scholarly journals Applied tracers for the observation of subsurface stormflow at the hillslope scale

2009 ◽  
Vol 6 (2) ◽  
pp. 2961-3006 ◽  
Author(s):  
J. Wienhöfer ◽  
K. Germer ◽  
F. Lindenmaier ◽  
A. Färber ◽  
E. Zehe
Keyword(s):  
Large Scale ◽  
Preferential Flow ◽  
Unsaturated Flow ◽  
Dispersion Model ◽  
Breakthrough Curves ◽  
Flow Paths ◽  
Transient Flows ◽  
Natural Rainfall ◽  
Flow Features ◽  
Hillslope Scale

Abstract. Rainfall-runoff response in temperate humid headwater catchments is mainly controlled by hydrological processes at the hillslope scale. Applied tracer experiments with fluorescent dye and salt tracers are well known tools in groundwater studies at the large scale and vadose zone studies at the plot scale, where they provide a means to characterise subsurface flow. We extend this approach to the hillslope scale to investigate saturated and unsaturated flow paths concertedly at a forested hillslope in the Austrian Alps. Dye staining experiments at the plot scale revealed that cracks and soil pipes function as preferential flow paths in the fine-textured soils of the study area, and these preferential flow structures were active in fast subsurface transport of tracers at the hillslope scale. Breakthrough curves obtained under steady flow conditions could be fitted well to a one-dimensional convection-dispersion model. Under natural rainfall a positive correlation of tracer concentrations to the transient flows was observed. The results of this study demonstrate qualitative and quantitative effects of preferential flow features on subsurface stormflow in a temperate humid headwater catchment. It turns out that, at the hillslope scale, the interactions of structures and processes are intrinsically complex, which implies that attempts to model such a hillslope satisfactorily require detailed investigations of effective structures and parameters at the scale of interest.

scholarly journals Applied tracers for the observation of subsurface stormflow at the hillslope scale

2009 ◽  
Vol 13 (7) ◽  
pp. 1145-1161 ◽  
Author(s):  
J. Wienhöfer ◽  
K. Germer ◽  
F. Lindenmaier ◽  
A. Färber ◽  
E. Zehe
Keyword(s):  
Large Scale ◽  
Preferential Flow ◽  
Unsaturated Flow ◽  
Dispersion Model ◽  
Breakthrough Curves ◽  
Flow Paths ◽  
Transient Flows ◽  
Natural Rainfall ◽  
Flow Features ◽  
Hillslope Scale

Abstract. Rainfall-runoff response in temperate humid headwater catchments is mainly controlled by hydrological processes at the hillslope scale. Applied tracer experiments with fluorescent dye and salt tracers are well known tools in groundwater studies at the large scale and vadose zone studies at the plot scale, where they provide a means to characterise subsurface flow. We extend this approach to the hillslope scale to investigate saturated and unsaturated flow paths concertedly at a forested hillslope in the Austrian Alps. Dye staining experiments at the plot scale revealed that cracks and soil pipes function as preferential flow paths in the fine-textured soils of the study area, and these preferential flow structures were active in fast subsurface transport of tracers at the hillslope scale. Breakthrough curves obtained under steady flow conditions could be fitted well to a one-dimensional convection-dispersion model. Under natural rainfall a positive correlation of tracer concentrations to the transient flows was observed. The results of this study demonstrate qualitative and quantitative effects of preferential flow features on subsurface stormflow in a temperate humid headwater catchment. It turns out that, at the hillslope scale, the interactions of structures and processes are intrinsically complex, which implies that attempts to model such a hillslope satisfactorily require detailed investigations of effective structures and parameters at the scale of interest.

scholarly journals Dye staining and excavation of a lateral preferential flow network

2009 ◽  
Vol 13 (6) ◽  
pp. 935-944 ◽  
Author(s):  
A. E. Anderson ◽  
M. Weiler ◽  
Y. Alila ◽  
R. O. Hudson
Keyword(s):  
Slope Stability ◽  
Solute Transport ◽  
Preferential Flow ◽  
Runoff Generation ◽  
Flow Paths ◽  
Soil Matrix ◽  
Preferential Flow Paths ◽  
Dye Staining ◽  
Hillslope Scale ◽  
Surrounding Soil

Abstract. Preferential flow paths have been found to be important for runoff generation, solute transport, and slope stability in many areas around the world. Although many studies have identified the particular characteristics of individual features and measured the runoff generation and solute transport within hillslopes, very few studies have determined how individual features are hydraulically connected at a hillslope scale. In this study, we used dye staining and excavation to determine the morphology and spatial pattern of a preferential flow network over a large scale (30 m). We explore the feasibility of extending small-scale dye staining techniques to the hillslope scale. We determine the lateral preferential flow paths that are active during the steady-state flow conditions and their interaction with the surrounding soil matrix. We also calculate the velocities of the flow through each cross-section of the hillslope and compare them to hillslope scale applied tracer measurements. Finally, we investigate the relationship between the contributing area and the characteristics of the preferential flow paths. The experiment revealed that larger contributing areas coincided with highly developed and hydraulically connected preferential flow paths that had flow with little interaction with the surrounding soil matrix. We found evidence of subsurface erosion and deposition of soil and organic material laterally and vertically within the soil. These results are important because they add to the understanding of the runoff generation, solute transport, and slope stability of preferential flow-dominated hillslopes.

scholarly journals Tracing Septic Pollution Sources Using Synthetic DNA Tracers: Proof of Concept

2019 ◽  
Vol 12 ◽  
pp. 117862211986379 ◽  
Author(s):  
Christine B Georgakakos ◽  
Paul L Richards ◽  
M Todd Walter
Keyword(s):  
Preferential Flow ◽  
Quantitative Polymerase Chain Reaction ◽  
Breakthrough Curves ◽  
Septic Systems ◽  
Proof Of Concept ◽  
Septic System ◽  
Flow Paths ◽  
Synthetic Dna ◽  
Preferential Flow Paths ◽  
Polymerase Chain

Contamination from septic systems is one of the most difficult sources of nonpoint source (NPS) pollution to quantify. Quantification is difficult in part because locating malfunctioning septic systems within a watershed is challenging. This study used synthetic-DNA-based tracers to track flows from 2 septic systems. Sample DNA was quantified using quantitative polymerase chain reaction (qPCR). This technology could be especially useful for simultaneously assessing multiple septic systems because there are essentially infinite unique combinations of DNA bases such that unique tracers could be engineered for each septic system. Two studies were conducted: the first, to determine whether the tracers move through septic systems (experiment 1), and the second, to determine whether the tracers were detectable at watershed scales (experiment 2). In both cases, clear, although complex, breakthrough curves were detected. Experiment 1 revealed possible preferential flow paths that might not have been otherwise obvious, indicative of short circuiting systems. This proof of concept suggests that these tracers could be applied to watersheds suspected of experiencing NPS septic system pollution.

Leaching patterns in soil under pasture and crop

Soil Research ◽  
1982 ◽  
Vol 20 (2) ◽  
pp. 193 ◽  
Author(s):  
P Kanchanasut ◽  
DR Scotter
Keyword(s):  
Preferential Flow ◽  
Unsaturated Flow ◽  
Soil Depth ◽  
Vegetative Cover ◽  
Natural Rainfall ◽  
Soil Structures ◽  
Stem Flow ◽  
Flow Pathways ◽  
Preferential Flow Pathways ◽  
Log Normal

The distribution of surface-applied bromide, after leaching with 50 mm of ponded water, was measured in soil profiles under long-term pasture and under an oat crop. Also measured was the bromide distribution under pasture after leaching with natural rainfall. The method of water application, the vegetative cover, and the soil structure interacted to produce quite different leaching patterns. However, in all experiments the highest bromide concentrations after leaching were in the top 20 mm of soil. It is suggested that the vegetation, by inducing preferential flow pathways, retarded the leaching of bromide from the soil near the surface. Also rainfall on pasture apparently was subject to interception and stem-flow, which caused less effective leaching from the topsoil than would have occurred under fallow. Rainfall did, however, leach more efficiently than ponded water, probably as it induced largely unsaturated flow. But, even after 182 mm of rain in excess of evapotranspiration, 10% of the applied bromide was still recoverable from the top 50 mm of soil under pasture. Different soil structures under cropping and pasture affected the leaching patterns with ponded water. A compacted layer at 100-140 mm depth in the cropped soil apparently throttled infiltration, resulting in unsaturated flow, and hence more uniform miscible displacement below than above it. In all cases the bromide concentration at any soil depth was highly variable, with replicates tending toward a log-normal rather than normal frequency distribution.

scholarly journals Structural geology and geophysics as a support to build a hydrogeologic model of granite rock

Solid Earth ◽  
2016 ◽  
Vol 7 (3) ◽  
pp. 881-895 ◽  
Author(s):  
Lurdes Martinez-Landa ◽  
Jesús Carrera ◽  
Andrés Pérez-Estaún ◽  
Paloma Gómez ◽  
Carmen Bajos
Keyword(s):  
Structural Geology ◽  
Large Scale ◽  
Preferential Flow ◽  
Three Dimensional ◽  
Pumping Test ◽  
Discrete Elements ◽  
Flow Paths ◽  
Preferential Flow Paths

Abstract. A method developed for low-permeability fractured media was applied to understand the hydrogeology of a mine excavated in a granitic pluton. This method includes (1) identifying the main groundwater-conducting features of the medium, such as the mine, dykes, and large fractures, (2) implementing this factors as discrete elements into a three-dimensional numerical model, and (3) calibrating these factors against hydraulic data . A key question is how to identify preferential flow paths in the first step. Here, we propose a combination of several techniques. Structural geology, together with borehole sampling, geophysics, hydrogeochemistry, and local hydraulic tests aided in locating all structures. Integration of these data yielded a conceptual model of the site. A preliminary calibration of the model was performed against short-term (< 1 day) pumping tests, which facilitated the characterization of some of the fractures. The hydraulic properties were then used for other fractures that, according to geophysics and structural geology, belonged to the same families. Model validity was tested by blind prediction of a long-term (4 months) large-scale (1 km) pumping test from the mine, which yielded excellent agreement with the observations. Model results confirmed the sparsely fractured nature of the pluton, which has not been subjected to glacial loading–unloading cycles and whose waters are of Na-HCO3 type.

scholarly journals Field experimental design for pesticide leaching – a modified large-scale lysimeter

2005 ◽  
Vol 7 ◽  
pp. 41-44
Author(s):  
Bertel Nilsson ◽  
Jens Aamand ◽  
Ole Stig Jacobsen ◽  
René K. Juhler
Keyword(s):  
Large Scale ◽  
Preferential Flow ◽  
Fracture Network ◽  
Transport Processes ◽  
Natural Fracture ◽  
Field Scale ◽  
Flow Paths ◽  
Undisturbed Soil ◽  
Flow And Transport ◽  
Preferential Flow Paths

Recent research on Danish groundwater has focused on clarifying the fate and transport of pesticides that leach through clayey till aquitards with low matrix permeability. Previously, these aquitards were considered as protective layers against contamination of underlying groundwater aquifers due to their low permeability characteristics. However, geological heterogeneities such as fractures and macropores have been recognised as preferential flow paths within low permeable clayey till (e.g. Beven & Germann 1982). The flow velocities within these preferential flow paths can be orders of magnitude higher than in the surrounding clay matrix and pose a major risk of transport of contaminants to the underlying aquifers (e.g. Nilsson et al. 2001). Previous studies of transport in fractured clayey till have focused on fully saturated conditions (e.g. Sidle et al. 1998; McKay et al. 1999). However, seasonal fluctuations of the groundwater table typically result in unsaturated conditions in the upper few metres of the clay deposits, resulting in different flow and transport conditions. Only a few experiments have examined the influence of unsaturated conditions on flow and solute (the dissolved inorganic and organic constituents) transport in fractured clayey till. These include smallscale laboratory column experiments on undisturbed soil monoliths (e.g. Jacobsen et al. 1997; Jørgensen et al. 1998), intermediate scale lysimeters (e.g. Fomsgaard et al. 2003) and field-scale tile drain experiments (e.g. Kjær et al. 2005). The different approaches each have limitations in terms of characterising flow and transport in fractured media. Laboratory studies of solute transport in soils (intact soil columns) are not exactly representative of field conditions due to variations in spatial variability and soil structure. In contrast, field studies hardly allow quantification of fluxes and mechanisms of transport. Column and lysimeter experiments are often limited in size, and tile-drain experiments on field scale do not provide spatial resolution and often have large uncertainties in mass balance calculations. Thus, in order to represent the overall natural fracture network systems on a field scale with respect to acquiring insights into flow and transport processes, the lysimeter needs to be larger than normal lysimeter size (< 1 m3). A modified large-scale lysimeter was therefore constructed by the Geological Survey of Denmark and Greenland (GEUS) at the Avedøre experimental field site 15 km south of Copenhagen (Fig. 1). This lysimeter consisted of an isolated block (3.5 ×3.5 ×3.3 m) of unsaturated fractured clayey till with a volume sufficient to represent the overall preferential flow paths (natural fracture network) within lowpermeable clayey till at a field scale.

scholarly journals Geostatistic Interpolation of Soil Moisture

1997 ◽  
Vol 28 (4-5) ◽  
pp. 307-328 ◽  
Author(s):  
Nils-Otto Kitterød ◽  
E. Langsholt ◽  
W. K. Wong ◽  
L. Gottschalk
Keyword(s):  
Soil Moisture ◽  
Unsaturated Zone ◽  
Preferential Flow ◽  
Unsaturated Flow ◽  
Three Dimensional ◽  
Indicator Kriging ◽  
Flow Paths ◽  
Flow Models ◽  
Semivariogram Analysis ◽  
Preferential Flow Paths

The spatial distribution of soil moisture defines preferential flow paths in the unsaturated zone. Hence, three dimensional (3D) estimates of soil moisture are of great importance to understand transport of contaminants as well as remediation processes in the unsaturated zone. In this study 3D estimates conditioned on spatially frequent observations of soil moisture, have been obtained by kriging. The observations were divided into subdomains consistent with the local stratigraphy and directional semivariogram analysis was applied. It was found difficult to clearly identify a 3D semivariogram function in this case, but from a georadar survey two semivariogram functions were derived, describing two different sedimentological units. By conditioning the estimates of soil moisture on the sedimentological architecture computed by indicator kriging, more accurate estimates were achieved. These improvements were quantified by a ‘jackknife’ cross validation procedure. Besides the practical aspects of finding the most important flow paths estimates of soil moisture are valuable when validating unsaturated flow models.

scholarly journals Subsurface flow and large-scale lateral saturated soil hydraulic conductivity in a Mediterranean hillslope with contrasting land uses

2017 ◽  
Vol 65 (3) ◽  
pp. 297-306 ◽  
Author(s):  
Mario Pirastru ◽  
Vincenzo Bagarello ◽  
Massimo Iovino ◽  
Roberto Marrosu ◽  
Mirko Castellini ◽  
...  
Keyword(s):  
Hydraulic Conductivity ◽  
Large Scale ◽  
Subsurface Flow ◽  
Soil Layer ◽  
Soil Surface ◽  
Point Estimation ◽  
Natural Rainfall ◽  
Artificial Rainfall ◽  
Soil Heterogeneities ◽  
Hillslope Scale

AbstractThe lateral saturated hydraulic conductivity,Ks,l, is the soil property that mostly governs subsurface flow in hillslopes. Determinations ofKs,lat the hillslope scale are expected to yield valuable information for interpreting and modeling hydrological processes since soil heterogeneities are functionally averaged in this case. However, these data are rare since the experiments are quite difficult and costly. In this investigation, that was carried out in Sardinia (Italy), large-scale determinations ofKs,lwere done in two adjacent hillslopes covered by a Mediterranean maquis and grass, respectively, with the following objectives: i) to evaluate the effect of land use change onKs,l, and ii) to compare estimates ofKs,lobtained under natural and artificial rainfall conditions. HigherKs,lvalues were obtained under the maquis than in the grassed soil since the soil macropore network was better connected in the maquis soil. The lateral conductivity increased sharply close to the soil surface. The sharp increase ofKs,lstarted at a larger depth for the maquis soil than the grassed one. TheKs,lvalues estimated during artificial rainfall experiments agreed with those obtained during the natural rainfall periods. For the grassed site, it was possible to detect a stabilization ofKs,lin the upper soil layer, suggesting that flow transport capacity of the soil pore system did not increase indefinitely. This study highlighted the importance of the experimental determination ofKs,lat the hillslope scale for subsurface modeling, and also as a benchmark for developing appropriate sampling methodologies based on near-point estimation ofKs,l.

Influence of local splitting behavior at intersections on infiltration in an unsaturated fracture network 

2021 ◽  
Author(s):  
Song Xue ◽  
Zhibing Yang ◽  
Yi-Feng Chen
Keyword(s):  
Large Scale ◽  
Preferential Flow ◽  
Unsaturated Flow ◽  
Flow Characteristics ◽  
Fracture Network ◽  
Liquid Volume ◽  
Complex Flow ◽  
Local Flow ◽  
Divergent Flow ◽  
Macro Scale

&lt;p&gt;Understanding and predicting the macro-scale flow characteristics in the fractured vadose zone is of great importance for subsurface hydrological applications. Here we develop a network model to study infiltration in unsaturated fracture networks. We consider an idealized honeycomb-like fracture network composed of a series of Y-shaped and inverted Y-shaped intersections. At the scale of intersections, liquid storage/release and splitting/convergence behaviors are modeled according to local splitting relationships obtained from detailed laboratory work and numerical simulations. By varying the splitting relationships, the influence of local flow behaviors on large scale flow structures is systematically investigated. We find that when the water split tends to split equally at the intersection, a divergent flow structure forms in the network. Conversely, unequal splitting leads to preferential pathways. We also find that an avalanche infiltration mode, i.e., sudden release of a large amount of water from the network, emerges spontaneously, and is modulated by the local splitting behavior. The pathways of preferential flow is controlled by the liquid volume triggered by avalanches and the network structure. The improved understanding from this study may shed new light on the complex flow dynamics for unsaturated flow in fractured media.&lt;/p&gt;

scholarly journals Modeling of NO3 transport in gypsiferous soil under unsaturated flow

2021 ◽  
Vol 8 (3) ◽  
Author(s):  
Ramzi M. Shihab ◽  
Ahmed A. Fattah ◽  
Noor Aldeen M. Muhawish
Keyword(s):  
Unsaturated Flow ◽  
Nitrate Concentration ◽  
Dispersion Model ◽  
Soil Column ◽  
Potassium Nitrate ◽  
Breakthrough Curves ◽  
Retardation Factor ◽  
Soil Columns ◽  
Water Head ◽  
Gypsum Content

"This study was conducted to determine the effect of gypsum content and depth of water head on displacement and transport of nitrate in gypsiferous soil under unsaturated flow conditions. Also, to predict the concentration of nitrate using convection dispersion model (CDE). Soil columns with 63, 97, 142, 180, and 236 g kg-1 of gypsum were prepared. 200 mg L-1 of potassium nitrate were added to the surface of each soil column. The soil columns were leached by intermittent ponding in 2 pore volumes of water. A constant head depth of 0.005, 0.01, and 0.015 m of water was kept on the top of soil column. Samples of effluent were collected for measuring nitrate concentration. The CDE model was analyzed to estimate the best fitting between measured and predicted nitrate concentration, and to calculate dispersion coefficient (D), the retardation factor (R), and Peclet number (P). Results showed that CDE can be used to predict nitrate concentration in soil. Good fit was observed to describe breakthrough curves (BTC's), and predict the transport of nitrates in the leachate of gypsum soil columns. D values increased with the increase in the content of soil gypsum and decrease with increase the water head. Its values ranged between 6.59-9.87 m 2h-1. P and pore water velocity (v) decreased with the increase in soil gypsum content. The R values were less than 1 for all treatments"

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