Water Table Response Research Articles

Water-table response to extreme precipitation events

Extreme precipitation events (EPEs) will play a significant role in influencing soil–water and groundwater storage worldwide. We examined water-table depth (WTD) response to EPEs for 17 cases representative of soils and climate settings across the United States. Precipitation data from NOAA’s Precipitation Frequency Data Server were used for each case to characterize 1-day extreme precipitation events (EPEs) with annual exceedance probabilities of 0.1 % over an average baseline date range of 1981–2011. The inverse solution in the HYDRUS-1D modeling software was used to obtain the soil–water retention curve for each case. Non-EPE and EPE scenarios were modeled and compared to examine water-table displacement (ΔWTD) and recession time (trec). The ΔWTD ranged from 0.6 to 2.4 m across cases and were not directly controlled by EPE amount; instead, ΔWTD was inversely related to available porosity. Soils with low available porosity experienced large ΔWTD compared to soils with higher available porosity. In cases with larger diffusivity values, the modeled water table receded faster than in cases with smaller diffusivity values. This was because water-table recession times, trec, were inversely related to hydraulic diffusivity. For all cases, recession back to pre-EPE levels ranged from months to years suggesting an increased role by the unsaturated zone in buffering EPEs that should be considered in future EPE-groundwater modeling studies.

Base flow simulation using a physically based subsurface model – The case of a tropical basin in the Western Ghats, India

A novel framework that integrally uses groundwater and streamflow observations to calibrate a physically based sub surface model to generate base flow on a daily time step is presented in this study. Trend analysis on mean annual base flow time series showed that a declining trend was present in the basin though the upstream humid region was devoid of any trend. GLUE analysis was adopted to the simulation of base flow in the humid region and the most sensitive parameters were identified as the recharge factor (rf) and discharge factor (pd). The model was able to satisfactorily simulate base flow as observed values fell within the 95CI bands for the calibration period. The mean annual BFI values were computed at Muthankera to be 0.236 ± 0.02. The mean seasonal BFI varied from 48 % during post monsoon periods to 21 % during monsoon periods. The base flow simulated by the model was comparable to the output from the Eckhardt filter which has been widely cited to be a suitable baseflow separation method for many river basins. Due to the absence of groundwater level data in the transition region, a combination of model and digital filter was used to calibrate that region. The draft from the groundwater storage computed from the model was found to be highly nonlinear. The rf was seen to be lower and pd to be higher in the transition region than in the humid region. This would imply that in the transition region, the base flow is generated more gradually in comparison to the humid region. This was characteristic of forested basins where the uptake of water by deep rooted trees during evapotranspiration from the unsaturated zone causes delay in the water table response which in turn could result in delay in the base flow generation process. The consequence of the calibration exercise on Kabini basin was establishing that the heterogeneity in terms of precipitation and land use has resulted in the distinct hydrologic responses from the two regions in the basin.

Large‐scale lateral saturated soil hydraulic conductivity as a metric for the connectivity of subsurface flow paths at hillslope scale

AbstractLateral saturated soil hydraulic conductivity, Ks,l, is the soil property governing subsurface water transfer in hillslopes, and the key parameter in many numerical models simulating hydrological processes at the hillslope and catchment scales. Likewise, the hydrological connectivity of the lateral flow paths plays a significant role in determining the rate of the subsurface flow at various spatial scales. This study investigates the relationship between Ks,l and hydrological connectivity at the hillslope spatial scale. Ks,l was determined by the subsurface flow rates intercepted by drains and water table depths observed in a well network. The hydrological connectivity was evaluated by the synchronicity among water table peaks, and between these and the peaks of the drained flow. Rainfall and soil moisture were used to investigate the influence of the transient hydrological soil condition on connectivity and Ks,l. As the synchronicity of the water table response between wells increased, the lag times between the peaks of water levels and those of the drained subsurface flow decreased. Moreover, the most synchronic water table rises determined the highest drainage rates. The relationships between Ks,l and water table depths were highly non‐linear, with a sharp increase in the values for water table levels close to the soil surface. Estimated Ks,l values for the full saturated soil were in the order of thousands of mm h−1, suggesting the activation of macropores in the root zone. The Ks,l values determined at the peak of the drainage events were correlated with the indicators of synchronicity. The sum of cumulative rainfall and antecedent soil moisture was correlated with the connectivity indicators and Ks,l. We suggest that, for simulating realistic processes at the hillslope scale, the hydrological connectivity could be implicitly considered in hydrological modelling through an evaluation of Ks,l at the same spatial scale.

Water table response to rainfall and groundwater simulation using physics-based numerical model: WASH123D

Study regionFour districts (Meinong, Qishan, Dashu, and Daliao) of Kaohsiung city, Southern Taiwan Study focusThe understanding of aquifer recharge in terms of water table response to rainfall is of critical importance to groundwater systems management and various endeavors have been made to estimate the amount of recharge using rainfall data. The purpose of this study is to evaluate the groundwater level response to rainfall and determine the recharge potential for shallow aquifers. We showed a simple approach to estimate specific yield (Sy) and hydraulic conductivity (k) as functions of rainfall and water level data. New hydrological insights for the regionCorrelation method is applied to investigate groundwater level response to associated rainfall and it was found that the rise in water table linearly depends on the rainfall amount per event. Results show the annual recharge rates of 244–1472 mm year─1, which represent 12–43% of rainfall in the study area. The estimated k (order of 10─4 to 10─5 m s─1) and Sy (0.20–0.51) were used as prior values to setup groundwater numerical modeling using WASH123D. The real-time case scenario simulation using pumping and rainfall data indicated the reasonable hydrological response of groundwater levels to rainfall. The long-term simulations should be performed with WASH123D to deal with the subjectivity of sustained groundwater pumping and sustainability of aquifers for better groundwater resource planning and management.

Influence of Subsurface Pipe Perforations on Transient Water Table Response and Steady Soil-Water Flux under Subirrigation

HighlightsWater table rise was slower under a sparsely perforated pipe as compared to a pipe that was densely perforated.Response time increased as buried pipe depth decreased for both combinations of perforation characteristics.Fluxes from buried pipes spaced at 15 m in loamy sand satisfied the water demand for cereal/grain crops (6 mm d-1).Increasing perforation density on the pipe wall is the most effective way to reduce exit head losses.Abstract. It is important to consider the water table rise into the unsaturated zone when designing subsurface irrigation systems that consist of buried perforated corrugated pipes. Corrections to pipe spacing equations for head losses due to perforations are based on the entrance resistance, which is derived for buried pipes operating in drainage mode. However, the boundary condition at the soil-pipe interface when operated in subsurface irrigation mode requires the use of the exit resistance to accurately account for perforations in the pipe wall. Simulations of a subsurface irrigation system with four soil textures, three lateral pipe spacings, and three buried depths were carried out, with the numerical model COMSOL, to demonstrate the effects of variable perforation characteristics on the transient water table rise into the unsaturated zone. Soil-water fluxes were also computed for the system when operated under steady-state conditions. The simulated water table rise exceeded or approached a predetermined target water level of 1.65 m above the buried pipes in coarse-textured soils (loamy sands and silt loams) with lateral pipe spacings as large as 10 m. Increasing the number and length of rectangular slots in the pipe wall (densely perforated) can reduce the water table response time to reach the target level by 15 h in a silt loam soil and 25 h in a clay soil. The optimum pipe spacing needed to sustain a soil-water flux of 6 mm d-1 (common to eastern Canada and the U.S. Midwest) can be increased from 15.1 to 16.2 m in loamy sands by using densely perforated pipes. In contrast, increasing perforations in pipes buried in clays and sandy clays will result in pipe spacing increases of less than 0.2 m because these fine-textured soils have lower hydraulic conductivity. This study has demonstrated that variable perforation characteristics can be included in the analysis and design of subsurface drainage systems for improving water management. Keywords: Corrugated perforated pipes, Exit resistance, Head loss, Subirrigation, Unsaturated zone, Water table response.

Hydrological functioning of a constructed peatland watershed in the Athabasca oil sands region: Potential trajectories and lessons learned

Mine reclamation in the Athabasca oil sands region is legally required as companies must reconstruct disturbed landscapes into functioning ecosystems which previously existed in the Boreal landscape. Upland-wetland systems are relatively new in the constructed landscape and only two exist to date. The objective of this work is to understand the key hydrological changes post-management of a constructed peatland watershed and provide insight on the overall system function. Six years of hydrometric data are presented from the Sandhill Fen Watershed (SFW), a 52-ha upland-wetland catchment built on soft tailings with a pump system to provide fresh water, support drainage, and limit salinization. Wet years (seasonal precipitation > evapotranspiration) occurred in 2013, 2016 and 2018 and dry years (seasonal precipitation < evapotranspiration) occurred in 2014, 2015 and 2017 where wet years had large 5-, 10- and 100-year storms which were absent in dry years. Surface conductance and solar radiation explained most of the variation in ET fluxes. Changes in management practices drove many of the observed hydrological changes. Heavy management in 2013 muted water table (WT) responses to climate as inflow and outflow (via pumps) controlled WT response. After 2014, management efforts declined and hydrological exchanges were predominantly vertical, and saturated storage across the wetland increased. As a result, WT variability was tightly coupled to ET regardless of WT position relative to the ground surface, with greater changes related to deeper water tables, suggesting the absence of water conserving feedback mechanisms. Intra-watershed water movement was primarily towards the wetland from recharge areas in the upland swale, whereas surface runoff was rare and only occurred during extreme rain events and spring snowmelt. Peat properties were degraded compared to those observed in undisturbed peatlands, and natural stratification of the peat profile was absent. Results suggest that current conditions are not favorable for fen-peatland development as marsh-like conditions have developed, limiting water conserving functions and the ability to persist long-term in a changing climate.

A Method for Integrating Delayed Recharge Flux Through Unsaturated Zones into Analytical and Numerical Groundwater Flow Modeling

AbstractThe temporal delay in the water table's response to precipitation is a common phenomenon. Using a mathematical model, we developed a function that represents the recharge flux through unsaturated zones of varying thickness to model the delayed response of groundwater level due to precipitation. The recharge flux from the developed function was integrated into the analytical and numerical models to estimate the actual groundwater levels in the unsaturated zone. The analytical and numerical models accurately determined the actual groundwater levels. Additionally, calibrated hydraulic parameters from numerical estimates reflected the values measured in the actual aquifer, thereby highlighting the potential application of the developed function to wide‐ranging groundwater problems. Based on the recharge function, a recharge module can be developed for existing flow simulators to enhance groundwater modeling.

Canal blocking optimization in restoration of drained peatlands

Abstract. Drained peatlands are one of the main sources of carbon dioxide (CO2) emissions globally. Emission reduction and, more generally, ecosystem restoration can be enhanced by raising the water table using canal or drain blocks. When restoring large areas, the number of blocks becomes limited by the available resources, which raises the following question: in which exact positions should a given number of blocks be placed in order to maximize the water table rise throughout the area? There is neither a simple nor an analytic answer. The water table response is a complex phenomenon that depends on several factors, such as the topology of the canal network, site topography, peat hydraulic properties, vegetation characteristics and meteorological conditions. We developed a new method to position the canal blocks based on the combination of a hydrological model and heuristic optimization algorithms. We simulated 3 d dry downs from a water saturated initial state for different block positions using the Boussinesq equation, and the block configurations maximizing water table rise were searched for by means of genetic algorithm and simulated annealing. We applied this approach to a large drained peatland area (931 km2) in Sumatra, Indonesia. Our solution consistently outperformed traditional block locating methods, indicating that drained peatland restoration can be made more effective at the same cost by selecting the positions of the blocks using the presented scheme.

Groundwater recharge and water table response to changing conditions for aquifers at different physiography: The case of a semi-humid river catchment, northwestern highlands of Ethiopia

Groundwater recharge estimation, aquifer response to meteorological variables, and evapotranspiration calculations have been performed on a semi-humid catchment, in northwestern Ethiopian plateau. The Soil Moisture Balance (SMB), WetSpass water balance model, Water Table Fluctuation (WTF), and Chloride Mass Balance (CMB) methods are applied to estimate the groundwater recharge. Accordingly, 431 mm, 462 mm, and 477 mm recharge amounts are estimated as mean annual value, respectively, using SMB, WetSpass, and CMB methods. Based on the WTF method, the annual recharge rates of the volcanic aquifers range from 157 mm to 760 mm. The SMB and WetSpass methods are less effective for the flat physiographic area, where the recharge rate is storage controlled rather than precipitation amount. The calculated high recharge for maintain-front aquifers using WTF is attributed to extra rising due to lateral groundwater flow, which restricts the reliability of the method for such aquifer geometries. High groundwater level rising rate (121 mm/day) has been observed for the steeply sloping, low rates (11 mm/day) for the flat floodplain, and intermediate rate (52 mm/day) for the gently sloping volcanic aquifers. Similarly, receding rates of 3.18 mm/day were found for the steeply sloping, 0.40 mm/day for the floodplain, and 1.14 mm/day for the gentle sloping aquifers. The recession, in all of the topographies, is happening with second-order polynomial decay function. A strong connection between the shallow and deep groundwater aquifers is noted. Storage change in the relatively deeper volcanic aquifers is due to vertical groundwater flow from the overlying alluvial aquifer. This indicates that the recharge mechanism is local, and may be the reason for the low aquifer productivity of the Dangila wellfield. Diurnal water table fluctuation is detrended from the receding trend of the dry period, and evapotranspiration from the groundwater is estimated at 28% of total ET.

Long-term rewetting of degraded peatlands restores hydrological buffer function

Precipitation is a key factor affecting shallow water table fluctuations. Although the literature on shallow aquifers is vast, groundwater response to precipitation in peatlands has received little attention so far. Characterizing groundwater response to precipitation events in differently managed peatlands can give insight into ecohydrological processes. In this study we determined the groundwater table response rate following precipitation events at a drained and a rewetted fen to characterize the effect of rewetting on hydrological buffer capacity. Multiple regression analysis revealed that the groundwater table at the rewetted fen has more than two times lower rate of response to precipitation events than that of the drained fen, even after adjusting for antecedent groundwater levels. Thus, the rewetted fen delivers a better hydrological buffer function against heavy precipitation events than the drained fen. We found that for the depths at which the groundwater interacts with incoming precipitation, the peat of the rewetted fen has a higher specific yield causing groundwater to rise slower compared to the response at the drained fen. A period of 20 years of rewetting was sufficient to form a new layer of organic material with a significant fraction of macropores providing storage capacity. Long-term rewetting has the potential to create favorable conditions for new peat accumulation, thereby altering water table response. Our study has implications for evaluating the success of restoration measures with respect to hydrological functions of percolation fens.

Catchment-Scale Integrated Surface Water-Groundwater Hydrologic Modelling Using Conceptual and Physically Based Models: A Model Comparison Study

This paper presents a comparative analysis of the use of an externally linked (MOBIDIC-MODFLOW) and a physically based (MIKE SHE) surface water-groundwater model to capture the integrated hydrologic responses of the Thomas Brook catchment, in Canada. The main objective of the study is to investigate the effect of simplification in representation of the hydrological processes in MOBIDIC-MODFLOW on its simulation accuracy. To this aim, MOBIDIC and MODFLOW were coupled in order to sequentially exchange the groundwater recharge and baseflow discharges within each computation time step. Using identical sets of hydrogeological properties for the two models, the coefficients of the gravity and capillary reservoirs in MOBIDIC were calibrated so as to closely predict the hydrological budget of the catchment simulated with MIKE SHE. The simulated results show that the two models can closely replicate the observed water table responses at two monitoring wells. However, in very shallow water table locations, the instantaneous response of the water table was not precisely captured in MOBIDIC-MODFLOW. Additionally, the simplified conceptualization of the unsaturated flow in MOBIDIC-MODFLOW resulted in overestimated groundwater recharge during spring and underestimation during summer. Moreover, the computational efficiency of MOBIDIC-MODFLOW, as compared to MIKE SHE, along with less required input data, confirms its potential for regional scale groundwater-surface water interaction modelling applications.

Fill and Spill Hillslope Runoff Representation With a Richards Equation‐Based Model

AbstractIntegrated surface‐subsurface hydrological models (ISSHMs) are well established numerical tools to investigate water flow and contaminant transport processes over a wide range of spatial and temporal scales. However, their ability to correctly reproduce the response of hydrological systems to natural and anthropogenic forcing depends largely on the accuracy of model parameterization, including the level of detail in the representation of the bedrock. This latter is typically incorporated in some way via the bottom boundary of the model domain. Issues of bedrock topography, variable soil depth, and the resulting hillslope storage distribution representation in ISSHMs are vitally important but to date have received little attention. A standard treatment of the bottom boundary, especially in large catchment and continental scale applications, is to model it as a flat or inclined (e.g., parallel to the surface) impermeable base (sometimes with some simple leakage term). This approach does not allow the model to correctly reproduce bedrock‐controlled threshold responses such as the fill and spill process, as observed across many hillslope and catchment scale field studies. It is still unclear whether Richards equation‐based numerical models are actually able to generate such responses. Here we use a Richards equation‐based model (CATHY) to simulate internal transient subsurface stormflow dynamics observed at the well‐characterized Panola experimental hillslope in Georgia (USA). Soil and bedrock properties were calibrated starting from values reported in previous studies at the site. Our simulation results show that the model was able to reproduce threshold mechanisms, which in turn affected both the integrated and distributed hydrologic responses of the Panola hillslope. We then developed a set of virtual experiments with modified boundary conditions and base topography at the soil‐bedrock interface to explore the bedrock boundary control on transient groundwater flow patterns. Our results show that accurate representation of the lower boundary is crucial for ISSHM simulations of hillslope‐scale storm runoff and for connectivity of transient groundwater. We summarize our findings with the development of a new bedrock topographic wetness index that takes into account the unsaturated infiltration dynamics. The index is able to help represent the spatial variability of water table response over the bedrock surface compared to standard surface topography‐based indices. This new index may be useful in larger‐scale ISSHM applications where an exact bedrock topography representation is not feasible or possible.

Dynamics of groundwater flow and upwelling pressure heads at a wetland zone in a headwater catchment

The rate and direction of groundwater flow are a function of the gradient of the hydraulic head, whose components are gravity head and pressure head. This paper presents results and analyses of field observations of pressure head responses to some rainfall events of 2000/2001 summer season in a headwater catchment in South Africa. A transect spanning from a steep hillslope zone, through a transition zone and a flat low-lying wetland zone, to a stream channel zone was instrumented with tensiometers to monitor the responses of pore-water pressure to rainfall. The season’s late rainfall events simultaneously caused the pressurized pore-air driven Lisse effect water table response at the transition zone, and the capillary fringe-assisted groundwater ridging water table response at the wetland zone. During the events, the Lisse effect dissipated, but followed by sequences of stepped increases in pressure head in the deep soil profile at the transition zone. These stepped increases in pressure head, whose magnitudes increased with depth, were caused by the upwelling pressure heads induced by rainfall spike intensities at the wetland zone. These upwelling pressure heads could have major and disproportionate influence on the dynamics of groundwater flow.

Evaluation of Hantush’s S Function Estimation Methods for Predicting Rise in Water Table

Hantush’s model is widely used for predicting rise in water table in response to groundwater recharge. Several approximate methods of the Hantush mound function, S(α, β) have been developed to overcome the limitations of Hantush’s tabulated values of the S(α, β) function. These approximate methods have their own advantages and disadvantages, and it is difficult to identify the most accurate and computationally efficient S(α, β) estimation method. In this study, performance of four different algebraic approximate S(α, β) estimation methods are compared with the Hantush method using the published data. The four different methods considered are Swamee and Ohja (1997) (SO), Singh (2012) (SI), Vatankhah (2013) (VA) and Gauss-Legendre quadrature (GL) method with various Gaussian points (GP). Seven statistical accuracy and computation efficiency indicators are used to assess the performance of different S(α, β) estimation methods. The GL method with 100 to16 GPs is found to be the most accurate S(α, β) estimation method. This is followed by the SO, GL with 14 to 12 GPs, VA, GL with 10 GP, SI, and GL with 9 to 3 GPs. A good trade off between accuracy and efficiency is found with the SO, VA, and GL method with 14, 12 and 10 GPs. Comprehensive analysis of different S(α, β) estimation methods, and their ranking based on overall performance index will be helpful in modelling water table rise due to groundwater recharge, optimum design of recharge basin, and evaluation of effectiveness of recharge basins in groundwater recharging.

Accurate approximate semi-analytical solutions to the Boussinesq groundwater flow equation for recharging and discharging of horizontal unconfined aquifers

The Boussinesq equation is usually used to describe one-dimensional unconfined groundwater movement. Solutions of this equation are important as they provide useful insights regarding the water table response to stream level variations and allow us to quantify the exchange flow between the stream and the aquifer. Due to the nonlinearity of the Boussinesq equation, the solutions are generally obtained using numerical methods. However, for certain classes of initial and boundary conditions there are both exact and approximate analytical solution techniques. This work focuses on the latter approach. A new mathematical technique for approximate solutions of the Boussinesq equation describing flow in horizontal unconfined aquifers induced by sudden change in boundary head is presented. The method applies to the problems of recharging and dewatering of an unconfined aquifer, and approximate solutions to both problems are derived. The solutions were obtained by introducing an empirical function with four parameters which might be obtained using a numerical fitting procedure. Results based on this technique were found to be easily calculated and to be in good agreement with those obtained using numerical calculation based on Runge-Kutta approach. A benchmark between the proposed solutions and five existing approximate analytical solutions shows that the present solutions are the most accurate approximate solutions among those tested. Applications of the solutions are presented in the context of estimating aquifer hydraulic parameters.

Water table dynamics in a constructed wetland, Fort McMurray, Alberta

AbstractSurface mining in northern Alberta transforms wetlands and forests into open pits, tailings ponds, and overburden. As part of their license to operate, mine operators are required to reclaim this altered landscape to a predisturbance capacity. In 2012, Syncrude Canada Limited constructed one of the first of two reclaimed wetlands, the Sandhill Fen Watershed (SFW), to evaluate wetland reclamation strategies. SFW is a 52‐ha system atop soft‐tailings that includes an inflow/outflow pump system, underdrains, upland hummocks, and a fen lowland. In this study, water table dynamics of the fen lowland were evaluated in the 2 years following commissioning (2014–2015) to assess whether this newly constructed watershed has hydrological conditions that facilitate hydric soils with water table regimes similar to reference systems. Results indicate that the location and hydrophysical properties of placed materials control water table responses to both water management and precipitation. This differential water table response in the SFW lowland drove lateral fluxes between adjacent landforms, suggesting periods of intermittent water supply from uplands to wetlands along hummock margins. As in natural systems, the lowland fen exhibited several lateral flow reversals over the 2 years depending upon water level. Water tables on‐average were greater than those observed in natural analogues. Comparison during these first 2 years following commissioning contribute to the increasing insight as to how construction and management practices support reclamation postmining.

The effect of brine pumping on the natural hydrodynamics of the Salar de Atacama: The damping capacity of salt flats

The Salar de Atacama is used as a case study to analyse and quantify coupled natural (evaporation and recharge) and anthropogenic processes (pumping of lithium-rich brine) to abstract their patterns to other salt flats using a three-dimensional groundwater flow model. Important changes in the dynamics of the water table between the pre-operational period (1986–1994) and operational period (1994–2015) are observed. The water table exhibited a gradual drawdown during the pre-operational period because the evaporation was greater than the recharge for most of these periods. This negative balance was counteracted by some sharp rises that were produced by direct rainfall events on the salt flat. The deep lateral recharge that arrived from the mountains did not produce abrupt changes in the water table because the rainfall events in the mountains were damped by the distance of the recharge zone and great thickness of the unsaturated zone.The natural evolution of the water table was modified by the intensive brine pumping that was performed in the south-western Salar de Atacama during the operational period. As evaporation depends on the water table depth, the pumping caused a drawdown of the water table, resulting in an evaporation rate reduction that partially compensated for the pumped brine in the water balance of the basin. This effect is defined as the damping capacity of salt flats. Thus, salt flats have a high capacity for dampening oscillations in their water table in response to both natural and anthropogenic disturbances which is of great importance for the management of lake and wetland ecosystems and brine exploitation. The limit of the dampening capacity of salt flats is defined by the evaporation extinction depth, which is in the range of 0.5–2 m.

Effects of capillary fringe and truncation factor on pore-water pressure and water table variation in dewatering and watering sand column experiments

Abstract Spatiotemporal variations of the pore-water pressure and water table response to small amounts of water exchange were measured in a sand column. In the dewatering experiment, the pressure head variation can be divided into three stages: the initial pressure head declining phase when water table is above the sand surface, a sudden drop in accordance with the capillary fringe when water level passes through the sand surface, and a slow declining phase with respect to the specific yield of the sand. As for the watering experiment of the shallow groundwater with different initial truncation factors (TF), the addition of a minute amount of water results in a rapid rise of the pressure head initially, then a gradually increase to its equilibrium. When the upper extent of the fully saturated capillary fringe coincides with the sand surface (TF ≤ 1), a thin film of water addition produces nearly instantaneous increase in pore-water pressure, corresponding to a rapid rise of groundwater table to the sand surface. Pressure head increment increases linearly with the TF value and reaches its maximum when TF value approaches unity. Considering the vertical distribution of the pressure head, its gradient becomes larger right after the water addition, then decreases to its initial value of hydrostatic condition in the end. In the case of TF > 1, there is an unsaturated layer above the groundwater table, the pressure head increases after the water addition, whose magnitude however decreases as the increase of TF value. Nevertheless, the final position of the groundwater table is still below the sand surface, and the gradient of the pressure head vertical distribution dose not vary significantly throughout the entire process. In consideration of hydrostatic pressure assumption, temporal variation of the water table was also quantitatively obtained based on the measured instantaneous pore-water pressure data, which is consistent with time-varying process of the pressure head during both the dewatering and watering experiments.

Groundwater Responses on Pumping Analysis for Clayey Aquifer

The relationship between water quantity and clayey layer shows that water storage was very limited to an infiltration into the ground layer which is still retains as a surface water during recharge by precipitation. This paper consists of pumping analysis by using AQTESOLV model in a groundwater response for clayey area to identify the capability of water quantity actions during the discharge and recharge flows. Based to pumping analysis, including type of pump used, discharge rate, water table response, recharge rate, type of soil, and remaining time shows that this area was unconfined aquifer with has low hydraulic conductivity below than 9.6 mm/hr. Therefore, this simulation shows that the quantity and capacity of water intake able to withdrawal more than 40 m3/day by using 1hp pump and above with a constant rate after 4 days pumping continuously. The capability of storage and intake should be considered by natural (rainfall) or man-made recharge to show the water balance in the system whiles the process of pumping continuously. Therefore, this analysis able to predicts the capacity of groundwater storage at the clayey characteristics while it needs to improve any strategy to generate more water intake.

Land use impacts on floodplain water table response to precipitation events

AbstractTwo floodplain sites were instrumented, a bottomland hardwood forest and a historic agricultural field. Continuous, automated, in situ shallow groundwater monitoring was paired with a gridded sampling design to facilitate detailed spatiotemporal analysis of water table response to precipitation events. Data were collected at 30‐min intervals for the duration of the 2011, 2012, 2013, and 2014 water years. Four hundred three precipitation events were observed, with median depth of 3 mm. Results show significantly (p &lt; .001) greater study site median water table response at the agricultural site (0.02 m), relative to the forest (0.01 m). The ratio of water table response magnitude to precipitation depth was 8.3 and 3.3 at the agricultural and forest sites, respectively, a difference of more than 150%. Median shallow groundwater level lag time was shorter with respect to both precipitation and streamflow at the agricultural site (10 and 2 hr for precipitation and flow, respectively), relative to the forest (11.5 and 4.5 hr for precipitation and flow, respectively). Longer lag times indicated slower water table response and potentially increased flood attenuation capacity by the forest site. Results show the agricultural site water table responded to a greater number of precipitation events (including smaller events), reflecting potentially reduced relative flood attenuation capacity. Observed differences highlight the various impacts of forest vegetation on water table dynamics and emphasize the benefits of floodplain forests as a water resource management tool, including for flood mitigation, in mixed‐land‐use watersheds.