Shallow Water Table Environments Research Articles

Proline Accumulation and Growth of Bean Leaf (Phaseolus vulgaris L.) With Biochar Application in The Shallow Water Table Environment

Agronomic constraints for vegetable cultivation in riparian wetlands are low soil quality and shallow water table conditions. This study aims to identify the effect of biochar application and shallow water table on proline accumulation and plant growth of bean leaf (Phaseolus vulgaris L.) at the generative stage. This study was carried out from April to August 2018 in factorial randomized block design. The first factor was doses of biochar (0, 1, and 2 kg.m-2), and the second was shallow water table condition (20 cm and 10 cm below the soil surface) given in the generative stage. The results showed that biochar application and the shallow water table significantly affected leaf parameters; proline accumulation and increases in the sucrose levels occurred on the leaves. Proline content increased started at 3 days after treatment (DAT) and decreased at 6 DAT until recovery day (7 DAT). The biochar application of 2 kg.m-2 provided good aeration in the soil, which enhanced the bean's ability to survive under excess water. Proline accumulation is one of the adaptation mechanisms of beans to abiotic stress in shallow water table conditions.

Investigating compound flooding in a low elevation coastal karst environment using multivariate statistical and 2D hydrodynamic modeling

Miami-Dade County is vulnerable to flash, pluvial, fluvial, coastal and groundwater flooding due to its low-elevation karst morphology. Despite considerable advances in understanding the impact of compound flooding events by considering major flood drivers (precipitation, river discharge, and coastal surge), little is known regarding the severity of groundwater hazards in this region. This study links a multivariate statistical analysis with a coupled physically-based 2D hydraulic model to estimate the flood hazard in the Arch Creek Basin located in North Miami. A bivariate copula analysis was used to capture the joint probability of key flood drivers with predefined water table thresholds to set-up the flood modeling conditions. Results demonstrate the high vulnerability to extreme precipitation events compared to coastal surge in the study area. Similarly, groundwater flooding is relevant in shallow water table environments, as it influences the severity of flood hazards in terms of flood inundation depth, extent, and damage to the built environment. This research demonstrates that groundwater flooding is a latent risk that should be incorporated in flood hazard mapping in regions susceptible to high water tables and sea level rise.

Growing season water and salt migration between abandoned lands and adjacent croplands in arid and semi-arid irrigation areas in shallow water table environments

In arid and semi-arid irrigation areas with shallow water tables and fragmented arrangement of croplands and abandoned lands, dry drainage could be an optional management practice mitigating soil salinization. A dry drainage system lets non-irrigated abandoned lands serve as evaporative salt sinks receiving water and salt fluxes from adjacent irrigated croplands. Therefore, this research takes a typical dry drainage unit in the Hetao Irrigation District—one abandoned land and its adjacent croplands—as an example to directly reveal the field scale water and salt migration between abandoned lands and adjacent croplands. It was found that during the growing season, the water input, i.e. field irrigation and precipitation, raised the water table of the croplands and drove water and salt migration from croplands to the abandoned lands. However, the evapotranspiration in the croplands was also larger than that in the abandoned lands. Thus, during the intervals of irrigation (the “phreatic evaporation periods”), in some circumstances, evapotranspiration could drive water and salt flux from the abandoned lands to the croplands, which would influence the groundwater salinity of the croplands. Therefore, it is recommended to plant halophytes on the abandoned lands to enhance its evapotranspiration and hinder the water and salt flux from the abandoned lands to the croplands during intervals of irrigation. This management practice could help form more effective dry drainage systems between abandoned lands and adjacent croplands, and help better control the root zone salinity of the croplands.

Analytical Expressions of Drainable and Fillable Porosity for Layered Soils Under Shallow Groundwater Environments

AbstractThis study presents the analytical expressions of drainable and fillable porosity for layered soils under shallow groundwater environments. The expressions of drainable porosity λd and fillable porosity λf for two‐layered soils are first derived with water table depth change ∆d→0 under dynamic soil moisture conditions. The expressions of λd and λf consider the dynamic soil moisture conditions through the assumption of vertical fluxes in the unsaturated zone, varying as functions of water table elevation h. The analytical expressions of λd and λf have the same formula form but different values under evapotranspiration and recharge conditions, which is also verified using the numerical calculation. The case comparisons indicate that the vertical distribution of soil layers and the fluxes have significant effects on the performance of λd and λf. Our proposed expressions could effectively characterize the effects of soil layering and vertical fluxes on λd and λf. They could improve the accuracy of the previous expressions for single‐layer soils, and complement the lack of description for layered soils under dynamic soil moisture conditions in previous expressions. Furthermore, under the hydrostatic assumption (static equilibrium of soil water pressure distribution) in the unsaturated zone, the expressions of drainable porosity λd* and fillable porosity λf* for two‐layered soils with large water table fluctuations are derived based on λd and λf (asterisks in λd* and λf* is to distinguish them from λd and λf derived based on ∆d→0). Verification with drainage experimental data indicates that the proposed expressions can be extended to well capture the λd* and λf* changes for two‐layered soils. Application scenarios suggest that our analytical expressions of drainable and fillable porosity are useful to improve the application performance of related subsurface modeling and groundwater estimation for layered soils under shallow water table environments.

The other side of tropical forest drought: do shallow water table regions of Amazonia act as large-scale hydrological refugia from drought?

Tropical forest function is of global significance to climate change responses, and critically determined by water availability patterns. Groundwater is tightly related to soil water through the water table depth (WT), but historically neglected in ecological studies. Shallow WT forests (WT < 5 m) are underrepresented in forest research networks and absent in eddy flux measurements, although they represent c. 50% of the Amazon and are expected to respond differently to global-change-related droughts. We review WT patterns and consequences for plants, emerging results, and advance a conceptual model integrating environment and trait distributions to predict climate change effects. Shallow WT forests have a distinct species composition, with more resource-acquisitive and hydrologically vulnerable trees, shorter canopies and lower biomass than deep WT forests. During 'normal' climatic years, shallow WT forests have higher mortality and lower productivity than deep WT forests, but during moderate droughts mortality is buffered and productivity increases. However, during severe drought, shallow WT forests may be more sensitive due to shallow roots and drought-intolerant traits. Our evidence supports the hypothesis of neglected shallow WT forests being resilient to moderate drought, challenging the prevailing view of widespread negative effects of climate change on Amazonian forests that ignores WT gradients, but predicts they could collapse under very strong droughts.

Comparison of specific-yield estimates for calculating evapotranspiration from diurnal groundwater-level fluctuations

Methods that use diurnal groundwater-level fluctuations are commonly used for shallow water-table environments to estimate evapotranspiration (ET) and recharge. The key element needed to obtain reliable estimates is the specific yield (Sy), a soil-water storage parameter that depends on unsaturated soil-moisture and water-table fluxes, among others. Soil-moisture profile measurement down to the water table, along with water-table-depth measurements, can provide a good opportunity to calculate Sy values even on a sub-daily scale. These values were compared with Sy estimates derived by traditional techniques, and it was found that slug-test-based Sy values gave the most similar results in a sandy soil environment. Therefore, slug-test methods, which are relatively cheap and require little time, were most suited to estimate Sy using diurnal fluctuations. The reason for this is that the timeframe of the slug-test measurement is very similar to the dynamic of the diurnal signal. The dynamic characteristic of Sy was also analyzed on a sub-daily scale (depending mostly on the speed of drainage from the soil profile) and a remarkable difference was found in Sy with respect to the rate of change of the water table. When comparing constant and sub-daily (dynamic) Sy values for ET estimation, the sub-daily Sy application yielded higher correlation, but only a slightly smaller deviation from the control ET method, compared with the usage of constant Sy.

An analytical solution of Richards' equation providing the physical basis of SCS curve number method and its proportionality relationship

AbstractThe empirical proportionality relationship, which indicates that the ratio of cumulative surface runoff and infiltration to their corresponding potentials are equal, is the basis of the extensively used Soil Conservation Service Curve Number (SCS‐CN) method. The objective of this paper is to provide the physical basis of the SCS‐CN method and its proportionality hypothesis from the infiltration excess runoff generation perspective. To achieve this purpose, an analytical solution of Richards' equation is derived for ponded infiltration in shallow water table environment under the following boundary conditions: (1) the soil is saturated at the land surface; and (2) there is a no‐flux boundary which moves downward. The solution is established based on the assumptions of negligible gravitational effect, constant soil water diffusivity, and hydrostatic soil moisture profile between the no‐flux boundary and water table. Based on the derived analytical solution, the proportionality hypothesis is a reasonable approximation for rainfall partitioning at the early stage of ponded infiltration in areas with a shallow water table for coarse textured soils.

Effect of watertable depth and salinity on growth dynamics of Rhodes grass (Chloris gayana)

Depending on their depth, watertables can have a positive effect on plants by supplying water, a negative effect by creating waterlogged and/or saline conditions or a neutral effect. Rhodes grass (Chloris gayana), a tropical perennial forage adapted to saline soils, floods and droughts, is a viable choice for the lowlands in the Pampas region of Argentina. The effects of the depth and salt concentration of the watertable on the growth dynamics and biomass accumulation of Rhodes grass were quantified in a greenhouse experiment. The experiment consisted of 10 treatments, resulting from the factorial combination of five watertable depths (25, 75, 125, 175 and 225 cm) and two salt treatments (EC 1.4 and 20.5 dS m–1). The presence of non-saline watertable at a depth of 25 cm produced a 5-fold greater biomass and showed an increase in water consumption of equal magnitude compared with deeper watertables. The increase in shoot biomass was explained primarily by higher tiller and stolon density, which increased 3.3- and 7.7-fold respectively, at watertables that were 25 cm deep compared with deeper treatments. Furthermore, groundwater use efficiency was 30% higher in non-saline watertables at 25 cm depth. Similarly, at this depth, the leaf blades were 50% longer compared with the deepest watertables evaluated. In contrast, the presence of saline watertables at 25 cm depth had a detrimental effect on the production of biomass and its components, whereas the effect at 125 cm and greater depths was neutral. Therefore, Rhodes grass is a species that can take advantage of the widespread shallow watertable environments of the Pampas region as long as the salinity levels are low.

Infiltration in Shallow Water Table Environments: Simple Two-Phase Model Accounting for Air Compression and Counterflow

AbstractA new method is introduced to simulate air compression and counterflow during infiltration into a shallow water table. The method retains the simplicity of Green and Ampt but with one added term, the air pressure resistance below the wetting front. The method differs from existing methods because it couples air compression and counterflow flux dynamically with infiltration. The new method is original and simple, yet it allows the extension of Green and Ampt to simulate infiltration into shallow water environments or a shallow impervious zone where soil-air pressurization is likely to develop. In shallow water table environments, it is shown that neglecting counterflow of air will cause a rapid decline in infiltration due to unrealistic buildup of air pressure below the wetting front. Accounting for air compression and counterflow seemed necessary to bridge between Hortonian (infiltration excess) and Dunne (saturation excess) mechanisms of runoff.

Diurnal Method for Evapotranspiration Estimation from Soil Moisture Profile

Abstract Water use of plants can be manifested in diurnal signal of soil moisture changes, and also of water table fluctuations in shallow water table environments. The signal can be especially strong in case of groundwater dependent forest vegetation with high water demand, where the water uptake is partly happening across the capillary zone. A new technique for water uptake estimation was elaborated on the basis of high frequency soil moisture profile data taking into account diurnally changing replenishment rate. The method is of great benefit to provide sufficient accuracy without soil specific calibration. The method was tested on the soil moisture dataset of a riparian alder forest in Hidegvíz Valley experimental catchment. Using this new method significantly higher and more realistic water uptake can be calculated compared to the traditional soil moisture method. The method is taking into account soil moisture replenishment from groundwater, which can provide high portion (up to 90%) of evapotranspiration in dry periods. For the above mentioned reason the new technique is recommended to be used for evapotranspiration estimation in groundwater discharge areas, where the traditional methods and simple one-dimensional hydrological models generally work inaccurate.

Estimating groundwater recharge and evapotranspiration from water table fluctuations under three vegetation covers in a coastal sandy aquifer of subtropical Australia

• We estimated groundwater recharge and ET g under three vegetation covers. • Depth-dependent S y were determined under rising and falling water table conditions. • Lower forest recharge was due to higher interception and reduced recharge capacity. • ET g was controlled by meteorological drivers but mediated by depth to water table. To evaluate potential hydrological impacts of changes in vegetation over a shallow sandy aquifer in subtropical Australia, we estimated groundwater recharge and discharge by evapotranspiration ( ET g ) under three vegetation covers. Estimates were obtained over two years (November 2011–October 2013) using the water table fluctuation method and the White method, respectively. Depth-dependent specific yields were determined for estimation of recharge and ET g . Our results show that the average annual gross recharge was largest at the sparse grassland (∼52% of net rainfall), followed by the exotic pine plantation (∼39% of net rainfall) and then the native banksia woodland (∼27% of net rainfall). Lower recharge values at forested sites resulted from higher rainfall interception and reduced storage capacity of the vadose zone due to lower elevations when the water table approaches the soil surface. During 169 rain-free days when the White method was applied, pine trees extracted nearly twice as much groundwater through ET g as the banksia, whereas no groundwater use by grasses was detected. Groundwater use is largely controlled by meteorological drivers but further mediated by depth to water table. The resulting annual net recharge (gross recharge minus ET g ) at the pine plantation was comparable to that of the banksia woodland but only half of the corresponding value at the grassland. Vegetation cover impacts potential groundwater recharge and discharge, but in these subtropical shallow water table environments estimates of potential recharge based on rainfall data need to take into account the often limited recharge capacity in the wet season.

Water and Nitrogen Management Effects on Water and Nitrogen Fluxes in Florida Flatwoods

The effects of water and fertilizer best management practices (BMPs) have not been quantified for groundwater nitrogen (N) beneath seepage irrigated vegetable fields with shallow water table environments. This effect was evaluated by a 3-yr study conducted in the Flatwoods of south Florida for watermelon ( cv. Mardi Gras and Tri-X 313) and tomato ( cv. BHN 586) using three treatments of water and inorganic fertilizer N (N) rates: (i) high fertilizer and water rates with seepage irrigation (HR), (ii) recommended fertilizer and water rates (BMP) with seepage irrigation (RR); and (iii) RR with subsurface drip irrigation (RR-SD). These treatments were implemented on six hydraulically isolated plots. The N rate treatments for high (HR) and recommended (RR and RR-SD) were based on a grower survey and BMP recommendations, respectively. Water applied, water table depth, and soil moisture content were regularly monitored for each treatment. Plant, soil, and groundwater N sampling and analyses were conducted for each season of the 3-yr study. The average water applied in HR (187 cm) was greater than RR (172 cm) and RR-SD (94 cm). Soil N maintained in crop beds for HR was significantly higher than RR and RR-SD. Soil solution analyses showed that N leached beneath HR (112 mg L) was greater ( = 0.053) than RR (76 mg L) and RR-SD (88 mg L). Shallow groundwater concentrations of dissolved inorganic nitrogen (NH-N + NO-N) were higher ( = 0.02) in HR (37 mg L) compared with RR (15 mg L) and RR-SD (19 mg L). Decreased N and water table levels can improve groundwater quality by reducing N leachate in shallow water table environments with seepage irrigated vegetable production systems.

Distinguishing between management-induced and climatic trends in phreatic groundwater levels

Summary A method is proposed for distinguishing between climatic and anthropogenic or management-induced contributions to observed trends in phreatic groundwater levels. The method is tested on 245 phreatic screens distributed over 168 wells in Northern Belgium that were monitored monthly during 1999–2009. The SWAP (Soil Water Atmosphere Plant), an existing physically-based model, is used to simulate the observed time series of groundwater levels at each of the screens. SWAP simulates 1-D water transport by applying the Richards’ equation for the unsaturated–saturated zone, while accounting for interception and water extraction by vegetation. The model thus incorporates climatic effects on the groundwater level but ignores management-induced impacts such as groundwater abstraction. The management-induced contribution to observed trends in groundwater levels can therefore be derived by analysing the model residuals, i.e. observed minus predicted groundwater levels. Five and 10 year management-induced trends in groundwater levels (cm/year) were estimated for each screen by a simple linear regression of the residuals of a SWAP model that was calibrated to optimise the agreement between observed and predicted groundwater levels at that screen. This management-induced trend was compared with the trend in observed groundwater levels. It is concluded that a correct interpretation of monitoring data in the context of the evaluation of the effectiveness of water management strategies, requires that observed trends are adjusted for climatic variation. In shallow water table environments, this climatic correction can be associated with precipitation surplus. However, when the water table is more than 3 m below the soil surface, the relation with precipitation surplus is less straightforward and varies from place to place, because of differences in vadoze zone travel time.

Modeling Evapotranspiration of Two Land Covers Using Integrated Hydrologic Model

Modeling evapotranspiration (ET) distribution in shallow water table environments is of great importance for understanding and reproducing other hydrologic fluxes such as runoff and recharge. Unfortunately, ET distribution can be the most difficult hydrologic process to analyze. The partitioning of ET into upper zone ET, lower zone ET, and groundwater ET is complex because it depends on land cover and subsurface characteristics. One comprehensive distributed parameter model, integrated hydrologic model (IHM), builds on an improved understanding and characterization of ET partitioning between surface storages, vadose zone storage, and saturated groundwater storage. It provides a smooth transition to satisfy ET demand between the vadose zone and the deeper saturated groundwater. In this paper, the IHM was used to analyze ET contribution from different regions of the vadose zone and saturated zone. Rigorous testing was done on two distinct land covers, grass land and forest land, at a study site in West-Cent...

Statistical Changes of Lake Stages in Two Rapidly Urbanizing Watersheds

Understanding changes induced by watershed urbanization is integral to developing an effective long-term management strategy. In this research, the authors study statistical changes of lake water surface levels in two urbanizing watersheds by evaluating serial change in time series parameters, autocorrelation, and variance as well as by developing a regression model to estimate weekly lake level fluctuations. The authors fit a seasonal integrated autoregressive moving average model to lake levels over subperiods of the data record to identify trends in parameter values. The authors fit the regression model with rainfall, lake stage, and temperature components for pre-urbanized and urbanized time periods to identify changes in baseflow. The lakes were located in Pasco County, Florida, USA and have not been significantly influenced by changes in rainfall patterns, pumping, surface water extraction or physical modification. Furthermore, the lakes exhibit consistent watershed urbanization and have sufficiently long and complete records. Based upon the research, the authors reach the following general conclusions about lakes in urbanizing watersheds: (1) the statistical structure of lake level time series is systematically altered, (2) in the absence of other forcing mechanisms, autocorrelation and baseflow decrease, (3) the presence of wetlands adjacent to lakes can offset the reduction in baseflow. These conclusions can be applied globally to similar regions that consist of lakes undergoing urbanization in flat, humid, shallow water table environments with wetlands. Furthermore, the methodology utilized can be applied at lakes in both similar and dissimilar environments to those studied in this research.

Observations of long term air entrapment affecting runoff and water table

Air entrapment plays a significant role in controlling infiltration and observed depth to water table in shallow water table environments. The current study incorporates multi-event field measurements with varying antecedent conditions and numerical modelling, using HYDRUS-1D to quantify the variation of air pressurisation values. The observations of water table in the field data depart significantly on occasions from the theoretical values using a calibrated Richards' equation solution. Antecedent conditions were also found to be very important in controlling air pressurisation. A simple analysis based on ideal gas law was also done to help understand air pressurisation effects.

An object-oriented hydrologic model for humid, shallow water-table environments

Summary Humid, shallow water-table environments such as the flatwoods of the southeastern United States are characterized by flat topography and moderately to poorly drained soils where significant interaction between surface water and groundwater occurs. A Java-based, object-oriented hydrologic model has been created specifically for shallow water-table environments within the framework of the ACRU2000 model. Using the object-oriented design concept of inheritance allows for new modeling approaches to be incorporated into a model by extension, without modifying existing functionality. The object-oriented programming properties of inheritance, aggregation, and association provide a flexible, modular, and readily extensible platform for model development. The physically based, conceptual model represents the effect of the water-table on evapotranspiration, local groundwater flow, and runoff generation. The model is physically based in that it uses physically measurable parameters and is conceptual to the extent that the model domain is idealized. Model validation to two experimental sites in the southeastern US indicated the model’s ability to predict water-table depths, soil moisture distributions, evapotranspiration, and saturation-excess runoff.

EQUIVALENCE BETWEEN TOPMODEL AND THE NRCS CURVE NUMBER METHOD IN PREDICTING VARIABLE RUNOFF SOURCE AREAS1

ABSTRACT:An equivalence is proposed between two rainfall‐runoff methods with a long history of use in the United States and Europe. In watersheds where variable source areas dominate runoff, the two methods can have comparable probability distribution functions of moisture deficit, and therefore predict similar saturated runoff source areas. A novel approach is introduced to determine the S parameter in the Natural Resources Conservation Service (NRCS) method. This approach constrains S by the physical soil and topography characteristics of the catchment and depth to water table. The NRCS curve number method is at the core of many rainfall‐runoff models in hydrology. As a simple lumped parameter method, it is often scrutinized because it is not obvious how to derive S from catchment hydromorphological characteristics. The novel approach provides a clear physical meaning for S, allowing better estimation of this parameter in humid shallow water table environments where the variable source area can be the dominant runoff mechanism.

Evapotranspiration of Two Vegetation Covers in a Shallow Water Table Environment

A method is introduced to estimate evapotranspiration (ET) in shallow water table environments. The method involves measuring the diurnal fluctuations in total soil moisture above the water table to estimate (i) the net lateral and vertical subsurface flux in the aquifer and (ii) evapotranspiration from the vegetation cover. In a hillslope discharge zone, the net lateral subsurface flux was calculated from the recovery rate of soil moisture between midnight and 0400 h. Evapotranspiration was then estimated from a daily water balance in a soil column that included the water table. The method was tested on two vegetation covers, a pasture in a groundwater recharge area, and a riparian zone with woody vegetation in a groundwater discharge area. A moisture probe carrying eight sensors was used in each area to estimate the total soil moisture in a sandy soil environment. The observed water table fluctuated between land surface and a depth of 1.2 m during the study period, allowing observation and estimation of the total soil moisture in a soil column that included the water table. The results of this investigation support another hypothesis that, in humid, shallow water table environments, ET demand may be supported by adjacent ecosystems. This method provided reasonable results for the two landscapes investigated and was able to capture the variability of evapotranspiration in heterogeneous vegetation covers. It provided a relatively inexpensive alternative to characterize ET within regionally heterogeneous but microhomogenous landscapes. Though tested for coarse‐textured soil, the method involving soil moisture monitoring can be easily adapted to other soil types with shallow water table. Another advantage of using this method is that ET can be successfully estimated without detailed knowledge of soil hydraulic properties, subsurface flow patterns, or vegetation characteristics.

MODELING RUNOFF FROM VARIABLE SOURCE AREAS IN HUMID, SHALLOW WATER TABLE ENVIRONMENTS1

ABSTRACT: Variable Source Areas (VSAs) are zones with water saturated soils in forested wetlands fringing streams and creeks. Runoff from these areas is generated by saturation excess after a shallow water table rises and inundates the ground surface. In humid regions, like Florida and the Southeast, VSAs are believed to produce most of the runoff in shallow water table environments. Modeling the spatial extent and temporal fluctuation of a VSA is difficult because the formation of a VSA depends on a number of hydrological and morphological factors like rainfall intensity, soil texture, water table depth, and topographic attributes of the terrain. In this paper, we couple a digital elevation model with a two‐dimensional variable saturation model to illustrate the formation of a VSA at the hillside scale. The topography derived from the digital elevation model forms the upper domain geometry for the two‐dimensional finite element simulations of variable saturated flow. The objectives are: (1) to model the spatial and dynamic fluctuation of a VSA, and (2) to understand the roles of rainfall variability and terrain attributes on the formation of a VSA. Results show that hillsides with shallow water table depths, low saturated hydraulic conductivity, mild slopes, and concave slope curvature were more susceptible to runoff from a variable source. Runoff from a variable source showed little sensitivity to rainfall intensity. In general, landscapes with steep slopes generated a small VSA and a seepage face that vanished rapidly with time. In contrast, flat terrains are more amenable to VSA and retain ground surface inundation for longer periods of time.