Subsurface flow velocities in a hillslope with lateral preferential flow

Abstract. The phrase form and function was established in architecture and biology and refers to the idea that form and functionality are closely correlated, influence each other, and co-evolve. We suggest transferring this idea to hydrological systems to separate and analyze their two main characteristics: their form, which is equivalent to the spatial structure and static properties, and their function, equivalent to internal responses and hydrological behavior. While this approach is not particularly new to hydrological field research, we want to employ this concept to explicitly pursue the question of what information is most advantageous to understand a hydrological system. We applied this concept to subsurface flow within a hillslope, with a methodological focus on function: we conducted observations during a natural storm event and followed this with a hillslope-scale irrigation experiment. The results are used to infer hydrological processes of the monitored system. Based on these findings, the explanatory power and conclusiveness of the data are discussed. The measurements included basic hydrological monitoring methods, like piezometers, soil moisture, and discharge measurements. These were accompanied by isotope sampling and a novel application of 2-D time-lapse GPR (ground-penetrating radar). The main finding regarding the processes in the hillslope was that preferential flow paths were established quickly, despite unsaturated conditions. These flow paths also caused a detectable signal in the catchment response following a natural rainfall event, showing that these processes are relevant also at the catchment scale. Thus, we conclude that response observations (dynamics and patterns, i.e., indicators of function) were well suited to describing processes at the observational scale. Especially the use of 2-D time-lapse GPR measurements, providing detailed subsurface response patterns, as well as the combination of stream-centered and hillslope-centered approaches, allowed us to link processes and put them in a larger context. Transfer to other scales beyond observational scale and generalizations, however, rely on the knowledge of structures (form) and remain speculative. The complementary approach with a methodological focus on form (i.e., structure exploration) is presented and discussed in the companion paper by Jackisch et al.(2017).

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

Hydrology and Earth System Sciences ◽

10.5194/hess-21-3025-2017 ◽

2017 ◽

Vol 21 (6) ◽

pp. 3025-3040 ◽

Cited By ~ 4

Author(s):

Lukáš Vlček ◽

Kristýna Falátková ◽

Philipp Schneider

Keyword(s):

Pipe Flow ◽

Preferential Flow ◽

Subsurface Flow ◽

Peat Bog ◽

Catchment Scale ◽

Tree Roots ◽

Flow Paths ◽

Runoff Formation ◽

Shallow Subsurface ◽

Preferential Flow Paths

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 (> 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.

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Subsurface flow velocities through selected forest soils, South Island, New Zealand

Journal of Hydrology ◽

10.1016/0022-1694(82)90121-4 ◽

1982 ◽

Vol 55 (1-4) ◽

pp. 65-92 ◽

Cited By ~ 146

Author(s):

M.P. Mosley

Keyword(s):

New Zealand ◽

Forest Soils ◽

Subsurface Flow ◽

Flow Velocities

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Quantification of the influence of preferential flow on slope stability using a numerical modelling approach

Hydrology and Earth System Sciences ◽

10.5194/hess-19-2197-2015 ◽

2015 ◽

Vol 19 (5) ◽

pp. 2197-2212 ◽

Cited By ~ 33

Author(s):

W. Shao ◽

T. A. Bogaard ◽

M. Bakker ◽

R. Greco

Keyword(s):

Slope Stability ◽

High Intensity ◽

Preferential Flow ◽

Water Pressure ◽

Subsurface Flow ◽

Permeability Model ◽

Rainfall Events ◽

Matrix Domain ◽

Low Intensity ◽

Flow Domain

Abstract. The effect of preferential flow on the stability of landslides is studied through numerical simulation of two types of rainfall events on a hypothetical hillslope. A model is developed that consists of two parts. The first part is a model for combined saturated/unsaturated subsurface flow and is used to compute the spatial and temporal water pressure response to rainfall. Preferential flow is simulated with a dual-permeability continuum model consisting of a matrix domain coupled to a preferential flow domain. The second part is a soil mechanics model and is used to compute the spatial and temporal distribution of the local factor of safety based on the water pressure distribution computed with the subsurface flow model. Two types of rainfall events were considered: long-duration, low-intensity rainfall, and short-duration, high-intensity rainfall. The effect of preferential flow on slope stability is assessed through comparison of the failure area when subsurface flow is simulated with the dual-permeability model as compared to a single-permeability model (no preferential flow). For the low-intensity rainfall case, preferential flow has a positive effect on drainage of the hillslope resulting in a smaller failure area. For the high-intensity rainfall case, preferential flow has a negative effect on the slope stability as the majority of rainfall infiltrates into the preferential flow domain when rainfall intensity exceeds the infiltration capacity of the matrix domain, resulting in larger water pressure and a larger failure area.

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Field observations of subsurface flow path evolution over 10 Millennia

10.5194/egusphere-egu2020-17961 ◽

2020 ◽

Author(s):

Anne Hartmann ◽

Ekaterina Semenova ◽

Markus Weiler ◽

Theresa Blume

Keyword(s):

Preferential Flow ◽

Subsurface Flow ◽

Soil Surface ◽

Flow Path ◽

Physical Characteristics ◽

Swiss Alps ◽

Spatial And Temporal Variability ◽

Hydrological Process ◽

Flow Paths ◽

Soil Physical Characteristics

Where water goes when it rains, is to a large part controlled by subsurface storage and subsurface flow paths. While these aspects are essential for basic hydrological process understanding, their large spatial and temporal variability makes both systematic studies and extraction of generalizable results challenging. We investigate systematically how subsurface storage and flow paths change during the temporal evolution of hillslopes. In order to do so we selected 4 moraines of different ages (30, 160, 3000 and 10.000 years) in a glacial foreland in the Swiss Alps. We then studied both soil physical characteristics as well as flow path evolution across this chronosequence by extensive sampling and soil physical laboratory analyses on the one hand and 36 in-situ dye tracer experiments (Brilliant Blue) &#160;on the other hand. We find that soil physical characteristics change significantly over the millennia. However, vegetational development seems to have a similarly strong effect on flow path evolution. Flow paths evolve from mainly matrix flow at the youngest moraine to increasingly more dominant preferential flow. At the oldest moraine we furthermore find increased subsurface storage, especially in the now strongly developed organic horizon. At intermediate ages preferential flow is less dominated by flow in macropores but is initiated at the soil surface through spatially variable vegetation and microtopography. With this study we provide a first systematic and detailed study of flow path evolution across the first ten millennia of hillslope evolution.

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Flow recession behavior of dendritic subsurface flow patterns

10.5194/egusphere-egu2020-9191 ◽

2020 ◽

Author(s):

Jannick Strüven ◽

Stefan Hergarten

Keyword(s):

Energy Dissipation ◽

Hydraulic Conductivity ◽

Power Law ◽

Preferential Flow ◽

Minimum Energy ◽

Subsurface Flow ◽

Flow Patterns ◽

Short Term ◽

Physically Based ◽

Two Parameters

Discharge curves of springs are the fingerprint of aquifers. In particular, the recession of flow after strong recharge events has been widely used for aquifer characterization. While an exponential decay is often found at long time scales, the short-term behavior is less unique and widely used in the context of characterizing karst systems. Several empirical and a few physically-based models describing the short-term recession behavior were proposed.This study investigates the flow recession behavior of aquifers with preferential flow paths with a structure according to the concept of minimum energy dissipation. Assuming a power-law relationship between hydraulic conductivity and porosity, the subsurface flow patterns used in our model are organized towards an optimal spatial distribution of these two parameters in a way that the total energy dissipation of the flow is minimized. This leads to two-dimensional dendritic network structures similar to river networks. Starting from a steady-state initial condition with a constant recharge rate we model the decrease of discharge over time, under the assumption of a linear storage behavior. As expected the long-term flow recession can be approximated by an exponential function. At short times, however, our model predicts a power-law behavior with exponents ranging from 0.7 to 0.9. For the most realistic scenario, a quadratic relationship between hydraulic conductivity and porosity, the power-law exponent approximates 0.8 which corresponds well to what other studies have found for suitable recession events of karst springs.

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Transferring the concept of minimum energy expenditure from river networks to subsurface flow patterns

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-11-5831-2014 ◽

2014 ◽

Vol 11 (6) ◽

pp. 5831-5857

Author(s):

S. Hergarten ◽

G. Winker ◽

S. Birk

Keyword(s):

Energy Expenditure ◽

Power Law ◽

Preferential Flow ◽

Minimum Energy ◽

Subsurface Flow ◽

Flow Patterns ◽

River Networks ◽

Data Sets ◽

Residence Times ◽

Minimum Energy Expenditure

Abstract. Principles of optimality provide an interesting alternative to modeling hydrological processes in detail on small scales. However, the concepts still seem to be on a visionary level except for the theory of minimum energy expenditure for river networks. Inspired by this approach, we present a theory of minimum energy expenditure in subsurface flow in order to obtain a better understanding of preferential flow patterns in the subsurface. The concept describes flow patterns which are optimal in the sense that they minimize the total energy expenditure at given recharge under the side condition of a given total porosity. Results are illustrated using two examples: two-dimensional flow towards a spring with a radial symmetric distribution of the porosity and dendritic flow patterns. The latter are found to be similar to river networks in their structure and, as a main result, the model predicts a power-law distribution of the spring discharges. In combination with two data sets from the Austrian Alps, this result is used for validating the model. Both data sets reveal power-law distributed spring discharges with similar scaling exponents. These are, however, slightly larger than the exponent predicted by the model. As a further result, the distributions of the residence times strongly differ between homogeneous porous media and optimized flow patterns, while the mean residence times seem to be similar in both cases.

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Wavelet Analysis of Soil Water State Variables for Identification of Lateral Subsurface Flow: Lysimeter versus Field Data

10.5194/ismc2021-3 ◽

2021 ◽

Author(s):

Annelie Ehrhardt ◽

Jannis Groh ◽

Horst H. Gerke

Keyword(s):

Time Series ◽

Soil Water ◽

Preferential Flow ◽

Response Times ◽

Subsurface Flow ◽

Agricultural Landscapes ◽

Field Soil ◽

State Variables ◽

Rain Events ◽

Wavelet Coherency

Preferential and lateral subsurface flow may be responsible for the accelerated transport of water and solutes in sloping agricultural landscapes; however, the process is difficult to observe. One idea is to compare time series of soil moisture observations in the field with those in lysimeters, where flow is vertically oriented. This study aims at identifying periods of deviations in soil water contents and pressure heads measured in the field and in a weighing lysimeter with the same soil profile. Wavelet Coherency Analysis (WCA) was applied to time series of hourly soil water content and pressure head data (15, 32, 60, 80, and 140 cm depths) from Colluvic Regosol soil profiles in summer 2017. The phase shifts and periodicities indicated by the WCA plots reflected the response times to rain events in the same depth of lysimeter and field soil. For many rain events and depths, sensors installed in the field soil showed a faster response than those in the lysimeters soil. This could be explained by either vertical preferential flow or lateral subsurface flow from upper hillslope positions. Vice versa, a faster sensor response in the lysimeter soil could be indicative for vertical preferential effects. The WCA plots comprise all temporal patterns of time shifts and correlations between larger data time series in a condensed form to identify potentially relevant periods for more detailed analyses of subsurface flow dynamics.&#160;

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

10.5194/hess-2017-77 ◽

2017 ◽

Author(s):

Lukáš Vlček ◽

Philipp Schneider ◽

Kristýna Falátková

Keyword(s):

Preferential Flow ◽

Hydrological Cycle ◽

Subsurface Flow ◽

Sodium Fluorescein ◽

Peat Bog ◽

Catchment Scale ◽

Tree Roots ◽

Runoff Formation ◽

Shallow Subsurface ◽

Preferential Flowpaths

Abstract. Subsurface flow in Peat Bog areas and its role in the hydrological 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 (> 2 m below surface). Similarities and differences in infiltration, percolation, and preferential flowpaths between both hillslopes could be identified by sprinkling experiments with Brilliant Blue and Sodium-Fluorescein. To our knowledge, this is the first time these two dyes have been compared in their ability to stain preferential flowpaths 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 pipeflow 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 pipeflow, 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.

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Phosphorus Transport in Subsurface Flow at Beech Forest Stands: Does Phosphorus Mobilization Keep up with Transport?

10.5194/bg-2020-118 ◽

2020 ◽

Author(s):

Michael Rinderer ◽

Jaane Krüger ◽

Friederike Lang ◽

Heike Puhlmann ◽

Markus Weiler

Keyword(s):

Forest Ecosystems ◽

Preferential Flow ◽

Soil Depth ◽

Mineral Soil ◽

Subsurface Flow ◽

Climatic Conditions ◽

Strong Increase ◽

Limiting Factor ◽

Phosphorus Transport ◽

Soil P

Abstract. Phosphorus (P) is a limiting factor of primary productivity in most forest ecosystems but little is known about retention within and losses of P from forests. Subsurface flow (SSF) is one of the important pathways of P export but few attempts exist to quantify it. We present results of sprinkling experiments with ca. 150 mm, 2H labelled, total rainfall conducted at 200 m2 plots on hillslopes with slopes between 14° and 28° at three beech forests in Germany in summer and spring. We aimed at quantifying vertical and lateral SSF and associated P transport in the forest floor, the mineral soil and the saprolite. The study sites differed regarding soil depth, skeleton content and soil P stocks (between 678 g/m2 and 209 g/m2, in the first 1 m soil depth). Vertical SSF in the mineral soil and in the saprolite was at least two orders of magnitude larger than lateral SSF in the same depth. Vertical and lateral SSF consisted mainly of pre-event water that was replaced by sprinkling water (piston flow mechanism). Short spikes of event water at the beginning of the experiment at two of the sites with high skeleton content indicate that preferential flow occurred in parallel to matrix flow. We observed a significant decrease in P concentrations in SSF with increasing soil depth suggesting effective retention of P by adsorption to soil particles in all three forest ecosystems. Higher P concentrations in SSF at the beginning of the experiments indicate nutrient flushing but P concentrations were nearly constant thereafter despite strong increase in SSF. P concentrations did also not change significantly with increasing share of event water in SSF. These chemostatic transport conditions suggests that P mobilization rates were similar to transport rates in both, P-rich and P-poor sites. The observed first flush effect implies that P export by SSF will increase as rainfall events with high transport capacity are predicted to occur more frequent under future climatic conditions.

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