Groundwater Table Depth Research Articles

Performance Evaluation of The Subsurface Drainage System in A Dakahlia Region, Egypt.(Dept.C)

This study is conducted to evaluate the performance of subsurface drainage system in the 30000 hectares Integrated Soil and Water improvement Project (ISAWIP) Dakahlia, Nile Della, Egypt (ISAWIP, 1994). The drainage collectors rates and its relationship with collectors hydraulic gradient. The overpressure in the drainage system and the fluctuation of groundwater cable were measured as indicators for the performance of the subsurface drainage system. Three cropping seasons, summer 1996, winter 1996-1997 and summer 1997 were considered. Results show that the drainage collectors rates are under the design one in most or the time except in summer season in the case of cultivation rice in majority of the area served by the drainage system. The collector drainage rate based on the measured hydraulic gradient did not represent the actual drained rate of the system and the overpressure in the collector pipes was observed in the summer season only. The groundwater table depths were acceptable most of the lime except the areas cropped with rice or adjacent to rice fields. The lateral drain spacing was underestimated in both the winter season and in the non-rice fields of the summer season. However, the lateral spacing required to manage the rice cultivation was three to four times the designed spacing. Results, which were achieved, could be widely applied under similar conditions.

Simulation study on performance of nitrogen loss of an improved subsurface drainage system for one-time drainage using HYDRUS-2D

Improved subsurface drainage has been verified as a more efficient drainage technique for solving problems of farmland shortage and frequent floods in South China. However, the environmental effects of improved subsurface drainage with different parameters have rarely been studied. In this study, nitrogen loss in outflow and soil nitrogen content under improved subsurface drainage for one-time drainage is evaluated based on a calibrated HYDRUS model, considering the precipitation process, initial groundwater table depth, initial soil nitrogen content, submerged pipe height, drain spacing, drain depth, filter width, and filter height during a 3-day individual drainage. The results indicate that HYDRUS performed well for the simulation. Under conditions of homogeneous soil and nitrogen content distribution, when rainfall occurred on the first, second, and third days, the total ammonia nitrogen (NH4‒N) and nitrate nitrogen (NO3‒N) losses under a rainfall of 141 mm are approximately 1.26, 1.31, 1.39 and 1.2, 1.25, 1.36 times that under a rainfall of 44 mm, respectively. The NH4‒N and NO3‒N losses in the outflow of the improved subsurface drainage increased significantly 0.5 days after the rain began. Compared with the 10 cm initial groundwater table depth case, the nitrogen loss under a 30 cm initial groundwater table depth reduced by approximately 23%. The NH4‒N losses of the improved subsurface drainage with 20 and 40 cm submerged heights of the pipe reduced by 23% and 48%, respectively, whereas the NO3‒N losses reduced by 24% and 51%, respectively, compared with those under a free outflow. The initial soil nitrogen content contributed primarily to the nitrogen loss of the outflow. The relationship between nitrogen loss per pipe and drain spacing/drain depth can be described as second-degree parabolic/linear. The effects of filter width and height are similar to that of drain spacing. In the improved subsurface drainage, the maximum decrease percentage of soil nitrogen mass occurred in the filter profile at all times, whereas the NH4‒N mass increased at the 0–20 cm soil layer, and the soil NO3‒N mass increased slightly at the 60–80 cm soil layer with increasing drainage time. The results of this study provide a scientific basis for nitrogen management.

Soil aeration using air injection in a citrus orchard with shallow groundwater

Soil aeration is considered the third most important factor affecting soil fertility (after water and nutrient availability). The main reasons for poor soil aeration are slow drainage, excessive precipitation or irrigation, or a sealing soil cover. Shallow groundwater impedes drainage by reducing the downwardly hydraulic gradient, which consequently increases the water content of the soil in the root zone, thus limiting soil aeration. In this study, we examined the effects of different parameters (e.g., soil texture, depth of groundwater table) on the severity of oxygen deficiency in the root zone of a mature Valencia orange (Citrus sinensis) grove planted above shallow groundwater. In addition, we examined the effect of the O2 stress level on tree growth, yield, and fruit quality. We also evaluated the effects of air injection and of irrigation intensity on tree growth, yield, fruit quality, and O2 concentration in the soil’s air, and looked into the (technical and economic) feasibility of air injection into the soil. We found that insufficient soil aeration significantly inhibited tree growth and reduced the yield. The soil texture (i.e., clay content) had a substantial effect on the yield, mainly because of its effect on the soil’s water retention. While soil O2 concentration slightly increased by air injection, the differences in tree growth, yield, and fruit quality parameters were not significant. The O2 concentration of the soil air alone was found to be a poor quantifier of soil aeration status. The Damkholer number (Da), evaluated from the measured soil O2 profiles and groundwater table depths is a superior quantifier for the prevailing aeration status. It can also be used for analyzing the effect of irrigation water quality on soil aeration status and respiration rates.

Attributing Terrestrial Water Storage Variations across China to Changes in Groundwater and Human Water Use

AbstractThis study investigated the attribution of terrestrial water storage (TWS) variations across China to changes in groundwater and human water use. As one vital storage component, the groundwater storage (GWS) derived from the Jet Propulsion Laboratory’s GRACE (Gravity Recovery and Climate Experiment) mass concentration solution compared reasonably well with the in situ groundwater table depth, with the correlation coefficients ranging from −0.83 to −0.18, all of which were statistically significant at the 95% confidence level. About 71% of the trends in derived GWS had the same sign as those of observations, without systematic deviation, across China. The GWS variation contributed a large portion of the TWS trend in most regions of China, and the majority of contribution values reached 50%–150% in the Hai River basin, the Loess Plateau, and the middle portion of the Yangtze River basin. The dominant role of GWS is closely related to the detected long-term “memories” in both TWS and GWS. The increase of irrigation consumption accelerated the TWS depletion trend by 13.4% in the Huai River basin, while the decrease of consumptive agricultural water use alleviated the TWS decline rate by 4.1% in the Hai River basin. Importantly, the correlation coefficients reached 0.74–0.95 between the TWS change and the residual of precipitation, evapotranspiration, flow into the sea, and irrigation consumption in the four river basins of particular interest. The findings of this study are helpful for understanding regional water cycles in China.

Effects of Shallow Saline Groundwater Table Depth and Evaporative Flux on Soil Salinity Dynamics using Hydrus-1D

Soil salinization is a major environmental problem and critical concern in arid and semiarid regions. Hydrus-1D model was used to simulate effects of shallow saline groundwater table depth and evaporative flux on soil salinity movement in a saline environment. After successful calibration and validation with recorded soil moisture and soil salinity data, the model was used to evaluate two hypothetical scenarios for managing soil salinity, i.e., with 5 groundwater table depths (WTD) (WTD as on 2015, 25% and 50% rise; 25% and 50% decline in WTD based on the 2015 reference depth) and 3 different evaporative flux conditions (25, 50 and 75% reduction in evaporative flux). The model was calibrated, validated and run for scenarios with 2015 weather and WTD condition for the periods of 288 days. During calibration periods, root mean square error (RMSE) value of soil moisture content was 0.023 cm3 cm−3 and for soil salinity was 2.58 dS m−1, while during validation period RMSE of 0.023 cm3 cm−3 and 1.5 dS m−1, respectively, was recorded for soil moisture and soil salinity. Simulation results indicated that summer season (March to May, 60–150 Julian days) is the most important time to control soil salinity in this region. Considerable upward salt movement occurred during this period with 25 and 50% rise in groundwater table depth. Average root zone soil salinity increased by 6 and 12 dS m−1 when WTD raised by 25 and 50%, respectively, but negligible change in soil salinity was observed when groundwater table declined by 25 and 50%. The effective way to control this upward salt movement was reducing evaporative demands. Simulation study indicated that reducing evaporative flux of 25, 50 and 75% reduced profile soil salinity by 3.53, 6.95 and 12.38 dS m−1, respectively, during peak summer period.

A GIS-based Methodology for Assigning a Flux Boundary to a Numerical Groundwater Flow Model and Its Effect on Model Calibration

Abstract Groundwater flow modeling is an important tool for understanding and computing hydrology and water availability of an aquifer zone. However, an accurate representation of boundaries and their initial conditions are vital for simulation of the groundwater flow phenomena. In this study, efforts have been made to develop a GIS based methodology for estimating flux across boundaries of the study area using Darcy flow tool. The spatial maps of topography, bore log, transmissivity, hydraulic conductivity, porosity and groundwater levels for the study area were created in ArcGIS 9.3.1 using krigging method. A buffer zone of 1×1 km2 cell size was created on inner and outer side of the boundaries and Darcy flow model was used to estimate specified flux across boundaries. The groundwater behavior of the study area was simulated with specified flux boundary condition (Neumann boundary condition) and no flow boundary condition to assess importance and estimation accuracy of estimated flux. Darcy model output indicates that flux across the boundaries contributed about 36.20 mm in average annual change in groundwater table depth. With estimated specified flux, simulation accuracy of groundwater flow model (R2) increased to 0.97 from 0.90. The satisfactory level (R2=0.97) of simulation accuracy reveals that developed methodology can be used for estimating flux across boundaries in the absence of physical boundaries.

Remote Sensing Monitoring Method for Groundwater Level on Aeolian Desertification Area

Groundwater is one of the most important natural resources. Regional groundwater depth is an important parameter for understanding groundwater resources and maintaining sustainable development of water resources and environment. The middle reaches of the Tarim River in Xinjiang are the most primitive and well-preserved place in the world, which provides valuable resources in studying the response mechanism of surface vegetation to the groundwater level. The ecological environment of Tarim River Basin has been deteriorating, and Populuseuphratica forest has died, which is directly related to the decrease of water inflow and groundwater level around the Tarim River. To obtain the spatial distribution of the groundwater level, this study uses the MODIS satellite remote sensing image data and the remote sensing-mathematical-model of a fusion science research methods, based on the field investigation of the groundwater level, soil moisture, and other supporting information on Aeolian desertification area in the middle reaches of Tarim River in Xinjiang. Through the experimental equation of the soil moisture and groundwater level, a simple and effective remote sensing method was proposed. This method is used to evaluate the spatial distribution of groundwater level based on the MODIS image data when there is capillary supply in the soil. This model was field-proven on the desertification area in the middle reaches of Tarim River. The results indicate that the correlation coefficient between the inversion of groundwater depth and the measured groundwater level is 0.89, which are realistic with small errors. So it is feasible to monitor and assess the spatial distribution of groundwater table depth in desertification areas with a large groundwater depth of 6 m or less. This study is helpful to provide critical area for the ecological environment monitoring and restoration, and ultimately serve the sustainable development of water and environment.

Assessing groundwater irrigation sustainability in the Euro-Mediterranean region with an integrated agro-hydrologic model

Abstract. We assess the sustainability of groundwater irrigation in the Euro-Mediterranean region. After analysing the available data on groundwater irrigation, we identify areas where irrigation causes groundwater depletion. To prevent the latter, we experiment with guidelines to restrict groundwater irrigation to sustainable levels, simulating beneficial and detrimental impacts in terms of improved environmental flow conditions and crop yield losses. To carry out these analyses, we apply the integrated model of water resources, irrigation and crop production LISFLOOD-EPIC. Crop growth is simulated accounting for atmospheric conditions and abiotic stress factors, including transpiration deficit. Four irrigation methods are modelled: drip, sprinkler, and intermittent and permanent flooding. Hydrologic and agricultural modules are dynamically coupled at the daily time scale through soil moisture, plant water uptake, and irrigation water abstraction and application. Water abstractions of other sectors are simulated based on requirement data. Water may be withdrawn from groundwater, rivers, lakes and reservoirs. As groundwater is abstracted to buffer the effects of drought, we use groundwater depletion to detect unsustainable water exploitation. We characterise reported data of annual groundwater abstractions for irrigation available at country and sub-national levels. Country data are the most complete, but their spatial resolution is often coarse. While the resolution of sub-national data is finer, their coverage is heterogeneous. Simulated and reported irrigation groundwater abstractions compare well in several areas, particularly in France, while some structural discrepancies emerge: simulated values tend to be larger than those reported, especially in southern Spain; and simulated inter-annual variability is significantly smaller than reported in some areas, most remarkably in Turkey. Potential causes of these discrepancies are simplified model assumptions influencing irrigation frequency and amounts; lack of high temporal and spatial resolution data on irrigated areas, and irrigation technologies and distribution; and possible unreported abstractions in areas where groundwater irrigation is significant. We identify areas undergoing groundwater depletion from model simulations. In the southern Iberian Peninsula, Greece, Middle East and northern Africa, most simulated depletion is caused by irrigation. In other Mediterranean areas, depletion is caused by all sectors combined. From well measurements of groundwater table depth in Spain, we find statistically significant decline rates affecting large areas of the south, thus in agreement with the model, but also areas in the north-eastern and central parts where model estimates detect no depletion. The comparison of model- and well-based depletion rates is limited by spatial scale differences and groundwater model assumptions, for which we suggest potential research directions. We design rules restricting irrigation groundwater abstraction to prevent groundwater depletion and minimise severe irrigation shortages. We optimise them and simulate their effects in the southern Iberian Peninsula. Irrigation restrictions cause crop yield reductions in groundwater-dependent irrigated areas, particularly in the Algarve and Segura river basin districts. At the same time, they positively impact environmental flows. This study shows the potential of integrated agro-hydrologic modelling for detecting water resources over-exploitation and exploring trade-offs between crop production, sustainable irrigation and ecosystem support.

Artificial Neural Network Optimized with a Genetic Algorithm for Seasonal Groundwater Table Depth Prediction in Uttar Pradesh, India

Accurate information about groundwater level prediction is crucial for effective planning and management of groundwater resources. In the present study, the Artificial Neural Network (ANN), optimized with a Genetic Algorithm (GA-ANN), was employed for seasonal groundwater table depth (GWTD) prediction in the area between the Ganga and Hindon rivers located in Uttar Pradesh State, India. A total of 18 models for both seasons (nine for the pre-monsoon and nine for the post-monsoon) have been formulated by using groundwater recharge (GWR), groundwater discharge (GWD), and previous groundwater level data from a 21-year period (1994–2014). The hybrid GA-ANN models’ predictive ability was evaluated against the traditional GA models based on statistical indicators and visual inspection. The results appraisal indicates that the hybrid GA-ANN models outperformed the GA models for predicting the seasonal GWTD in the study region. Overall, the hybrid GA-ANN-8 model with an 8-9-1 structure (i.e., 8: inputs, 9: neurons in the hidden layer, and 1: output) was nominated optimal for predicting the GWTD during pre- and post-monsoon seasons. Additionally, it was noted that the maximum number of input variables in the hybrid GA-ANN approach improved the prediction accuracy. In conclusion, the proposed hybrid GA-ANN model’s findings could be readily transferable or implemented in other parts of the world, specifically those with similar geology and hydrogeology conditions for sustainable planning and groundwater resources management.

Response of shelterbelt transpiration to shallow groundwater in arid areas

Shelterbelts play an important ecological function in arid irrigation land, while competing for water which otherwise supports crop growth. Estimation of shelterbelt water consumption from groundwater is essential to better manage shelterbelts in irrigation districts, but often a challenging task due to its geometry and varying accessibility to groundwater. In the study, sap flow of Populus popularis planted along an irrigation canal was measured during two growing seasons (2016–2017) to investigate its response to varying shallow groundwater. Considering the radial pattern of sap flux density (Js) and measurement azimuthal effect, corrected Js was adopted to better represent transpiration. The results indicate that increased soil moisture and groundwater table during irrigation periods with water flowing in the canal enhance relative Js of shelterbelt by 5.5–25.8% from the non-irrigation intervals. The threshold of groundwater depth (3.6 m) is identified, beyond which transpiration of the seven-year-old shelterbelt becomes very low. Greenbelt transpiration strongly depends on groundwater within the threshold, and can be estimated through an exponential function of the ratio of atmospheric demand and groundwater depth. Besides, with the decrease of reference evapotranspiration from June to September, the sensitivity of shelterbelt transpiration response to groundwater table depth was increased. This study provides necessary information to evaluate farmland shelterbelt transpiration for rational water resource allocation to meet the ecological water requirement in arid areas with shallow groundwater.

Spatial-temporal Variations and the Regulators of Nitrate Status in Shallow Groundwater of the Typical Mountainous Agricultural Watershed in the Upper Reaches of the Yangtze River

Shallow groundwater is the main drinking water supply for the mountainous area in the upper reaches of the Yangtze River, while its quality is often degraded by nitrate (NO3--N) pollution due to intensive agricultural production activities. In the present study, we selected a mountainous agricultural watershed in the upper reaches of the Yangtze River to investigate the land use, management, and hydrogeological conditions, aiming to clarify the spatial-temporal variations in NO3--N concentration of shallow groundwater, thereby exploring the key regulators. The results showed that the NO3--N concentrations of the groundwater ranged from 0.40 to 12.51 mg ·L-1in the study area, and the exceeding ratio was nearly 30%. On an average, NO3--N concentrations for the wet season were higher than that for the dry season, indicating great variations in NO3--N concentration across different seasons. In addition, the spatial variations of NO3--N concentration in groundwater were also significant among different sub-catchment, which was mainly due to variations in the groundwater table depth and land uses. Furthermore, the significant correlations between the NO3--N concentrations and concentrations of Cl-, NH4+-N, DOC, and SO42- in the shallow groundwater were also explored in this study, suggesting that the NO3--N concentrations were likely to depend on the chemical factors of the shallow groundwater in the study area. Overall, our current study highlights that the characterization of spatial-temporal variations of NO3--N status in shallow groundwater and illustration of key regulators are essential to mitigate NO3--N pollution and prevent quality degradation of shallow groundwater in mountainous rural areas of the upper Yangtze River watershed.

Effects of Groundwater Table Decline on Vegetation Transpiration in an Arid Mining Area: A Case Study of the Yushen Mining Area, Shaanxi Province, China

We studied the effects of coal mining on the shallow groundwater regime and vegetation in the Yushen mining area (YMA) in northwestern China using a Hydrus-1D numerical model, which was calibrated and validated with field observations, and then used to simulate the effects of groundwater table (GWT) changes on transpiration rates. The actual transpiration (Ta) was influenced by both GWT depth (GWTD) and precipitation. The ratios of Ta and potential transpiration (Tp) vs. GWTD were fitted to a mono-exponential decay of GWTD with correlation coefficients as high as 0.98. Two threshold values, d(Ta/Tp)/d(H) ≤ − 2% and Ta/Tp = 0.30, were then used to calculate the unaffected and critical depths. The average unaffected and critical water depths were 3.60 and 2.20 m, respectively, which coincided fairly well with the field investigation. The sensitivity analysis showed that although reducing hydraulic conductivity (Ks) caused the Ta/Tp to decline, decreasing the inverse of the air-entry pressure (α) caused the Ta/Tp to increase, so variations in Ks and α had only a minor effect. Considering that the pre-mining GWTD is between 0 and 4.0 m for about half of the YMA, the vegetation there might be degraded or lost by a GWT decline due to mining. Also, the influence of a GWT decline on transpiration was more obvious during a drought in the YMA. Therefore, effective measures must be taken to avoid a decrease in the GWT. For example, mine water should be reinjected and the mining height reduced to protect the YMA’s shallow groundwater.

Effects of Irrigation on Water, Carbon, and Nitrogen Budgets in a Semiarid Watershed in the Pacific Northwest: A Modeling Study

AbstractIn this study, we use the Community Land Model Version 5 (CLM5) to investigate how irrigation modulates hydrologic and biogeochemical dynamics in the Upper Columbia‐Priest Rapids (UCPR) watershed, a typical semiarid watershed located in the northwestern United States dominated by cropland. To our knowledge, this constitutes the first application of CLM5 with landscape heterogeneity fully resolved over a watershed. The model is calibrated and evaluated against flux measurements from an AmeriFlux site and the Moderate Resolution Imaging Spectroradiometer (MODIS) products. Two numerical experiments (i.e., irrigated and rainfed) are performed at hyperresolution (~1 km) over the period of 2010–2018, accounting for realistic crop types and management practices. Our results show that irrigation fundamentally alters hydrologic and biogeochemical dynamics of the watershed. By adding 79.6 mm year−1 water in addition to the mean annual precipitation of 204.0 mm year−1, irrigation leads to increases in evapotranspiration and runoff, accompanied by shallower groundwater table depths. Increases in crop productivity in response to irrigation result in more carbon storage in the watershed, and drastically large seasonal fluctuations in soil organic carbon in response to changes in soil temperature and moisture. Irrigation also intensifies the rate of denitrification and mineralization during the growing season, enhancing the interactions between soil mineral nitrogen, the atmosphere, and freshwater systems. Our study demonstrates the potential of CLM5 as an effective tool for understanding hydrological and biogeochemical dynamics in highly managed semiarid watersheds.

Experiment and numerical simulation for designing layout parameters of subsurface drainage pipes in arid agricultural areas

Subsurface drainage is effective for not only controlling groundwater table depth but also alleviating soil salinization especially in arid and semi-arid agricultural areas. While substantial research efforts have been spent to determine the parameters (e.g., drain depth, drain spacing, and pipe diameter) of subsurface drainage pipe layout for water drainage, less attention has been paid to determine the parameters for salt discharge, which is important in arid and semi-arid regions. This paper presents a comprehensive study that used experimental and numerical methods to determine the pipe layout parameters for both water and salt drainage. A total of nine field experiments were conducted in Yanqi County, an arid area of Xinjiang Province, China, for a combination of different values of drain depth, drain spacing, and pipe diameter. The experimental results indicate that drain depth and spacing are significantly more important than pipe diameter for soil desalinization. Soil water content and salinity measured during the experiments were used to calibrate and validate a numerical model developed for simulating soil water flow and salt transport under drainage conditions. Two proposed indices (critical depth of soil desalinization and ratio of salt discharge and leaching), combined with two existing indices (salt discharge amount and soil desalinization rate), were used to represent the soil desalinization and salt discharge effects under different subsurface pipe layout parameters. The results suggest that drain depth has a significant influence on all indices, while the drain spacing has a significant influence on salt discharge amount and ratio of salt discharge and leaching. The relationships between layout parameters of subsurface pipes and proposed indices were quantified and used to determine appropriate layout parameters of subsurface pipes.

Protection of recovery projects and developed areas from flooding

The article discusses the formulation and solution of scientific, theoretical, and practical problems in the field of land reclamation of irrigated lands in general and, in particular, the protection of land reclamation facilities and the territory of cities and settlements from the effects of groundwater. In the Aral Sea basin, due to the intensive commissioning of new irrigated areas and various types of hydraulic structures (reservoir, village storage, canals, etc.), on a large scale, there is a violation of the natural laws of the regime and balance of groundwater. As a result of the hydrotechnical impact on water resources, the usual “losses” affecting the water balance and runoff, in the initial stage of their formation, cause processes such as flooding and flooding of adjacent territories, excessive wetting of non-irrigated lands and worsen the operation of reclamation projects. The open collector-drainage network existing around the land reclamation projects and cities does not provide a normal outflow of groundwater; its maintenance into a working and sanitary state requires large capital expenditures. High groundwater level with high salinity leads to the destruction of the basement of buildings and structures, the complete flooding of groundwater communications, the death of green spaces. According to some available data, losses incurred from exposure to aggressive groundwater in a number of cities in Uzbekistan range from 2.5 to 10 million dollars. The objects of reclamation control are established depending on the main factor determining the reclamation state of irrigated lands, on the degree of their natural drained. Essential criteria for determining the relationship of groundwater with soil – soils and their influence on the reclamation state of irrigated lands are the depth of groundwater table and the degree of mineralization, as well as their seasonal and long-term regime. The presented dissertation is devoted to the study of this insufficiently solved problem. Scientific and technical solutions to this problem are considered on the example of the built-up areas of irrigated areas of the Republic of Uzbekistan, where there are problems of engineering protection from the negative effects of groundwater.

Weather, pollution and biotic factors drive net forest - atmosphere exchange of CO2 at different temporal scales in a temperate-zone mixed forest

Understanding the drivers of net ecosystem exchange of carbon (NEE) between forests and the atmosphere is crucial for the prediction of future global carbon dynamics. We therefore analyzed the long-term (1999–2014) ecosystem carbon fluxes of a mixed coniferous/deciduous forest (Brasschaat forest) in the Campine ecoregion of Belgium. The carbon uptake of this forest increased over the 16-year study period. By consecutively performing time series decomposition and the statistical technique of random forests, the correlative strength between multiple meteorological drivers, tropospheric pollutants and biotic indices with NEE was quantified at different time scales: i.e., long-term, seasonal and weekly, and separately for day- and nighttime NEE fluxes. The drivers that were most correlated with the trend in carbon sink capacity were the increasing atmospheric CO2 level and soil recovery from acidification. The radiation-saturated carbon uptake increased remarkably and explained much of the long-term variability of daytime NEE. When the long-term and seasonal variation were extracted the remaining weekly variation in daytime NEE was most strongly correlated with variation in the incoming radiation and cloudiness, and to a lesser extent by variation in vapor pressure deficit. In contrast to daytime NEE, nighttime NEE did not show a steady trend over time, but fluctuated, peaking in 1999 and in 2011. The long-term variability in nighttime NEE was most strongly correlated with the groundwater table depth. Air temperature was highly correlated to the seasonal as well as to the remaining weekly variation, i.e., after removal of the long-term and seasonal variability, in nighttime NEE. Biotic drivers (e.g., quantum yield and radiation-saturated carbon uptake) explained less of the variation in NEE on a seasonal and short-term scale, but were more important at the long term.

Evaluation of dynamic compaction to improve saturated foundation based on the fluid-solid coupled method with soil cap model

Abstract This paper presented a dynamic fluid-solid coupled finite element (FE) method incorporating the soil cap yield hardening model to analyze the improvement on saturated foundation under dynamic compaction (DC). Biot’s dynamic u–U–p formulation was employed to describe the coupling of pore fluid and solid phases, which was discretized into finite elements by application of the Galerkin method and viscous Cartesian connectors. The proposed numerical model showed reasonably good agreement with the existing analytical solutions of one-dimensional transient loading problems and field measurement of dynamic compaction. The effects of groundwater table and soil permeability were examined via the development of excess pore water pressure, effective soil stress and void ratio. Results showed that groundwater table had a significant effect on the foundation improvement by DC. Higher groundwater table resulted in larger excess pore water pressure, and effective soil stress was not found to develop under the groundwater table during the compaction process. The decrement in the void ratio was only limited to soils located above the groundwater table, and a critical depth of groundwater table existed for the DC reinforcement in fine soil foundation, which was suggested to be 6 m for the DC reinforcement with the tamping energy of 2500 kN·m per blow. Four soil permeability coefficients of k = 10−2 m/s, 10−3 m/s, 10−5 m/s and 10−7 m/s were chosen in the parametric analysis, which represented gravel, coarse sand, silt and silty clay, respectively. Higher permeability resulted in lower excess pore water pressure and larger decrease in void ratio. However, the saturated foundation was not suitable to reinforce by dynamic compaction, no matter how much the soil permeability was. Compared to the increase in soil permeability, it was more crucial to lower the groundwater table before implementing dynamic compaction. Moreover, the gravel columns were preferred to be used to accelerate the drainage of groundwater than the sand columns.

A novel regional irrigation water productivity model coupling irrigation- and drainage-driven soil hydrology and salinity dynamics and shallow groundwater movement in arid regions in China

Abstract. The temporal and spatial distributions of regional irrigation water productivity (RIWP) are crucial for making decisions related to agriculture, especially in arid irrigated areas with complex cropping patterns. Thus, in this study, we developed a new RIWP model for an irrigated agricultural area with complex cropping patterns. The model couples the irrigation- and drainage-driven soil water and salinity dynamics and shallow groundwater movement in order to quantify the temporal and spatial distributions of the target hydrological and biophysical variables. We divided the study area into 1 km × 1 km hydrological response units (HRUs). In each HRU, we considered four land use types: sunflower fields, wheat fields, maize fields, and uncultivated lands (bare soil). We coupled the regional soil hydrological processes and groundwater flow by taking a weighted average of the water exchange between unsaturated soil and groundwater under different land use types. The RIWP model was calibrated and validated using 8 years of hydrological variables obtained from regional observation sites in a typical arid irrigation area in North China, the Hetao Irrigation District. The model simulated soil moisture and salinity reasonably well as well as groundwater table depths and salinity. However, overestimations of groundwater discharge were detected in both the calibration and validation due to the assumption of well-operated drainage ditch conditions; regional evapotranspiration (ET) was reasonably estimated, whereas ET in the uncultivated area was slightly underestimated in the RIWP model. A sensitivity analysis indicated that the soil evaporation coefficient and the specific yield were the key parameters for the RIWP simulation. The results showed that the RIWP decreased from maize to sunflower to wheat from 2006 to 2013. It was also found that the maximum RIWP was reached when the groundwater table depth was between 2 and 4 m, regardless of the irrigation water depth applied. This implies the importance of groundwater table control on the RIWP. Overall, our distributed RIWP model can effectively simulate the temporal and spatial distribution of the RIWP and provide critical water allocation suggestions for decision-makers.

Improved groundwater table and L-band brightness temperature estimates for Northern Hemisphere peatlands using new model physics and SMOS observations in a global data assimilation framework

There is an urgent need to include northern peatland hydrology in global Earth system models to better understand land-atmosphere interactions and sensitivities of peatland functions to climate change, and, ultimately, to improve climate change predictions. In this study, we introduced for the first time peatland-specific model physics into an assimilation scheme for L-band brightness temperature (Tb) data from the Soil Moisture Ocean Salinity (SMOS) mission to improve groundwater table estimates. We conducted two sets of model-only and data assimilation experiments using the Catchment Land Surface Model (CLSM), applying (over peatlands only) in one of them a peatland-specific adaptation (PEATCLSM). The evaluation against in-situ measurements of peatland groundwater table depth indicates the superiority of PEATCLSM model physics and additionally improved performance after assimilating SMOS Tb observations. The better performance of PEATCLSM over nearly all Northern Hemisphere peatlands is further supported by the better agreement between SMOS Tb observations and Tb estimates from the model-only and data assimilation runs. Within the data assimilation scheme, PEATCLSM reduces Tb observation-minus-forecast residuals and leads to reduced data assimilation updates of water storage components and, thus, reduced water budget imbalances in the assimilation system.

Assessing socio-environmental sustainability at the level of irrigation and drainage network

Assessing pre- vs. post environmental and social effects of present irrigation projects is vital to provide sustainable socio-environmental roadmaps for the upcoming similar development projects. Such sustainability was assessed for the first time in the present study at a 20- year old irrigation and drainage network (TIDN) area in the north of Iran covering about 70 thousands ha. A 32- year period data on groundwater level and surface- and groundwater quality as well as data on harvested area and crop production was analyzed to evaluate environmental sustainability. Inverse distance weighting (IDW) method was used to prepare the zoning maps and to analyze the descriptive data. Social response to the TIDN was assessed using a cross-sectional survey through completing a questionnaire. The raw data obtained from the questionnaires were analyzed using SPSS software. During the operation of the TIDN, the cropping area increased gradually from about 34,000 ha to about 53,000 ha. In this period, the average yield of early- and late- matured rice (Oryza sativa L.) varieties, predominant crops grown in the area, increased steadily from about 5300 to 6700 kg ha−1. Groundwater table depth declined gradually with an annual reduction of 7.5 cm mainly due to agricultural intensification. Groundwater quality parameters such as electrical conductivity, total dissolved solids, sodium, chloride, bicarbonate and magnesium decreased substantially especially in the semi- deep wells, while nitrate concentration showed a little increase without human effects. The TIDN project improved rural sustainability, hope feeling, security feeling, tourism development, cultural development, trust, social solidarity, social participation and life quality. The results indicate that similar comprehensive analyses can provide an important contribution to assess socio- environmental sustainability in irrigated catchments.