Subsurface Water Dynamics Research Articles

Characterization of a Contaminated Site Using Hydro-Geophysical Methods: From Large-Scale ERT Surface Investigations to Detailed ERT and GPR Cross-Hole Monitoring

This work presents the results of an advanced geophysical characterization of a contaminated site, where a correct understanding of the dynamics in the unsaturated zone is fundamental to evaluate the effective management of the remediation strategies. Large-scale surface electrical resistivity tomography (ERT) was used to perform a preliminary assessment of the structure in a thick unsaturated zone and to detect the presence of a thin layer of clay supporting an overlying thin perched aquifer. Discontinuities in this clay layer have an enormous impact on the infiltration processes of both water and solutes, including contaminants. In the case here presented, the technical strategy is to interrupt the continuity of the clay layer upstream of the investigated site in order to prevent most of the subsurface water flow from reaching the contaminated area. Therefore, a deep trench was dug upstream of the site and, in order to evaluate the effectiveness of this approach in facilitating water infiltration into the underlying aquifer, a forced infiltration experiment was carried out and monitored using ERT and ground-penetrating radar (GPR) measurements in a cross-hole time-lapse configuration. The results of the forced infiltration experiment are presented here, with a particular emphasis on the contribution of hydro-geophysical methods to the general understanding of the subsurface water dynamics at this complex site.

Precise estimation of subsurface moisture content based on laboratory measurement and 3D GPR field survey

The Sponge City construction currently undergoing in China aims to enhance the moisture capacity of urban pedosphere, and subsurface moisture content (SMC) is proposed to evaluate the effect of improvement. Different ground-penetrating radar (GPR) techniques have been used in previous studies to estimate moisture content, however, very few has assessed the potential of combing 2D common offset (CO) GPR with 3D multichannel GPR to resolve SMC estimates at the complex filed scale. In this paper, modified velocity analysis of in-situ 3D GPR common-midpoint (CMP) datasets was used together with 2D GPR laboratory calibration procedure to investigate spatial moisture variation and the impact of surface pavement and soil heterogeneity on subsurface water dynamics. Precise and reliable moisture information under two field sites (i.e., sponge pavement site and asphalt pavement site) was obtained, which further allowed us to quantitative characterize SMC distribution and its associated dynamics within the shallow vadose zone, and most importantly to investigate the coupling mechanism between subsurface water fluctuations with surface pavement conditions and subsoil moisture capacity in urban near surface environment. Additionally, through contrastive analysis, the superior performance of novel sponge material to detain and transit rainwater was highlighted. Data and results presented in this research provide pioneer reference for Sponge City construction and other engineering applications.

Modified Model for Simulating Water Flow in Furrow Irrigation

Quantifying surface and subsurface water dynamics is essential to design and manage furrow irrigation systems. Many furrow irrigation models estimate infiltration using empirical functions without considering the variable ponding depth and the initial soil moisture. Other models, such as the detail coupled models, which describe subsurface flow with the 2D Richards equation, are complex and difficult to apply in practical use. In this paper, we propose a modified furrow irrigation model (MFIM) that couples the approximate furrow infiltration model with the zero-inertia model. The finite difference method and an iterative procedure were used to couple computations of surface flow and infiltration. The influence of time resolution on simulating results was also examined. Results showed that the simulated water advance of the MFIM agreed reasonably well with that of the detail coupled model. More accurate simulation results were obtained by using smaller time step size. The proposed model has shown high computational efficiency. The MFIM may be an effective alternative tool for furrow irrigation design and management.

Landscape Water Storage and Subsurface Correlation From Satellite Surface Soil Moisture and Precipitation Observations

AbstractSurface soil moisture measurements are typically correlated to some degree with changes in subsurface soil moisture. We calculate a hydrologic length scale, λ, which represents (1) the mean‐state estimator of total column water changes from surface observations, (2) an e‐folding length scale for subsurface soil moisture profile covariance fall‐off, and (3) the best second‐moment mass‐conserving surface layer thickness for a simple bucket model, defined by the data streams of satellite soil moisture and precipitation retrievals. Calculations are simple, based on three variables: the autocorrelation and variance of surface soil moisture and the variance of the net flux into the column (precipitation minus estimated losses), which can be estimated directly from the soil moisture and precipitation time series. We develop a method to calculate the lag‐one autocorrelation for irregularly observed time series and show global surface soil moisture autocorrelation. λ is driven in part by local hydroclimate conditions and is generally larger than the 50‐mm nominal radiometric length scale for the soil moisture retrievals, suggesting broad subsurface correlation due to moisture drainage. In all but the most arid regions, radiometric soil moisture retrievals provide more information about ecosystem‐relevant water fluxes than satellite radiometers can explicitly “see”; lower‐frequency radiometers are expected to provide still more statistical information about subsurface water dynamics.

A Simple Modelling Framework for Shallow Subsurface Water Storage and Flow

Water storage and flow in shallow subsurface drives runoff generation, vegetation water use and nutrient cycling. Modelling these processes under non-steady state conditions is challenging, particularly in regions like the subtropics that experience extreme wet and dry periods. At the catchment-scale, physically-based equations (e.g., Richards equation) are impractical due to their complexity, while conceptual models typically rely on steady state assumptions not found in daily hydrological dynamics. We addressed this by developing a simple modelling framework for shallow subsurface water dynamics based on physical relationships and a proxy parameter for the fluxes induced by non-unit hydraulic gradients. We demonstrate its applicability for six generic soil textures and for an Acrisol in subtropical China. Results showed that our new approach represents top soil daily fluxes and storage better than, and as fast as, standard conceptual approaches. Moreover, it was less complex and up to two orders of magnitude faster than simulating Richards equation, making it easy to include in existing hydrological models.

A coupled surface water storage and subsurface water dynamics model in SWAT for characterizing hydroperiod of geographically isolated wetlands

Wetlands play an important role in watershed hydrology and biogeochemistry. A geographically isolated wetland (GIW) module for Soil and Water Assessment Tool (SWAT) was developed to couple surface water storage and subsurface water dynamics to characterize hydroperiod. The new GIW module includes the following features: (1) a flexible geometric formula to characterize wetland surface water area, volume, and depth; (2) a revised algorithm to account for evaporation from both water and soil surfaces in wetlands; (3) application of the Richards equation to couple surface water storage and subsurface water dynamics; (4) use of Darcy's law with an effective hydraulic conductivity parameter to simulate groundwater discharge. We tested the GIW module using observed daily water level data from four wetlands at two sites (including restored and natural wetlands with and without a low-permeability soil layer) in the Delmarva Peninsula, USA. The results show that the wetland module reasonably reproduced observed water levels for both restored and natural wetlands with and without a low-permeability soil layer. The module was also able to reasonably simulate saturated and unsaturated portions of the soil corresponding to wet and dry periods. The ability of the GIW module to describe inundation conditions for wetlands holds promise to enhance the understanding and quantification of hydrological and biogeochemical roles of GIWs in a watershed context.

Three Two‐Dimensional Approaches for Simulating the Water Flow Dynamics in a Heterogeneous Tile‐Drained Agricultural Field in Denmark

Core Ideas Simulating water flow dynamics in a clayey subsurface drained agricultural field. Three two‐dimensional models incorporating preferential water flow were used. All models produced a reasonably good fit to the hydrograph features. Examine models' capabilities and weaknesses for simulating the drainage dynamics. Non‐equilibrium preferential flow has received increasing attention in modeling water flow dynamics across tile‐drained agricultural fields. The HYDRUS‐2D software package was used in this study to generate a hydrogeological model for simulating the water flow dynamics across hydro‐topographical gradients and drainage sequences at drainage subcatchment (western part of Norsminde catchment in Denmark). The selected study area is characterized by spatial variability in the geological, stratified heterogeneity. Three two‐dimensional models incorporating preferential water flow were used to examine the ability of each approach to predict the drainage dynamics and water balance in a clayey subsurface drained agricultural field: (i) a single‐porosity model, (ii) a dual‐porosity model, and (iii) a dual‐permeability model. The initial parameterization of the models relied on in situ observations of soil structure, soil hydraulic property maps of Denmark and pedotransfer functions. The models, once calibrated against observed drainage data, were used for the reproduction of the subsurface drainage water dynamics for different time periods for the specific agricultural landscape. The different conceptual approaches gave a fairly good fit to the hydrograph features for both the calibration and validation datasets. The predictive ability of all models for the calibration dataset was fairly similar, while for the first and second validation datasets better results were obtained with the dual‐porosity and dual‐permeability models, respectively. The calibrated values of the effective parameters had been examined using laboratory data and in situ measurements of the groundwater level to evaluate how well these parameters physically represent the flow domain.

Frequency-domain electromagnetic sensing of leaching in a Californian substratum

Frequency-domain electromagnetic sensing can be an effective tool for ascertaining subsurface water dynamics. In California, the paucity of available irrigation water, recurrence of drought and presence of indigenous salts within the geological parent materials affect crop health. Subsurface leaching variability analyses were performed using dual dipolar induction surveys and stochastic computations to determine salinity conditions conducive to plant growth. Soils in the study area had randomly variable salinity with elevated salt levels within the substratum. The salinity values were mostly above 300 mS m−1 and some areas exceeded the 1500 mS m−1 level. The leaching conditions across the fields varied generally from 5 to 50%. Both variables showed slightly positive skewness with minutely asymmetrical tailing. The salinity distribution had less peakedness than the leaching distribution. Albeit with spatially dependent variability and skewness, the distribution patterns had low errors. There was a strong and significant correlation (r = 0.939 at P < 0.05) between the observed and predicted conductivity data. The leaching variables exhibited directional dependence along vertical and horizontal gradients. Spatial increase in salinity within the substratum conformed to salt leaching and water percolation processes. All observed salinity values within the substratum exceeded salt tolerance threshold limits for major crops and favorable leaching conditions were observed at low salinity levels. Sustainability of agriculture in California is heavily dependent on adequate water use planning and our approach of leaching variability analyses can facilitate water management and crop production by assessing removal of superfluous salts from the soil substratum.

Partial Desilting of Irrigation Tank to Enrich the Recharge Capacity

The hydrology of Groundwater movement depends upon the physical and chemical characteristics of both soil and water. These features must be measured and related to subsurface storage space and water dynamics, so as to decide the feasibility of a site for recharge and to select suitable methods and systems of recharge. So that water may be efficiently stored underground and then used independently or conjunctively with releases from surface storage reservoirs. In irrigation tanks, heavy siltation is the main limiting factor for percolation efficiency. The study of geology or soil characteristics in the tank bed for the infiltration recharging system is rather more important. At the same time Hydraulic conductivity is also very important parameter. Therefore, estimates of initial infiltration rates are must for estimating hydraulic conductivities of infiltration system in irrigation tanks. In this study, it has been planned to assess the recharge behavior of the tank bed in order to locate the highly permeable zone for desilting by conducting geophysical survey to demarcate the location for infiltration test. The results obtained from the infiltration test were correlated with the soil properties. From the analysis, the recharge characteristics of the tank bed were assessed.

Partial Desilting of Irrigation Tank to Enrich the Recharge Capacity

The hydrology of Groundwater movement depends upon the physical and chemical characteristics of both soil and water. These features must be measured and related to subsurface storage space and water dynamics, so as to decide the feasibility of a site for recharge and to select suitable methods and systems of recharge. So that water may be efficiently stored underground and then used independently or conjunctively with releases from surface storage reservoirs. In irrigation tanks, heavy siltation is the main limiting factor for percolation efficiency. The study of geology or soil characteristics in the tank bed for the infiltration recharging system is rather more important. At the same time Hydraulic conductivity is also very important parameter. Therefore, estimates of initial infiltration rates are must for estimating hydraulic conductivities of infiltration system in irrigation tanks. In this study, it has been planned to assess the recharge behavior of the tank bed in order to locate the highly permeable zone for desilting by conducting geophysical survey to demarcate the location for infiltration test. The results obtained from the infiltration test were correlated with the soil properties. From the analysis, the recharge characteristics of the tank bed were assessed.

High-frequency climate fluctuations over the last deglaciation in the Alboran Sea, Western Mediterranean: Evidence from calcareous plankton assemblages

A high resolution study, with a centennial scale resolution, has been performed on the calcareous plankton assemblage (coccolithophores and planktonic foraminifera) at Ocean Drilling Program Site 976, Alboran Sea (Western Mediterranean), focusing on the interval between 20 and 9 ka, in order to reconstruct changes in surface and subsurface water dynamics and productivity. The biotic surface water proxies integrate the extremely detailed (multi-decadal scale) geochemical data set and the pollen record already available at the core, thus providing a complete paleoenvironmental/paleoceanographic reconstruction. The results highlight the sensitivity of the calcareous plankton in recording stadial/interstadial phases and higher-frequency climatic events, that produced changes in sea water features. Wind-induced upwelling and river discharge during the Last Glacial Period favored nutrient availability and moderate productivity. During Heinrich Stadial 1 (HS1), the arrival of cold and fresher waters from iceberg melting in the North Atlantic, significantly hampered productivity, at its lowest values of the whole investigated interval. Calcareous plankton behavior supports the hypothesis that HS1 is a composite event, marked by three phases: HS1a characterized by the coldest SST, polar Atlantic water inflow into the basin and a first step toward a dry climate on the continent; HS1b recording enhanced freshwater inflow and drought on land, and HS1c indicating reduced polar water influx. The Bølling-Allerød (BA) interstadial sees the highest rate of productivity in the entire interval and accompanies the deposition of Organic Rich Layer 1; during the BA coccolithophore assemblage also marks higher frequency changes in hydrographic conditions, apparently in relation with Greenland Interstadial I (GI-I) high variability. The Younger Dryas Stadial (YD) is characterized by refunding cold and dry conditions, although not as severe as during HS1, and by enhanced detrital input in surface water during drier conditions on land. The Holocene onset records climate amelioration both in the marine and continental environment, although coccolithophore productivity is not as high as during the BA. The rapid shifts in climate sensitive taxa support the hypothesis that each of the climate phases-subphases is characterized by a complex pattern forced by strong interaction between ice-sheet instability, meltwater discharge entering the Gibraltar Strait, North Atlantic westerlies and moisture availability, clearly impacting over surface water temperature, productivity and land masses.

Modelling hydrological response to a fully‐monitored urban bioretention cell

AbstractMunicipalities and agencies use green infrastructure to combat pollution and hydrological impacts (e.g., flooding) related to excess stormwater. Bioretention cells are one type of infiltration green infrastructure intervention that infiltrate and redistribute otherwise uncontrolled stormwater volume. However, the effects of these installations on the rest of the local water cycle is understudied; in particular, impacts on stormwater return flows and groundwater levels are not fully understood. In this study, full water cycle monitoring data were used to construct and calibrate a two‐dimensional Richards equation model (HYDRUS‐2D/3D) detailing hydrological implications of an unlined bioretention cell (Cleveland, Ohio) that accepts direct runoff from surrounding impervious surfaces. Using both preinstallation and postinstallation data, the model was used to (a) establish a mass balance to determine reduction in stormwater return flow, (b) evaluate green infrastructure effects on subsurface water dynamics, and (c) determine model sensitivity to measured soil properties. Comparisons of modelled versus observed data indicated that the model captured many hydrological aspects of the bioretention cell, including subsurface storage and transient groundwater mounding. Model outputs suggested that the bioretention cell reduced stormwater return flows into the local sewer collection system, though the extent of this benefit was attenuated during high inflow events that may have exhausted detention capacity. The model also demonstrated how, prior to bioretention cell installation, surface and subsurface hydrology were largely decoupled, whereas after installation, exfiltration from the bioretention cell activated a new groundwater dynamic. Still, the extent of groundwater mounding from the cell was limited in spatial extent and did not threaten other subsurface infrastructure. Finally, the sensitivity analysis demonstrated that the overall hydrological response was regulated by the hydraulics of the bioretention cell fill material, which controlled water entry into the system, and by the water retention parameters of the native soil, which controlled connectivity between the surface and groundwater.

Redistribution of soil metals and organic carbon via lateral flowpaths at the catchment scale in a glaciated upland setting

Emerging evidence shows that interactions between soils and subsurface flow paths contribute to spatial variations in stream water chemistry in headwater catchments. However, few have yet attempted to quantify chemical variations in soils at catchment and hillslope scales. Watershed 3 (WS3) at Hubbard Brook Experimental Forest, New Hampshire, USA, was studied in order to better understand pedogenesis and its relationship to subsurface water dynamics. In WS3, 99 soil profiles were described, sampled by horizon, and assigned to a hydropedologic unit (HPU), a functional classification previously developed using landscape and morphological metrics which corresponded with distinct water table regimes. Soil samples were extracted with 1) citrate-dithionite (d) and analyzed for Fed and Mnd; and 2) acid ammonium oxalate (o) and analyzed for Alo, Feo and the rare earth elements Lao, Ceo, and Pro. Total organic C was also measured. These elements were redistributed via vertical and lateral podzolization. Typical (horizontally layered) podzols developed in the majority of the catchment due to predominantly vertical, unsaturated flow. However, lateral flow produced four other podzol types with distinct chemistry; thicker spodic horizons of laterally accumulating soils generally reflected larger pools of trace metals and subsoil organic C. The spatial distribution of positive cerium-anomalies (Ce/Ce*) in soil profiles proved to be a consistent hydropedologic indicator of lateral flow and seasonally high water table in three hillslopes. Despite occasional high water table in some of the HPUs, they were not hydric soils and were distinct from wetter podzols of coastal plains due to their high Fe content. This study suggests that vertical and lateral spatial variation in soil chemical composition, including the complexity of Ce distribution, as it relates to subsurface water dynamics should be considered when studying or predicting catchment scale functions such as stream solute export and biogeochemical processes.

Soil moisture prediction of bare soil profiles using diffuse spectral reflectance information and vadose zone flow modeling

Soil hydraulic property information of the vadose zone is key to quantifying the temporal and spatial variability of soil moisture, and for modeling water flow and contaminant transport processes in the near surface. This study deals with exploring the feasibility of using diffuse soil spectral information in the visible, near-infrared and shortwave infrared range (350–2500 nm) to estimate coarse-scale soil hydraulic parameters and predict soil moisture profiles using a topography-based aggregation scheme in conjunction with a 1D mechanistic water flow model. Three different types of parametric transfer functions (so-called spectrotransfer functions, STFs; pedotransfer functions, PTFs; and spectral pedotransfer functions, SPTFs) were aggregated from the point scale to 1 km2 pixel size. to provide coarse scale estimates of van Genuchten-Mualem (VGM) hydraulic parameters. The coarse scale hydraulic parameters were evaluated by simulating soil water dynamics of the 1 km2 pixels across the Zanjanrood River sub-watershed (ZRS) in northwest Iran. Resultant soil water states were compared with ground-truth measurements and advanced synthetic aperture radar (ASAR) estimates of soil water content. The topography-based aggregation scheme was found to provide effective values of the VGM hydraulic parameters across the ZRS study site. The coarse scale STFs performed best in terms of simulating surface, near-surface and subsurface soil water dynamics, followed by the coarse scale SPTFs and PTFs, which performed similarly. The average simulated soil water contents of the surface layer closely correlated with ASAR estimates during relatively wet periods. Simulated subsurface soil water dynamics matched well with the ground-truth measurements. These findings indicate the feasibility of using spectral data to predict VGM hydraulic parameters and, ultimately, to predict soil water dynamics at the larger scales.

Quantifying shallow subsurface water and heat dynamics using coupled hydrological-thermal-geophysical inversion

Abstract. Improving our ability to estimate the parameters that control water and heat fluxes in the shallow subsurface is particularly important due to their strong control on recharge, evaporation and biogeochemical processes. The objectives of this study are to develop and test a new inversion scheme to simultaneously estimate subsurface hydrological, thermal and petrophysical parameters using hydrological, thermal and electrical resistivity tomography (ERT) data. The inversion scheme – which is based on a nonisothermal, multiphase hydrological model – provides the desired subsurface property estimates in high spatiotemporal resolution. A particularly novel aspect of the inversion scheme is the explicit incorporation of the dependence of the subsurface electrical resistivity on both moisture and temperature. The scheme was applied to synthetic case studies, as well as to real datasets that were autonomously collected at a biogeochemical field study site in Rifle, Colorado. At the Rifle site, the coupled hydrological-thermal-geophysical inversion approach well predicted the matric potential, temperature and apparent resistivity with the Nash–Sutcliffe efficiency criterion greater than 0.92. Synthetic studies found that neglecting the subsurface temperature variability, and its effect on the electrical resistivity in the hydrogeophysical inversion, may lead to an incorrect estimation of the hydrological parameters. The approach is expected to be especially useful for the increasing number of studies that are taking advantage of autonomously collected ERT and soil measurements to explore complex terrestrial system dynamics.

The role of water management and environmental factors on field irrigation requirements and water productivity of rice

Rice cultivation requires a significant share of irrigation water, mostly because of the practice of continuous flooding; therefore, interest for alternative water managements is increasing. The paper presents results of a 2-year experiment in Northern Italy comparing three rice water managements: Water seeding-continuous FLooding (WFL), Dry seeding-delayed FLooding (DFL) and Dry seeding-intermittent IRrigation (DIR). The main objective was to assess the effects of water regimes on the agroecosystem as a whole (from water use and yield components to nutrient dynamics, etc.). This paper is focussed on water use aspects with the aim of: (1) comparing and discussing water balance terms, water use efficiencies and water productivities; (2) analysing percolation fluxes of flooded treatments (WFL and DFL); and (3) discussing interannual variations of paddy irrigation requirements due to environmental factors. Net irrigation requirements of WFL ranged between 1500 and 3000 mm in the two seasons, while DFL and DIR determined average reductions by 20 and 60 %. On the other hand, WFL provided an average yield of 10.2 t ha−1, which decreased by 3 and 28 % in DFL and DIR, respectively. Between-years variability can be attributed to environmental factors including groundwater levels and soil responses to abiotic and biotic factors. Percolations of flooded treatments showed a strong correlation with groundwater levels, especially during the first part of the season (R 2 0.90 and 0.95, respectively). Data analysis highlighted complex subsurface water dynamics dependent on groundwater levels and influenced by soil characteristics.

A land data assimilation system for simultaneous simulation of soil moisture and vegetation dynamics

AbstractDespite the importance of the coupling between vegetation dynamics and root‐zone soil moisture in land‐atmosphere interactions, there is no land data assimilation system (LDAS) that currently addresses this issue, limiting the capacity to positively impact weather and seasonal forecasting. We develop a new LDAS that can improve the skill of an ecohydrological model to simulate simultaneously surface soil moisture, root‐zone soil moisture, and vegetation dynamics by assimilating passive microwave observations that are sensitive to both surface soil moisture and terrestrial biomass. This LDAS first calibrates both hydrological and ecological parameters of a land surface model, which explicitly simulates vegetation growth and senescence. Then, it adjusts the model states of soil moisture and leaf area index (LAI) sequentially using a genetic particle filter. We can adjust the subsurface soil moisture, which is not observed directly by satellites, because we simulate the interactions between vegetation dynamics and subsurface water dynamics. From a point‐scale evaluation, we succeed in improving the performance of our land surface model and generate ensembles of the model state whose distribution reflects the combined information in the land surface model and satellite observations. We show that the adjustment of the subsurface soil moisture significantly improves the capacity to simulate vegetation dynamics in seasonal forecast timescales. This LDAS can contribute to the generation of ensemble initial conditions of surface and subsurface soil moisture and LAI for a probabilistic framework of weather and seasonal forecasting.

Total water storage dynamics derived from tree-ring records and terrestrial gravity observations

Summary For both societal and ecological reasons, it is important to understand past and future subsurface water dynamics but estimating subsurface water storage is notoriously difficult. In this pilot study, we suggest the reconstruction of subsurface water dynamics by a multi-disciplinary approach combining hydrology, dendrochronology and geodesy. In a first step, nine complete years of high-precision gravimeter observations are used to estimate water storage changes in the subsurface at the Geodetic Observatory Wettzell in the Bavarian Forest, Germany. The record is extended to 63 years by calibrating a hydrological model against the 9 years of gravimeter observations. The relationship between tree-ring growth and water storage changes is evaluated as well as that between tree-ring growth and supplementary hydro-meteorological data. Results suggest that tree-ring growth is influenced primarily by subsurface water storage. Other variables related to the overall moisture status (e.g., Standardized Precipitation Index, Palmer Drought Severity Index, streamflow) are also strongly correlated with tree-ring width. While these indices are all indicators of water stored in the landscape, water storage changes of the subsurface estimated by depth-integral measurements give us the unique opportunity to directly reconstruct subsurface water storage dynamics from records of tree-ring width. Such long reconstructions will improve our knowledge of past water storage variations and our ability to predict future developments. Finally, knowing the relationship between subsurface storage dynamics and tree-ring growth improves the understanding of the different signal components contained in tree-ring chronologies.

Análise morfoestrutural aplicada para avaliação de suscetibilidade à degradação ambiental por erosões hídricas lineares no interior do Estado de São Paulo

The Westside of the State of Sao Paulo, in Brazil, is known by its strong agricultural vocation and erosion problems. The natural conditions and the occupation dynamic were propitious to the emergence of this kind of environmental degradation in the soil, resulting in loss of usable area, siltation of water bodies, and demands on infrastructure. Linear hydraulic erosions, such as gullies, have as forming factors the climate, soil, land slope, and usage. In order to enrich the knowledge on this subject, the present work aimed at an analysis of the ductile geologic deformations, and subordinate brittle, and its relations to the accelerated linear hydraulic erosions in the region of Marilia, in the State of Sao Paulo, through the interpretation of the elements of drainage and remote sensing images. In general, there was correspondence between the areas potentially susceptible to erosion diagnosed by morphostructural mapping and topography, with the current state of degradation that is a result from a century of exploitation of the land. The morphostructural and topographic analyses bring the understanding of subsurface water dynamics, and can be applied to territorial planning.

Simulating coupled surface and subsurface water flow in a tile-drained agricultural catchment

Summary The impact of shallow tile drainage networks on groundwater flow patterns, and associated transport of chemical species or sediment particles, needs to be quantified to evaluate the effects of agricultural management on water resources. A current challenge is to represent tile drainage networks in numerical models at the scale of a catchment for which proper simulation and reproduction of subsurface drainage water dynamics are essential. This study investigates the applicability of various tile drainage modeling concepts by comparing their results to a reference model. The models were setup for a 3.5 ha regularly monitored tile-drained area located in the clayey till Lillebaek catchment in Denmark, where the main input of water to the streams originates from subsurface drainage. Several simulations helped identify the most efficient way of modeling tile-drained areas using the integrated surface water and groundwater HydroGeoSphere code, which also simulates one-dimensional water flow in tile drains. The aim was also to provide insight on the design of larger scale models of complex tile drainage systems, for which computational time can become very large. A reference model that simulated coupled surface flow, groundwater flow and flow in tile drains was setup and showed a rapid response in drain outflow when precipitation is applied. A series of additional simulations were performed to test the influence of flow boundary conditions, temporal resolution of precipitation data, conceptual representations of clay tills and drains, as well as spatial discretization of the mesh. For larger scale models, the simulations suggest that a simplification of the geometry of the drainage network is a suitable option for avoiding highly discretized meshes. Representing the drainage network by a high-conductivity porous medium layer reproduces outflow simulated by the reference model. This approach greatly reduces the mesh complexity and simulation time and thus represents an alternative to a discrete representation of drains at the field scale, but specifying the hydraulic properties of the layer requires calibration against observed drain discharge.