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Peter Troch - One of the best experts on this subject based on the ideXlab platform.
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Coupling machine learning with mechanistic models to study runoff production and river flow at the Hillslope scale
2016Co-Authors: Jean Marçais, Hoshin Vijai Gupta, Jean-raynald De Dreuzy, Peter TrochAbstract:Geomorphological structure and geological heterogeneity of Hillslopes are major controls on runoff responses. The diversity of Hillslopes (morphological shapes and geological structures) on one hand, and the highly non linear runoff mechanism response on the other hand, make it difficult to transpose what has been learnt at one specific Hillslope to another. Therefore, making reliable predictions on runoff appearance or river flow for a given Hillslope is a challenge. Applying a classic model calibration (based on inverse problems technique) requires doing it for each specific Hillslope and having some data available for calibration. When applied to thousands of cases it cannot always be promoted. Here we propose a novel modeling framework based on coupling process based models with data based approach. First we develop a mechanistic model, based on Hillslope storage Boussinesq equations (Troch et al. 2003), able to model non linear runoff responses to rainfall at the Hillslope scale. Second we set up a model database, representing thousands of non calibrated simulations. These simulations investigate different Hillslope shapes (real ones obtained by analyzing 5m digital elevation model of Brittany and synthetic ones), different Hillslope geological structures (i.e. different parametrizations) and different hydrologic forcing terms (i.e. different infiltration chronicles). Then, we use this model library to train a machine learning model on this physically based database. Machine learning model performance is then assessed by a classic validating phase (testing it on new Hillslopes and comparing machine learning with mechanistic outputs). Finally we use this machine learning model to learn what are the Hillslope properties controlling runoffs. This methodology will be further tested combining synthetic datasets with real ones.
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Hillslope hydrology under glass confronting fundamental questions of soil water biota co evolution at biosphere 2
Hydrology and Earth System Sciences, 2009Co-Authors: Luisa Hopp, C J Harman, Sharon L E Desilets, Chris B Graham, Jeffrey J Mcdonnell, Peter TrochAbstract:Abstract. Recent studies have called for a new unifying hydrological theory at the Hillslope and watershed scale, emphasizing the importance of coupled process understanding of the interactions between hydrology, ecology, pedology, geochemistry and geomorphology. The Biosphere 2 Hillslope Experiment is aimed at tackling this challenge and exploring how climate, soil and vegetation interact and drive the evolution of the hydrologic Hillslope behavior. A set of three large-scale Hillslopes (18 m by 33 m each) will be built in the climate-controlled experimental biome of the Biosphere 2 facility near Tucson, Arizona, USA. By minimizing the initial physical complexity of these Hillslopes, the spontaneous formation of flow pathways, soil spatial heterogeneity, surface morphology and vegetation patterns can be observed over time. This paper documents the hydrologic design process for the Biosphere 2 Hillslope Experiment, which was based on design principles agreed upon among the Biosphere 2 science community. Main design principles were that the Hillslopes should promote spatiotemporal variability of hydrological states and fluxes, facilitate transient lateral subsurface flow without inducing overland flow and be capable of supporting vegetation. Hydrologic modeling was used to identify a Hillslope configuration (geometry, soil texture, soil depth) that meets the design objectives. The recommended design for the Hillslopes consists of a zero-order basin shape with a 10 degree overall slope, a uniform soil depth of 1 m and a loamy sand soil texture. The sensitivity of the hydrologic response of this design to different semi-arid climate scenarios was subsequently tested. Our modeling showed that the timing of rainfall in relation to the timing of radiation input controls the spatiotemporal variability of moisture within the Hillslope and the generation of lateral subsurface flow. The Biosphere 2 Hillslope Experiment will provide an excellent opportunity to test hypotheses, observe emergent patterns and advance the understanding of interactions.
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A steady-state analytical slope stability model for complex Hillslopes
Hydrological Processes, 2008Co-Authors: Ali Talebi, Peter Troch, Remko UijlenhoetAbstract:This paper presents a steady-state analytical Hillslope stability model to study the role of topography on rain-induced shallow landslides. We combine a bivariate continuous function of the topographic surface, a steady-state hydrological model of Hillslope saturated storage, and the infinite slope stability assumption to investigate the interplay between terrain characteristics, saturated storage within Hillslopes and soil mechanics. We demonstrate the model by examining the stability of nine characteristic Hillslope types (landform elements) with three different profile curvatures (concave, straight and convex) and three different plan shapes (convergent, parallel and divergent). For each Hillslope type, the steady-state saturated storage corresponding to given recharge rates is computed for three different average bedrock slope angles. On the basis of the infinite slope stability method, the factor of safety (FS) along the Hillslopes is determined. Our results demonstrate that in the steep slopes, the least stable situation occurs in Hillslopes with convergent plan shapes and concave length profiles, while the convex ones are more stable. In addition to testing our method for nine characteristic Hillslope types, a general relationship between plan shape and profile curvature of landform elements and the factor of safety is derived for a pre-defined Hillslope length scale. Our results show that slope stability increases when profile curvature changes from concave to convex. In terms of plan shapes, changing from convergent to divergent, slope stability increases for all length profiles. However, we find that the effect of plan shape is more pronounced for convex length profiles. Overall, we demonstrate that, in addition to bedrock slope, Hillslope shape as represented by plan shape and profile curvature is an important control on Hillslope stability.
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Hillslope subsurface flow similarity: Real‐world tests of the Hillslope Péclet number
Water Resources Research, 2007Co-Authors: Steve W Lyon, Peter TrochAbstract:[1] Similarity analysis offers the ability to model hydrological response using quantifiable landscape descriptors. It is possible to develop similarity indices based on analytical solutions to the governing dynamic equations (Brutsaert, 2005). Berne et al. (2005) provide derivation of such a similarity index (the Hillslope Peclet number) of subsurface flow and saturation for Hillslopes with exponential width functions. They showed that the Hillslope Peclet number depends only on geometric properties of the Hillslope. Their work was validated using laboratory experiments conducted on constructed Hillslopes with homogeneous soil structure and varying bedrock slope angle. This study applies the similarity analysis of Berne et al. (2005) to two data sets: (1) the trench Hillslope study at the Maimai research catchment conducted by Woods and Rowe (1996) and (2) the isolated Hillslope study near Troy, Idaho, United States, conducted by Brooks et al. (2004). The Maimai trench study was selected because it provides subsurface flow data from Hillslopes with different planform geometries. The Troy Hillslope study was selected because the experimental results of Brooks et al. (2004) provide an estimate of hydraulic conductivity consistent with the support scale of the Hillslope. We estimated the Hillslope Peclet number of the Hillslopes on the basis of elevation data and reported values of average soil depth. This Hillslope Peclet number quantifies the geomorphological control on how water moves through these Hillslopes and creates a basis for comparison independent of hydraulic properties. We then estimated the first and second moments of the characteristic subsurface response function of each Hillslope on the basis of subsurface flow data. To compare the empirical and theoretical moments, the hydraulic properties (saturated hydraulic conductivity and drainable porosity) of the Hillslopes were related using a base flow recession analysis. Then we were able to derive the dimensionless moments of the Hillslopes' observed characteristic response function using hydraulic conductivities reported in the literature. The agreement between the observed and theoretical moments shows the promise of implementing the Hillslope Peclet number as a similarity parameter to describe first-order hydrological response in humid environments.
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Hillslope subsurface flow similarity real world tests of the Hillslope peclet number
Water Resources Research, 2007Co-Authors: Steve W Lyon, Peter Troch, Peter TrochAbstract:[1] Similarity analysis offers the ability to model hydrological response using quantifiable landscape descriptors. It is possible to develop similarity indices based on analytical solutions to the governing dynamic equations (Brutsaert, 2005). Berne et al. (2005) provide derivation of such a similarity index (the Hillslope Peclet number) of subsurface flow and saturation for Hillslopes with exponential width functions. They showed that the Hillslope Peclet number depends only on geometric properties of the Hillslope. Their work was validated using laboratory experiments conducted on constructed Hillslopes with homogeneous soil structure and varying bedrock slope angle. This study applies the similarity analysis of Berne et al. (2005) to two data sets: (1) the trench Hillslope study at the Maimai research catchment conducted by Woods and Rowe (1996) and (2) the isolated Hillslope study near Troy, Idaho, United States, conducted by Brooks et al. (2004). The Maimai trench study was selected because it provides subsurface flow data from Hillslopes with different planform geometries. The Troy Hillslope study was selected because the experimental results of Brooks et al. (2004) provide an estimate of hydraulic conductivity consistent with the support scale of the Hillslope. We estimated the Hillslope Peclet number of the Hillslopes on the basis of elevation data and reported values of average soil depth. This Hillslope Peclet number quantifies the geomorphological control on how water moves through these Hillslopes and creates a basis for comparison independent of hydraulic properties. We then estimated the first and second moments of the characteristic subsurface response function of each Hillslope on the basis of subsurface flow data. To compare the empirical and theoretical moments, the hydraulic properties (saturated hydraulic conductivity and drainable porosity) of the Hillslopes were related using a base flow recession analysis. Then we were able to derive the dimensionless moments of the Hillslopes' observed characteristic response function using hydraulic conductivities reported in the literature. The agreement between the observed and theoretical moments shows the promise of implementing the Hillslope Peclet number as a similarity parameter to describe first-order hydrological response in humid environments.
Jeffrey J Mcdonnell - One of the best experts on this subject based on the ideXlab platform.
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Hydrological connectivity of Hillslopes and streams: Characteristic time scales and nonlinearities
Water Resources Research, 2010Co-Authors: Kevin J. Mcguire, Jeffrey J McdonnellAbstract:[1] Subsurface flow from Hillslopes is widely recognized as an important contributor to streamflow generation; however, processes that control how and when Hillslopes connect to streams remain unclear. We investigated stream and Hillslope runoff dynamics through a wet-up period in watershed 10 of the H. J. Andrews Experimental Forest in the western Cascades of Oregon where the riparian zone has been removed by debris flows. We examined the controls on Hillslope-stream connectivity on the basis of observations of hydrometric, stable isotope, and applied tracer responses and computed transit times for multiple runoff components for a series of storms during the wet-up phase of the 2002–2003 winter rainy season. Hillslope discharge was distinctly threshold-like with a near linear response and average quick flow ratio of 0.58 when antecedent rainfall was greater than 20 mm. Hillslope and stream stormflow varied temporally and showed strong hysteretic relationships. Event water mean transit times (8–34 h) and rapid breakthrough from applied Hillslope tracer additions demonstrated that subsurface contributing areas extend far upslope during events. Despite rapid Hillslope transport processes during events, soil water and runoff mean transit times during nonstorm conditions were greater than the time scale of storm events. Soil water mean transit times ranged between 10 and 25 days. Hillslope seepage and catchment base flow mean transit times were between 1 and 2 years. We describe a conceptual model that captures variable physical flow pathways, their synchronicity, threshold activation, hysteresis, and transit times through changing antecedent wetness conditions that illustrate the different stages of Hillslope and stream connectivity.
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Hillslope hydrology under glass confronting fundamental questions of soil water biota co evolution at biosphere 2
Hydrology and Earth System Sciences, 2009Co-Authors: Luisa Hopp, C J Harman, Sharon L E Desilets, Chris B Graham, Jeffrey J Mcdonnell, Peter TrochAbstract:Abstract. Recent studies have called for a new unifying hydrological theory at the Hillslope and watershed scale, emphasizing the importance of coupled process understanding of the interactions between hydrology, ecology, pedology, geochemistry and geomorphology. The Biosphere 2 Hillslope Experiment is aimed at tackling this challenge and exploring how climate, soil and vegetation interact and drive the evolution of the hydrologic Hillslope behavior. A set of three large-scale Hillslopes (18 m by 33 m each) will be built in the climate-controlled experimental biome of the Biosphere 2 facility near Tucson, Arizona, USA. By minimizing the initial physical complexity of these Hillslopes, the spontaneous formation of flow pathways, soil spatial heterogeneity, surface morphology and vegetation patterns can be observed over time. This paper documents the hydrologic design process for the Biosphere 2 Hillslope Experiment, which was based on design principles agreed upon among the Biosphere 2 science community. Main design principles were that the Hillslopes should promote spatiotemporal variability of hydrological states and fluxes, facilitate transient lateral subsurface flow without inducing overland flow and be capable of supporting vegetation. Hydrologic modeling was used to identify a Hillslope configuration (geometry, soil texture, soil depth) that meets the design objectives. The recommended design for the Hillslopes consists of a zero-order basin shape with a 10 degree overall slope, a uniform soil depth of 1 m and a loamy sand soil texture. The sensitivity of the hydrologic response of this design to different semi-arid climate scenarios was subsequently tested. Our modeling showed that the timing of rainfall in relation to the timing of radiation input controls the spatiotemporal variability of moisture within the Hillslope and the generation of lateral subsurface flow. The Biosphere 2 Hillslope Experiment will provide an excellent opportunity to test hypotheses, observe emergent patterns and advance the understanding of interactions.
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testing nutrient flushing hypotheses at the Hillslope scale a virtual experiment approach
Journal of Hydrology, 2006Co-Authors: Markus Weiler, Jeffrey J McdonnellAbstract:The delivery mechanisms of labile nutrients (e.g. NO3, DON and DOC) to streams are poorly understood. Recent work has quantified the relationship between storm DOC dynamics and the connectedness of catchment units and between pre-storm wetness and transient groundwater NO3 flushing potential. While several studies have shown N and C flushing during storm events as the important mechanism in the export of DOC and DON in small catchments, the actual mechanisms at the Hillslope scale have remained equivocal. The difficulty in isolating cause and effect in field studies is made difficult due to the spatial variability of soil properties, the limited ability to detect flow pathways within the soil, and other unknowns. Some Hillslopes show preferential flow behavior that may allow transmission of Hillslope runoff and labile nutrients with little matrix interaction; others do not. Thus, field studies are only partially useful in equating C and N sources with water flow and transport. This paper presents a new approach to the study of hydrological controls on labile nutrient flushing at the Hillslope scale. We present virtual experiments that focus on quantifying the first-order controls on flow pathways and nutrient transport in Hillslopes. We define virtual experiments as numerical experiments with a model driven by collective field intelligence. We present a new distributed model that describes the lateral saturated and vertical unsaturated water flow from hypothetical finite nutrient sources in the upper soil horizons. We describe how depth distributions of transmissivity and drainable porosity, soil depth variability, as well as mass exchange between the saturated and unsaturated zone influence the mobilization, flushing and release of labile nutrients at the Hillslope scale. We argue that this virtual experiment approach may provide a well-founded basis for defining the first-order controls and linkages between hydrology and biogeochemistry at the Hillslope scale and perhaps form a basis for predicting flushing and transport of labile nutrients from upland to riparian zones.
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The role of lateral pipe flow in Hillslope runoff response: an intercomparison of non-linear Hillslope response
Journal of Hydrology, 2005Co-Authors: Taro Uchida, Ilja Tromp-van Meerveld, Jeffrey J McdonnellAbstract:The importance of lateral pipe flow on runoff generation in wet steep Hillslopes has been described in many case studies from around the world. However, most Hillslope studies are done in isolation and usually focus on the idiosyncrasies of individual Hillslope characteristics and pipe flow response at a single site. Consequently, the first order controls on pipe flow responses remain poorly understood. We present a new intercomparison of pipe flow response to storm rainfall at four well instrumented sites: Panola (Georgia, USA), Toinotani (Kyoto, Japan), Jozankei (Hokkaido, Japan) and Hakyuchi (Tokyo, Japan). Our objective was to minimize the complexities of lateral pipe flow on Hillslopes by looking for commonality across different Hillslope types. Despite the large differences between the study sites in topography, climate, soil type and soil matrix hydraulic conductivity, we found several common pipe flow responses to storm rainfall: (1) the relationship between total rainfall amount and total pipe flow volume was highly non-linear at each site, (2) initiation of measurable pipe flow was threshold-dependent, controlled by the total rainfall amount and the pre-storm wetness, (3) once significant pipe flow response occurred, the maximum pipe flow rate was sensitive to the measured rainfall intensity, and (4) the ratio of total pipe flow to total Hillslope discharge for each site was constant, regardless of total rainfall amount once the precipitation threshold for significant pipe flow response was reached. We used these results to develop a decision tree to determine the general conditions necessary for significant pipe flow to occur. The controls derived from our comparisons agree largely with the controls reported by the previous individual Hillslope pipe flow studies in the literature. The commonality of response between our four very different forested Hillslope settings indicates that site intercomparison may be effective for extracting common first order controls on complex Hillslope processes. We argue that a decision tree may be a useful organizational framework to summarize and organize comparative analyses and may provide a structure for defining the hierarchy of process controls necessary for model development.
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quantifying the relative contributions of riparian and Hillslope zones to catchment runoff
Water Resources Research, 2003Co-Authors: Brian L Mcglynn, Jeffrey J McdonnellAbstract:[1] The spatial and temporal sources of headwater catchment runoff are poorly understood. We quantified the contributions of Hillslopes and riparian zones to streamflow for two storm events in a highly responsive, steep, wet watershed located on the west coast of the South Island of New Zealand. We examined the spatial and temporal components of catchment storm flow using a simple continuity-based approach. We tested this with independent isotopic/solute mass balance hydrograph separation techniques. We monitored catchment runoff, internal hydrological response, isotopic, and solute dynamics at a trenched Hillslope, and at Hillslope and riparian positions in a 2.6-ha catchment. The gauged Hillslope was used to isolate and quantify (by difference) riparian and Hillslope zone contributions to the 2.6-ha headwater catchment. Utilizing flow-based approaches and a tracer-based mass balance mixing model, we found that Hillslope runoff comprised 2–16% of total catchment storm runoff during a small 27-mm event and 47–55% during a larger 70-mm event. However, less than 4% of the new water collected at the catchment outlet originated from the Hillslopes during each event. We found that in the 27-mm rain event, 84–97% of total storm runoff was generated in the riparian zone. In a larger 70-mm event, riparian water dominated total flow early in the event, although the Hillslope became the main contributor once Hillslope runoff was initiated. Despite the large amount of subsurface Hillslope runoff in total storm runoff during the second larger event, riparian and channel zones accounted for 96% of the new water measured at the catchment outlet. Riparian water dominated between events, throughout small runoff events, and during early portions of large events. While this sequencing of catchment position contributions to flow has been conceptualized for some time, this is the first study to quantify this timing, constrained by hydrometric, isotopic, and solute approaches.
J. J. Roering - One of the best experts on this subject based on the ideXlab platform.
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Landscape evolution experiments - Hillslope process control on drainage density
2016Co-Authors: J. J. Roering, K. E. Sweeney, C. EllisAbstract:These data are the raw and processed digital elevation models for the sandbox experiments detailed in "Experimental evidence for Hillslope control of landscape scale" by K.E. Sweeney, J.J. Roering, and C. Ellis, which was published in Science in July of 2015. Landscape evolution theory suggests that climate sets the scale of landscape dissection by modulating the competition between diffusive processes that sculpt convex Hillslopes and advective processes that carve concave valleys. However, the link between the relative dominance of Hillslope and valley transport processes and landscape scale is difficult to demonstrate in natural landscapes due to the episodic nature of erosion. Here we report results from laboratory experiments combining diffusive and advective processes in an eroding landscape. We demonstrate that rainsplash-driven disturbances in our experiments are a robust proxy for Hillslope transport, such that increasing Hillslope transport efficiency decreases drainage density. Our experimental results demonstrate how the coupling of climate-driven Hillslope- and valley-forming processes, such as bioturbation and runoff, dictates the scale of eroding landscapes.
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Experimental evidence for Hillslope control of landscape scale
Science, 2015Co-Authors: K. E. Sweeney, J. J. Roering, C. EllisAbstract:Landscape evolution theory suggests that climate sets the scale of landscape dissection by modulating the competition between diffusive processes that sculpt convex Hillslopes and advective processes that carve concave valleys. However, the link between the relative dominance of Hillslope and valley transport processes and landscape scale is difficult to demonstrate in natural landscapes due to the episodic nature of erosion. Here, we report results from laboratory experiments combining diffusive and advective processes in an eroding landscape. We demonstrate that rainsplash-driven disturbances in our experiments are a robust proxy for Hillslope transport, such that increasing Hillslope transport efficiency decreases drainage density. Our experimental results demonstrate how the coupling of climate-driven Hillslope- and valley-forming processes, such as bioturbation and runoff, dictates the scale of eroding landscapes.
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how well can Hillslope evolution models explain topography simulating soil transport and production with high resolution topographic data
Geological Society of America Bulletin, 2008Co-Authors: J. J. RoeringAbstract:The morphology of Hillslopes is a direct refl ection of tectonic forcing and climatic and biologic processes that drive soil production, mobilization, and transport. Soil transport on Hillslopes affects river incision by providing tools for channel abrasion and controls the distribution of sediment that infl uences aquatic habitat. Although numerous Hillslope transport relationships have been proposed over the past 60+ years, a comprehensive analysis of model predictions for a real landscape has not been performed. Here, we use high-resolution topographic data obtained via airborne laser swath mapping (ALSM) to simulate the long-term evolution of Oregon Coast Range Hillslopes and test three published transport models and a new model that accounts for nonlinear depth- and slopedependent transport. Analysis of one-dimensional, steady-state solutions for these four models suggests that plots of gradient-curvature may be diagnostic for distinguishing model predictions. To evaluate two-dimensional model predictions for our fi eld site, we assumed local steady-state erosion for a 72,000 m 2 sequence of Hillslopes and valleys. After calibrating each of the four models, we imposed constant base-level lowering for cells within the valley network, simulated 500,000 yr of soil production and transport, and determined which transport model best preserved morphologic patterns that describe the current landscape form. Models for which fl ux varies proportionally with Hillslope gradient generated broadly convex hilltops inconsistent with the sharp-crested, steep-sided slopes of our study site, whereas the two nonlinear slope-dependent models produced convex-planar slopes consistent with current Hillslope form. Our proposed nonlinear slope- and depth-dependent model accounts for how soil thickness controls the magnitude of biogenic disturbances that drive transport; this model best preserved the current landscape form, particularly the narrow, sharply convex hilltops characteristic of the Oregon Coast Range. According to our formulation, which provides an explicit linkage for relating the distribution of biota to Hillslope processes, the degree of hilltop convexity varies nonlinearly with the ratio of erosion rate to maximum soil production rate, highlighting the profound infl uence of soil depth on Hillslope evolution.
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Functional relationships between denudation and Hillslope form and relief
Earth and Planetary Science Letters, 2007Co-Authors: J. J. Roering, J. Taylor Perron, James W KirchnerAbstract:Abstract Functional relationships between landscape morphology and denudation rate allow for the estimation of sediment fluxes using readily available topographic information. Empirical studies of topography-erosion linkages typically employ data with diverse temporal and broad spatial scales, such that heterogeneity in properties and processes may cloud fundamental process-scale feedbacks between tectonics, climate, and landscape development. Here, we use a previously proposed nonlinear model for sediment transport on Hillslopes to formulate 1-D dimensionless functions for Hillslope morphology as well as a generalized expression relating steady-state Hillslope relief to erosion rate, Hillslope transport parameters, and Hillslope length. For study sites in the Oregon Coast Range and Gabilan Mesa, CA, model predictions of local relief and average Hillslope gradient compare well with values derived from high-resolution topographic data acquired via airborne laser altimetry. Our formulation yields a nondimensional number describing the extent to which the nonlinearity in our gradient-flux model affects slope morphology and landscape response to tectonic and climatic forcing. These results should be useful for inferring rates of Hillslope denudation and sediment flux from topography, or for coarse-scale landscape evolution simulations, in that first-order Hillslope properties can be calculated without explicit modeling of individual Hillslopes.
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Hillslope evolution by nonlinear slope dependent transport steady state morphology and equilibrium adjustment timescales
Journal of Geophysical Research, 2001Co-Authors: J. J. Roering, James W Kirchner, William E. DietrichAbstract:Soil-mantled Hillslopes are typically convex near the crest and become increasingly planar downslope, consistent with nonlinear, slope-dependent sediment transport models. In contrast to the widely used linear transport model (in which sediment flux is proportional to slope angle), nonlinear models imply that sediment flux should increase rapidly as Hillslope gradient approaches a critical value. Here we explore how nonlinear transport influences Hillslope evolution and introduce a dimensionless parameter Ψ L to express the relative importance of nonlinear transport. For steady state Hillslopes, with increasing Ψ L (i.e., as slope angles approach the threshold angle and the relative magnitude of nonlinear transport increases), the zone of Hillslope convexity becomes focused at the hilltop and side slopes become increasingly planar. On steep slopes, rapid increases in sediment flux near the critical gradient limit further steepening, such that Hillslope relief and slope angle are not sensitive indicators of erosion rate. Using a one-dimensional finite difference model, we quantify Hillslope response to changes in baselevel lowering and/or climate-related transport efficiency and use an exponential decay function to describe how rapidly sediment flux and erosion rate approach equilibrium. The exponential timescale for Hillslope adjustment decreases rapidly with increasing Ψ L . Our results demonstrate that the adjustment timescale for Hillslopes characteristic of the Oregon Coast Range and similar steep, soil-mantled landscapes is relatively rapid (≤ 50 kyr), less than one quarter of the timescale predicted by the linear transport model.
Dalla G Fontana - One of the best experts on this subject based on the ideXlab platform.
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soil moisture temporal stability at different depths on two alpine Hillslopes during wet and dry periods
Journal of Hydrology, 2013Co-Authors: Daniele Penna, Luca Brocca, Marco Borga, Dalla G FontanaAbstract:Summary This paper investigates the temporal stability of near-surface soil moisture at various depths at the Hillslope scale. Detailed soil water content data were acquired at 0–6 cm, 0–12 cm and 0–20 cm during three 30-day field campaigns in 2005, 2006 and 2007. Two small alpine Hillslopes with relatively homogeneous soil properties and vegetation cover but contrasting morphology were chosen to assess the persistence of spatial organization of soil moisture over time and along the soil profile, to identify the representative sampling locations and to evaluate the temporal stability during wet and dry states. Results show that both study Hillslopes exhibited a strong degree of time stability, as revealed by very high autocorrelation values persisting for several days. The ranking stability approach allowed the identification of sampling locations representative of the average Hillslope soil water content. These locations, one for each experimental site, proved to act as good indicators of soil moisture at other depths and even on the other Hillslope. The spatial structure of soil moisture fields was not affected by the occurrence of piezometric response and was well preserved at all depths during both wet and dry periods, with a slightly higher degree of temporal stability in dry conditions and for deeper layers. The remarkable persistence of soil moisture spatial patterns over time and along the soil profile on the study sites was mainly related to the macro- and micro-topographic properties of the two Hillslopes but the soil wetness conditions generally skewed towards the wet state and the negligible variability of climatic forcing due to the small study scale might have contributed significantly.
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the influence of soil moisture on threshold runoff generation processes in an alpine headwater catchment
Hydrology and Earth System Sciences, 2010Co-Authors: Daniele Penna, Marco Borga, H Trompvan J Meerveld, A Gobbi, Dalla G FontanaAbstract:This study investigates the role of soil moisture on the threshold runoff response in a small headwater catchment in the Italian Alps that is characterised by steep Hillslopes and a distinct riparian zone. This study focuses on: (i) the threshold soil moisture-runoff relationship and the influence of catchment topography on this relation; (ii) the temporal dynamics of soil moisture, streamflow and groundwater that characterize the catchment's response to rainfall during dry and wet periods; and (iii) the combined effect of antecedent wetness conditions and rainfall amount on Hillslope and riparian runoff. Our results highlight the strong control exerted by soil moisture on runoff in this catchment: a sharp threshold exists in the relationship between soil water content and runoff coefficient, streamflow, and Hillslope-averaged depth to water table. Low runoff ratios were likely related to the response of the riparian zone, which was almost always close to saturation. High runoff ratios occurred during wet antecedent conditions, when the soil moisture threshold was exceeded. In these cases, subsurface flow was activated on Hillslopes, which became a major contributor to runoff. Antecedent wetness conditions also controlled the catchment's response time: during dry periods, streamflow reacted and peaked prior to Hillslope soil moisture whereas during wet conditions the opposite occurred. This difference resulted in a hysteretic behaviour in the soil moisture-streamflow relationship. Finally, the influence of antecedent moisture conditions on runoff was also evident in the relation between cumulative rainfall and total stormflow. Small storms during dry conditions produced low stormflow amounts, likely mainly from overland flow from the near saturated riparian zone. Conversely, for rainfall events during wet conditions, higher stormflow values were observed and Hillslopes must have contributed to streamflow.
Yunqiang Wang - One of the best experts on this subject based on the ideXlab platform.
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Hillslope scale temporal stability of soil water storage in diverse soil layers
Journal of Hydrology, 2013Co-Authors: Xiaoxu Jia, Mingan Shao, Xiao Rong Wei, Yunqiang WangAbstract:Knowledge of the soil water storage (SWS) of soil profiles on the scale of a Hillslope is important for the optimal management of soil water and revegetation on sloping land in semi-arid areas. This study aimed to investigate the temporal stability of SWS profiles (0–1.0, 1.0–2.0, and 2.0–3.0 m) and to identify representative sites for reliably estimating the mean SWS on two adjacent Hillslopes of the Loess Plateau in China. We used two indices: the standard deviation of relative difference (SDRD) and the mean absolute bias error (MABE). We also endeavored to identify any correlations between temporal stability and soil, topography, or properties of the vegetation. The SWS of the soil layers was measured using neutron probes on 15 occasions at 59 locations arranged on two Hillslopes (31 and 28 locations for Hillslope A (HA) and Hillslope B (HB), respectively) from 2009 to 2011. The time-averaged mean SWS for the three layers differed significantly (P < 0.05) between HA and HB and was greatly affected by topography and vegetation. Temporal–spatial analyses showed that the temporal variation of SWS decreased with increasing soil depth, while the spatial variation increased on both Hillslopes. Comparisons of the values for SDRD and MABE and the number of time-stable locations with SDRD and MABE < 5% among various depths indicated that temporal stability increased with an increase in soil depth. The representative sites identified for each Hillslope (two on HA and one on HB) accurately estimated the mean SWS for the three soil layers (R2 ⩾ 0.95, P < 0.001). SWS on the scale of a Hillslope was strongly time stable, and the temporal–spatial patterns of SWS were highly dependent on sampling depth. The temporal stability of SWS patterns was controlled by soil texture, organic carbon content, elevation, and properties of the vegetation in the study area, which was characterised by diverse or complex terrains and plant cover. Such effects, however, might vary across Hillslopes due to different conditions of wetness and patterns of land use. This study provides useful information on the profiles of mean SWS on the scale of a Hillslope, which is necessary for improving the management of soil water on sloping land on the Loess Plateau.
