terms of differing rates of P mobilisation from the 2 fertiliser blends and an interaction with soil hydrology. The rapidly infiltrating water at the wetting front of irrigation-induced overland flow is likely to carry with it P mobilised at, or near, the soil surface and P infiltration will be proportional to mobilisation rates. It is suggested that higher rates of P mobilisation from DAP than SSP would reduce P exports in border irrigation systems where DAP is applied to the soil.

scholarly journals Testing soil water repellency in a Sicilian area two years after a fire

2019 ◽  
Author(s):  
Vincenzo Bagarello ◽  
Giuseppe Basile ◽  
Gaetano Caltabellotta ◽  
Giuseppe Giordano ◽  
Massimo Iovino
Keyword(s):  
Soil Water ◽  
Water Drop ◽  
Soil Layer ◽  
Soil Surface ◽  
Water Repellency ◽  
Soil Conditions ◽  
Small Scale ◽  
Water Repellent ◽  
Soil Water Repellency ◽  
Mountain Area

The water drop penetration time (WDPT) technique was applied in 2018 to check persistence of soil water repellency (SWR) in a Sicilian mountain area affected by a wildfire on June 2016. A total of four sites, that were severely water repellent immediately after burning, were sampled. Depending on the site, wettable soil conditions, less SWR and maintenance of a noticeable SWR were detected two years later. At the site showing a near-constant SWR, WDPTs were particularly high in the top soil layer (0-0.03 m) and they appreciably decreased more in depth. Signs of decreasing SWR in drier soil conditions and in association with coarser soil particles were also detected at this site. High gradients of the WDPT can occur at very small vertical distances and a depth increment of approximately 0.01 m should be appropriate to capture small-scale vertical changes in SWR, especially close to the soil surface. Occurrence of SWR phenomena is easily perceivable and explainable if an inverse relationship between WDPTs and antecedent soil water content is obtained. A direct relationship between these two variables is more difficult to interpret because infiltration times that increase in wetter soil are expected according to the classical infiltration theory. A hypothesis that should be tested in the future is to verify if WDPTs that decrease in drier soil conditions signal less SWR as a consequence of a reduced biological activity of the soil. Finally, long-term monitoring projects on longevity of fire effects on SWR should be developed, even because an in depth knowledge of the involved processes is relevant for the civil protection system.

Irrigation controlled by a wetting front detector: field evaluation under sprinkler irrigation

Soil Research ◽  
2005 ◽  
Vol 43 (8) ◽  
pp. 935 ◽  
Author(s):  
R. J. Stirzaker ◽  
P. A. Hutchinson
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Unsaturated Flow ◽  
Free Water ◽  
Sprinkler Irrigation ◽  
Field Evaluation ◽  
Wetting Front ◽  
Irrigation Amount ◽  
Irrigation Interval

The accuracy of scheduling irrigation to turf by sprinkler was evaluated using a simple wetting front detector that automatically switched the water off after the wetting front had reached a prescribed depth in the soil. The detector consists of a funnel-shaped container that is buried in the soil. When a wetting front reaches the detector, the unsaturated flow lines are distorted so that the water content at the base of the funnel reaches saturation. The free water produced is detected electronically and this provides the signal to stop irrigation. The performance of the detector was evaluated over 38 consecutive irrigation events to test the theory that the velocity of a wetting front depends on the difference in water content ahead of and behind the front. The experimental data plotting the irrigation amount permitted by the wetting front detectors as a function of the soil water content before and after irrigation yielded a linear relationship with a slope of 0.95 and a correlation coefficient of 0.73. Thus, if the soil is dry before irrigation the front will move slowly and an irrigation of long duration will be permitted, with the converse applying to wet soil. Independent monitoring of soil water content showed that irrigation was, for the most part, scheduled accurately. Irrigation interval was the key variable to control. When the interval was too short then over irrigation occurred.

scholarly journals Soil water flow due to surface topography in research drainage plots

age ◽  
2020 ◽  
Vol 3 (1) ◽  
Author(s):  
Sally Logsdon ◽  
Cindy Cambardella
Keyword(s):  
Surface Topography ◽  
Soil Water ◽  
Water Flow ◽  
Soil Water Flow
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