Graham Sander - Academia.edu (original) (raw)
Papers by Graham Sander
Water Resources Research, 1989
Sediment transport in overland flow interacts dynamically with the soil surface morphology, which... more Sediment transport in overland flow interacts dynamically with the soil surface morphology, which is often assumed to be static. This assumption, although it limits the predictive capacity of models, is reasonable since the morphological evolution is difficult to quantify, particularly when rill networks form. Rill networks evolve due to hydraulic interactions with local features of the surface, the measurement of which are challenging even in well controlled laboratory experiments. In nature, river basins with different sizes and at different places are found to have power law relations for the exceedance probabilities of area and upstream length. We hypothesize that similar scaling relations exist for rill networks. Here we present the initial results of laboratory experiments to test this hypothesis.
Frontiers in Earth Science
Despite numerous applications of physically-based models for incised landscapes, their applicabil... more Despite numerous applications of physically-based models for incised landscapes, their applicability for overland flow on unchanneled surfaces is not known. This work challenges a widely used landscape evolution model for the case of non-uniform rainfall and absence of rills using laboratory flume experiment. Rainfall with an average intensity of 85 mm h−1 was applied for 16 h during which high resolution laser scans of the morphology were captured. The overland flow was modeled as a network that preserves the water flux for each cell in the discretized domain. This network represented the gravity-driven surface flow and determined the evolution direction. The model was calibrated using the first 8 h of the experiment and was then used to predict the second 8 h. The calibrated model predicted, as expected, a smoother surface morphology (and less detailed overland flow network) than that measured. This difference resulted from quenched randomness (e.g., small pebbles) within the expe...
Journal of Hydrology, 2021
An extremely fast and accurate pseudospectral numerical method is presented, which can be used in... more An extremely fast and accurate pseudospectral numerical method is presented, which can be used in inverse methods for estimating soil hydraulic parameters from horizontal infiltration or desorption experiments. Chebyshev polynomial differentiation in conjunction with the flux concentration formulation of Philip (1973) results in a numerical solution of high order accuracy that is directly dependent on the number of Chebyshev nodes used. The level of accuracy (< 0.01% for 100 nodes) is confirmed through a comparison with two different, but numerically demanding, exact closed-form solutions where an infinite derivative occurs at either the wetting front or the soil surface. Application of our computationally efficient method to estimate soil hydraulic parameters is found to take less than one second using modest laptop computer resources. The pseudospectral method can also be applied to evaluate analytical approximations, and in particular, those of Parlange and Braddock (1980) and Parlange et al (1994) are chosen. It is shown that both these approximations produce excellent estimates of both the sorptivity and moisture profile across a wide range of initial and boundary conditions and numerous physically realistic diffusivity functions.
Ecohydrology, 2012
ABSTRACT An approximate analytical solution of the Hairsine–Rose model of erosion is obtained by ... more ABSTRACT An approximate analytical solution of the Hairsine–Rose model of erosion is obtained by interpolation of asymptotic expressions for large times and great distances. The solution, when erosion is initiated by rainfall impact, is both simple and accurate. The results are illustrated by comparison with a numerical solution. Copyright © 2012 John Wiley &amp; Sons, Ltd.
Temporally variable rainfall was applied on an initially dry, ploughed and smoothed agricultural ... more Temporally variable rainfall was applied on an initially dry, ploughed and smoothed agricultural soil to investigate the hysteresis pattern in the sediment concentration- discharge relation using laboratory flume experiments. The erosion flume had dimensions of 5-m × 2-m and consisted of two collectors at either side of the outlet. The slope was fixed at 2% and seven sequential events involved 20-min precipitation rates of 15, 30, 45, 60, 45, 30 and 15 mm h -1, were performed. Due to the cohesive agricultural soil, and low discharge and slope, rainfall detachment was the only erosion mechanism operating. The data collected at the two flume exits were analyzed by measuring the discharge and total sediment concentration. A clockwise hysteresis loop was found for total sediment concentration because of the easily erodible soil condition at the beginning of the experiment. It was also found that the Hairsine-Rose model was in agreement with the experimental data, which showed its capabi...
<strong>Data organization:</strong> <strong>Input: </strong> The experime... more <strong>Data organization:</strong> <strong>Input: </strong> The experimental data. The experimental setup are described at: Cheraghi, M., A. Rinaldo, G. Sander, P. Perona, and D.A. Barry. (2018), Catchment drainage network scaling laws found experimentally in overland flow morphologies, <em>Geophys. Res. Lett.</em>, 45. https://doi.org/10.1029/2018GL078351 <strong>model: </strong> The C++ code to numerically solve the landscape evolution model <strong>Results:</strong> The model results at different time-steps are saved in this folder
We evaluated the applicability of a large-scale river network evolution model used to simulate mo... more We evaluated the applicability of a large-scale river network evolution model used to simulate morphological changes of a laboratory-scale landscape on which there were no visible rills. Previously, such models were used only at the landscape scale, or in laboratory experiments where rills form in the soils surface. The flume-scale experiment (1-m × 2-m surface area) was de- signed to allow model calibration. Low-cohesive fine sand was placed in the flume while the slope and relief height were 5% and 25 cm, respectively. Non-uniform rainfall with an average intensity of 85 mmh −1 and a standard deviation of 26% was applied to the sediment surface for 16 h. High resolution Digital Elevation Models were captured at intervals during the experiment. Estimates of the overland flow drainage network were derived and, using these, the river network evolution model was numerically solved and calibrated. A noticeable feature of the experiment was a steep transition zone in soil elevation that...
Landscape evolution models (LEMs) refer to a class of models that simulate key features of networ... more Landscape evolution models (LEMs) refer to a class of models that simulate key features of network structures at the catchment scale, along with runoff and sediment deposition. Such models can reproduce landscape features as captured by different (statistical) metrics. Similarly, at the laboratory scale, LEMs produce results that are consistent with experimental data, for instance in the generation of landscape incisions. One relatively simple LEM consists of a Fokker-Planck equation accounting for surface elevation changes due to raindrop impact and shear-driven erosion due to overland flow, coupled with a flux-conserving overland flow model. In this work, this LEM was modified to account for non-uniform rainfall, and applied to laboratory data from an erosion flume subjected to intense rainfall. The experiment was designed to produce erosion from raindrop impact and sheet flow. Several detailed laser scans quantified the surface evolution. The LEM was capable of reproducing the ov...
Rain splash soil erosion in the presence of rock fragments was tested in laboratory flume experim... more Rain splash soil erosion in the presence of rock fragments was tested in laboratory flume experiments under controlled conditions. The surface area exposed to rain splash erosion was adjusted by placing rock fragments onto the surface of differently prepared soil in laboratory flumes (surface initially dry and hand cultivated or sealed due to the pre-wetting). The laboratory results showed that the eroded cumulative mass depended on the cumulative runoff, and that soil erosion was proportional to the soil surface area exposed to raindrops, in situations where an initially dry, hand cultivated and smoothed soil surface were ensured. The results showed that this relationship was controlled to a smaller extent by the soil’s initial moisture content, bulk density and soil surface characteristics. More in detail, it was observed that sediment concentrations during the first part of the erosion event were more sensitive to the initial state of the soil surface, whereas at steady state it ...
This is an abstract of a conference paper. It is published by Copenicus Gmbh under the Creative C... more This is an abstract of a conference paper. It is published by Copenicus Gmbh under the Creative Commons Attribution 3.0 Unported Licence (CC BY). Full details of this licence are available at: http://creativecommons.org/licenses/by/3.0
The ability of a large-scale Landscape Evolution Model (LEM) to simulate the soil surface morphol... more The ability of a large-scale Landscape Evolution Model (LEM) to simulate the soil surface morphological evolution as observed in a laboratory flume (1-m × 2-m surface area) was investigated. The soil surface was initially smooth, and was subjected to heterogeneous rainfall in an experiment designed to avoid rill formation. Low-cohesive fine sand was placed in the flume while the slope and relief height were 5 % and 20 cm, respectively. Non-uniform rainfall with an average intensity of 85 mm h -1 and a standard deviation of 26 % was applied to the sediment surface for 16 h. We hypothesized that the complex overland water flow can be represented by a drainage discharge network, which was calculated via the micro-morphology and the rainfall distribution. Measurements included high resolution Digital Elevation Models that were captured at intervals during the experiment. The calibrated LEM captured the migration of the main flow path from the low precipitation area into the high precipi...
... A Simple Illustration of a Conceptual Soil Erosion Model. ... This study's objectives ar... more ... A Simple Illustration of a Conceptual Soil Erosion Model. ... This study's objectives are to experimentally address some of the model's fundamental aspects not addressed by earlier experiments and, perhaps more importantly, to present the conceptual model and associated ...
Water Resources Research, 2016
A detailed laboratory study was conducted to examine the effects of particle size on hysteretic s... more A detailed laboratory study was conducted to examine the effects of particle size on hysteretic sediment transport under time-varying rainfall. A rainfall pattern composed of seven sequential stepwise varying rainfall intensities (30, 37.5, 45, 60, 45, 37.5 and 30 mm h−1), each of 20-mins duration, was applied to a 5-m × 2-m soil erosion flume. The soil in the flume was initially dried, ploughed to a depth of 20 cm and had a mechanically smoothed surface. Flow rates and sediment concentration data for seven particle size classes ( 1000 µm) were measured in the flume effluent. Clockwise hysteresis loops in the sediment concentration versus discharge curves were measured for the total eroded soil and the finer particle sizes ( 1000 µm). Overall, it is found that hysteresis varies amongst particle sizes and that the predictions of the HR model are consistent with hysteretic behavior of different sediment size classes. This article is protected by copyright. All rights reserved.
Water Resources Research, 1989
Sediment transport in overland flow interacts dynamically with the soil surface morphology, which... more Sediment transport in overland flow interacts dynamically with the soil surface morphology, which is often assumed to be static. This assumption, although it limits the predictive capacity of models, is reasonable since the morphological evolution is difficult to quantify, particularly when rill networks form. Rill networks evolve due to hydraulic interactions with local features of the surface, the measurement of which are challenging even in well controlled laboratory experiments. In nature, river basins with different sizes and at different places are found to have power law relations for the exceedance probabilities of area and upstream length. We hypothesize that similar scaling relations exist for rill networks. Here we present the initial results of laboratory experiments to test this hypothesis.
Frontiers in Earth Science
Despite numerous applications of physically-based models for incised landscapes, their applicabil... more Despite numerous applications of physically-based models for incised landscapes, their applicability for overland flow on unchanneled surfaces is not known. This work challenges a widely used landscape evolution model for the case of non-uniform rainfall and absence of rills using laboratory flume experiment. Rainfall with an average intensity of 85 mm h−1 was applied for 16 h during which high resolution laser scans of the morphology were captured. The overland flow was modeled as a network that preserves the water flux for each cell in the discretized domain. This network represented the gravity-driven surface flow and determined the evolution direction. The model was calibrated using the first 8 h of the experiment and was then used to predict the second 8 h. The calibrated model predicted, as expected, a smoother surface morphology (and less detailed overland flow network) than that measured. This difference resulted from quenched randomness (e.g., small pebbles) within the expe...
Journal of Hydrology, 2021
An extremely fast and accurate pseudospectral numerical method is presented, which can be used in... more An extremely fast and accurate pseudospectral numerical method is presented, which can be used in inverse methods for estimating soil hydraulic parameters from horizontal infiltration or desorption experiments. Chebyshev polynomial differentiation in conjunction with the flux concentration formulation of Philip (1973) results in a numerical solution of high order accuracy that is directly dependent on the number of Chebyshev nodes used. The level of accuracy (< 0.01% for 100 nodes) is confirmed through a comparison with two different, but numerically demanding, exact closed-form solutions where an infinite derivative occurs at either the wetting front or the soil surface. Application of our computationally efficient method to estimate soil hydraulic parameters is found to take less than one second using modest laptop computer resources. The pseudospectral method can also be applied to evaluate analytical approximations, and in particular, those of Parlange and Braddock (1980) and Parlange et al (1994) are chosen. It is shown that both these approximations produce excellent estimates of both the sorptivity and moisture profile across a wide range of initial and boundary conditions and numerous physically realistic diffusivity functions.
Ecohydrology, 2012
ABSTRACT An approximate analytical solution of the Hairsine–Rose model of erosion is obtained by ... more ABSTRACT An approximate analytical solution of the Hairsine–Rose model of erosion is obtained by interpolation of asymptotic expressions for large times and great distances. The solution, when erosion is initiated by rainfall impact, is both simple and accurate. The results are illustrated by comparison with a numerical solution. Copyright © 2012 John Wiley &amp; Sons, Ltd.
Temporally variable rainfall was applied on an initially dry, ploughed and smoothed agricultural ... more Temporally variable rainfall was applied on an initially dry, ploughed and smoothed agricultural soil to investigate the hysteresis pattern in the sediment concentration- discharge relation using laboratory flume experiments. The erosion flume had dimensions of 5-m × 2-m and consisted of two collectors at either side of the outlet. The slope was fixed at 2% and seven sequential events involved 20-min precipitation rates of 15, 30, 45, 60, 45, 30 and 15 mm h -1, were performed. Due to the cohesive agricultural soil, and low discharge and slope, rainfall detachment was the only erosion mechanism operating. The data collected at the two flume exits were analyzed by measuring the discharge and total sediment concentration. A clockwise hysteresis loop was found for total sediment concentration because of the easily erodible soil condition at the beginning of the experiment. It was also found that the Hairsine-Rose model was in agreement with the experimental data, which showed its capabi...
<strong>Data organization:</strong> <strong>Input: </strong> The experime... more <strong>Data organization:</strong> <strong>Input: </strong> The experimental data. The experimental setup are described at: Cheraghi, M., A. Rinaldo, G. Sander, P. Perona, and D.A. Barry. (2018), Catchment drainage network scaling laws found experimentally in overland flow morphologies, <em>Geophys. Res. Lett.</em>, 45. https://doi.org/10.1029/2018GL078351 <strong>model: </strong> The C++ code to numerically solve the landscape evolution model <strong>Results:</strong> The model results at different time-steps are saved in this folder
We evaluated the applicability of a large-scale river network evolution model used to simulate mo... more We evaluated the applicability of a large-scale river network evolution model used to simulate morphological changes of a laboratory-scale landscape on which there were no visible rills. Previously, such models were used only at the landscape scale, or in laboratory experiments where rills form in the soils surface. The flume-scale experiment (1-m × 2-m surface area) was de- signed to allow model calibration. Low-cohesive fine sand was placed in the flume while the slope and relief height were 5% and 25 cm, respectively. Non-uniform rainfall with an average intensity of 85 mmh −1 and a standard deviation of 26% was applied to the sediment surface for 16 h. High resolution Digital Elevation Models were captured at intervals during the experiment. Estimates of the overland flow drainage network were derived and, using these, the river network evolution model was numerically solved and calibrated. A noticeable feature of the experiment was a steep transition zone in soil elevation that...
Landscape evolution models (LEMs) refer to a class of models that simulate key features of networ... more Landscape evolution models (LEMs) refer to a class of models that simulate key features of network structures at the catchment scale, along with runoff and sediment deposition. Such models can reproduce landscape features as captured by different (statistical) metrics. Similarly, at the laboratory scale, LEMs produce results that are consistent with experimental data, for instance in the generation of landscape incisions. One relatively simple LEM consists of a Fokker-Planck equation accounting for surface elevation changes due to raindrop impact and shear-driven erosion due to overland flow, coupled with a flux-conserving overland flow model. In this work, this LEM was modified to account for non-uniform rainfall, and applied to laboratory data from an erosion flume subjected to intense rainfall. The experiment was designed to produce erosion from raindrop impact and sheet flow. Several detailed laser scans quantified the surface evolution. The LEM was capable of reproducing the ov...
Rain splash soil erosion in the presence of rock fragments was tested in laboratory flume experim... more Rain splash soil erosion in the presence of rock fragments was tested in laboratory flume experiments under controlled conditions. The surface area exposed to rain splash erosion was adjusted by placing rock fragments onto the surface of differently prepared soil in laboratory flumes (surface initially dry and hand cultivated or sealed due to the pre-wetting). The laboratory results showed that the eroded cumulative mass depended on the cumulative runoff, and that soil erosion was proportional to the soil surface area exposed to raindrops, in situations where an initially dry, hand cultivated and smoothed soil surface were ensured. The results showed that this relationship was controlled to a smaller extent by the soil’s initial moisture content, bulk density and soil surface characteristics. More in detail, it was observed that sediment concentrations during the first part of the erosion event were more sensitive to the initial state of the soil surface, whereas at steady state it ...
This is an abstract of a conference paper. It is published by Copenicus Gmbh under the Creative C... more This is an abstract of a conference paper. It is published by Copenicus Gmbh under the Creative Commons Attribution 3.0 Unported Licence (CC BY). Full details of this licence are available at: http://creativecommons.org/licenses/by/3.0
The ability of a large-scale Landscape Evolution Model (LEM) to simulate the soil surface morphol... more The ability of a large-scale Landscape Evolution Model (LEM) to simulate the soil surface morphological evolution as observed in a laboratory flume (1-m × 2-m surface area) was investigated. The soil surface was initially smooth, and was subjected to heterogeneous rainfall in an experiment designed to avoid rill formation. Low-cohesive fine sand was placed in the flume while the slope and relief height were 5 % and 20 cm, respectively. Non-uniform rainfall with an average intensity of 85 mm h -1 and a standard deviation of 26 % was applied to the sediment surface for 16 h. We hypothesized that the complex overland water flow can be represented by a drainage discharge network, which was calculated via the micro-morphology and the rainfall distribution. Measurements included high resolution Digital Elevation Models that were captured at intervals during the experiment. The calibrated LEM captured the migration of the main flow path from the low precipitation area into the high precipi...
... A Simple Illustration of a Conceptual Soil Erosion Model. ... This study's objectives ar... more ... A Simple Illustration of a Conceptual Soil Erosion Model. ... This study's objectives are to experimentally address some of the model's fundamental aspects not addressed by earlier experiments and, perhaps more importantly, to present the conceptual model and associated ...
Water Resources Research, 2016
A detailed laboratory study was conducted to examine the effects of particle size on hysteretic s... more A detailed laboratory study was conducted to examine the effects of particle size on hysteretic sediment transport under time-varying rainfall. A rainfall pattern composed of seven sequential stepwise varying rainfall intensities (30, 37.5, 45, 60, 45, 37.5 and 30 mm h−1), each of 20-mins duration, was applied to a 5-m × 2-m soil erosion flume. The soil in the flume was initially dried, ploughed to a depth of 20 cm and had a mechanically smoothed surface. Flow rates and sediment concentration data for seven particle size classes ( 1000 µm) were measured in the flume effluent. Clockwise hysteresis loops in the sediment concentration versus discharge curves were measured for the total eroded soil and the finer particle sizes ( 1000 µm). Overall, it is found that hysteresis varies amongst particle sizes and that the predictions of the HR model are consistent with hysteretic behavior of different sediment size classes. This article is protected by copyright. All rights reserved.