Shallow Groundwater Environment Research Articles

Characteristics of sediments and regolith alterations in the Plio-Pleistocene succession, coastal cliff sections, St Vincent Basin, South Australia

Syn- and post-depositional alterations are distinguished in a detailed lithological and mineralogical study of the largely unconsolidated Plio-Pleistocene non-marine succession in coastal cliff sections in the St Vincent Basin south of Adelaide. At its base, the sequence interfingers with Late Pliocene estuarine marine sediments in places but mostly unconformably overlies older Cenozoic marine sediments or Neproterozoic bedrock. The fluvial and alluvial siliclastics have bioturbation, blocky-prismatic macro-peds and subtle Fe-mottling indicators of hiatuses in deposition, and imprints of soil and shallow groundwater environments. A relative abundance of kaolinite, illite and randomly interstratified illite-smectite reflects both sediment source and conditions in the local depositional environment. A thick deposit of aeolian calcareous silt with associated pedogenic calcretes blankets the succession. Conspicuous bleached Fe mega-mottled intervals and zones of alunite-halloysite within the sequence record post-depositional, groundwater-related alterations in regolith environments. These formed during incision and erosion of the sedimentary fill in the basin in response to regional falls in base level. Each marks a different time and specific geomorphic environment according to the chemistry of the discharge of local groundwaters from aquifers that were intersected by incision and scarp retreat.

Release dynamics, risk evolution and driving mechanisms of heavy metals in superalkaline fly ash co-disposed by MSW landfill

Fly ash from waste incineration is growing rapidly and has become a global problem. Landfill is the main treatment method, but the release behavior of ultra-alkaline fly ash needs further study. In this study, the release pattern of heavy metals from fly ash, the long-term risk after seepage, and the main control mechanisms were explored by indoor simulation experiments and process simulation modeling. The results show that carbonation is the main control mechanism for the release rate of heavy metals from super-alkaline fly ash, and the release rate is slow at the initial stage, but the release concentration of Zn and Pb may increase tens of times with the continuous reaction between the acidic substances in the leachate and the alkaline substances in the fly ash. The heavy metals released into the leachate can cause the concentration of Zn, Cd and Pb in the groundwater to exceed the standard by 39.50, 6.70 and 5.99 times due to seepage. Furnace type is the key controlling factor for background concentrations of heavy metals in ultra-alkaline fly ash, and the exposure concentrations of Cu, Cd, Zn, and Pb in ultra-alkaline fly ash from grate furnaces as well as the GT1 facility are 4.19, 4.19, 4.14, and 37.5 times greater than those of fluidized beds, respectively, with a higher risk of long-term landfill. Regionally, the regional occupancy rate of heavy metal concentrations indicated that the risk of adequate rainfall was high in the southeastern coastal region, which was five times higher than that in the inland northwest. Therefore, the long-term dynamics and risk evolution of Zn, Cd, and Pb in the groundwater around MSWLs in the coastal area should be paid attention to after the landfilling of ultra-alkaline fly ash in order to ensure the safety of the shallow groundwater environment after landfilling.

Surface Water (SW) and Shallow Groundwater (SGW) Nutrient Concentrations in Riparian Wetlands of a Mixed Land-Use Catchment

Precipitation patterns, water flow direction, and local land-use practices affect surface water (SW) and shallow groundwater (SGW) nutrient concentrations in riparian wetlands. Given physical process complexities, spatiotemporal quantification of nutrients and physical factors influencing nutrient concentrations are needed to advance wetland water resource management. To address these needs, a study was conducted in riparian wetlands of a mixed land-use catchment in West Virginia (WV), USA. Observed data included SW–SGW levels and nutrient concentrations, including nitrate (NO3-N), nitrite (NO2-N), ammonium (NH4-N), orthophosphate (PO43-P), total nitrogen (total_N), and total phosphorus (total_P) from January 2020 to December 2021. Water samples were collected monthly from stream gauge sites (n = 4) and co-located piezometers (n = 13). Results showed that, on average, gaining stream conditions were observed in upstream sites, and losing stream conditions were observed in downstream sites. Observed nutrient profiles between SW and SGW included SW exhibiting a higher average NO3-N concentration (0.42 mg/L), while SGW displayed an elevated NH4-N concentration (1.55 mg/L) relative to other nitrogen species. Significantly high (p < 0.05) SW NO3- concentrations in summer and fall were attributed to increased precipitation and corresponding water level and, therefore, pressure head and transport fluctuations. Principal Component Analysis (PCA) showed differences in nutrient concentrations based on the water source type and catchment land use, explaining 65% of data variability. Spearman correlation analysis illustrated the correlation among nutrient concentrations, land use, and water level changes in SW and SGW environments. This study provides needed baseline data on nutrient dynamics for a riparian wetland in a mixed land-use catchment, supplying science-based information to advance land and water management practices in the study watershed and similar physiographic watersheds globally.

An Integrated Multiobjective Optimization Model Considering Water-Balance Processes for Supporting Sustainable Irrigated Agriculture under Shallow Groundwater Environments

An Integrated Multiobjective Optimization Model Considering Water-Balance Processes for Supporting Sustainable Irrigated Agriculture under Shallow Groundwater Environments

A modified SWAT model for mechanistic simulation of soil water‐salt transport and the interactions with shallow groundwater

AbstractCurrent hydrological models still face difficulties in accurately simulating vadose zone (VZ) hydrological processes in arid watersheds with shallow groundwater environments. Therefore, this article introduces a new mechanistic VZ module coupled with an improved groundwater‐balance (GWB) module to enhance the capabilities of the well‐known Soil Water Assessment Tools (SWAT) model. The main improvements and features of the modified SWAT model (M‐SWAT) include: a numerical VZ module to accurately simulate soil water‐salt transport under variably saturated conditions by solving the head‐formed Richards' equation and advection‐dispersion equation; a GWB module (on a sub‐basin scale for shallow aquifer) coupled with VZ module by proposing an effective way of boundary information exchanges; and a more reasonable water‐salt stress functions (i.e., based on matric head and osmotic head) to calculate root water uptake and plant growth. The M‐SWAT was then tested and evaluated with two‐year observation data from the Yangchang canal command area (YCA, an experimental site) and the Jiyuan Irrigation System (Jiyuan, region‐scale), located in the arid upper Yellow River basin of northwest China. The model produced a good agreement between the simulated and observed data in both calibration and validation with sufficiently small root mean square error (RMSE). The determination coefficient (R2) was greater than 0.51, 0.36, and 0.87 in simulating the soil water‐salt dynamics, groundwater depth fluctuations, and leaf area index development, respectively. Case testing also proved that the M‐SWAT had sufficient computational efficiency and stability for regional application. Further comparisons with previous studies indicated that the M‐SWAT could more accurately and rationally simulate the soil water‐salt dynamics and their interactions in arid watersheds with shallow groundwater tables.

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.

Runoff Mitigation by Underdrained Permeable Pavements in Shallow Groundwater Environments: A Field Investigation

Runoff Mitigation by Underdrained Permeable Pavements in Shallow Groundwater Environments: A Field Investigation

Spatial and temporal patterns of soil salinization in shallow groundwater environments of the Bahía Blanca estuary: Influence of topography and land use

AbstractSoil salinization is considered an environmental threat as high salt content hinders plant growth. Soil salinity is usually associated with climate aridity at a regional scale, while topography, subsurface hydrology, and land use combine with climate to produce salinization patterns at landscape scale. In this study, the first such assessment for the study area, we investigated the relationship between climate, groundwater level (GWL) changes, and soil salinity. For comparison, two adjacent vegetation units used as marginal grazing lands were selected: thickets of Allenrolfea patagonica (Ap thicket), located at the base of a scarp, and bushes of Cyclolepis genistoides (Cg bush), located away from the topographic discontinuity. Electrical conductivity (ECrs) maps derived from LANDSAT‐8/OLI were used to analyze salinity patterns. The results showed that GWL rose in coincidence with precipitation events and fell during dryer and warmer periods. GWL was always closer to the surface in the Ap thicket, and level changes were more likely to occur there. ECrs showed a seasonal pattern with significantly higher (p < 0.05) values in the Ap thicket during summer. Within the Cg bush, relatively higher ECrs appeared around a permanent water trough. Within this zone, ECrs values during summer were significantly higher (p < 0.05). Coupled evaluation of GWL dynamics and soil salinization patterns showed that GWL changes interact with land use practices to produce local‐scale patterns of salinization. Topography played an important role in controlling soil surface properties through its influence on groundwater dynamics and small topographic changes produced largely different conditions for vegetation growth.

Modeling agro-hydrological processes and analyzing water use in a super-large irrigation district (Hetao) of arid upper Yellow River basin

High water consumption in large irrigation districts has resulted in large river water diversion and serious water use conflicts in the Yellow River basin (YRB). The excessive water applied is also a cause of the dual problems of soil salinity and water logging in the upper YRB, which further negatively impacts crop yields. This study is aimed at modeling and analyzing the agro-ecohydrological processes and water use performance in large irrigation districts of the YRB. The Hetao Irrigation District (Hetao), a super-large irrigation district located in the upper YRB, was selected as a typical research area. A watershed hydrological model (SWAT-AG) with enhanced capacity for simulating regional agro-ecohydrological processes was adopted in this study. We simulated the agro-ecohydrological processes in Hetao and analyzed the regional characteristics of depth to groundwater table, soil moisture and salt content, evapotranspiration and crop yield. Water accounting was further carried out to interpret water cycle processes and evaluate water use performance in Hetao. Results indicated that Hetao was characterized by shallow depth to groundwater table, high soil moisture and high evapotranspiration. For farmland, there was a decreasing trend for both soil moisture and evapotranspiration from the upper to lower regions in Hetao, but this decreasing trend was not found for natural land. Further, results showed soil salt content has strong spatial variations with land use type, crops and shallow groundwater environments. Correspondingly, crop yields presented a decreasing trend from the upper to lower regions of Hetao, with large spatial variabilities closely related to the spatial distribution of soil water and salt conditions across Hetao. It was worth noting that the regional water use efficiency was relatively low in Hetao, especially with large proportions of non-beneficial water consumption to total water consumption. Overall, this study provided a thorough understanding of agro-ecohydrological processes and their regional characteristics, and the current situation of irrigation water use issues in the whole Hetao district, and further provided valuable insights in improving water use and management in large irrigation districts of the upper YRB.

Dealing with shallow groundwater contexts for the modelling of urban hydrology – A simplified approach to represent interactions between surface hydrology, groundwater and underground structures in hydrological models

Hydrological modelling can be a relevant tool to support sustainable planning decisions. However, urban hydrological models usually rely on simplified underground representation that may limit their applicability in shallow groundwater environments. This paper introduces a set of modules designed to describe the numerous interactions between subsurface processes and surface hydrology that may occur in such contexts. The modules provide a rather straightforward approach to simulate the influence of the groundwater on the surface as well as the influence of several underground structures (sewer systems, building basements, …) on subsurface storage and the volumes to be managed by the sewerage network. The modules are evaluated by comparison with reference models over a set of theoretical test cases and integrated within the URBS hydrological model. An application to a realistic hypothetical watershed is carried out to illustrate the benefits and the feasibility of these focussed development in existing urban hydrological models.

Improved analytical expressions for transient specific yield in shallow groundwater drainage

This paper presents the new analytical expressions to improve the description of transient specific yield (Sy) in shallow groundwater drainage. A new expression of the transient Sy (i.e. Sy,G (t)) that only considers the gravity effect is first derived based on the modified van Genuchten model. This analytical expression is still valid when water table depth (WTD) is less than the soil air-entry pressure head, and thus completes the lack of description in the near-saturated segment in previous expressions. Further, we propose an approximate method to dealing with the diffusivity (capillary) effect, and derive an improved approximate expression of Sy with both considering the gravity and diffusivity (capillary) effects. The accuracy of the improved expression of Sy,GD (t) is evaluated with the test cases that cover all of soil types (under the USDA soil classification system) and different changes in water table, also compared with the expression derived with only considering the gravity effect. The comparisons show that the Sy,GD (t) expression could more accurately capture the dependence of the transient Sy on time and WTD, and significantly reduce the errors of ignoring the diffusivity effect. In addition, the analytical expression of ultimate Sy and the final time td required to reach its ultimate value are both derived based on the initial and final equilibrium states. Results indicate that our improved expressions can expand the application range of analytical expression and significantly improve the calculation accuracy of transient Sy in the shallow groundwater environments.

Modeling the behavior of shallow groundwater system in sustaining arid agroecosystems with fragmented land use

Shallow groundwater often presents multiple behaviors in supporting the sustainability of arid agroecosystems. The behaviors are especially important and complicated for the arid irrigated areas with fragmented land-use types. In the view of understanding the role of shallow groundwater in such areas, the MODFLOW and MT3DMS (with the assistance of HYDRUS-1D) were used to simulate groundwater flow and salt transport in a typical observation site of the arid upper Yellow River basin (YRB). The original MODFLOW was modified with introducing a variable expression of specific yield, aiming to improve the modeling accuracy in shallow groundwater environments. The model was calibrated and validated using the observation data of groundwater depth and drainage in 2013 and 2012, respectively. Groundwater evapotranspiration and lateral water-salt exchange among different land-use types were simulated and analyzed; meanwhile, the dry drainage effect of non-cultivated natural land was quantitatively interpreted. Results indicated that the fragmented land-use/planting pattern (with different irrigation scheduling) resulted in significant lateral groundwater flow and water/salt redistribution among different land-use fields during irrigation. The groundwater evapotranspiration ranged at about 160–220 mm for different land-use types, reaching to 0.30–0.45 of plant evapotranspiration (ETpt) during the growing seasons. This effectively supplemented the plant water use in arid climate, especially for the unirrigated cultivated land (during some stages) and the non-irrigated natural land. Meanwhile, the lateral groundwater flow drove salt migrating from the cultivated land to the natural land. The natural land accumulated 27–40% of salts introduced by irrigation, playing a significant role in accommodating salts (i.e. the dry drainage effect). Moreover, our modeling work further implied that the reliable groundwater modeling in arid and shallow groundwater areas required a more detailed model conceptualization and more accurate information of land-use distribution, irrigation scheduling, and local microrelief than the general understanding in the past.

Predicting agroecosystem responses to identify appropriate water-saving management in arid irrigated regions with shallow groundwater: Realization on a regional scale

Scenario analysis is the basis of developing rational water management practices (WMPs) for watersheds. How to predict future hydrological responses on a regional-scale is still a challenge for modeling work in irrigated watersheds with shallow groundwater environments. Therefore, this paper presents an efficient realization of predicting regional agroecosystem responses and searching for appropriate WMPs, through using a water balance-based, semi-distributed hydrological model (SWAT-AG). The scenario case study is carried out in the Jiyuan Irrigation System located in the Hetao of upper Yellow River basin, based on the calibrated and validated modeling work in our previous companion paper. Eight scenarios of water-saving practices (WSPs) are proposed, with consideration for reducing irrigation depth and controlling initial groundwater depth. Then the coupled responses of agroecosystem processes to various WSPs are predicted for the case study region in 2012 and 2013, mainly related to the groundwater depth, root zone soil water and salinity, and crop yield/natural vegetation biomass. Based on the analysis for proposed scenarios, the 100% of present irrigation depth combined with increasing initial GWD by 50 cm are recommended as appropriate WSPs for dry years, and the 80% of present irrigation depth combined with increasing initial GWD by 100 cm are recommended for wet years, in order to maintain good environmental conditions for both crops and natural vegetation. In addition, results show that SWAT-AG could overcome the scale/function limitations of traditional soil/crop models and also avoid computational issues of numerical models. We further point out that the scenarios in reality will be more complicated and comprehensive in time and space, and thus the predictions should be updated accordingly. Overall, this case study fully presents the feasibility and practicality of using the SWAT-AG model to realize the scenario response analysis and water management decision-making on a region scale for irrigated watersheds with shallow groundwater environments.

Risk of groundwater pollution in open dug wells in the Pungudutivu Island of the Jaffna Peninsula, Sri Lanka

Un-protected open dug wells of shallow groundwater environments are subjected to high risk of chemical and microbial pollution in many parts of the world. The present study was initiated in Pungudutivu, one of the surrounding islands of the Jaffna Peninsula, Sri Lanka, because the island totally relies on its limited groundwater resources extracted from open dug wells to meet all its needs. The study assessed the risk of pollution within the limited fresh groundwater found in unconfined aquifer systems of Pungudutivu, where high risk of pollution was expected mainly from organic sources, derived from human and animal wastes and easy infiltration and runoff returns. The fresh groundwater pockets of Pungudutivu were however found to be with less serious contamination risks other than high Fe2+ and high faecal coliform counts. Low nitrate and phosphate concentrations with high COD and low BOD demonstrated less pollution from biodegradable organic sources in the midst of high oxidising potentials in the shallow dug wells as implied by the stability field of Fe(OH)3 on the Eh-pH diagram; the argument of high Fe2+ in groundwater however, wasn't supported by the said oxidation potential. High faecal coliform counts with high DO in groundwater probably indicated conditions implied by on site waste disposal in groundwater of Pungudutivu.

The South West Hub In-Situ Laboratory – A Facility for CO2 Injection Testing and Monitoring in a Fault Zone

The In-Situ Laboratory Project entails a configuration of wells at approximately 400 m depth for monitoring a small volume of CO2 for testing purposes in a fault zone at the South West Hub CCS Flagship project in Western Australia. This is one of four wells drilled to obtain data from a greenfield site for potential commercial scale geological storage of carbon dioxide. The Harvey-2 well intersects a major fault zone with a maximum throw up to 1,000 m. This provides an opportunity to establish a complementary monitoring well configuration around the original well to conduct a deeper, more complex shallow release test than others conducted in Australia to date. The purpose of the In-Situ Lab project is to evaluate the ability to monitor and detect unwanted leakage of carbon dioxide from a storage complex at the South West Hub CCS site, a site which will contribute to broadening the global portfolio of shallow CO2 release tests. The project will develop the first part of an enduring research facility at the South West Hub to enable further research of the characterisation of CO2 migration in fault zones and the shallow groundwater environment.

AHC: An integrated numerical model for simulating agroecosystem processes—Model description and application

This article introduces the AHC model as a new tool for modeling and assessing the agroecosystem processes. The AHC, as a one-dimensional numerical physical model, simulates the soil water and salt/nitrogen dynamics, heat transport, and crop growth and yield in various soil-crop environments. The key features of the AHC include that it provides the optional function for simulating the fate of salt or nitrogen; it has an efficient global method for sensitivity analysis and parameter estimation; and it is useful in a wide range of field conditions, especially for those in northern China. A menu-driven program is developed as a user-friendly interface for efficient data manipulation. This paper primarily describes the main structures and algorithms of the AHC and presents its field applicability. Model testing and application was conducted with two cases: (1) a salinity case with maize growing in salt-affected fields under arid and shallow groundwater environments (Hetao, upper Yellow River basin, northwest China); and (2) a nitrogen case with a wheat-maize rotation system in the semihumid monsoon region (Tai’an, North China Plain). Good agreement was obtained between the simulated and observed data, including the soil water contents, salt/nitrogen contents, and crop growth indicators. The soil water and salt/nitrogen dynamics, crop growth processes, and their complex interactive effects were also well interpreted using the AHC. Rational simulation proves the good applicability of the AHC for practical field use.

Interactions between shallow groundwater and low‐impact development underdrain flow at different temporal scales

AbstractLow‐impact development (LID) practices are effective in managing surface run‐off, mitigating nonpoint source pollution, and recharging groundwater. However, they are often less effective in shallow groundwater environments as their surface infiltration and bottom exfiltration rates could be reduced, and the underdrains (i.e., underground drains within the media of the LID practices) may drain groundwater and alter groundwater dynamics. To evaluate and better understand the interactions between shallow groundwater and LID underdrain flow at different temporal scales, multiple statistical analyses were conducted on the monitored groundwater table depth and underdrain flow of porous pavements at the Central Kitsap Community Campus (Washington) and both porous pavements and bioretention cells at the IMAX parking lot (Ontario, Canada). The wavelet power, which represents oscillation behaviour and is obtained by continuous wavelet transform, of underdrain flow was a hybrid of that of rainfall and groundwater table depth. Rainfall variations at finer temporal scales (5 min to 10 days) resulted in finer scale underdrain flow, whereas groundwater fluctuations at coarser temporal scales (10 to 30 days) accounted for coarser scale underdrain flow and extended the duration of it. The impact of groundwater on underdrain flow was greater when the groundwater table was shallower than the underdrain (e.g., <0.6 m), particularly at finer temporal resolutions (5 min to 1 hr), which correspond to short‐term responses of LID practices and their corresponding effects on flooding. It was possible that the local groundwater mounds formed by infiltrated water instead of regional groundwater fluctuations that affected the underdrain flow in these conditions. Finally, through an evolutionary polynomial regression, two simple equations were obtained to predict the total amount and peak of LID underdrain flow using event‐based rainfall, groundwater table depth, and the hydraulic conductivity of media and in situ soils. The results may facilitate LID design and planning, and their implementation in shallow groundwater areas. The derived equations may benefit the real‐time control of LID‐related sewer and treatment systems in shallow groundwater urban catchments.

Simulating the hydrological performance of low impact development in shallow groundwater via a modified SWMM

Low impact development (LID) practices are effective in restoring natural hydrological processes, but they may be affected by groundwater and pose additional risk to groundwater dynamics and contamination in shallow groundwater conditions. Their performance in shallow groundwater is not well understood due to monitoring difficulty and the deficiency of modeling tools. The Storm Water Management Model (SWMM) is an urban hydrology-hydraulic model that has been widely used to evaluate the performance of LID practices. However, it cannot accurately simulate the hydrological processes of LID practices in shallow groundwater. This study presents the development, calibration, validation, and testing of a modified SWMM (SWMM-LID-GW) that incorporates groundwater feedbacks into LID simulations. The hydrological performance of LID practices under different environmental conditions was simulated, based on which the impacts of initial groundwater table depth, rainfall type, and in-situ soil type were evaluated, and a number of general nonlinear multivariate formulas were proposed to predict the hydrologic performance of LID practices in shallow groundwater environment and support the feasibility analysis of LID practices before project implementation. The reduction of exfiltration and increase of groundwater drainage in shallow groundwater accounted for a significant proportion of the water budget of LID practices. The influence of shallow groundwater was greater for shallower groundwater tables, in less permeable in-situ soils, and for events of higher intensities and longer durations. However, due to the dominant role of shallow groundwater, the impacts of both rainfall type and in-situ soil type on the hydrological performance of LID practices in shallow groundwater were minimal in general, in contrast to the impacts on deep groundwater tables. The SWMM-LID-GW outperformed the current SWMM for a wide range of groundwater conditions, particularly for locations in which the groundwater table frequently rises to 1.0 m or less below ground.

Groundwater uptake of different surface cover and its consequences in great Hungarian plain

IntroductionForest cover in Hungary has increased from 1.1 to 2.0 million hectares during the last century. The EU (European Union) promotes further afforestation; thus, 15,000–18,000 ha are being forested each year, mainly in the Hungarian Great Plain. In terms of species used for afforestation, poplar plantations are preferred over native oak woodlands.The groundwater uptake of trees can be a significant water balance element of forested areas in shallow groundwater environments within the Hungarian Great Plain. Forests can cause water table depressions and subsurface salt accumulation in areas with negative water balance. This study examined the hydrological impact of forest cover in the Hungarian Great Plain. Within the framework of this research, climatic water balance, water table depth and salinity, subsoil layering, tree species and stand age were analysed as influencing factors. This paper compares the effect which an oak forest, a poplar plantation and a pasture have on groundwater uptake and salt accumulation.ResultsThe water table level was roughly 0.4–0.5 m lower beneath the oak forest and the poplar plantation than it was beneath the pasture. Forest groundwater use was 1.5–2 times higher than that of grassland. Groundwater uptake of oak forest was greater than that of poplar plantation during the monitoring period. Salt accumulation, which shows water use in the longer run, was slightly higher for poplar in deeper layers.ConclusionsThe greater amount of groundwater used by trees does not lead to a higher salt uptake as only a slight accumulation of salt was measured beneath the forests. Overall, hybrid poplar was slightly less favourable than native oak when considering salinization effects. However, even greater groundwater uptake by trees over longer timescales could cause more significant salt accumulation under pronounced drought conditions due to climate change.

Evaluating hydrologic performance of bioretention cells in shallow groundwater

AbstractBioretention cells, which are generally effective in controlling surface runoff and recharging groundwater, have been widely adopted as low impact development practices. However, shallow groundwater has limited their implementation in some locations due to the potential problems of a reduction in surface runoff control, groundwater pollution, and continuous groundwater drainage through the underdrain. Many guidelines have established minimum requirements for the groundwater depth below bioretention cells, but they may not be optimized for certain environmental conditions and bioretention cell designs. This study made use of a variably saturated flow model to examine the hydrologic performance of a single bioretention cell in shallow groundwater with event‐based simulations, considering a wide range of initial groundwater depths, media and in situ soil types, surface runoff loads, and underdrain sizes. Performance indicators (e.g., runoff reduction, time for infiltrated water to reach the bioretention cell bottom and the groundwater table, and height and dissipation time of groundwater mound) were evaluated to examine the processes of runoff generation, the formation and dissipation of groundwater mounds, and the bioretention cell's performance in a shallow groundwater environment. The most influential factors were the initial groundwater depth, the hydraulic conductivity of the media soil, and the rainfall runoff load. With a deeper initial groundwater table, infiltrated water took longer to reach the bioretention cell bottom and groundwater table. Groundwater mounds, however, took longer to dissipate even though they were smaller. The groundwater quality can be better protected if relatively less‐permeable soil types (e.g., sandy loam) are used as the media, although it may compromise the performance in runoff quantity control. However, only very high surface runoff loads would cause concerns regarding a reduction in runoff quantity control and possible groundwater contamination due to the shallow groundwater. A distance of 1.5–3 m between the bioretention cell bottom and the groundwater table is generally sufficient. The results of this study could help to guide the planning and design of bioretention cells in areas of shallow groundwater.