Spatio-temporal relevance and controls of preferential flow at the landscape scale

Abstract. The spatial and temporal controls of preferential flow (PF) during infiltration are still not fully understood. As soil moisture sensor networks allow us to capture infiltration responses in high temporal and spatial resolution, our study is based on a large-scale sensor network with 135 soil moisture profiles distributed across a complex catchment. The experimental design covers three major geological regions (slate, marl, sandstone) and two land covers (forest, grassland) in Luxembourg. We analyzed the responses of up to 353 rainfall events for each of the 135 soil moisture profiles. Non-sequential responses (NSRs) within the soil moisture depth profiles were taken as one indication of bypass flow. For sequential responses maximum porewater velocities (vmax⁡) were determined from the observations and compared with velocity estimates of capillary flow. A measured vmax⁡ higher than the capillary prediction was taken as a further indication of PF. While PF was identified as a common process during infiltration, it was also temporally and spatially highly variable. We found a strong dependence of PF on the initial soil water content and the maximum rainfall intensity. Whereas a high rainfall intensity increased PF (NSR, vmax⁡) as expected, most geologies and land covers showed the highest PF under dry initial conditions. Hence, we identified a strong seasonality of both NSR and vmax⁡ dependent on land cover, revealing a lower occurrence of PF during spring and increased occurrence during summer and early autumn, probably due to water repellency. We observed the highest fraction of NSR in forests on clay-rich soils (slate, marl). vmax⁡ ranged from 6 to 80 640 cm d−1 with a median of 120 cm d−1 across all events and soil moisture profiles. The soils in the marl geology had the highest flow velocities, independent of land cover, especially between 30 and 50 cm depth, where the clay content increased. This demonstrates the danger of treating especially clay soils in the vadose zone as a low-conductive substrate, as the development of soil structure can dominate over the matrix property of the texture alone. This confirms that clay content and land cover strongly influence infiltration and reinforce PF, but seasonal dynamics and flow initiation also have an important impact on PF.

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Relevance and controls of preferential flow at the landscape scale

10.5194/hess-2019-80 ◽

2019 ◽

Author(s):

Dominic Demand ◽

Theresa Blume ◽

Markus Weiler

Keyword(s):

Soil Moisture ◽

Water Content ◽

Soil Water ◽

Preferential Flow ◽

Clay Content ◽

Wetting Front ◽

Moisture Sensor ◽

Soil Moisture Sensor ◽

Landscape Units ◽

Moisture Profiles

Abstract. The spatial and temporal controls of preferential flow (PF) during infiltration are still not fully understood. Soil moisture sensor networks give the possibility to measure infiltration response in high temporal and spatial resolution. Therefore, we used a large-scale sensor network with 135 soil moisture profiles distributed across a complex catchment. The experimental design covers three major geological regions (Slate, Marl, Sandstone) and two land covers (forest, grassland) in Luxembourg. We analyzed the responses of up to 353 rainfall events for every of the 135 soil moisture profiles. Non-sequential responses within the soil moisture depth-profiles were taken as an indication of PF. For sequential responses wetting front velocities were determined from the observations and compared with predictions by capillary flow. A measured wetting front velocity higher than the capillary prediction was also taken as a proxy for PF. We observed the highest fraction of non-sequential response (NSR) in forests on clay-rich soils (Slate, Marl). Furthermore, these two landscape units showed an increase of NSR with lower initial soil water content and higher maximum rainfall intensity. Wetting front velocities ranged from 6 cm day−1 to 80 640 cm day−1 with a median of 113 cm day−1 across all events and landscape units. The soils in the Marl geology had the highest flow velocities, independent of land cover, especially between 30 and 50 cm depth where the clay content increased. For Marl the median water content change was highest for the deepest soil moisture sensor (50 cm), whereas the other two geologies (Slate, Sandstone) showed a decrease of soil moisture change with depth. This confirms that clay content and vegetation strongly influence infiltration and reinforce preferential flow. Capillary-based soil water flow modelling was unable to predict the observed patterns. This demonstrates the danger of treating especially clay soils in the vadose zone as a low-conductivity layer, as the development of soil structure can dominate over the effect of low-conductive texture.

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Identifying erosive periods by using RUSLE factors in mountain fields of the Central Spanish Pyrenees

Hydrology and Earth System Sciences ◽

10.5194/hess-12-523-2008 ◽

2008 ◽

Vol 12 (2) ◽

pp. 523-535 ◽

Cited By ~ 53

Author(s):

M. López-Vicente ◽

A. Navas ◽

J. Machín

Keyword(s):

Soil Moisture ◽

Moisture Content ◽

Soil Loss ◽

Rainfall Intensity ◽

Soil Moisture Content ◽

Rainfall Erosivity ◽

Soil Erodibility ◽

Maximum Rainfall ◽

Freeze Thaw ◽

Soil Losses

Abstract. The Mediterranean environment is characterized by strong temporal variations in rainfall volume and intensity, soil moisture and vegetation cover along the year. These factors play a key role on soil erosion. The aim of this work is to identify different erosive periods in function of the temporal changes in rainfall and runoff characteristics (erosivity, maximum intensity and number of erosive events), soil properties (soil erodibility in relation to freeze-thaw processes and soil moisture content) and current tillage practices in a set of agricultural fields in a mountainous area of the Central Pyrenees in NE Spain. To this purpose the rainfall and runoff erosivity (R), the soil erodibility (K) and the cover-management (C) factors of the empirical RUSLE soil loss model were used. The R, K and C factors were calculated at monthly scale. The first erosive period extends from July to October and presents the highest values of erosivity (87.8 MJ mm ha−1 h−1), maximum rainfall intensity (22.3 mm h−1) and monthly soil erosion (0.25 Mg ha−1 month−1) with the minimum values of duration of erosive storms, freeze-thaw cycles, soil moisture content and soil erodibility (0.007 Mg h MJ−1 mm−1). This period includes the harvesting and the plowing tillage practices. The second erosive period has a duration of two months, from May to June, and presents the lowest total and monthly soil losses (0.10 Mg ha−1 month−1) that correspond to the maximum protection of the soil by the crop-cover ($C$ factor = 0.05) due to the maximum stage of the growing season and intermediate values of rainfall and runoff erosivity, maximum rainfall intensity and soil erodibility. The third erosive period extends from November to April and has the minimum values of rainfall erosivity (17.5 MJ mm ha−1 h−1) and maximum rainfall intensity (6.0 mm h−1) with the highest number of freeze-thaw cycles, soil moisture content and soil erodibility (0.021 Mg h MJ−1 mm−1) that explain the high value of monthly soil loss (0.24 Mg ha−1 month−1). The interactions between the rainfall erosivity, soil erodibility, and cover-management factors explain the similar predicted soil losses for the first and the third erosive periods in spite of the strong temporal differences in the values of the three RUSLE factors. The estimated value of annual soil loss with the RUSLE model (3.34 Mg ha−1 yr−1) was lower than the measured value with 137Cs (5.38 Mg ha−1 yr−1) due to the low values of precipitation recorded during the studied period. To optimize agricultural practices and to promote sustainable strategies for the preservation of fragile Mediterranean agrosystems it is necessary to delay plowing till October, especially in dryland agriculture regions. Thus, the protective role of the crop residues will extend until September when the greatest rainfall occurs together with the highest runoff erosivity and soil losses.

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Use of soil moisture dynamics and patterns at different spatio-temporal scales for the investigation of subsurface flow processes

Hydrology and Earth System Sciences ◽

10.5194/hess-13-1215-2009 ◽

2009 ◽

Vol 13 (7) ◽

pp. 1215-1233 ◽

Cited By ~ 71

Author(s):

T. Blume ◽

E. Zehe ◽

A. Bronstert

Keyword(s):

Soil Moisture ◽

High Resolution ◽

Unsaturated Zone ◽

Preferential Flow ◽

Temporal Dynamics ◽

Rainfall Simulation ◽

Small Scale ◽

Temporal Scales ◽

Flow Processes ◽

Moisture Profiles

Abstract. Spatial patterns as well as temporal dynamics of soil moisture have a major influence on runoff generation. The investigation of these dynamics and patterns can thus yield valuable information on hydrological processes, especially in data scarce or previously ungauged catchments. The combination of spatially scarce but temporally high resolution soil moisture profiles with episodic and thus temporally scarce moisture profiles at additional locations provides information on spatial as well as temporal patterns of soil moisture at the hillslope transect scale. This approach is better suited to difficult terrain (dense forest, steep slopes) than geophysical techniques and at the same time less cost-intensive than a high resolution grid of continuously measuring sensors. Rainfall simulation experiments with dye tracers while continuously monitoring soil moisture response allows for visualization of flow processes in the unsaturated zone at these locations. Data was analyzed at different spacio-temporal scales using various graphical methods, such as space-time colour maps (for the event and plot scale) and binary indicator maps (for the long-term and hillslope scale). Annual dynamics of soil moisture and decimeter-scale variability were also investigated. The proposed approach proved to be successful in the investigation of flow processes in the unsaturated zone and showed the importance of preferential flow in the Malalcahuello Catchment, a data-scarce catchment in the Andes of Southern Chile. Fast response times of stream flow indicate that preferential flow observed at the plot scale might also be of importance at the hillslope or catchment scale. Flow patterns were highly variable in space but persistent in time. The most likely explanation for preferential flow in this catchment is a combination of hydrophobicity, small scale heterogeneity in rainfall due to redistribution in the canopy and strong gradients in unsaturated conductivities leading to self-reinforcing flow paths.

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Identifying erosive periods by using RUSLE factors in mountain fields of the Central Spanish Pyrenees

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-4-2111-2007 ◽

2007 ◽

Vol 4 (4) ◽

pp. 2111-2142 ◽

Cited By ~ 8

Author(s):

M. López-Vicente ◽

A. Navas ◽

J. Machín

Keyword(s):

Soil Moisture ◽

Moisture Content ◽

Rainfall Intensity ◽

Soil Moisture Content ◽

Rainfall Erosivity ◽

Soil Erodibility ◽

Maximum Rainfall ◽

Freeze Thaw ◽

Tillage Practices ◽

Soil Losses

Abstract. The Mediterranean environment is characterized by strong temporal variations in rainfall volume and intensity, soil moisture and vegetation cover along the year. These factors play a key role on soil erosion. The aim of this work is to identify different erosive periods in function of the temporal changes in rainfall and runoff characteristics (erosivity, maximum intensity and number of erosive events), soil properties (soil erodibility in relation to freeze-thaw processes and soil moisture content) and current tillage practices in a set of agricultural fields in a mountainous area of the Central Pyrenees in NE Spain. To this purpose the rainfall and runoff erosivity (R), the soil erodibility (K) and the cover-management (C) factors of the empirical RUSLE soil loss model were used. The R, K and C factors were calculated at monthly scale. The first erosive period extends from July to October and presents the highest values of erosivity (87.8 MJ mm ha−1 h−1), maximum rainfall intensity (22.3 mm h−1) and monthly soil erosion (0.10 Mg ha−1 month−1) with the minimum values of duration of erosive storms, freeze-thaw cycles, soil moisture content and soil erodibility (0.007 Mg h MJ−1 mm−1). This period includes the harvesting and the plowing tillage practices. The second erosive period has a duration of two months, from May to June, and presents the lowest total and monthly soil losses (0.04 Mg ha−1 month−1) that correspond to the maximum protection of the soil by the crop-cover (C factor = 0.05) due to the maximum stage of the growing season and intermediate values of rainfall and runoff erosivity, maximum rainfall intensity and soil erodibility. The third erosive period extends from November to April and has the minimum values of rainfall erosivity (17.5 MJ mm ha−1 h−1) and maximum rainfall intensity (6.0 mm h−1) with the highest number of freeze-thaw cycles, soil moisture content and soil erodibility (0.021 Mg h MJ−1 mm−1) that explain the high value of monthly soil loss (0.09 Mg ha−1 month−1). The interactions between the rainfall erosivity, soil erodibility, and cover-management factors explain the similar predicted soil losses for the first and the third erosive periods in spite of the strong temporal differences in the values of the three RUSLE factors. To optimize agricultural practices and to promote sustainable strategies for the preservation of fragile Mediterranean agrosystems it is necessary to delay plowing till October, especially in dryland agriculture regions. Thus, the protective role of the crop residues will extend until September when the greatest rainfall occurs together with the highest runoff erosivity and soil losses.

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Run-Off and Soil Movement on Mid-Slopes in North-East Queensland [Australia] Grazed Woodlands.

The Rangeland Journal ◽

10.1071/rj9960033 ◽

1996 ◽

Vol 18 (1) ◽

pp. 33 ◽

Cited By ~ 45

Author(s):

JC Scanlan ◽

AJ Pressland ◽

DJ Myles

Keyword(s):

Soil Moisture ◽

Rainfall Intensity ◽

Sediment Concentration ◽

Concentration Data ◽

Maximum Rainfall ◽

Rainfall Events ◽

Soil Movement ◽

Heteropogon Contortus ◽

Run Off ◽

Soil Moisture Status

Run-off, bedload and sediment concentration data were collected over a five-year period from unbounded catchments in grazed and exclosed pastures in woodlands. Cover varied from 4% during drought conditions to almost 100% in exclosed areas after above-average rainfall. High bedload soil loss, sediment concentration and run-off percentages were associated with low cover (<30%). Run-off as a percentage of rainfall increased linearly with rainfall intensity; decreased linearly with cover; decreased slightly as soil moisture status declined; and reached a maximum at intermediate rainfall events. Interactions between these factors were observed. Run-off was up to 30% of rainfall in moderate rainfall events (30-40 mm) where maximum rainfall intensity over any 15 minute period (I15) exceeded 70 mm/h. When soil moisture status was high, mean run-off exceeded 30% for 40-80 mm rainfall events. For all rainfall event sizes, run-off exceeded 20% where I15 exceeded 60 mm/h. Cover had very little effect on run-off when rainfall intensity was low (I15<20 mm/h), soil water deficit was low (<10 mm) or when rainfall events were >75 mm or <10 mm. Bedload plus suspended sediment loads ranged from negligible to 1000 kg/ha/a, depending principally on cover. Soil movement from areas with >40-50% cover was very low. Pastures dominated by Bothriochloa pertusa (a stoloniferous, naturalised grass) had lower run-off and lower rates of soil movement than pastures dominated by Heteropogon contortus (a native tussocky perennial grass) when compared at the same level of cover. Differences between grazed and exclosed areas could be attributed solely to differences in cover.

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Evaluation of land cover effects on soil-moisture dynamics: adaptation measures from the territory (Bidasoa catchment, Western Pyrenees).

10.5194/egusphere-egu2020-15114 ◽

2020 ◽

Author(s):

María Valiente ◽

Ane Zabaleta ◽

Maite Meaurio ◽

Jesus A. Uriarte ◽

Iñaki Antigüedad

Keyword(s):

Climate Change ◽

Soil Moisture ◽

Land Cover ◽

Soil Properties ◽

Hydrological Modelling ◽

Soil Conditions ◽

Adaptation Measures ◽

Soil Moisture Dynamics ◽

Land Covers ◽

Moisture Dynamics

The Pyrenees mountain range is the main source of water resources for a large surrounding region, extending from the Atlantic to the Mediterranean. This area is particularly vulnerable to the consequences of climate change. The PIRAGUA project (Interreg-POCTEFA) evaluates the components of the hydrological cycle in the Pyrenees, with the central objective of improving the adaptation of territories to climate change. One of its tasks focuses on the analysis of the effect that land cover and associated soil properties have on different hydrological services. Indeed, land use and its management directly affect soil hydrology, which is a key factor in streamflow temporal distribution. A better understanding of the water-soil-vegetation system is essential for a reliable hydrological modelling which results should be considered in adaptation strategies to climate change.To this aim, chemical and physical characterization of soil properties is being conducted at the 681 km2 humid Bidasoa catchment (Pyrenees). In order to understand the soil-moisture dynamics, a monitoring network was established in July 2019 in a 0.4 km2 experimental site within the catchment. Four soil-moisture stations and a meteorological one were installed within the same geological setting, same rainfall conditions and similar soil texture characteristics (silt-loamy texture and about one meter deep), but different land covers (pine forest, oak forest, grassland and fernery). Continuous soil-moisture data obtained to date show that upper soil layers (0-20 cm) are deeply influenced by top vegetation cover. Grassland has the highest soil-moisture variations, ranging from 16.2 to 36.6 %, as they closely mirror precipitation patterns. Pine and oak forests present similar variation trend, varying from 33.9 to 42.8 % and from 35.3 to 41.9 %, respectively. Soil-moisture at fernery goes from 30.5 to 36 %. Minimum soil-moisture values coincide in all plots with the end of the dry period (end of September). Maximum values, occurring during very heavy and continuous precipitation in November (647 mm registered from 1 to 24 November), are considered as a proxy for saturated soil conditions. In all the plots, fluctuations in soil-moisture diminish significantly with increasing soil depth. However, considerable differences are found in the vertical soil-moisture profile across land covers. In both forest plots, a decreasing trend of soil-moisture within the profile is observed, while grassland and fernery show an increasing trend. Preliminary results show that soil water infiltration is different among different land covers, which give some insight into the hydrological functionality of soil under different vegetation types. Longer records of soil-moisture dynamics in the area would contribute to better assess the linkages between water, soil and vegetation and, in turn, to improve hydrological modelling in humid mountainous areas. This knowledge is necessary for a better consideration of the adaptation measures that should be taken from the territory.

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A quality assessment of spatial TDR soil moisture measurements in homogenous and heterogeneous media with laboratory experiments

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-7-269-2010 ◽

2010 ◽

Vol 7 (1) ◽

pp. 269-311 ◽

Cited By ~ 6

Author(s):

T. Graeff ◽

E. Zehe ◽

S. Schlaeger ◽

M. Morgner ◽

A. Bauer ◽

...

Keyword(s):

Soil Moisture ◽

Laboratory Experiments ◽

Heterogeneous Media ◽

Clay Content ◽

Reconstruction Algorithm ◽

Telegraph Equation ◽

Moisture Profile ◽

Near Surface ◽

Small Influence ◽

Moisture Profiles

Abstract. Investigation of transient soil moisture profiles yields valuable information of near- surface processes. A recently developed reconstruction algorithm based on the telegraph equation allows the inverse estimation of soil moisture profiles along coated, three rod TDR probes. Laboratory experiments were carried out to prove the results of the inversion and to understand the influence of probe rod deformation and solid objects close to the probe in heterogonous media. Differences in rod geometry can lead to serious misinterpretations in the soil moisture profile but have small influence on the average soil moisture along the probe. Solids in the integration volume have almost no effect on average soil moisture but result in locally slightly decreased moisture values. Inverted profiles obtained in a loamy soil with a clay content of about 16% were in good agreement with independent measurements.

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A quality assessment of Spatial TDR soil moisture measurements in homogenous and heterogeneous media with laboratory experiments

Hydrology and Earth System Sciences ◽

10.5194/hess-14-1007-2010 ◽

2010 ◽

Vol 14 (6) ◽

pp. 1007-1020 ◽

Cited By ~ 13

Author(s):

T. Graeff ◽

E. Zehe ◽

S. Schlaeger ◽

M. Morgner ◽

A. Bauer ◽

...

Keyword(s):

Soil Moisture ◽

Laboratory Experiments ◽

Heterogeneous Media ◽

Clay Content ◽

Reconstruction Algorithm ◽

Telegraph Equation ◽

Moisture Profile ◽

Near Surface ◽

Small Influence ◽

Moisture Profiles

Abstract. Investigation of transient soil moisture profiles yields valuable information of near- surface processes. A recently developed reconstruction algorithm based on the telegraph equation allows the inverse estimation of soil moisture profiles along coated, three rod TDR probes. Laboratory experiments were carried out to prove the results of the inversion and to understand the influence of probe rod deformation and solid objects close to the probe in heterogeneous media. Differences in rod geometry can lead to serious misinterpretations in the soil moisture profile, but have small influence on the average soil moisture along the probe. Solids in the integration volume have almost no effect on average soil moisture, but result in locally slightly decreased moisture values. Inverted profiles obtained in a loamy soil with a clay content of about 16% were in good agreement with independent measurements.

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Use of soil moisture dynamics and patterns for the investigation of runoff generation processes with emphasis on preferential flow

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-4-2587-2007 ◽

2007 ◽

Vol 4 (4) ◽

pp. 2587-2624 ◽

Cited By ~ 10

Author(s):

T. Blume ◽

E. Zehe ◽

A. Bronstert

Keyword(s):

Soil Moisture ◽

High Resolution ◽

Unsaturated Zone ◽

Preferential Flow ◽

Temporal Dynamics ◽

Rainfall Simulation ◽

Small Scale ◽

Runoff Generation ◽

Flow Processes ◽

Moisture Profiles

Abstract. Spatial patterns as well as temporal dynamics of soil moisture have a major influence on runoff generation. The investigation of these dynamics and patterns can thus yield valuable information on hydrological processes, especially in data scarce or previously ungauged catchments. The combination of spatially scarce but temporally high resolution soil moisture profiles with episodic and thus temporally scarce moisture profiles at additional locations provides information on spatial as well as temporal patterns of soil moisture at the hillslope transect scale. This approach is better suited to difficult terrain (dense forest, steep slopes) than geophysical techniques and at the same time less cost-intensive than a high resolution grid of continuously measuring sensors. Rainfall simulation experiments with dye tracers while continuously monitoring soil moisture response allows for visualization of flow processes in the unsaturated zone at these locations. Data was analyzed at different spacio-temporal scales using various graphical methods, such as space-time colour maps (for the event and plot scale) and indicator maps (for the long-term and hillslope scale). Annual dynamics of soil moisture and decimeter-scale variability were also investigated. The proposed approach proved to be successful in the investigation of flow processes in the unsaturated zone and showed the importance of preferential flow in the Malalcahuello Catchment, a data-scarce catchment in the Andes of Southern Chile. Fast response times of stream flow indicate that preferential flow observed at the plot scale might also be of importance at the hillslope or catchment scale. Flow patterns were highly variable in space but persistent in time. The most likely explanation for preferential flow in this catchment is a combination of hydrophobicity, small scale heterogeneity in rainfall due to redistribution in the canopy and strong gradients in unsaturated conductivities leading to self-reinforcing flow paths.

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