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Tammo S Steenhuis - One of the best experts on this subject based on the ideXlab platform.

  • revisiting storm runoff processes in the upper blue nile basin the debre mawi Watershed
    Catena, 2016
    Co-Authors: Seifu A Tilahun, Tammo S Steenhuis, Essayas K Ayana, Christian D Guzman, Dessalegn C Dagnew, Assefa D Zegeye, Tigist Y Tebebu, Birru Yitaferu
    Abstract:

    Abstract There is a scientific knowledge gap in locating runoff producing areas and their spatial variation in the landscape of the Ethiopian highlands and the upper Blue Nile basin. Identification of these spatial variations and runoff generation mechanisms is needed for optimum implementation of conservation measures. In many cases poor performance of soil and Water conservation practices for erosion control can be traced back to non-optimum placement. A 95 ha Watershed in the headWaters of the Blue Nile basin was used to investigate the runoff processes using the 2010 and 2011 monsoon, precipitation and runoff measurements made at sub-Watersheds and Watershed outlets. Perched Water Table heights and infiltration rates were also recorded. With the median infiltration rate exceeded by the rainfall intensity only 3% of the time the dominant runoff generation mechanism is found to be a saturation excess runoff process. Using the saturation excess interpretation of the Natural Resources Conservation Service Curve Number method, the seven day cumulative runoff fits better to the input as 7-day cumulative effective rainfall amount than to the rainfall intensity. In a monsoon climate where the Watershed is dry at the onset of the rainfall, the saturated areas and the runoff coefficients varied in the landscape (upslope locations vs downslope locations) as the rainy season progresses and available Water storage adjusts.

  • re conceptualizing the soil and Water assessment tool swat model to predict runoff from variable source areas
    Journal of Hydrology, 2008
    Co-Authors: Zachary M Easton, Daniel R Fuka, Todd M Walter, Dillon M Cowan, Elliot M Schneiderman, Tammo S Steenhuis
    Abstract:

    Many Water quality models use some form of the Natural Resources Conservation Services (formerly Soil Conservation Service) curve number (CN) equation to predict storm runoff in ways that implicitly assume an infiltration-excess response to rainfall. Because of this, these models may fail to predict variable source areas (VSAs) correctly, i.e. where runoff is typically generated in rural, humid regions. In this study, the Soil and Water Assessment Tool (SWAT) model was re-conceptualized to distribute overland flow in ways consistent with VSA hydrology by modifying how the CN and available Water content were defined; the new modeling approach is called SWAT-VSA. Both SWAT and SWAT-VSA were applied to a sub-Watershed in the Cannonsville basin in upstate New York to compare model predictions of integrated and distributed responses, including surface runoff, shallowly Perched Water Table depth, and stream phosphorus loads against direct measures. Event runoff was predicted similarly well for SWAT-VSA and SWAT. However, the distribution of shallowly Perched Water Table depth was predicted better by SWAT-VSA and it is this shallow groundWater that governs VSAs. Event based dissolved phosphorus export from the Watershed was also predicted better by SWAT-VSA, presumably because the distribution of runoff source areas was better predicted particularly from areas where manure was applied. This has important consequences for using models to evaluate and guide Watershed management because correctly predicting where runoff is generated is critical to locating best management practices to control non-point source pollution.

Tian Huat Low - One of the best experts on this subject based on the ideXlab platform.

  • Water infiltration characteristics of unsaturated soil slope and its effect on suction and stability
    Geotechnical and Geological Engineering, 2006
    Co-Authors: Bujang B K Huat, Faisal Haji Ali, Tian Huat Low
    Abstract:

    Rainfall has been considered the cause of the majority of slope failures and landslides that happened in regions experiencing high seasonal rainfalls. The mechanism of the failures was mainly due to the lost of matric suction of soils by rainWater. This paper presents the results of a laboratory model study on the effect of slope angle and surface cover on Water infiltration into soil and soil matric suction. A field infiltration test is carried out for comparison. A parametric study is also done to examine the effect of permeability ratio, development of Perched Water Table and rainfall intensity on the factor of safety against instability of a soil slope. Results of the model study show that different surface covers on slopes have an effect on the Water infiltration. Generally the covered surface (grass or geosynthetic net) has a lower infiltration rate compared with the bare (no cover) surface. On the effect of slope angle, it was observed that Water infiltration decrease with increase in the slope steepness. With regards to the movement of the wetting front, it appears that Water infiltration is more at the toe compared with the top of the model slope. Based on the parametric study, it is found factor of safety of the slope against instability drops for slope with higher ratio of permeability for the permeable and impermeable stratum. As the Perched Water Table is formed, the factor of safety decreased. The rainfall intensity also has a marked effect on the slope factor of safety. The higher the intensity of the rainfall, the higher is the infiltration rate into the soil, hence the lower is the factor of safety against slope instability.

S. Kar - One of the best experts on this subject based on the ideXlab platform.

  • Field Investigation of Water Movement and Nitrate Transport under Perched Water Table Conditions
    Biosystems Engineering, 2005
    Co-Authors: Kaushal K. Garg, Madan K. Jha, S. Kar
    Abstract:

    Increasing amounts of potentially hazardous chemicals such as nitrate (NO3−) arising from various agricultural operations are polluting soil and Water ecosystems worldwide. In the present study, the perching process and the simultaneous movement of Water and nitrate through lateritic soils under Perched Water Table conditions were investigated through two field experiments. The piezometric head and soil matric suction at five depths as well as the Perched Water Table fluctuations in nine vadose zone wells were monitored daily. Also, a 20 mm pulse of calcium nitrate was displaced in two experimental plots (called ‘plot I’ and ‘plot II’) by maintaining a constant depth of Water throughout the leaching period, and the leaching of nitrate was monitored at six soil depths and in all the observation wells at suiTable time intervals. The results of saturated hydraulic conductivity and bulk density at different depths in plot II suggested that the soil profile is heterogeneous. The analysis of hydraulic head and soil matric suction data revealed that the top 1·25 m of the soil profile responds rapidly to rainfall in both the plots, with plot I more permeable than plot II. Relatively long perching conditions at 1·71 m depth in both the plots indicated the presence of a more effective Water-resisting layer at this depth. The maximum nitrate concentration in soil Water was found after 8–12 h of leaching at shallower depths (up to 0·33 m) and after 12–18 h at greater depths. The enhanced rate of nitrate leaching in both the plots indicated the presence of macropores in the soil profile. Lateral flow due to perching conditions was also found to considerably affect the contamination process in lateritic soils. Furthermore, the dispersion coefficients of nitrate based on the breakthrough curves were found to range between 0·004 and 1·67 m2/day, suggesting heterogeneity in the soil profile. Finally, it is concluded that the relatively shallow aquifers of the lateritic region are vulnerable to nitrate contamination due to the current practice of nitrogenous fertiliser application in agricultural fields. Long-term and large-scale field studies under actual field conditions, together with simulation modeling, are recommended to generalise the flow and transport behaviour in lateritic soils.

  • Dynamics of Water flow and fertilizer solute leaching in lateritic soils of Kharagpur region, India
    Agricultural Water Management, 2003
    Co-Authors: S Behera, Madan K. Jha, S. Kar
    Abstract:

    Abstract In the lateritic tract of West Bengal, India, Perched Water Table conditions exist in the soil profile during the rainy season. Consequently, the agro-chemicals present in the vadose zone are convected downwards by the declining Perched Water Table after the cessation of the rainy season, and thereby may pollute the freshWater aquifer. A field experiment was carried out to evaluate the Water flow and fertilizer solute transport through the vadose zone in presence of shallow Perched Water Table and to assess the risk of groundWater pollution due to the leaching of fertilizer solutes. An experimental plot was developed for this study and the hydraulic head, matric suction and Perched Water Table were monitored daily at different soil depths. In order to explore the dynamics of the NO3− and K+ leaching, KNO3 was applied in the slug form and it was displaced by applying a constant depth of Water in the experimental plot. Leachates from the soil-Water samplers, and the Water samples from the nine observation wells were collected initially at short intervals and thereafter at relatively long intervals and were subject to chemical analysis. The analysis of the hydraulic head and the total Water potential data at different depths suggested the presence of a relatively impermeable layer at about 1 m depth. The Water flux through four soil layers was estimated ranging between 0.05 and 1.62 cm per day, with significantly high values in the upper layers compared to the lower layers. The accelerated transport of NO3− and K+ in the experimental plot just 1 day after the initiation of miscible displacement, indicated the presence of macropores in soil profile and their role in accentuating the groundWater contamination by fertilizer leaching. However, the mobility of K+ was found to be lower than that of NO3−. The present study also revealed that a substantial amount of NO3− was apparently convected from the upper soil profile and added to the lower soil profile during the recession of Perched Water Table. Finally, it is concluded that the regional groundWater is under a serious threat of NO3− contamination. Future, long-term studies on a macro-scale are recommended to develop strategies for controlling or avoiding NO3− contamination in the Kharagpur region.

Francesco Colleselli - One of the best experts on this subject based on the ideXlab platform.

  • Modelling of an accidentally triggered shallow landslide in Northern Italy
    Landslides, 2019
    Co-Authors: Alex Sanzeni, Marco Peli, Stefano Barontini, Francesco Colleselli
    Abstract:

    The paper presents a case study of a landslide event, accidentally triggered by an unexpected and extraordinary infiltration in an otherwise sTable slope. The work aims at modelling the slope failure mechanism with a simplified two-dimensional framework based on the formation of a Perched Water Table. The landslide occurred in Val Venosta/Vinschgau Valley, in Northern Italy, in April 2010 and produced catastrophic consequences. It took place on a hillside with average slope angle 36° and affected an area of about 200 m2; the slip surface was located approximately 1.0 m below the slope profile, in the uppermost layers of a predominantly coarse, well-graded soil. A series of numerical simulations were performed to back-analyse the event, using a commercial computer program. The artificial Water infiltration and Water content evolution were modelled with a two-dimensional finite element model (FE) of the unsaturated/saturated domain with appropriate infiltration boundary conditions. The slope stability analyses were conducted with a classic limit equilibrium method (LE) and were performed at different time instants during the infiltration process. The soil-Water retention curves and conductivity functions were defined according to the van Genuchten-Mualem model. The combined FE and LE simulations showed the gradual formation of a Perched Water Table, whose associated localized pore pressure distribution resulted in the loss of the suction stabilizing effect and thus in the reduction of the safety factor. Although supported by basic soil mechanical and hydraulic characterization, the numerical simulations allowed to perform a back-analysis which effectively captured the timing of the event and the location and depth of the slip surface along the slope.

  • Back-analysis of an artificially triggered landslide: A case study in Northern Italy
    Advancing Culture of Living with Landslides, 2017
    Co-Authors: Alex Sanzeni, Marco Peli, Stefano Barontini, Tiziano Cancelli, Francesco Colleselli
    Abstract:

    Open image in new window The paper presents a case study of a landslide event, artificially triggered by an exceptional infiltration in an otherwise sTable slope. The work aims at investigating the slope failure mechanism within a simplified two-dimensional conceptual framework based on the formation of a Perched Water Table. The landslide occurred in Northern Italy in April 2010, on a hillside with average slope angle 36°–37°; the event affected an area of about 200 m2, the slip surface was located approximately 1 m below the slope profile, in the uppermost layers of a predominantly coarse, well graded soil. A series of numerical simulations were performed to back-analyze the event, using a commercial computer program. The artificial Water infiltration and Water content evolution were simulated with a two-dimensional finite element (FE) model of the unsaturated-saturated domain with appropriate infiltration boundary conditions. The slope stability analyses were conducted with classic limit equilibrium (LE) methods and were performed at different time instants during the infiltration process. The soil-Water retention curves and conductivity functions were defined according to the van Genuchten-Mualem model, with parameters estimated by means of the software Rosetta (United States Department of Agriculture). The combined FE and LE simulations showed the gradual formation of a Perched Water Table, whose associated localized pore pressure distribution results in the loss of the suction stabilizing effect and thus in the reduction of the safety factor. Although supported by basic soil mechanical and hydraulic characterization, the numerical simulations allowed to perform a back-analysis which effectively captured the timing of the event, the location and depth of the slip surface along the slope.

Tony Smith - One of the best experts on this subject based on the ideXlab platform.

  • Modelling Recharge from Irrigation Developments with a Perched Water Table and Deep Unsaturated Zone
    Water, 2020
    Co-Authors: Glen R. Walker, Dougal Currie, Tony Smith
    Abstract:

    Modelling of recharge under irrigation zones for input to groundWater modelling is important for assessment and management of environmental risks. Deep vadose zones, when coupled with Perched Water Tables, affect the timing and magnitude of recharge. Despite the temporal and spatial complexities of irrigation areas; recharge in response to new developments can be modelled semi-analytically, with most outputs comparing well with numerical models. For parameter ranges relevant to the western Murray Basin in southern Australia, perching can reduce the magnitude of recharge relative to irrigation accessions and will cause significant time lags for changes to move through vadose zone. Recharge in the vicinity of existing developments was found to be similar to that far from existing developments. This allows superposition to be implemented spatially for new developments, thus simplifying estimation of recharge. Simplification is further aided by the use of exponential approximants for recharge responses from individual developments.