Observed Water Table Depth Research Articles

Groundwater level prediction with meteorologically sensitive Gated Recurrent Unit (GRU) neural networks

Precise estimation of groundwater level (GWL) fluctuations has a substantial effect on water resources management. In the present study, to forecast the regional mean monthly time series groundwater level (GWL) with a range of 4.82 (m) in Urmia plain, three different layer structures of Gated Recurrent Unit (GRU) deep learning-based neural network models via the module of sequence-to-sequence regression are designed. In this sense, 180-time series datasets of regional mean monthly meteorological, hydrological, and observed water table depths of 42 different monitoring piezometers during the period of Oct 2002–Sep 2017 are employed as the input variables. By using Shannon entropy method, the most influential parameters on GWL are determined as regional mean monthly air temperature (Tam), precipitation (Pm), total (sum) water diversion discharge (Wdm) of four main rivers. Nevertheless, Cosine amplitude sensitivity analysis confirmed Tam as a dominant factor. For preventing overfitting problem, an algorithm tuning technique via different kinds of hyperparameters is operated. In this respect, several scenarios are implemented and the optimal hyperparameters are accomplished via the trial-and-error process. As stated by the performance evaluation metrics, Model Grading process, and Total Learnable Parameters (TLP) value, the innovative and unique suggested model (3), entitled GRU2+, (Double-GRU model coupled with Addition layer (+)) with seven layers is carefully chosen as the best model. The unique suggested model (3) in the optimal hyperparameters, resulted in an R2 of 0.91, a total grade (TG) of 7.76, an RMSE of 0.094 (m), and a running time of 47 (s). Thus, the model (3) can be certainly employed as an effective model to forecast GWL in different agricultural areas.

Groundwater influence on soil moisture memory and land–atmosphere fluxes in the Iberian Peninsula

Abstract. Groundwater plays an important role in the terrestrial water cycle, interacting with the land surface via vertical fluxes through the water table and distributing water resources spatially via gravity-driven lateral transport. It is therefore essential to have a correct representation of groundwater processes in land surface models, as land–atmosphere coupling is a key factor in climate research. Here we use the LEAFHYDRO land surface and groundwater model to study the groundwater influence on soil moisture distribution and memory, and evapotranspiration (ET) fluxes in the Iberian Peninsula over a 10-year period. We validate our results with time series of observed water table depth from 623 stations covering different regions of the Iberian Peninsula, showing that the model produces a realistic water table, shallower in valleys and deeper under hilltops. We find patterns of shallow water table and strong groundwater–land surface coupling over extended interior semi-arid regions and river valleys. We show a strong seasonal and interannual persistence of the water table, which induces bimodal memory in the soil moisture fields; soil moisture “remembers” past wet conditions, buffering drought effects, and also past dry conditions, causing a delay in drought recovery. The effects on land–atmosphere fluxes are found to be significant: on average over the region, ET is 17.4 % higher when compared with a baseline simulation with LEAFHYDRO's groundwater scheme deactivated. The maximum ET increase occurs in summer (34.9 %; 0.54 mm d−1). The ET enhancement is larger over the drier southern basins, where ET is water limited (e.g. the Guadalquivir basin and the Mediterranean Segura basin), than in the northern Miño/Minho basin, where ET is more energy limited than water limited. In terms of river flow, we show how dry season baseflow is sustained by groundwater originating from accumulated recharge during the wet season, improving significantly on a free-drain approach, where baseflow comes from water draining through the top soil, resulting in rivers drying out in summer. Convective precipitation enhancement through local moisture recycling over the semi-arid interior regions and summer cooling are potential implications of these groundwater effects on climate over the Iberian Peninsula. Fully coupled land surface and climate model simulations are needed to elucidate this question.

A diagnosis of sub-surface water table dynamics in low hydraulic conductivity soils in the sugar cane fields of Pongola, South Africa

Water and land are the two natural resources restraining crop production in South Africa. With the increasing demand for food, emphasis has shifted from the sole reliance on rain fed crop production, to irrigation. The deterioration in irrigation water quality from surface water sources is, however, posing a big challenge to the sustainability of irrigated crop production. This is because more water is required for leaching, resulting in shallow water tables in agricultural lands. The installation of well designed subsurface drainage systems alone is not enough; the provision of timely maintenance is also necessary. In this study, the extent and severity of problems as a consequence of shallow water tables and their possible causes were investigated at three sugarcane fields in Pongola, South Africa, having low hydraulic conductivity soils. Also investigated were soil salinity levels and the temporal variation in the salinity of the irrigation water. A water table map of a 32 ha sugarcane field was generated, using observed water table depth (WTD) data from 36 piezometers monitored from September 2011 to February 2012. Out of the total 32 ha under cultivation, 12% was found to be affected by shallow WTDs of less than the 1.0 m design WTD. The inability of natural drainage to cope with subsurface drainage needs and the poor maintenance of subsurface drainage systems contributed to the shallow water tables in the area. Furthermore, the currently adopted drainage design criteria also proved unsatisfactory with mean observed water table depth and drainage discharge (DD) of 20% and 50%, respectively, less than their respective design levels. The salinity of the irrigation water was, on average, 32% higher than threshold tolerance level of sugarcane. The root zone soil salinity levels at the three study sites were greater than the 1.7 dS m−1 threshold for sugar cane. The subsurface drainage design criteria adopted at the site needs to be revisited by ensuring that the slope of the land is taken into consideration in the drainage design in addition to adhering to a recommended maintenance schedule.

排水沟蓄水条件下农田与排水沟水盐监测研究

PDF HTML阅读 XML下载 导出引用 引用提醒 排水沟蓄水条件下农田与排水沟水盐监测 DOI: 10.5846/stxb201307261948 作者: 作者单位: 西安理工大学教育部西北水资源与环境生态重点实验室,西安理工大学教育部西北水资源与环境生态重点实验室,西安理工大学教育部西北水资源与环境生态重点实验室 作者简介: 通讯作者: 中图分类号: S276.7 基金项目: 国家自然科学基金资助项目（51079122，51279159） Monitoring salt and water dynamics in farmland and drainage ditch in a saline environment under reduced drainage intensity Author: Affiliation: Northwest Key Laboratory of Water Resource and Environment Ecology,Ministry of Education Xi’an University of Technology,Xi’an;China,Northwest Key Laboratory of Water Resource and Environment Ecology,Ministry of Education Xi’an University of Technology,Xi’an;China,Northwest Key Laboratory of Water Resource and Environment Ecology,Ministry of Education Xi’an University of Technology,Xi’an;China Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为了查明盐碱地排水沟蓄水条件下农田与排水沟之间的水盐交换，基于两年现场观测试验数据，分析了农田与排水沟的水位响应以及电导率变化规律。结果发现：研究区排水沟蓄水条件下，相邻排水沟水位与农田地下水位变化基本一致，作物生长期较为强烈的蒸发蒸腾作用进一步降低了田间地下水位；排水沟水位变化可以直接或间接地影响周围农田的地下水位和水质状况，在无外界来水干扰的情况下，农田地下水和排水沟水样的电导率变化趋势一致，当排水沟受到外来淡水补给时，沟内浓缩的盐分得到稀释，电导率明显低于农田地下水。研究结果可为类似地区盐碱地治理和生态环境保护提供参考依据。 Abstract:The fast population growth and rapid urban development in China have made it necessary to develop marginal lands for agricultural use. One approach to meet such land requirement is to reclaim the existing salinized wasteland through engineering measures through artificial drainage. As salt content in soils poses potential threat to crop growth, understanding the relationships of salt and water exchange between farmland and drainage ditches is of great importance for salinity control in the saline agricultural environment. In this paper, we present a 2 year monitoring study on salt and water dynamics in a reclaimed salt affected farmland area in Shaanxi, China. In 2 strip fields of 100×400m, we observed water table depth and measured electrical conductivity (EC) of water samples taken from monitoring wells, those wells were installed at 1, 2 and 3 m in depth in a cluster in each field; in the mean time, we measured the depth to water level in drainage ditches along the strip fields and sampled the ditch water for their salinity levels. Weather data analysis showed that the rainfall during the monitoring period was close to the long term average values. Rainfall pattern in the study area is generally in accordance with the potential evapotranspiration, making irrigation only necessary when prolonged dry period appears during the growing season. The monitoring data showed that the drainage ditches have effectively controlled the water table in the crop fields: the depth to water table varied between 1.69 to 2.27 in field A and between 1.24 and 2.18 in field B, while the depth to water level in drainage ditches varied between 1.84 and 2.05 by the field A and between 1.16 and 2.0 by the field B. The salinity of the groundwater in the fields, however, was less variable than that in the drainage ditches: the EC in groundwater varied between 4.72 and 7.51ms/cm in field A and between 6.58 and 11.4 in field B, while the EC in drainage ditches varied between 4.86 and 8.69 by the field A and between 1.9 and 14.75 by the field B. The greater variability of EC in the drainage ditches was caused by the dilution effect of freshwater recharge in the end of the irrigation season, when a large amount of irrigation return flow from an upstream irrigation district was discharged to the study area due to its lower elevation. The elevated water level in the drainage ditches had no significant impact on field water table depth due to the short duration. When no additional freshwater recharge is available, salinity in the drainage ditches increased with time due to evaporation concentration.Findings from this research may provide technical guidance for salinity management in the similar salt affected agricultural regions. 参考文献 相似文献 引证文献

English

  This study evaluates the subsurface lithologies as well as examines the properties of the soils at a University location within the fresh water swamp terrain in the Niger Delta. Borings for subsurface exploration in the area were made at five well spaced locations with a hand auger to a maximum depth of 4.00 m in each borehole. Soil samples were retrieved at 0.5 m interval and at positions where changes in lithology were noticed during the boring process. Laboratory tests were carried out on selected and representative soil samples recovered from the borings in accordance with BS 1377 (1975) and ASTM (1979) standards. Moisture content range from 20.6% to a maximum of 26.5% in the silty clay and gravelly, silty clay soils located at 2 m depth and low to medium plasticity range (12 to 18%). The undrained friction angle was determined to be 30 while the undrained cohesion has a value of 58 KN/m2, the computed coefficient of volume compressibility (Mv) gave 1.24 m2/MN while the coefficient of consolidation (Cv) resulted in 3.38 m2/year. Computed total settlements of 69 mm are within design limits for shallow foundation. Borehole 1 (BH1) was dry while BH2 recorded 3.80 m as the ground water level. Observed water table depths in BH3, BH4 and BH5 were 2.00 m, 1.70 and 1.50 m, respectively, at the time of the subsurface investigations. Higher values are expected especially at the peak of the rainy months. Foundation systems in the area must take special precaution to prevent seepage into the structures. This could be by drainage or waterproofing or a combination of both methods.   Key words: Geotechnical properties, subsurface soils, water table conditions, fresh water swamp terrain, Niger Delta.

Relative Elevation Topographic Surface Modelling of a Large Alluvial River Floodplain and Applications for the Study and Management of Riparian Landscapes

This paper presents a novel and useful spatial modelling technique to create a topographic surface that estimates a floodplain's elevation relative to the average low-flow water surface elevation of a river channel. This model was applied to a 121 km study area of the middle Sacramento River, California, USA, where it was tested as a surrogate for observed water table depth and an observed 3.3 year recurrence interval flood inundation surface using independent data sets. The modelled relative elevation topographic surface correlated significantly (p < 0.005) to observed well water depths suggesting that the modelled surface reflected a reasonable approximation of vertical distance to the water table. Results from a flood inundation pattern analysis indicated an overall accuracy of 79% for correctly predicting inundated and non-inundated zones. The model was then used to measure relative channel bank height and the distribution of riparian plant communities to examine landscape ecological relationships.

Contribution to irrigation from shallow water table under field conditions

The mathematical model SWBACROS was applied to estimate the contribution of a shallow groundwater to the water needs of a maize crop. The model was applied with the top and boundary conditions defined by the observed irrigation/rainfall events and the observed water table depth. The simulated water contents of the top zone were very close to the observed values. Furthermore the model was applied with an assumed free drainage bottom boundary condition. The difference of the computed water content profiles under the presence and absence of the water table gave a very good estimate of the capillary rise. It was found that under the specific field conditions about 3.6 mm/day of the water in the root zone originated from the shallow water table, which amounts to about 18% of the water, which was transpired by the maize crop.

Incorporating water table dynamics in climate modeling: 1. Water table observations and equilibrium water table simulations

Soil moisture is a key participant in land‐atmosphere interactions and an important determinant of terrestrial climate. In regions where the water table is shallow, soil moisture is coupled to the water table. This paper is the first of a two‐part study to quantify this coupling and explore its implications in the context of climate modeling. We examine the observed water table depth in the lower 48 states of the United States in search of salient spatial and temporal features that are relevant to climate dynamics. As a means to interpolate and synthesize the scattered observations, we use a simple two‐dimensional groundwater flow model to construct an equilibrium water table as a result of long‐term climatic and geologic forcing. Model simulations suggest that the water table depth exhibits spatial organization at watershed, regional, and continental scales, which may have implications for the spatial organization of soil moisture at similar scales. The observations suggest that water table depth varies at diurnal, event, seasonal, and interannual scales, which may have implications for soil moisture memory at these scales.

Evaluation of DRAINMOD for predicting water table heights in irrigated fields at the Jordan Valley

A detailed field experiment was carried out in the Jordan Valley, south of Lake Kinneret, Israel for evaluation of the water management model DRAINMOD. This field was chosen to represent the local agro-climate conditions of that zone. Banana crop was grown and was irrigated daily with about 3200 mm/year and 0.5 leaching fraction. Subsurface drainage system with 2.5 m drain depth and 160 m drain spacing existed in the field. The water table depth was measured with about 100 piezometers, in which most of them were observed weekly, and four were continuosly recording piezometers. Five identical drainage plots were selected, out of 10 existing, as replicates for the evaluation of DRAINMOD. Deviations in a range of 0.3–1.7 m between observed water table depth and that simulated by DRAINMOD were found in four out of the five replicates. A reasonable agreement was found only in one drainage plot out of the five tested. These findings contradict the world wide convention that DRAINMOD simulation is in a good agreement with observed field data. An additional study was therefore conducted to explore the reasons for these large deviations. Three reasons were suggested: (i) a strong side effect by the Jordan River, which flows some 350 m west to the test field; a very steep 4.6% gradient was found toward the Jordan River; (ii) presence of sandy permeable layers below the depth of the drains which magnifies the boundary condition effect of the Jordan River; (iii) a very significant component of deep and lateral seepage (more than 50% of the yearly irrigation plus rainfall). A combination of these three reasons was suggested as an explanation to the apparent large disagreement. It was therefore recommended not to use DRAINMOD or similar vertical flow models for simulation of water table depths in irrigated fields with subsurface drain pipe systems in the Jordan Valley.

RIPARIAN ECOSYSTEM MANAGEMENT MODEL: HYDROLOGY PERFORMANCE AND SENSITIVITY IN THE NORTH CAROLINA MIDDLE COASTAL PLAIN

A riparian buffer installed along streams is one alternative that can be used to reduce the delivery of nitrogen,phosphorus, and sediment to the stream. The Riparian Ecosystem Management Model (REMM) has been developed tosimulate surface and subsurface riparian buffer hydrology, sediment transport, litter and sediment interactions, vegetationgrowth, and soil carbon, nitrogen, and phosphorus dynamics. For this model to accurately simulate transport and fate ofnutrients in the shallow groundwater beneath a riparian buffer, the subsurface hydrology component must be verified. Twoyears of field data were utilized to evaluate and test the sensitivity of the hydrology component of REMM in the North CarolinaMiddle Coastal Plain. Daily simulated water table depth was compared to observed water table depths across a 15 m widebuffer. The simulated water table depth was sensitive to hydrologic parameters such as groundwater inputs from the uplandinto zone 3, stream depth, and buffer slope. Average absolute errors between simulated and observed water table depth werefound to be 0.35 to 0.36 m, while relative errors ranged from 0.12 to 0.15 m. Simulated evapotranspiration (ET) was higherin zone 3 compared to zones 1 and 2, although all three zones were parameterized alike. Flow into the buffer from the streamis not simulated by REMM, although it occurred frequently during data collection. Estimates of ET should be improved forherbaceous and grass vegetation types to improve water table depth predictions. Also, for conditions where the streamcontributes flow to the groundwater, an additional component in REMM is necessary.

Predicting water table depths in space and time using a regionalised time series model

A regionalised autoregressive exogenous variable (RARX) model is presented for the relationship between precipitation surplus and water table depth. The parameters of the RARX model are ‘guessed’ at unvisited locations using auxiliary information such as soil profile descriptions, topographic maps and digital elevation models (DEM). In the direct method, the guessed parameters are used to predict time series of water table depth at unvisited locations; observed water table depths are not used in the prediction procedure. In the indirect method, observed water table depths are used to correct the predictions resulting from the direct method for systematic prediction errors. The prediction performance is evaluated by cross-validation. The validation results show small random errors (standard deviation on average is 9.8 cm) but large systematic errors (absolute mean error on average is 18 cm). The root mean squared error of the predicted time series is, on average, 22 cm. Taking the uncertainty of both the future weather conditions and the RARX-model predictions into account, a map reflecting the risk that a critical depth will be exceeded at a critical day in a future year is constructed. Furthermore, maps showing the components of uncertainty in predicted water table depths are given.

Are Water Table Variations in a Shallow Forest Soil Consistent with the TOPMODEL Concept?

The TOPMODEL concept provides a simple method for parameterizing the effect of topography on the distribution of subsurface moisture and runoff production, and has been incorporated into models of catchment hydrology and forest ecology. Most evaluations of the TOPMODEL concept have been based on comparisons of stream flow hydrographs and do not necessarily provide a test of the predictions of subsurface flow and saturated source area dynamics. The objective of this study was to evaluate whether water table predictions based on the TOPMODEL concept agree with observed water table depths for a shallow forest soil in a small subcatchment drained by an ephemeral stream. Observed water table depths were fitted well by a linear statistical model that is mathematically consistent with the TOPMODEL assumptions and that specifies time and location effects independently. That is, the water table does not change shape but shifts uniformly up or down in response to changes in saturated zone storage. Residuals from the fitted model were generally less than 10 cm in absolute value, compared to observed ranges of water table depths up to 100 cm. The TOPMODEL concept predicts that the relation between the estimated location effects for the wells and the values of In (a/tan β) should be linear, where a is the drainage area per unit contour length, and tan β is the surface slope. Regression analysis revealed that the fitted linear relation was statistically significant (P=0.001), but weak (R2= 0.26). This weak fit could be caused by (1) significant spatial variability in soil transmissivity (assumed negligible in many applications of TOPMODEL) and/or (2) errors in specifying In (a/tan β) from a digital elevation model of the surface topography. Considering the increasingly common application of the TOPMODEL concept in hydrologic and ecological models, further research should be carried out to specify more clearly the bounds of applicability of its underlying assumptions and to identify workable extensions and modifications to the concept, where necessary.

Comparison of Daily Water Table Depth Prediction by Four Simulation Models

The Agricultural Drainage And Pesticide Transport (ADAPT) model was compared to the water management simulation models DRAINMOD, SWATREN, and PREFLO. SWATREN and PREFLO are one-dimensional finite-difference models while ADAPT and DRAINMOD are one-dimensional mass balance models. ADAPT, an extension of the computer model GLEAMS, also provides chemical transport information. All four models were tested against field data from Aurora, North Carolina. Observed water table depth data were collected during 1973 through 1977 from a water table management field experiment with three subsurface drain spacing treatments of 7.5, 15, and 30 m.

Field Evaluation of a Water Management Simulation Model

ABSTRACT THE water management simulation model, DRAINMOD, was tested using field data for over 5 yr of record from three locations in the NC Coastal Plains. Each site had field scale drainage systems with provisions for subirrigation and controlled drainage. Three soil types and five different drainage system designs were included in the experiment from which 21 site-yr of data were obtained. Rainfall intensity and water table elevations were measured continuously at each site and the observed day end water table elevations were compared to predicted values. Effective lateral hydraulic conductivity values were measured in the field using both auger hole and water table drawdown methods. Numerous other field and laboratory mea-surements were made for each soil to determine input soil property and site parameter data. Comparison of predicted and measured water table elevations were in excellent agreement with the daily water table depths having standard errors of estimate ranging from 7.5 to 19.6 cm. The average absolute devia-tion between predicted and observed water table depths for 21 site-years of data (approximately 7400 pairs of daily predicted and measured values) was only 8.1 cm. Based on the results of the study, DRAINMOD can be reliably used to predict the effect of drainage system design on water table elevations.

DEVELOPMENT AND VERIFICATION OF A WATER BALANCE MODEL FOR SUBSURFACE DRAINAGE DESIGN1

ABSTRACT: A water balance model was developed to predict daily water table depths in some corn fields with or without subsurface drainage systems, using pertinent soil and water properties and weather data. The model outputs were compared with the recorded data of observed water table depths. Some statistical parameters such as the mean, standard deviation, the coefficient of correlation, the sum of the squares of deviations, and a nonparametric statistical test were used to study the extent of agreement between the observed and the predicted water table depths. No significant difference was found between the distributions of the observed and the predicted water table depths at the 99% confidence level. The study was conducted on some sand and clay soils of the Ottawa‐St. Lawrence Lowlands region in Canada where there is a cool, moist climate and poor natural drainage.