Deep Water Table Research Articles

English

Soil salinity is a threat for agriculture under irrigation as it affects the growth and development of plants and the problem is widespread in middle Awash where Amibara irrigated farms are present. Therefore, Measurements of groundwater depth were taken from thirty piezometers in the months of August, September, October, November and December to investigate spatial variability and temporal fluctuation of groundwater depth in Amibara irrigation scheme. Based on the field measurement, relatively shallow water levels were recorded in Vertisols area as compared to that in Fluvisols area with a mean values of 1.47 m and 3.01 m, respectively. On the other hand groundwater depth was influenced by the type of field cover and irrigation practices taken place during the sampling periods. Relatively deep water table was recorded in fields covered by shrubs and tree plants as compared to cotton and sugarcane fields with mean groundwater depth values of 4.87, 2.48 and 1.78 m, respectively. Seasonal fluctuation of groundwater depth was influenced with the climatic condition and irrigation practices occurred at the study area. In general shallower water tables were recorded at most piezometers in both soil types in the study area, which is resulted from poor irrigation management and destruction of surface and subsurface drainage structures to drain and remove excess water. Therefore Regular monitoring and evaluation of groundwater depth is required to reduce the accumulation of salt and to protect the irrigated land from abandonment. Key words: groundwater, depth, spatial, temporal, fluvisols and vertisols.

Moving Multi-Front (MMF): A generalized Green-Ampt approach for vertical unsaturated flows

A Moving Multi-Front (MMF) method is developed and tested for solving the Richards equation governing unsaturated flow in vertical homogeneous porous columns. The MMF model is a gridless method. It can be viewed as a generalization of the Green-Ampt piston flow approach, which models flow as a single abrupt moving front separating saturated and dry regions during infiltration. The MMF model further generalizes this concept, using a parametrization of unsaturated water retention and conductivity-pressure curves. It reduces the Richards PDE to an ODE system governing “M” moving front positions. Different tests are developed to validate this approach for 1D transient downwards/upwards flows submitted to constant and time-varying pressure boundary conditions. They include: (i)infiltration to deep water tables; (ii) infiltration to shallow water tables; (iii) capillary rise from fixed water tables; (iv) gradual water table rise (partially saturated column with evolving pressure condition at bottom). The MMF results are compared favorably to finely discretized fixed grid solutions of Richards PDE. Analyses of error and accuracy show satisfactory results in terms of water content profiles and boundary fluxes (e.g. infiltration rate).

Barometric-pumping controls fugitive gas emissions from a vadose zone natural gas release

Subsurface natural gas release from leaking oil and gas wells is a major environmental concern. Gas migration can cause aquifer contamination, explosive conditions in soil gas, and greenhouse gas emissions. Gas migration is controlled by complex interacting processes, thus constraining the distribution and magnitude of “fugitive gas” emissions remains a challenge. We simulated wellbore leakage in the vadose zone through a controlled release experiment and demonstrate that fugitive gas emissions can be directly influenced by barometric pressure changes. Decreases in barometric-pressure led to surface gas breakthroughs (>20-fold increase in <24 hours), even in the presence of low-permeability surficial soils. Current monitoring strategies do not consider the effect of barometric pressure changes on gas migration and may not provide adequate estimates of fugitive gas emissions. Frequent or continuous monitoring is needed to accurately detect and quantify fugitive gas emissions at oil and gas sites with a deep water table.

Springwater provenance and flowpath evaluation in Blue Lake, Bonneville basin, Utah

Water in Utah and Nevada is important for agriculture, municipal use, solute transport, and ecosystem preservation. Large spring wetland systems occur on the playa margin of the Bonneville basin, including Blue Lake, 15 km south of the Bonneville Salt Flats on the Utah-Nevada state border. Large spring systems have historically been studied as water budgets don't apparently balance from direct mountain front recharge (Nelson and Mayo, 2014; Gardner and Heilweil, 2014; and others). Blue Lake is no exception; prior studies here have suggested discharge rates 0.04 - 0.05 km3/yr (Louderback and Rhode, 2009), greater than expected for modelled recharge in the surrounding mountain range (0.03 km3/yr). Three hypothesized recharge mechanisms for Blue Lake are tested: mountain-front recharge, interbasinal groundwater flow, and infiltration from historic Lake Bonneville. Remote sensing suggests that a conservative estimate of Blue Lake discharge constitutes 50-64% of modelled mountain-front recharge (Flint et al., 2011). Major ions, δ18O, δ2H, dissolved gases (14C, 3He, 4He, Ne, Ar, Kr, Xe) and trace elements (Sr and 87Sr/86Sr isotopes) comprehensively constrain recharge conditions, water-rock interactions, flowpaths, and groundwater provenance of this large spring system. 14C signatures suggest that Blue Lake discharge has a transit time between 5,600 and 12,200 years, older than that of Fish Springs. Noble gas concentrations in Blue Lake water suggest an elevated recharge temperature greater than 19°C and low salinity, indicating a deep water table and high geothermal gradient in the recharge area. 87Sr/86Sr ratios of playa-margin springs are elevated from that of mid-playa groundwaters, springwaters from the adjacent mountain range, and alluvial fill groundwater from the valley directly south of Blue Lake. Playa-margin spring Sr isotope values (0.713-0.714) are most similar to direct runoff from the Deep Creek Range granodiorite outcrop (>0.713). Interbasinal groundwater flow in combination with mountain-front recharge is best supported by chemical data rather than mountain-front recharge alone or the slow discharge of regional aquifers recharged by lacustrine infiltration from Lake Bonneville.

Active Layer Groundwater Flow: The Interrelated Effects of Stratigraphy, Thaw, and Topography

AbstractThe external drivers and internal controls of groundwater flow in the thawed “active layer” above permafrost are poorly constrained because they are dynamic and spatially variable. Understanding these controls is critical because groundwater can supply solutes such as dissolved organic matter to surface water bodies. We calculated steady‐state three‐dimensional suprapermafrost groundwater flow through the active layer using measurements of aquifer geometry, saturated thickness, and hydraulic properties collected from two major landscape types over time within a first‐order Arctic watershed. The depth position and thickness of the saturated zone is the dominant control of groundwater flow variability between sites and during different times of year. The effect of water table depth on groundwater flow dwarfs the effect of thaw depth. In landscapes with low land‐surface slopes (2–4%), a combination of higher water tables and thicker, permeable peat deposits cause relatively constant groundwater flows between the early and late thawed seasons. Landscapes with larger land‐surface slopes (4–10%) have both deeper water tables and thinner peat deposits; here the commonly observed permeability decrease with depth is more pronounced than in flatter areas, and groundwater flows decrease significantly between early and late summer as the water table drops. Groundwater flows are also affected by microtopographic features that retain groundwater that could otherwise be released as the active layer deepens. The dominant sources of groundwater, and thus dissolved organic matter, are likely wet, flatter regions with thick organic layers. This finding informs fluid flow and solute transport dynamics for the present and future Arctic.

An exact analytical model for fluid flow through finite rock matrix block with special saturation function

An exact analytical solution for one-dimensional fluid flow through rock matrix block is presented. The nonlinearity induced from flow functions makes the governing equations describing this mechanism difficult to be analytically solved. In this paper, an analytical solution to the infiltration problems considering non-linear relative permeability functions is presented for finite depth, despite its profound and fundamental importance. Elimination of the nonlinear terms in the equation, as a complex and tedious task, is done by applying several successive mathematical manipulations including: Hopf-Cole transformation to obtain a diffusive type PDE; an exponential type transformation to get a convective-diffusive type PDE with suitable boundary conditions; Laplace transformation; Integral transformation to homogenize the boundary condition in the Laplace domain; and finally Laplace inversion method to find the time domain solution. The obtained solution is used for developing a new matrix-fracture transfer function. The developed analytical equations are used for prediction of drying front in the case of evaporation from deep water table. The model results are in close agreement with the experimental data and numerical simulation of the process. Results of sensitivity analysis of different parameters on recovery rate and ultimate production based on design of experiment method are also discussed.

Random forests to detect subsoiling and subsurface drainage effects on corn plant height and water table depth

Soil compaction is an agricultural and environmental concern. Understanding the parameters affecting crop productivity is essential for an efficient agriculture. We compared two statistical methods: random forest (RF), and multiple linear regression (MLR), to evaluate the effects of various parameters, including subsoiling, on corn (Zea mays L.) plant height and on seasonal mean water table depth. We performed subsoiling treatments in a clay field of low permeability, provided with subsurface drains and remodeled with rounded beds. These experiments allowed comparing a control without subsoiling to four subsoiling treatments: a tractor and a bulldozer operated parallel and perpendicular to the subsurface drains. Each treatment was randomized and repeated three times. In the spring of 2016, we drilled 198 60-cm deep water table depth observation wells. The corn height was estimated by photogrammetry. The results showed that both RF and MLR allowed determining the main factors affecting plant height and seasonal mean water table depth, for which subsoiling treatments played a negligible role. Coefficients of determination were much higher and prediction intervals much smaller for RF (R2 ≥ 0.94) than for MLR (R2 : 0.28-0.69). RF allowed visualizing nonlinear relationships between mean water table depth, plant height and the predictor variables, such as XY coordinates, horizontal distance to the field open drain and depth to subsurface drains which are all related to the position on the beds. To maximize corn plant height in this type of soil, RF also showed that the horizontal distance to drain must be less than 3–4 m, and therefore optimal drain spacing is 7 m, horizontal distance to field open drains is more than 8 m, and optimal mean seasonal water table depth is greater than 0.25 m.

Differential effects of soil waterlogging on herbaceous and woody plant communities in a Neotropical savanna.

The impacts of soil properties and fire regime on Neotropical savannas are well-known, but the importance of hydrological regime for plant species assembly has received less attention. Here, we assessed changes in diversity patterns of herbaceous and woody communities along a water table gradient in a fire-excluded Neotropical savanna. We found that increased waterlogging of soils was associated with declines in both herbaceous and woody species richness. Woody species richness decreased once the water table depth is less than 4m and no woody species occurred once water table depth was less than 23cm. Herbaceous communities remained species rich until the shallowest water table depth, where there is flooding at some point in the year, and even there, over a dozen species occurred. Woody species that occurred in areas with shallower water tables were a nested subset of those in areas with deeper water tables. In contrast, herbaceous communities showed turnover over the hydrological gradient, with distinct species specialized for different water table levels. However, we found that those specialists are restricted to few evolutionary lineages, evidenced by increased phylogenetic clustering over the water table gradient in herbaceous communities. We suggest that evolutionarily conserved hydrological niches define the herbaceous layer over the hydrological gradient, whereas only generalist woody species persist under high water tables. Our findings show that the effect of soil waterlogging differs between the herbaceous and woody layer of savannas, indicating that these communities will respond differently to shifts in the hydrological regime under future environmental change.

A new approach to generalizing riparian water and air quality function across regions.

There is growing interest in generalizing the impact of hydrogeomorphology and weather variables on riparian functions. Here, we used RZ-TRADEOFF to estimate nitrogen, phosphorus, water table (WT) depth, and greenhouse gas (GHG: N2O, CO2, CH4) functions for 80 riparian zones typical of the North American Midwest, Northeast (including Southern Ontario, Canada), and Mid-Atlantic. Sensitivity to weather perturbations was calculated for temperature and precipitation-dependent functions (CO2, phosphate concentration, and water table), and multivariate statistical analysis on model outputs was conducted to determine trade-offs between riparian functions. Mean model estimates were 93.10cm for WT depth, 8.45mgNL-1 for field edge nitrate concentration, 51.57% for nitrate removal, 0.45mg PO43-L-1 for field edge phosphate concentration, 1.5% for subsurface phosphate removal, 91.24% for total overland phosphorus removal, 0.51mgNm-2day-1 for N2O flux, 5.5gCm-2day-1 for CO2 fluxes, and - 0.41mgCm-2day-1 and 621.51mgCm-2day-1 for CH4 fluxes in non-peat sites and peat sites, respectively. Sites in colder climates were most sensitive to weather perturbations for CO2, sites with deep water tables estimates had the highest sensitivity for WT, and sites in warm climates and/or with deep confining layers had the lowest sensitivity for phosphate concentration. Slope, confining layer depth, and temperature were the primary characteristics influencing similarities and trade-offs between sites. This research contributes to understanding how to optimize riparian restoration and protection in watersheds based on both water (nitrogen, phosphorus) and air quality (GHG) goals.

Evidence for ecosystem state shifts in Alaskan continuous permafrost peatlands in response to recent warming

Peatlands in continuous permafrost regions represent a globally-important store of organic carbon, the stability of which is thought to be at risk under future climatic warming. To better understand how these ecosystems may change in a warmer future, we use a palaeoenvironmental approach to reconstruct changes in two peatlands near Toolik Lake on Alaska's North Slope (TFS1 and TFS2). We present the first testate amoeba-based reconstructions from peatlands in continuous permafrost, which we use to infer changes in water-table depth and porewater electrical conductivity during the past two millennia. TFS1 likely initiated during a warm period between 0 and 300 CE. Throughout the late-Holocene, both peatlands were minerotrophic fens with low carbon accumulation rates (means of 18.4 and 14.2 g C m−2 yr−1 for cores TFS1 and TFS2 respectively). However, since the end of the Little Ice Age, both fens have undergone a rapid transition towards oligotrophic peatlands, with deeper water tables and increased carbon accumulation rates (means of 59.5 and 48.2 g C m−2 yr−1 for TFS1 and TFS2 respectively). We identify that recent warming has led to these two Alaskan rich fens to transition into poor fens, with greatly enhanced carbon accumulation rates. Our work demonstrates that some Arctic peatlands may become more productive with future regional warming, subsequently increasing their ability to sequester carbon.

Seasonal changes in water sources used by woody species in a tropical coastal dune forest

Our aim was to investigate the water sources used by woody species under contrasting water availability and the extent of water-sources-use differentiation among dominant woody species in a tropical coastal dune forest. We sampled 15 woody species in a Brazilian restinga forest and, through Bayesian isotope mixing models, we estimated the proportion of water sources used. We tested whether water-sources-use was (i) different between contrasting water availability conditions; (ii) dependent on growth form, plant size or crown illumination; and (iii) influenced by stand density, evenness or biomass. We found a seasonal variation in water-sources-use, but no vertical soil-water partitioning among woody species. In wetter periods, plants used mainly water from top-soil, as a shallow water table limited water uptake to top-soil layers recharged with rainwater. Contrastingly, during drier periods, with the absence of rain and a deeper water table, plants generally relied on deeper (50 cm) soil layers. Only under less-wet conditions, a greater evenness and density implied higher water-uptake depth heterogeneity among plants. However, changes in the main water-sources used by plants were neither evoked in more dense or diverse plots, nor induced by plant size. Our study shows that restinga species have dynamic shifts in water-uptake depth caused by seasonal water availability changes, influenced by the combined effect of insufficient moisture at shallow soil layers and water-table lowering in drier periods. These temporal shifts are common among species, implying that restinga woody community has a homogeneous strategy of water-resources acquisition. This study enhances our understanding of the effects that water variations can have on water-resource use in restinga forests.

Comparison of Hydrology of Two Atlantic Coastal Plain Forests

Abstract. This article compares the short-term and long-term hydrology of two typical forests in the humid Atlantic Coastal Plain, including a relatively undisturbed forest with natural drainage in South Carolina (SC) and a drained pine plantation in North Carolina (NC), using monitoring and modeling approaches. Highly dynamic outflow (O) from both of these systems is driven by the water table (WT) position, as influenced by rainfall (R) and evapotranspiration (ET). The annual runoff coefficient (ROC) varied from 5% in dry years to 56% in wet years, depending on the soil water storage (SWS), with a significantly higher average value for the NC site despite its deeper WT, on average, than the SC site. Although both sites behaved similarly in extreme climate conditions, the change in SWS above the WT influenced the annual RO, ROC, and ET. The 17-year average annual ET of 1114 mm (R – O, assuming annual balanced SWS) for the SC site was significantly higher (p = 0.014) than the ET of the drained NC site (997 mm) despite the SC site’s lower mean annual R of 1370 mm, compared to 1520 mm for the NC site. This may be due to both the higher potential ET (PET) and soil water-holding capacity of the SC site. The SC site had higher frequency and duration of WT near the surface during winter, deeper summer WT, and higher correlation of annual ET to annual R (r2 = 0.90 vs. 0.15), suggesting that the SC site was often moisture-limited, particularly during the growing season. Most of the streamflow in these systems occurred during winter, with low ET demands. However, summer periods with tropical storms also resulted in large RO events, generally with higher frequency and longer durations at the drained NC site. These results are similar to an earlier short-term comparison with an unstable behavior period at the SC site after Hurricane Hugo (1989). This study highlighted (1) the differences in hydrology between coastal forests drained for silvicultural production and undrained natural forests managed only for restoration, (2) the importance of long-term monitoring and the effects of regeneration as well as vegetation management on flow regime, and (3) the application and limitations of two widely used models (MIKESHE and DRAINMOD) in describing the hydrology of these forests. Long-term studies can be a basis for testing new hypotheses on water yield, stormwater management, wetland hydrology, vegetation restoration, bioenergy production, and climate change, in addition to applications of proper models for assessing the eco-hydrologic impacts of land use and climate change on freshwater coastal forests linked with downstream riparian rivers and estuaries affected by tidal fluxes and sea level rise.HighlightsOutflow, driven by water table position on these forest systems, is highly variable, depending on its soil water storage.The hydrologic responses of both forest sites were similar during extreme climatic events or disturbances.Effect of forestry drainage on runoff was obscured by its large interannual differences.Long-term monitoring provides better insights on climate and vegetation management effects on flow regime and model validation Keywords: Drainage, Evapotranspiration, Hydrologic models, Pine forest, Poorly drained soils, Runoff coefficient, Water table.

Short- and long-term hydrologic controls on smouldering fire in wetland soils

Smouldering fire vulnerability in organic-rich, wetland soils is regulated by hydrologic regimes over short (by antecedent wetness) and long (through influences on soil properties) timescales. An integrative understanding of these controls is needed to inform fire predictions and hydrologic management to reduce fire vulnerability. The Great Dismal Swamp, a drained peatland (Virginia and North Carolina, USA), recently experienced large wildfires, motivating hydrologic restoration efforts. To inform those efforts, we combined continuous water levels, soil properties, moisture holding capacity and smouldering probability at four sites along a hydrologic gradient. For each site, we estimated gravimetric soil moisture content associated with a 50% smouldering probability (soil moisture smoulder threshold) and the water tension required to create this moisture threshold (tension smoulder threshold). Soil properties influenced both thresholds. Soils with lower bulk density smouldered at higher moisture content but also had higher moisture holding capacity, indicating that higher tensions (e.g. deeper water tables) are required to reach smouldering thresholds. By combining thresholds with water level data, we assessed smouldering vulnerability over time, providing a framework to guide fire prediction and hydrologic restoration. This work is among the first to integrate soil moisture thresholds, moisture holding capacities and water level dynamics to explore spatiotemporal variation in smouldering fire vulnerability.

Identifying resilient Eastern Massasauga Rattlesnake (Sistrurus catenatus) peatland hummock hibernacula

At the northern limit of the Eastern Massasauga Rattlesnake’s (Sistrurus catenatus (Rafinesque, 1818)) range, individuals spend up to half the year overwintering. In hummock hibernacula found in peatlands, it is likely that subsurface temperature and water table position are contributing factors dictating habitat suitability. As a step towards assessing the vulnerability of hibernacula to anthropogenic changes, we combined subsurface temperature and water table dynamics to assess the likelihood that unflooded and unfrozen conditions were present in hummock hibernacula. Our results indicate that taller hummocks are more resilient to an advancing frost line and fluctuating water table by providing a larger area and duration of unfrozen and unflooded conditions, and a critical overwintering depth that is farther from the hummock surface. In two study sites along eastern Georgian Bay, an unflooded and unfrozen zone was present for over 90% of the overwintering period for hummocks taller than 25–27 cm. Our findings highlight the vulnerability of peatland hummocks to variability of winter weather where deep freezing and (or) water table rise may nonlinearly reduce resilience. This suggests that height is not the only component affecting the suitability of hummock hibernacula and that further research should examine the structure and spatial arrangement of hummocks within a peatland.

Assessment of the impact of climate change on coastal aquifers in Oman

This paper evaluates numerically the effects of climate change (precipitation, temperature, and sea level rise (SLR)) on two selected coastal aquifers located in the north of Oman: (1) Jamma aquifer which is mainly used for irrigation and (2) Samail Lower Catchment aquifer (SLC) which is a strategic reserve for domestic water supply, hence it is of great economic value. Unlike Jamma aquifer, SLC maintains positive gradient seaward as the aquifer is currently well-managed. The water dynamics in both aquifers are studied numerically using MODFLOW and MT3DMS codes under the different Representative Concentration Pathway scenarios (RCPs) for years 2050 and 2070 according to the Intergovernmental Panel on Climate Change (IPCC). Results show that the salinized area in Jamma site, considering the intruded distance of the selected 1500 ppm iso-concentric line, will increase by 32 and 38% by years 2050 and 2070, respectively, compared to the situation for the base case year 2015. This effect is significant given the narrow agricultural strip area it covers which is also shared for urban and industrial land uses. Hence, the farming community will be severely affected. The positive hydraulic gradient seaward direction for SLC aquifer (because of proper management) helps to combat significant intrusion of saltwater. In general, the results show rapid climate change impacts during the next 15 years which urges implementation of measures to reduce the effect, before the farming community at large (along with other users) be severely affected and adaptation measures become infeasible. SLR was found to be the main climatic factor that will significantly affect the stressed coastal aquifers. The change in rainfall rate for north of Oman is small and the effect of evapotranspiration is relatively low given the high extinction depth (deep water table) and sparse vegetation. The extent of the effect of climate change on aquifers is site specific. Stressed aquifers like Jamma are highly vulnerable and severely affected. Alleviation of the impact and adaptation measures must be planned first for more vulnerable aquifers. The adaptation measures should include managed aquifer recharge using both ephemeral floods generated by irregular and limited rainfall events and by using treated wastewater, expanding in reuse of treated wastewater, and improving the efficiency of irrigation (main consumer of available water, > 80%) along with better water pricing policies. Although the currently well-managed aquifer systems (e.g., SLC) are not significantly affected by climate change, improper development and management of those systems would definitely shift them to be more vulnerable to adverse effects of climate change. The findings of this study are importance for the water resources managers as they stressed that precaution measures must be implemented for the deteriorated aquifer (like Jamma aquifer) while protecting and maintaining the well-managed groundwater systems (e.g., SLC aquifer) as these show more resilience to climate change. Efforts should be devoted to manage stressed aquifer systems as a priority in order to improve their resilience level to climate change.

A Daily Water Table Depth Computing Model for Poorly Drained Soils

The objective of this paper is to present a relatively simplified model to predict daily water table (WT) by solving ordinary differential equation dWT (t)/dt = F (α1, α2, α3, WT0(t), RF (t), PET (t)), with α1, α2, α3, WT0 as parameters, and RF (rainfall) and PET (potential evapotranspiration), respectively, as inputs. The model was calibrated and validated with WT on four poorly to moderately drained soils (Lenoir, Rains, Lynchburg, and Goldsboro) on a forested wetland. Calibration results were in good agreement with the measured WT for all soils, except the Goldsboro with deeper WT. r2 (coefficient of determination) and NSE (Nash-Sutcliffe Efficiency) statistics both ranged from 0.81 for the Lenoir to 0.89 and 0.87, respectively, for the Lynchburg. Average absolute daily deviation (AADD) varied from 10.8 cm for Lenoir to 16.7 cm for Rains. The performance was somewhat poorer, during relatively dry periods with deeper WT, yielding r2 and NSE as low as 0.55 and 0.29, respectively, for Lenoir, and large AADD for Lynchburg. Discrepancies were associated with WT overprediction for deeper depths. The new model is capable of describing the WT for poorly drained high water table soils, with a potential for assessing effects of land management, wetland hydrology, and climate changes.

Precision agriculture based on crop physiological principles improves whole-farm yield and profit: A case study

Abstract Precision agriculture has under delivered partially because it has been based on technologies focused on increasing the resolution of spatial variation in soil and yield and more recently automation, with less effort in incorporating the physiological principles of crop responses to environmental variation. Here we show how a whole-farm precision agriculture approach accounting for the physiological processes underlying the relationship between environment and crop development, growth and yield (“zone management”), bridge yield gaps, increased farmer profit and reduced risk, on San Lorenzo, a 5000 ha dryland farm in the southern Pampas. The farm grows wheat and barley in winter, and soybean, maize, and sunflower in summer; winter grain cereal/double-cropped soybean is a main activity. Four management zones were defined: i) Zone 1, shallow soils ( 3 m below surface); ii) Zone 2, intermediate soil depth (0.8 to 1.8 m) with low frost risk and deep water table; iii) Zone 3, deep soils (> 1.8 m) with low frost risk and deep water table; and iv) Zone 4, deep soils (> 1.8 m) with high frost risk and water table

Regulation of deep groundwater based on MODFLOW in the water intake area of the South-to-North Water Transfer Project in Tianjin, China

Abstract With the development of economy and society, deep groundwater exploitation has intensified, even to the point of over-exploitation, resulting in multiple geological disasters. Thus, it is essential to regulate the deep groundwater table to a reasonable range. This paper selected the water intake area of the South-to-North Water Transfer Project in Tianjin as a case study. First, the groundwater flow and land subsidence model with MODFLOW-2005 and SUB Package were constructed. Second, the regulation schemes were designed based on the corresponding regulation principles. Lastly, the established groundwater model was adopted to forecast and simulate deep water table and land subsidence under different exploitation scenarios, and regulation effects were analyzed from the viewpoints of exploitation total amount, exploitation distribution, and exploited horizon. The results showed that groundwater tables of different layers and land subsidence were effectively controlled and improved under the three exploitation schemes for different planning level years. The exploitation total amount of groundwater, exploitation distribution, and exploited horizon had a direct impact on water table and land subsidence. From the perspective of regulating deep groundwater, all three schemes could achieve this goal, hence the three schemes were reasonable and feasible. The results are of great significance for rational utilization of deep groundwater.

Interactive Effects of Soil Salinity and Water Table Depth on Soil Properties and Sorghum (Sorghum Bicolor L. Moench) Production

Soil salinity and water table are the most prevalent and widespread problems limiting crop productivity in irrigated agriculture. Our experiment aims to evaluate the effect of soil salinity and water table on some soil properties, growth, and yield of sorghum (variety Giza 15) grown along two successive seasons. Nine different sites were chosen, representing three levels of soil salinity (i.e. ECe < 4, 4-8 and 8-16 dS m-1). For each salinity level three water table were selected (i.e. shallow ≈ 55 cm, medium ≈ 80 cm and deep ≈ 120 cm). Results revealed that there are main considerable effects of salinity and water table on some soil properties. Increasing of salinity caused significant decreases in plant growth, weight of 1000 grains (g), protein content% and seed yield (t/ha) which decreased by 36.98%, 32.27%, 20.45%, 29.95 % and 57.46% respectively, when salinity increased from S1 to S3. On the other hand, decreasing of water table lead to improvement in all mentioned soil properties and plant growth. The results indicated that need to maintain low or moderate salinity and deep water table, which is essential for producing high sorghum grain yield with satisfactory quality.

Modelling Vadose Zone Processes for Assessing Groundwater Recharge in Semi-Arid Region

Normally groundwater recharge is estimated using methods based on water balance, water table fluctuations, fixed factor of annual rainfall and tracer movement. In many of these methods water stored in the vadose zone and evapotranspiration are not accounted properly. These factors control groundwater recharge to a large extent, particularly in arid and semi-arid regions which are normally characterized by a deep water table, thick vadose zone and high evapotranspiration. In this study, HYDRUS-1D and MODFLOW models were used to assess the recharge flux and groundwater recharge in an area under a semi-arid region giving due consideration to important vadose zone processes. Cumulative recharge flux at water table in various sub-areas varied from 20.01 cm to 23.43 cm (29.26% to 34.26% of the monsoon rainfall). The average groundwater recharge was 22.2%. Total surface runoff in various sub-areas varied from 3.39 cm to 14.36 cm (5% to 21% of the monsoon rainfall). Evapotranspiration was found to be a major recharge controlling factor. Reference evapotranspiration varied from 37.19 cm to 45 cm (54% to 66% of the monsoon rainfall). Natural recharge under the prevailing pumping rate and pumping schedule was 23.3% of the monsoon rainfall. Simulation results revealed that if all the surface runoff is retained in the area, water table will rise by 1.46 m.