Preferential Flow Patterns Research Articles

Investigating screw-agitator speed ratio impact on feeding performance in pharmaceutical manufacturing using discrete element method

In continuous powder handling processes, precise and consistent feeding is crucial for ensuring the quality of the final product. The intermixing effect caused by agitators, which alters the powder’s bulk density, flow rate, and flow patterns, plays a significant role in this process, yet it is often overlooked. This study combines discrete element method (DEM) modeling and experiments using a commercial-scale feeder to propose a Digital Twin (DT) framework. The DEM model accurately captures key flow features, such as bypass trajectories, stagnant zones, and preferential flow patterns, while providing quantitative predictions for the feed factor and zones prone to material accumulation. Scenario analysis is performed to identify the most favorable operating ranges of the screw-agitator ratio and screw speed, considering the cohesive properties of the powder. The study demonstrates that powders with poor flow characteristics require tighter operational constraints, as the screw-agitator ratio is susceptible to variations in mass feed rate. This contribution highlights the importance of selecting an appropriate screw-agitator ratio instead of maintaining a fixed value. Properly choosing this ratio helps determine an optimal operation window, which aims to achieve a minimum agitation level needed to induce unhindered flow and reduce variability in the mass flow rate.

Effects of Straw Incorporation and Decomposition on Soil Preferential Flow Patterns Using the Dye-Tracer Method

Effects of Straw Incorporation and Decomposition on Soil Preferential Flow Patterns Using the Dye-Tracer Method

Secondary vegetation succession following reforestation intensifies preferential flow by improving soil structure in the Chinese Karst region

Preferential flow benefits water storage in deep soils that contribute to hydrological sustainability under different vegetations in the Karst regions, however, how vegetation specializes preferential flow pattern by changing soil architecture remains unclear. The study investigated the variations of soil architecture and preferential flow patterns in the agricultural field, abandoned field, and young and mature woodlands that representing four vegetation succession stages during the implementation of returning cultivated land into forest in the Karst region, to explored how soil texture and structure interact to specialize preferential flow patterns under the vegetation succession, using the dye-tracing technique, the principal component analysis (PCA), and the variation partitioning analysis (VPA). The dyed soil profiles illustrated heavy preferential flow under the four vegetations. The maximum infiltration depth (Dmax), actual infiltration depth (Dactual), total dye coverage (Ctotal), and length index (LI) significantly increased following the sequence of vegetation succession stages (P < 0.05), and the preferential pathway contribution (Dpr) was the significantly lowest under the agricultural field and young woodland and the highest under the mature woodland (P < 0.05), which indicated of intensified preferential flow with ongoing vegetation succession. The preferential flow pattern index (PFP) was constructed by the Dmax, Dactual, Ctotal, Dpr, and LI after the PCA, which gradually increased (from −0.82 ± 0.69 to 1.37±0.80) during the succession, suggesting that preferential flow percolated deeper, more preferential flow was received, and preferential flow contribution increased during the succession. Soil texture (sand content, silt content, and geometric mean soil particle size) and structure (bulk density, air-filled porosity, total porosity, air-filled porosity, and ratio of air-filled and capillary porosity to total porosity) significantly correlated to the PFP (P < 0.05). The VPA revealed that soil texture and structure independently explained 9 % and 26 % variation of the PFP. This situation means although reforestation intensified preferential flow by improving soil structure, adverse impacts of improper soil texture management of could offset the intensification efficiency by reforestation. Therefore, the results benefit to meet ecological and hydrological sustainability challenges rooted by preferential flow in the Karst regions.

Flow recession behavior of preferential subsurface flow patterns with minimum energy dissipation

Abstract. Understanding the properties of preferential flow patterns is a major challenge in subsurface hydrology. Most of the theoretical approaches in this field stem from research on karst aquifers, where two or three distinct flow components with different timescales are typically considered. This study is based on a different concept: a continuous spatial variation in transmissivity and storativity over several orders of magnitude is assumed. The distribution and spatial pattern of these properties are derived from the concept of minimum energy dissipation. While the numerical simulation of such systems is challenging, it is found that a restriction to a dendritic flow pattern, similar to rivers at the surface, works well. It is also shown that spectral theory is useful for investigating the fundamental properties of such aquifers. As a main result, the long-term recession of the spring draining the aquifer during periods of drought becomes slower for large catchments. However, the dependence of the respective recession coefficient on catchment size is much weaker than for homogeneous aquifers. Concerning the short-term behavior after an instantaneous recharge event, strong deviations from the exponential recession of a linear reservoir are observed. In particular, it takes a considerable time span until the spring discharge reaches its peak. The order of magnitude of this rise time is one-seventh of the characteristic time of the aquifer. Despite the strong deviations from the linear reservoir at short time spans, the exponential component typically contributes more than 80 % to the total discharge. This fraction is much higher than expected for karst aquifers and even exceeds the fraction predicted for homogeneous aquifers.

Role of the preferential flow at rock–soil interface in the water leaking process in near-surface fissures filled with soils in the karst rock desertification area

Soil preferential flow infiltrating rapidly through the rock–soil interface is an important hydrological process in karst rocky desertification area. However, how does the water leakage in the near-surface fissures, especially those filled with soil, proceed? The role of preferential flow at rock–soil interface of those fissures on water leakage process still puzzles us. The goal of this study was to reveal the role of soil preferential flow at the rock–soil interface in the process of water leaking of near-surface fissures. Five typical types of near-surface fissures were selected in an area experiencing severe rocky desertification in Guizhou Province, China. Dye tracer testing was applied, combined with digital image processing techniques. The results indicated that the rock–soil interface flow on both sides of the fissures is the most important preferential flow form in the fissures in karst area. The dyed area ratio of preferential flow varied from 0.12 to 0.48 in the rock + soil profiles, from 0.06 to 0.37 in the soil profiles, and between 0.02 and 0.16 in the rock–soil interface. The rock–soil interface is the smallest in terms of both their variation range of dyed area ratio and preferential flow patterns compared with soil and rock–soil profiles. The soil preferential flow in near-surface fissures mainly occurs in the soil depth range of 0–20 cm. The preferential flow path is mainly affected by the rock–soil interface on both sides and can pass through the clay layer with poor permeability. However, the soil depth of the dyed part was more than 50 cm. The soil preferential flow at the rock–soil interface is the main form of rapid downward leakage of water in near-surface fissures in the karst rocky desertification area, which can flow to the bottom of clay layer with poor permeability.

Preferential flow patterns in forested hillslopes of east Tibetan Plateau revealed by dye tracing and soil moisture network

AbstractPreferential flow (PF) through soil and regolith results in a rapid vertical and lateral water movement within the profile. This study focused on quantifying PF in contrasting forested hillslopes of the Hailuo Valley, located on China's east Tibetan Plateau. Quantifying PF in this region is challenging since the underlying matrix is complex, with shallow soils, thick underlying saprolite, and the combined effect of moraines and weathered residual material. We developed new methods that integrated dye tracing with a high‐frequency soil moisture monitoring network to characterise PF pathways and quantity PF frequency on contrasting forested hillslopes (coniferous and broadleaved). Dye tracing experiments showed that soil‐root interfaces in the upper soil layer (10–50 cm) and soil‐rock interfaces in the deeper soil layer (50–100 cm) were the primary PF pathways and that large rocks strongly influence the percolation depth of water. The high‐frequency soil moisture network revealed that the mean PF frequency was 67.8% and 71.7% in the coniferous and broadleaved forests, respectively. The frequency of PF in the deeper soil layer increased from upslope to the downslope locations on both forested hillslopes, highlighting the tendency for PF to occur downslope. In addition to matrix conditions (e.g., stony saprolite soil), the total amount and maximum intensity of precipitation (as throughfall in this study) were identified as factors that control PF occurrence. In contrast, the initial soil water conditions (at 10, 50 and 100 cm depth) were insignificant in predicting PF occurrence. Results of this field‐based study highlight that PF is a ubiquitous and critical subsurface flow mechanism that regulates rainfall‐runoff relationships in forests of the Tibetan Plateau, underscoring the need to consider PF in hillslope hydrological modelling.Highlights Combined dye tracing and soil moisture monitoring network were applied to explore PF on forested hillslopes. Root networks and rock fragments constituted the main PF paths. PF frequency increased from upslope to downslope in two forest types. Initial soil moisture conditions showed no controlling effect on PF occurrence.

Store and pour: Evolution of flow systems in landscapes

Concentrated or preferential flow patterns occur at all scales in hydrologic systems. They shape, and are shaped by, geomorphic and pedologic patterns and structures. Preferential flow patterns in surface channel networks and dual-porosity subsurface flow systems are a way of achieiving maximum efficiency, as predicted by dissipative systems, constructal, network evolution, percolation, and ecohydrological theories. These all converge on the same predictions and interpretations of preferential flow, which satisfactorily answer “why” these patterns form and persist. However, as geomorphic and hydrologic systems have no intentionality or agency, and thus no ability to actively seek improved efficiency, how these systems evolve is an open question. I propose an emergent explanation based on five phenomena. First, concentrated flows form due to principles of gradient and resistance selection. Second, positive feedback reinforces the concentrated preferential flow paths and their relationship to potential moisture storage zones. Third, intersecting flow paths form networks. Fourth, the expansion of concentrated flow paths and networks is limited by thresholds of flow needed for channel, macropore, or conduit growth and maintenance. This results in a “store and pour” flow system that can retain water during dry periods and transport it efficiently during wet periods. These systems survive provided they develop “spillway” and/or secondary storage mechanisms to accommodate excess water inputs. Finally, store-and-pour systems are maintained (selected for) because they are often stable. Store-and-pour structures are advantageous for flow systems, and for vegetation and ecosystems. These entities cannot actively pursue goals, and no laws dictate evolution toward such patterns. Their development is an emergent phenomenon and their persistence a matter of selection, i.e., survival of the most stable.

Mechanisms of grazing management impact on preferential water flow and infiltration patterns in a semi-arid grassland in northern China

Grazing management is widely used to control grassland degradation in Inner Mongolia. However, the correlation between the soil physical properties, root traits, and infiltration patterns of different types of grazing management has seldom been studied. To reveal the effect of grazing management on water infiltration and preferential flow behavior, we first investigated the soil and plant properties in a grazing exclusion (19 years, GE), cold-season grazing (19 years, CG), and free-grazing grassland (19 years, FG) in a semi-arid grassland in Inner Mongolia. Dye tracer infiltration was adopted to obtain the water infiltration patterns from different types of grazing management. Finally, root biomass and root morphological traits were measured in a field experiment. The results showed that the plant height, vegetation coverage, richness index, Shannon-Wiener index, soil water content, total porosity, and mean weight diameter were higher at the GE site than at the FG site, whereas soil bulk density and sand content were lower at the GE site than at the FG site (P < 0.05). In addition, the root mean diameter, specific root length, and root mass density were higher at the GE site than at the FG site. As a result, differences in these root traits and soil and vegetation properties affected the preferential water flow behavior in the three types of grassland. The preferential flow evaluation index (PFI) of the GE, CG, and FG sites was 0.89, 0.30, and 0.15, respectively, which indicated that more obvious preferential flow occurred at the GE site than at the CG and FG sites. These findings highlight that the long-term GE enhanced plant density and root biomass, which could potentially promote the natural restoration of soil pores and preferential water infiltration. Therefore, local governments and herders should implement GE rather than other grazing management practices to prevent grassland degradation.

The impact of hydraulic retention time on the performance of two configurations of anaerobic pond for municipal sewage treatment

ABSTRACT Anaerobic ponds have the potential to contribute to low carbon wastewater treatment, however are currently restricted by long hydraulic residence time (HRT) which leads to large land requirements. A two-stage anaerobic pond (SAP) design was trialled against a single-stage control (CAP) over four HRTs down to 0.5 days, to determine the lowest HRT at which the ponds could operate effectively. No statistical differences were observed in particulate removal between the ponds over all four HRTs, suggesting solids loading is not a critical factor in AP design. Significantly higher biogas production rates were observed in the SAP than the CAP at 1.5 d and 1.0 d HRT, and microbial community profiling suggests the two-stage design may be facilitating spatial separation of the anaerobic digestion process along reactor length. Hydrogenotrophic methanogensis dominated over aceticlastic, with acetate oxidisation a likely degradation pathway. Experimental tracer studies were compared to CFD simulations, with the SAP showing greater hydraulic efficiency, and differences more pronounced at shorter HRTs. Greater flow recirculation between baffles was observed in CFD velocity profiles, demonstrating baffles can dissipate preferential flow patterns and increase effective pond volume, especially at high flow rates. The study demonstrates the potential of APs to be operated at shorter HRTs in psychrophilic conditions, presenting an opportunity for use as pre-treatments (in place of septic tanks) and primary treatment for full wastewater flows. Two-stage designs should be investigated to separate the stages of the anaerobic digestion process by creating preferential conditions along the pond length.

Analysis of Spatiotemporal Variability of Corn Yields Using Empirical Orthogonal Functions

We used empirical orthogonal functions (EOF) to analyze the spatial and temporal patterns of corn (Zea mays L.) yields at three hydrologically-bounded fields with shallow subsurface preferential lateral flow pathways. One field received uniform application of manure, the second field received the uniform applications of the chemical nitrogen fertilizer, and the third field received variable rate applications of the chemical fertilizer. The preferential subsurface flow and storage pathway locations were inferred from the ground penetration radar survey. Six-year monitoring data were analyzed. Statistical distributions of EOFs across fields were approximately symmetrical. Semivariograms of the first EOF differed between fields receiving manure and chemical fertilizer. This EOF accounted for 52 to 56% of the interannual variability of yields, and its values reflected the distance to the subsurface flow and storage pathways. The second and third EOF explained 17 to 20% and 10 to 13% of the interannual variability of yields, respectively. The precision applications of the nitrogen fertilizer minimized corn yield variability associated with subsurface preferential flow patterns. Investigating spatial patterns of yield variability under shallow groundwater flow control can be beneficial for the within-field crop management resource allocation.

Simulation of Preferential Flow in Snow With a 2‐D Non‐Equilibrium Richards Model and Evaluation Against Laboratory Data

AbstractRecent studies of water flow through dry porous media have shown progress in simulating preferential flow propagation. However, current methods applied to snowpacks have neglected the dynamic nature of the capillary pressure, such as conditions for capillary pressure overshoot, resulting in a rather limited representation of the water flow patterns through snowpacks observed in laboratory and field experiments. Indeed, previous snowmelt models using a water entry pressure to simulate preferential flow paths do not work for natural snowpack conditions where snow densities are less than 380 kg m−3. Because preferential flow in snowpacks greatly alters the flow velocity and the timing of delivery of meltwater to the base of a snowpack early in the melt season, a better understanding of this process would aid hydrological predictions. This study presents a 2‐D water flow through snow model that solves the non‐equilibrium Richards equation. This model, coupled with random perturbations of snow properties, can represent realistic preferential flow patterns. Using 1‐D laboratory data, two model parameters were linked to snow properties and model boundary conditions. Parameterizations of these model parameters were evaluated against 2‐D snowpack observations from a laboratory experiment, and the resulting model sensitivity to varying inputs and boundary conditions was calculated. The model advances both the physical understanding of and ability to simulate water flow through snowpacks and can be used in the future to parameterize 1‐D snowmelt models to incorporate flow variations due to preferential flow path formation.

GIS-based soil erosion modelling under various steep-slope vineyard practices

Soil erosion can cause a progressive degradation of hillslopes, especially in steep-slope agricultural landscapes. In this study, the formation of spatial erosion patterns was evaluated in three typical steep-slope vineyard cultivation practices in northern Italy: dry-stone wall terraces, earth bank terraces and vertical cultivation (Italian: rittochino). UAV surveys in three vineyards provided high-resolution data on topography and land use serving as input for two GIS-based erosion models: the Revised Universal Soil Loss Equation (RUSLE) and SIMulated Water Erosion model (SIMWE). Annual RUSLE simulations showed how the two terracing practices (i.e. dry-stone walls and earth banks) effectively safeguarded large areas from soil loss, whereas the non-terraced vertical cultivation produced widely distributed soil loss with increasing severity according to slope length and steepness. In intense single-event conditions simulated by SIMWE, all three practices showed the formation of critical preferential surface flow patterns, corresponding to several field-observed erosion patterns (piping of stone walls, landslides on earth banks, and rill erosion in the non-terraced vineyard), while also in this case showing the highest erosion rates for the non-terraced vertical cultivation. Simulated flow concentration was strongly determined by the spatial organisation of the hillslope, roads and vines, and several strategies were discussed for erosion mitigation (including drainage systems or enhanced soil cover). Furthermore, the results indicated that SIMWE is an optimal approach for the recognition of soil erosion processes occurring during intense rainfall conditions. This study provides an example of high-resolution erosion risk evaluation, which should play a crucial role in the design and management of steep-slope vineyards.

Preferential flow of surface‐applied solutes: Effect of lysimeter design and initial soil water content

AbstractUndisturbed lysimeters are widely used to study water and solute transport, where both natural and unnatural preferential flow can greatly influence leaching rates. The objective of this study was to use chemical and isotopic tracers to quantify the effect of initial soil water content and lysimeter design on preferential flows. Ten undisturbed lysimeters (900 cm2) were collected from an agricultural field, with the gap between the soil and lysimeter casing sealed with petroleum jelly for five lysimeters. Lysimeters were subjected to two rainfall simulations (3.3 cm h−1) under contrasting initial soil water contents, and leachate near the soil‐casing interface was collected separately from leachate through the bulk soil. Three‐component hydrograph separation revealed that event water comprised 21–59% of total leachate irrespective of initial soil water content and lysimeter design. Sealing the edges of the lysimeters with petroleum jelly greatly reduced but did not eliminate edge flow during rainfall simulations. Although water and solute transport were similar in both sealed and unsealed lysimeters under dry antecedent conditions due to the formation of shrinkage cracks on the soil surface, edge flow was substantially greater for the unsealed lysimeters under wet antecedent conditions. Unsealed edges under wet antecedent conditions facilitated the preferential transport of both event and pre‐event water, resulting in greater solute leaching. Using multiple tracers to contrast lysimeter designs under different initial soil water contents not only allowed for rigorous testing of a commonly used edge‐flow suppression technique but also provided new insights into preferential flow processes and patterns.

On the preferential flow patterns induced by transverse isotropy and non-Darcy flow in double porosity media

Fluid flow in isotropic porous media with one porosity scale is a well understood process and a common scenario in numerous simulations published in the literature. However, there exists a class of porous materials that exhibit two porosity scales with strong permeability contrast between the two scales. Examples of such materials are aggregated soils and fractured sedimentary rocks such as shale. In sedimentary rocks, fluid could flow through the micro-fractures at the larger scale as well as through the nanometer-size pores of the rock matrix at the smaller scale. In this paper, we shall refer to the larger and smaller pores of sedimentary rocks as the micro-fractures and nanopores, respectively. Due to preferentially oriented micro-fractures in the rock, fluid could flow predominantly in the direction of the discontinuities, resulting in an anisotropic flow pattern at the larger scale. We idealize such material as a transversely isotropic medium with respect to fluid flow. In addition, the nanopores of sedimentary rocks such as shale are so small that Darcy’s law may not hold at this scale. To better understand the impact of non-Darcy flow on the overall flow pattern, we present a hydromechanical model for materials with two porosity scales that accommodates both transverse isotropy at the larger scale and non-Darcy flow at the smaller scale. Even though this study is motivated by shale properties, the discussion revolves around a generic material with two porosity scales whose fluid flow characteristics are similar to those of shale. The overarching goal of this paper is to better understand the impacts of transverse isotropy and non-Darcy flow on the fluid flow pattern in this material.

The initial phase of cave formation: Aquifer-scale three-dimensional models with strong exchange flow

Limestone, dolomite, gypsum, anhydrite, and salt are rocks, which can be dissolved, either by water alone, or in the case of limestone and dolomite more efficiently by water enriched with carbon dioxide. With time, the secondary porosity in these rocks increases substantially, and flow through these soluble rocks becomes very effective and fast. The time period for a substantial increase in secondary porosity ranges from years (salt) to 10,000–100,000 years (limestone, dolomite).The temporal evolution of such a soluble rock can be described by numerical models, coupling flow, transport, and dissolution. On the fracture-scale, numerous models describe fingering and wormhole formation in soluble rocks. On the aquifer-scale, numerical models predict preferential flow patterns and a strong exchange-flow component.We present results from three-dimensional numerical models describing the evolution of a karst aquifer in its early stage. Our numerical approach, which describes the large aquifer-scale, is capable to simulate the strongly heterogeneous development of secondary permeability in the aquifer. Based on irregularities in the model (e.g. geometry, chemistry, lithology, hydrology), preferential pathways evolve under a catchment-control situation, limiting the inflow into the system through the amount of water available from a catchment. We compare qualitatively our large aquifer-scale results to small fracture-scale results and show that the fingering described by the latter models is driven by similar mechanisms as the preferential growth in the former models.

Dye Tracer Visualization of Infiltration Patterns in Soils on Relict Charcoal Hearths

Anthropogenically modified soils are often characterized by a high heterogeneity of substrates and show unique patterns of water infiltration. Such effects are not limited to intensively used or disturbed agricultural and technogenic soils, but can also occur as legacies of former land use in forested areas. The remains of historic charcoal hearths represent a widespread legacy of historic land use. Soils at relict charcoal hearths (RCHs) are most prominently altered by the deposition of a layer of charcoal-rich substrate on top of the natural soil surface. The presence of such a technogenic layer can considerably influence infiltration and soil wetness patterns on the sites. This study describes the spatial patterns of infiltration and soil wetness at charcoal hearth sites compared with undisturbed sandy forest soils for a historic charcoal production area north of Cottbus, Germany. We characterized six plots on RCH and reference soils under pine, oak and mixed forest by visualizing preferential flow patterns of infiltrating water in dye tracer experiments. Additionally, we characterized bulk density, soil organic matter contents and water repellency, using water drop penetration time (wdpt) tests, of the RCH and reference soil horizons. The results reflect that the persistence of water repellency of both the technogenic substrates and the natural topsoils is extremely high under dry conditions, but is drastically reduced after wet antecedent conditions. The dye tracer experiments reflect increased preferential flow on the RCHs for dry soil conditions, for which infiltration is limited to very few flow paths in the technogenic substrate layer. Differences between RCH and reference soils are less clear for higher antecedent soil wetness, for which the results indicate more uniform wetting of the technogenic substrates. We conclude that the structural properties of the additional technogenic substrate layer of RCHs have characteristic effects on water infiltration, causing a high temporal variation of preferential flow in relation to antecedent soil moisture conditions. These effects can result in high heterogeneity of soil moisture for dry conditions, and generally in a high temporal variation of soil wetness in RCHs soils.

Characterizing preferential flow in landfilled municipal solid waste

Municipal solid waste (MSW) is a porous medium comprising macropores and matrix, such that the flow pattern often takes the form of preferential flow. The objective of this paper was to study the preferential flow in MSW and to quantify the flow character. Dye tracing tests and solute breakthrough tests were carried out using MSW samples taken from different depths of a landfill. Test procedures were proposed to make the sectioning of MSW sample easy. The MSW columns were dyed and then sectioned in the horizontal and vertical direction. Digital image processing technology was used to investigate the preferential flow pattern. In order to quantitatively characterize the preferential flow in MSW, regression analysis was performed on the breakthrough curves using the bimodal probability density model. The dye tracing tests show that more preferential flow happened under a higher application rate, under higher initial water content, and in shallow MSW. The results of vertical sectioning tests are consistent with that of horizontal sectioning tests, showing that the test procedure has no obvious influence on the preferential flow pattern in MSW. The results of the solute breakthrough tests show that between 55 and 70% of the total solute was transported through large pores. The modeled proportion of solute movement through large pores decreases as the depth and age increase, and increases as the application rate increases. The results are beneficial to simulate water and solute migration in MSW using a dual-porosity model.

Experimental and Numerical Investigations of Influence on Overland Flow and Water Infiltration by Fracture Networks in Soil

Preferential flow is common in clay or expansive clay soils, involving water bypassing a large portion of the soil matrix. Dye tracer experiment and numerical modeling are used to simulate the surface runoff and subsurface preferential flow patterns influenced by the soil fracture network of a relatively steep hillslope system (slope angle equals to 10 degrees). The result of the experiments indicates that part of the water is infiltrated through cracks, leading to the delay of the initial runoff-yielding time and reduction of the discharge of the surface runoff. The soil water flow is mainly in the matrix when the intensity of precipitation is low. With the increasing of precipitation, soil water movement may become in the form of preferential flow through cracks. In addition, the nonuniformity of soil water infiltration and the depth of the average water infiltration increase as the precipitation intensity increases. To this end, the complete coupling model was established by using the surface-matrix-crack (SMC) model to simulate water flow within discrete fracture as well as to simulate water flow in the soil matrix based on the concept of dual permeability using the traditional Richards’ equation. In this model, the “cubic law” of fluid motion in cracks within smooth parallel plates and the two-dimensional diffusion wave approximation to Saint-Venant equations with momentum term ignored (two-dimensional shallow water equations) were used. The model divides soil water infiltration into two forms and uses the overall method to calculate the exchange of water between the crack networks and matrix regions as well as the exchange water between surface runoff and infiltration water. Results indicate that the SMC model has better performance compared with the traditional equivalent continuum model when those models are used to simulate the surface runoff movement and the soil water movement in the presence of cracks.

Identification of runoff formation with two dyes in a mid-latitude mountain headwater

Abstract. Subsurface flow in peat bog areas and its role in the hydrologic cycle has garnered increased attention as water scarcity and floods have increased due to a changing climate. In order to further probe the mechanisms in peat bog areas and contextualize them at the catchment scale, this experimental study identifies runoff formation at two opposite hillslopes in a peaty mountain headwater; a slope with organic peat soils and a shallow phreatic zone (0.5 m below surface), and a slope with mineral Podzol soils and no detectable groundwater (&gt; 2 m below surface). Similarities and differences in infiltration, percolation and preferential flow paths between both hillslopes could be identified by sprinkling experiments with Brilliant Blue and Fluorescein sodium. To our knowledge, this is the first time these two dyes have been compared in their ability to stain preferential flow paths in soils. Dye-stained soil profiles within and downstream of the sprinkling areas were excavated parallel (lateral profiles) and perpendicular (frontal profiles) to the slopes' gradients. That way preferential flow patterns in the soil could be clearly identified. The results show that biomat flow, shallow subsurface flow in the organic topsoil layer, occurred at both hillslopes; however, at the peat bog hillslope it was significantly more prominent. The dye solutions infiltrated into the soil and continued either as lateral subsurface pipe flow in the case of the peat bog, or percolated vertically towards the bedrock in the case of the Podzol. This study provides evidence that subsurface pipe flow, lateral preferential flow along decomposed tree roots or logs in the unsaturated zone, is a major runoff formation process at the peat bog hillslope and in the adjacent riparian zone.

Water Flow Path Characterization in Shallow Vadose Zone Using Tensiometers

In this project, we will present the findings of a study using Tensiometer systems designed to investigate the water flow path pattern in shallow vadose zone. The purpose of this paper is to evaluate water flow path in shallow vadose zone and to calculate the infiltration rate and hydraulic conductivity of a soil using Tensiometer. We have measured the subsurface water flow paths in sandy clay loam soil following infiltration experiment using Tensiometers. The matric potential and hydraulic conductivity measurements show that subsequent infiltration and water movement in unsaturated (vadose) zone are vertical, but it can have large lateral component under steady condition. This shows that water moves generally from high water content to lower water content region. Average pressure head for the percolation test conduction locations EB and HB was -30 and -80 cm respectively. Hysteresis produces another interesting situation when the soil is drained. We found that the wetter portion of the soil in vadose zone could be at a lower potential (head) than the dryer portions, resulting in lateral driving force for a preferential flow of water from the dryer to the wet soil. The infiltration rate for the 5 cm ponded water was calculated at 5.45 cm/hr. The infiltration rate curve shows that the rate of infiltration decreases with the time. When infiltration first starts, the wetting front is steep and very close to the surface. Similarly, due to the pressure head gradient, large value for infiltration is recorded. Under these conditions, we believe that the gradient in pressure head is responsible for the rapid movement of water into the dry soil. The effect of gravity is less on water during the initial stages of infiltration; however, it is more effective for preferential flow pattern. In the latter infiltration event, the wetting front has moved deeper into the soil. As a result, the pressure head gradient at the surface is much smaller and consequently has little effect. When the pressure head is equal zero, infiltration rate approaches almost to the lowest level. We also observed that even a minor change in soil-water pressure due to slope could change both direction and magnitude of water flux.