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• Determining the geometric shape of cracks generated from the physical crust crack. • Investigating cracks on the preferential flow under the control of physical crusts. • Examining the hydrological processes of physical crusts. • Indexes for crack properties in structural crusts were larger than deposition crusts. • Preferential flow in structural crust was superior to those of deposition crust. Studies have shown that preferential flow induced by cracks establishes multiple features such as morphology in different soil profiles. However, there has been little experimental evidence of the contribution of physical crust towards crack features and preferential flow. Essentially, this investigation focused on physical crusts (structural and deposition crust) of Lou soil, a loam and silt loam-textured soil, to demarcate the formation of cracks and preferential flow under artificial rainfall. The crack initiation and propagation processes were defined as the formation of primary cracks in the initial phase and narrow cracks around primary cracks, respectively. The cylindrical soil containers and cubical stainless-steel boxes were employed to trace preferential flow in the horizontal and vertical profile, respectively. The cracks in structural and deposition crusts were dominated by initiation and propagation cracks, respectively. The area, length, and width of the cracks in the structural crusts (5.7 cm2, 815, and 1.44 mm) were notably larger than deposition crusts (1.7 cm2, 604, and 0.96 mm). The maximum dyed depths of the structural and deposition crusts reached 35, 45, and 65 mm, and 35, 55, and 75 mm under the infiltration amounts of 10, 30, and 50 mm, respectively. The uniform infiltration depth, length index and PF-fr of structural crusts were in the ranges of 6.7 ∼ 25.5 mm, 19 ∼ 46 %, and 83 ∼ 111 %, respectively. Corresponding values for deposition crusts were 7.2 ∼ 26.2 mm, 10 ∼ 46 %, and 87 ∼ 103 %, respectively. The preferential flow in the soil profiles with structural crusts was superior to deposition crust. An assessment of the potential function of the physical crust for preferential flow is a supplement to study the effect of soil surface morphology on hydrological process. [ABSTRACT FROM AUTHOR]

Abstract While the supraglacial hydrology of debris-covered glaciers is relatively well studied, almost nothing is known about how water is transported beneath the glacier surface. Here, we report the results of sixteen fluorescent dye tracing experiments conducted in April–May 2018 over the lowermost 7 km of the high-elevation, debris-covered Khumbu Glacier, Nepal, to characterise the glacier's surface and subsurface drainage system. Dye breakthroughs indicated a likely highly sinuous and channelised subsurface hydrological system draining water from the upper part of the ablation area. This flowpath was distinct from the linked chain of supraglacial ponds present along much of the glacier's lower ablation area, through which water flow was extremely slow (∼0.003 m s−1), likely reflecting the study's timing during the pre-monsoon period. Subsurface drainage pathways emerged at the glacier surface close to the terminus, and flowed into small near-surface englacial reservoirs that typically delayed meltwater transit by several hours. We observed rapid pathway changes resulting from surface collapse, indicating a further distinctive aspect of the drainage of debris-covered glaciers. We conclude that the surface and subsurface drainage of Khumbu Glacier is both distinctive and dynamic, and argue that further investigation is needed to refine the characterisation and test its regional applicability to better understand future Himalayan debris-covered glacier meltwater delivery to downstream areas. Highlights • Dye tracing used to investigate hydrology of debris-covered Khumbu Glacier, Nepal. • A subsurface drainage system exists, and is likely highly sinuous and channelised. • The subsurface drainage system does not link to the chain of supraglacial ponds. • Flow through the pond chain is slow and comprises a small part of total discharge. • Rapid pathway changes are observed, resulting from variable surface lowering. [ABSTRACT FROM AUTHOR]

Highlights • Debris-covered glaciers have a distinct hydrological structure. • Debris cover reduces supraglacial catchment size and reduces melt rates. • Beneath continuous debris on the lower glacier the drainage network is inefficient. • An efficient conduit system drains the clean and dirty ice on the upper glacier. • A channelized and distributed system co-exist beneath the lower glacier. Abstract Supraglacial debris is known to strongly influence the distribution of glacier surface melt. Since melt inputs drive the formation and evolution of glacial drainage systems, it should follow that the drainage systems of debris-covered glaciers will differ from those of debris-free glaciers. This would have implications for the proglacial runoff regime, subglacial erosion and glacier dynamics. This paper presents analysis of return curves from 33 successful dye injections into the extensively debris-covered Miage Glacier, Italian Alps. It demonstrates that the spatial distribution of supraglacial debris influences the structure and seasonal evolution of the glacial drainage system. Where the debris cover is continuous, melt is lower and the surface topography is chaotic, with many small supraglacial catchments. These factors result in an inefficient englacial/subglacial drainage network beneath continuous debris, which drains to the conduit system emanating from the upper ablation zone. Melt rates are high in areas of clean and dirty ice above the continuous debris. Runoff from these areas is concentrated by inter-moraine troughs into large supraglacial streams, which encourages the early-season development of an efficient englacial/subglacial conduit system downstream of this area. Drainage efficiency from the debris-covered area increases over the melt season but dye-trace transit velocity remains lower than from moulins on the upper glacier. Future runoff models should account for the influence of supraglacial debris on the hydrological system. [ABSTRACT FROM AUTHOR]

• Secondary vegetation succession promotes preferential flow. • Secondary vegetation succession changes soil texture and structure. • Soil structure independently explains 26% variation of preferential flow pattern. • Reforestation intensifies preferential flow by improving soil structure. 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 (D max), actual infiltration depth (D actual), total dye coverage (C total), and length index (LI) significantly increased following the sequence of vegetation succession stages (P < 0.05), and the preferential pathway contribution (D pr) 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 D max , D actual , C total , D pr , 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. [ABSTRACT FROM AUTHOR]

Highlights • First attempt of coupling CFPv2 and OSTRICH for optimization of conduit parameters. • Calibration of CFPv2 based on considering both breakthrough and spring discharge. • A reliable scenario is selected that improves understanding of karst groundwater. • The results contributed to the decision of not constructing a dam at the site. Abstract In order to better define the characteristics of a karst conduit, an integrated hydrogeological study including numerical modeling using CFPv2 is conducted at a karst aquifer in the Zagros Mountain Region of Iran. The Sarvak limestone aquifer in the Nil Anticline is the main karst aquifer of the study area with major groundwater discharge taking place at Sarkur spring. An annual water balance and a dye tracing test confirmed that the karst system is mainly recharged through rainfall and the Maroon River. Several depressions are observed along the banks of the river with a major one classified as a sinkhole used for dye injection. A groundwater flow model was developed based on the available hydrogeological information. A probable direct conduit flow path with an estimated groundwater flow velocity of 96 m/h is estimated between the injection point and the Sarkur spring. Four scenarios are assumed to simulate the probable conduit flow path using the CFPv2 code. As one of the first attempts in regional groundwater flow modeling of a karst aquifer, CFPv2 is automatically calibrated with field measurements of spring discharge and a dye breakthrough curve through a parameter estimation code OSTRICH to optimize the characteristics of the conduit through the minimization of the weighted sum of square error. Simulated results reveal that a conduit with a diameter of 2.9 m is required to adequately simulate spring discharge and dye tracer migration between the injection and discharge points. Our new approach (linking of CFPv2 and OSTRICH) provides a deeper understanding of groundwater flow and solute transport in karst terrains even when available data are limited and the approach should be applicable to other areas. [ABSTRACT FROM AUTHOR]

The accurate measurement of velocities of shallow overland flows normally found in the field of hydrology is essential to understand the kinematics of these flows. In view of this, we have tested the capability of a new thermal particle tracer (cold oil droplets) under controlled laboratory conditions to measure the velocity of shallow overland flows (<2 mm depth) using the infrared-based particle tracking velocimetry (PTV) technique. Experimental apparatus comprised a soil flume 3 m long and 0.3 m wide with a feeder tank attached to the upstream end. Flow velocities acquired through infrared-based PTV were compared with corresponding values given by the volumetric discharge method, dye tracing, and conventional PTV (using polystyrene beads as tracer) for eleven flow conditions that combined different slopes (5, 7, 10 and 15%) and discharges (0.15 to 0.51 L s −1  m −1 ). The Reynolds number (569 to 1938) marked it as quasi-laminar flow. The results showed that acquired flow velocity given by through infrared-based PTV and conventional PTV techniques was closer to the mean velocity estimated by the volumetric discharge method than it was to dye tracing estimated velocity. The mean correction factor value (0.78) estimated by the infrared-based PTV technique was higher than the dye tracing estimated correction factor value (0.48). Furthermore, the detection of the leading edge of the dye tracer was difficult and the stagnation of polystyrene beads at lower discharges resulted in an underestimation of mean velocity. This research stresses the potential of using thermal imaging to estimate the velocity of shallow water bodies, because of the tracer's conspicuous visibility and independence from illuminating conditions. [ABSTRACT FROM AUTHOR]

Abstract: Persistence of subsoil compaction was investigated in a field experiment in southern Sweden. The investigation compared two treatments (control and compaction by four passes track-by-track), 14years after the experimental traffic. The compaction experiment was carried out in 1995 with a 6-row sugar beet harvester with a wheel load of c. 10.4Mg. Investigations included penetration resistance, bulk density, water retention, saturated hydraulic conductivity, in situ near-saturated hydraulic conductivity, and dye tracing experiments. The measurements of penetration resistance and bulk density clearly showed the persistence of subsoil compaction. In addition, both macroporosity and saturated and near-saturated hydraulic conductivity were smaller in the compacted plots, although these differences were not statistically significant. Dye tracing allowed us to visualize flow patterns in the soil and to quantitatively distinguish compacted and non-compacted subsoil profiles. Despite significant soil textural heterogeneity across the experimental field, the dye tracing data showed that persistent compaction may enhance preferential flow. [Copyright &y& Elsevier]

Abstract: Ten gravity springs from the slopes of the Biokovo Mt, Adriatic coast of Croatia were investigated. Three of them are included in the regional water supply system. The aim of this study was to investigate hydrogeological and geochemical characteristics of watershed, presenting one of the most typical karstic areas in the world. Hydrogeological investigations were performed during two seasons with dye tracing, using Na-fluoresceine which was poured into two pits, observing springs at distances of 1.82–8.8km. Apparent velocities were 0.21–0.51cms−1. Dye tracing was first time partially effective and second time ineffective, what could be due to immanent ore mineralization, which presents a natural barrier and was discovered by geochemical and mineralogical methods. Concentrations of 17 dissolved and total trace elements were determined first time in groundwater samples. Their concentrations were extremely low, more than 3 orders of magnitude less than allowed by the Croatian directives for the first category of groundwater and drinking water. The mass fractions of 60 elements were determined in 3 representative spring sediments. Highest concentrations of some metals in sediments (mgkg−1) are: lead 5440, chromium 118, manganese 935, zinc 116 and barium 238. Origin of some elements and mineralogy is discussed. [Copyright &y& Elsevier]

Summary: Preferential flow (PF) in soil has both environmental and human health implications since it favours contaminant transport to groundwater without interaction with the chemically and biologically reactive upper layer of soil. PF is, however, difficult to measure and quantify. This paper reviews laboratory and field techniques, such as breakthrough curves, dye tracing, and scanning techniques, for evaluating PF in soil at different scales. Advanced technologies, such as scanning techniques, have increased our capability to quantify transport processes within the soil with minimal soil disturbance. Important issues with respect to quantifying PF concern large-scale studies, frozen soil conditions, tracing techniques for particles and gases, a lack of simple mathematical tools for interpreting field data, and the lack of a systematic approach for comparing PF data resulting from different measurement techniques. Also, more research is required to quantify the relative importance of the various PF processes that occur in soil rather than the integrated result of all PF processes in soils. [Copyright &y& Elsevier]

Abstract: Cranefly larvae, often known as leatherjackets, are a well known horticultural pest, damaging garden lawns, plants and sporting venues. They burrow into the soil and feed on the roots of plants. However, little is known about the hydrological role of leatherjackets. Such information is needed by modellers to improve water and solute models. This paper investigates flow through leatherjacket burrows in grassland fields. It compares infiltration rates, patterns of dye tracer and pore size distributions in a grassland system with and without leatherjackets. It also compares these distributions to those in an adjacent cropped tillage system which was largely devoid of leatherjackets. Dye tracer distributions show the leatherjacket burrows to act as active preferential flowpaths for water during percolation. A significant relationship between leatherjacket density and infiltration rate was found which took the form of an exponential curve. Leatherjackets were predominately found in the upper 30 cm of the grassland where there was a significantly greater volume of pores that were greater than 2 mm than in the arable soil and where visible macropores, including those open to the surface were significantly more common, covered a significantly larger cross-sectional area and were more circular in cross-sectional area. Leatherjacket burrows significantly reduced the spread of water into the surrounding soil and thereby acted as effective conduits for water to bypass the soil matrix in the upper 30 cm of the grassland. Mean dye coverage was greater at between 30 and 36 cm in the grassland soil profile, where leatherjacket burrows ended, than any other parts of the soil profile deeper than 8 cm. Such dye distributions were rare in the arable soils where very few leatherjackets were present. In some regions fallow grassland is increasing in area in response to environmental policy. Therefore, since infiltration significantly increased with leatherjacket density, consideration of their role in macropore flow will be necessary to understand the full range of hydrological and water quality implications of conversion from arable to fallow grassland management. [Copyright &y& Elsevier]

• Irrigation method has substantial effect on crack closure. • Crack flow promotes greater infiltration depth in surface irrigation treatment. • Cracks restrict horizontal infiltration of drip irrigation as capillary barrier. • Irrigation method and cracks jointly affect flow regime and irrigation efficiency. Soil cracks, which are common in farmland, typically serve as preferential paths for water movement or solute transport and potentially result in deep percolation and groundwater contamination during crop production. The major objectives of this study were to investigate crack variation and flow regimes in cracked soil under different irrigation methods. Dye experiments were conducted in cracked soil columns using three different irrigation methods, i.e. surface irrigation, spray irrigation and drip irrigation. Superficial crack networks and dye patterns in soil profiles were photographed and quantified by image processing techniques. Soil water content was measured by Time Domain Reflectometry. Evaluation of irrigation efficiency was conducted based on the dye patterns and measured soil water content. The results showed that the cracks rapidly closed under surface irrigation but partially closed under spray irrigation, which was mainly attributed to the difference in application rate. Crack flow occurred under surface irrigation and caused striking 'V'-shaped regions of preferential flow in profiles, markedly increasing the infiltration depth compared with spray irrigation. Under drip irrigation, crack closure degree decreased with the distance from drip center. Cracks restricted the horizontal infiltration, giving rise to an inverted pear-shaped wetted zone in soil. Our results indicate that application rate and infiltration geometry of irrigation have substantial effect on crack closure degree, and flow regimes in upper soil are closely associated with both irrigation methods and soil cracks, which can appreciably affect the irrigation efficiency. These findings could bear management recommendation for irrigation in cracked fields to promote irrigation efficiency. Besides, this study implies that spraying at appropriate application rates may be able to facilitate crack closure without inducing large water loss via crack flow, which needs to be further investigated. [ABSTRACT FROM AUTHOR]