Shaoyuan Feng

Neural Networks to Simulate Regional Ground Water Levels Affected by Human Activities

In arid regions, human activities like agriculture and industry often require large ground water extractions. Under these circumstances, appropriate ground water management policies are essential for preventing aquifer overdraft, and thereby protecting critical ecologic and economic objectives. Identification of such policies requires accurate simulation capability of the ground water system in response to hydrological, meteorological, and human factors. In this research, artificial neural networks (ANNs) were developed and applied to investigate the effects of these factors on ground water levels in the Minqin oasis, located in the lower reach of Shiyang River Basin, in Northwest China. Using data spanning 1980 through 1997, two ANNs were developed to model and simulate dynamic ground water levels for the two subregions of Xinhe and Xiqu. The ANN models achieved high predictive accuracy, validating to 0.37 m or less mean absolute error. Sensitivity analyses were conducted with the models demonstrating that agricultural ground water extraction for irrigation is the predominant factor responsible for declining ground water levels exacerbated by a reduction in regional surface water inflows. ANN simulations indicate that it is necessary to reduce the size of the irrigation area to mitigate ground water level declines in the oasis. Unlike previous research, this study demonstrates that ANN modeling can capture important temporally and spatially distributed human factors like agricultural practices and water extraction patterns on a regional basin (or subbasin) scale, providing both high-accuracy prediction capability and enhanced understanding of the critical factors influencing regional ground water conditions.

Application of the SWAP model to simulate the field water cycle under deficit irrigation in Beijing, China

The evaluation of the field water cycle under deficit irrigation plays an important role in studying mechanism of field water dynamics, optimization of agricultural water management strategies, and assessment of regional water resources. In this study, the agro-hydrological Soil-Water-Atmosphere-Plant (SWAP) model was used to evaluate the field water cycle for a winter wheat-summer corn double cropping system in Beijing, China under deficit irrigation. A carefully designed field experiment was carried out from 2007 to 2009 with six irrigation treatments. The SWAP model was calibrated with soil water contents of two treatments. The dataset of the main field water balance components including soil water content, profile water storage and water flux through the bottom of the root zone were used to validate the SWAP model. The average root mean square error (RMSE) and the mean relative error (MRE) values of predicted soil water contents were 2.4% and 8.0%, respectively. The dataset of predicted and measured values were close to the 1:1 scale line for both the profile water storage and soil water flux. As an application of the SWAP model, the optimal irrigation management practices for the hydrologic years of 75%, 50% and 25%, respectively, in the Beijing area were obtained. The simulated average amount of water saving and groundwater recharge under the optimal irrigation schedules were about 190 mm and 16.1 mm, respectively. This study indicates that the SWAP model can be used as a powerful tool to simulate the field water cycle and evaluate irrigation practices.

Water Infiltration in Layered Soils with Air Entrapment: Modified Green-Ampt Model and Experimental Validation

Air entrapment in soil is common in cases of farmland flood irrigation or intense rain. A simple, physically based model would be more useful than the complex two-phase (gaseous and liquid phase) flow model to describe water infiltration in layered soils with air entrapment. This study proposed a modified Green-Ampt model (MGAM) to simulate water infiltration in layered soils with consideration of entrapped air. A saturation coefficient S(a) was introduced in MGAM to account for the resistance effect of air entrapment on infiltration. S(a) had robust physical meaning, and was approximately equal to one minus the plus of the residual air and residual water saturation degree that could be determined from the soil water retention curve equation. In MGAM, the actual water content and hydraulic conductivity of the wetted zone were determined by multiplying S(a) with the saturated values. Infiltration experiments in a 300-cm-long five-layered soil column and a 280-cm-deep eight-layered field soil profile were conducted to test the applicability of MGAM. For comparison, the infiltration process was also simulated by the traditional Green-Ampt model (TGAM), in which the wetted zone was assumed to be fully saturated, and the Bouwer Green-Ampt model (BGAM), in which the hydraulic conductivity of the wetted zone was half that of the saturated hydraulic conductivity. The estimated S(a) values were very close to the measured saturation degree of soil layers at the termination of the experiment. The simulation results indicated that the TGAM overestimated the infiltration rate and cumulative infiltration, whereas the BGAM underestimated the infiltration rate and cumulative infiltration. Furthermore, the depths of the wetting fronts simulated by TGAM and BGAM were considerably smaller than those measured. The MGAM provided satisfactory simulation results and adequately described the infiltration process in both the laboratory soil column and the field soil profile. DOI:10.1061/(ASCE)HE.1943-5584.0000360

Evaluation of optimal irrigation scheduling and groundwater recharge at representative sites in the North China Plain with SWAP model and field experiments

The SWAP model was established in representative sites in the North China Plain.Optimal irrigation schedulings of wheat and maize were compared among the sites.Groundwater recharge changes under optimal irrigation were compared among the sites.Precipitation, soil and water table effects on groundwater recharge were clarified. The application of water saving irrigation is essential to alleviate the rapid depletion of groundwater resources in water crisis areas such as the North China Plain (NCP). The integrated effects of climate, soil and groundwater conditions on water balance and crop response need to be further studied. It is imperative to investigate spatial differences of irrigation scheduling and groundwater recharge within the NCP for regional water management. In this study, three representative sites including Luancheng (LC), Tongzhou (TZ) and Yucheng (YC) with different precipitation, soil and water table conditions were selected. The SWAP model was established at each site to compare optimal irrigation scheduling and groundwater recharge of the winter wheat-summer maize double cropping system under different hydrological years. Largest optimal irrigation amount and additional irrigation at the winter-dormancy stage of wheat were required for the TZ site in each hydrological year. The optimal irrigation scheduling was almost same at the three sites for summer maize, except that no irrigation was needed at filling stage in dry year at the YC site. The average annual groundwater recharge under optimal irrigation was in the order of YC (108.4mm), TZ (63.8mm) and LC (0.4mm). Furthermore, the groundwater recharge occurred throughout the double cropping seasons in YC, but it occurred only in summer maize season at the LC and TZ sites. The net irrigation amount of the optimal irrigation scheduling was reduced by 51.2%, 24.9% and 77.2% compared to reference practice at the LC, TZ and YC sites, respectively. The amount of groundwater recharge depended on the local precipitation and irrigation, while water table depth and soil texture mainly influenced the delay time of groundwater recharge relative to the water input events.

Evaluation of Anomalous Solute Transport in a Large Heterogeneous Soil Column with Mobile-Immobile Model

This study uses the mobile-immobile model (MIM) and the traditional convection-dispersion equation (CDE) to analyze the observed breakthrough curves (BTCs) at different distances in a 1,250-cm-long saturated and highly heterogeneous soil column. It provides a simple method to determine the mobile water fraction independently as the ratio of effective porosity over total porosity of the packed soil materials. The effective porosity is calculated a priori as the ratio of measured flow rate and estimated pore-water velocity. It is found that there is a significant amount of immobile water in the soil column, resulting in the anomalous early breakthrough and tailing behaviors of the measured BTCs. Comparing to the CDE, the measured asymmetric BTCs at various scales can be better described by the MIM, especially their early arrival and long tailing parts. The degree of anomalous transport behavior in this large heterogeneous soil column is reduced with transport scale due to the increased mobile water fraction...

Simulation of effects of agricultural activities on groundwater level by combining FEFLOW and GIS

Abstract Effects of agricultural activities are obvious in arid‐inland regions. A numerical model for two‐dimensional phreatic groundwater flow was developed based on the water budget in the Minqin oasis, a typical arid‐inland region. The spatial data of source/sink terms were processed by combining global information system (GIS) and the finite element subsurface flow (FEFLOW) model. The verified results showed errors for the model of 0.37 and 0.48 m respectively in the Quanba and Huqu areas. The groundwater level changes were simulated with the developed model. The results indicate that groundwater level maintained a decreasing trend of 1.8 and 1.1m year‐1 respectively in the Quanba and Huqu areas under current water resource utilisation. Therefore, further study is needed to determine the rational exploitation volume of groundwater and distribution schemes for surface water.

The Response of Water-Land Environment to Human Activities in Arid Minqin Oasis, Northwest China

This article outlines the human activities and its impact on water-land environment in the Minqin oasis of northwest China which is an area of typical arid features. During the last century, human activities have caused a series of detrimental water-land environment responses. Analyses show that runoff into the Minqin oasis has been reduced, with the decreasing trend predominantly occurring during the periods of July to September and December to February, perpetrated by construction of reservoirs and diversion of runoff for irrigation in the upper and middle reaches of the Shiyang River basin. In addition, excessive quantities of groundwater in the Minqin oasis have been exploited, producing serious groundwater level declines. Groundwater quality has also degenerated, with total dissolved solids (TDS) concentrations in the northern portion of the oasis reaching 5.76 g l−1. The continual lowering of the groundwater surface and increased groundwater quality degradation has produced negative changes in the ecological environment. The area of salinized soil has doubled from the 1950s to the present value of 4000 ha, with vegetation cover in the Minqin oasis seriously degenerated, marred by land desertification and frequent dust storms. Strategies for improving the water-land environment of the oasis are proposed in this article, with guidelines for reconstruction of sustainable water-land management in Minqin oasis.

Effect of irrigation with saline water on soil water-salt dynamics and maize yield in Arid Northwest China

An experiment was conducted in non-weighing lysimeters to study the effect of irrigation with saline water on water movement and salt accumulation and maize yield. The experiment was carried out in northwest China, both sufficient and insufficient irrigation were applied in the first year, and only sufficient treatments in the second year. Irrigation with solute concentration of 9 g · L−1 and 6 g · L−1 led to salt accumulation about 6–8 dS · m−1 in certain depths, even downwards to 160 cm received about 4 dS · m−1 for 9 g · L−1 and 2 dS · m−1 for 6 g · L−1, which was two times more than initial. Salt-affected water extracted from soil behaved as low evapotranspiration under sufficient irrigation, and more water was left in the soil. Yield of spring maize was not affected when saturated soil paste electrical conductivity did not exceeded 1.2 dS · m−1.

Effects of deficit irrigation with saline water on spring wheat growth and yield in arid Northwest China

Field experiments were conducted in 2008 and 2009 to study the effects of deficit irrigation with saline water on spring wheat growth and yield in an arid region of Northwest China. Nine treatments included three salinity levels s1, s2 and s3 (0.65, 3.2, and 6.1 dS/m) in combination with three water levels w1, w2 and w3 (375, 300, and 225 mm). In 2008, for most treatments, deficit irrigation showed adverse effects on wheat growth; meanwhile, the effect of saline irrigation was not apparent. In 2009, growth parameters of w1 treatments were not always optimal under saline irrigation. At 3.2 and 6.1 dS/m in 2008, the highest yield was obtained by w1 treatments, however, in 2009, the weight of 1,000 grains and wheat yield both followed the order w2 > w1 > w3. In this study, spring wheat was sensitive to water deficit, especially at the booting to grain-filling stages, but was not significantly affected by saline irrigation and the combination of the two factors. The results demonstrated that 300-mm irrigation water with a salinity of less than 3.2 dS/m is suitable for wheat fields in the study area.

Quantifying long-term responses of crop yield and nitrate leaching in an intensive farmland using agro-eco-environmental model

Quantitatively ascertaining and analyzing long-term responses of crop yield and nitrate leaching on varying irrigation and fertilization treatments are focal points for guaranteeing crop yield and reducing nitrogen loss. The calibrated agricultural-hydrological RZWQM2 model was used to explore the long-term (2003-2013) transport processes of water and nitrogen and the nitrate leaching amount into groundwater in summer maize and winter wheat rotation field in typical intensive plant area in the North China Plain, Daxing district of Beijing. Simulation results showed that application rates of irrigation and nitrogen fertilizer have couple effects on crop yields and nitrogen leaching of root zone. When both the irrigation and fertilizer for summer maize and winter wheat were 400mm and 400kgNha-1, respectively, nitrate leaching into groundwater accounted for 47.9% of application amount of nitrogen fertilizer. When application amount of irrigation is 200mm and fertilization is 200kgNha-1, NUPE (nitrogen uptake efficiency), NUE (nitrogen use efficiency), NPFP (nitrogen partial factor productivity), and Wpi (irrigation water productive efficiency) were in general higher than that under other irrigation and fertilization condition (irrigation from 104-400mm, fertilizer 104-400kgNha-1). Irrigation bigger than 200mm could shorten the response time of nitrate leaching in deeper soil layer in different irrigation treatment.