Yan Zhu

• Wuhan University

It is a long-lasting challenge in subsurface hydrologic modeling to develop numerically efficient algorithm for coupling unsaturated and saturated flow, especially in regional-scale modeling. In this study, a new scheme is developed for coupled numerical simulation of unsaturated-saturated water flow at the regional scale. The modeling domain is di...

Purpose Tillage practices and crop growth play important roles in the soil erosion of sloping farmland. This study aims to investigate the effects of tillage practices on soil erosion in response to different crop growth stages and to determine the primary factors that affected the runoff reduction benefit of tillage practices among different growt...

Purpose Proper tillage management and crop plantation are two established approaches to control soil erosion in red soil slopes of southern China. This study aims to investigate the surface–subsurface runoff and soil losses processes on sloping farmland under different peanut growth stages and ridge treatments, and to quantify the combined effects...

Accurate estimation of seepage losses in large-scale canal systems and identification of their impact factors are important for improving water conveyance efficiency in agricultural districts. However, seepage losses can vary widely across different regions and periods, making it difficult to obtain a complete understanding of the variation process...

Accurate and efficient numerical simulations of soil water movement, as described by the highly nonlinear Richards' equation, often require local refinement near recharge or sink/source terms. In this paper, we present a novel numerical scheme for solving Richards' equation. Our approach is based on the vertex-centered finite volume method (VCFVM)...

Many algorithms have been proposed to cope with groundwater numerical simulation associated with local grid refinements typically for subsurface flow driven by sources acting on diverse scales. In this context, we focus on establishing an efficient local grid refinement method with nonmatching grids for groundwater flow modelling. The new model is...

Soil salinization is a major eco-environmental problem in irrigated agro-ecosystems. Understanding regional soil salinity spatial patterns and seasonal dynamics and their driving factors under changing environments is beneficial to managing soil salinity to maintain agricultural production in arid agricultural areas. To better investigate this topi...

Machine learning methods provide new perspective for more convenient and efficient prediction of groundwater flow. In this study, a deep learning method “GW-PINN” without labeled data for solving groundwater flow equations with wells was proposed. GW-PINN takes the physics inform neural network (PINN) as the backbone and uses either the hard or sof...

Accurate estimation of the spatial-temporal distribution of phreatic evapotranspiration (ET) is critical for managing water resources and preventing soil salinization in arid and semiarid agricultural areas where substantial water-saving efforts are needed. Traditional phreatic ET estimation approaches either are for small scales or cannot consider...

Irrigated agriculture in arid and semi-arid regions is seriously threatened by water shortage and soil salinization. The well-canal conjunctive irrigation scheme provides a stable groundwater resource for irrigation and can reduce surface salt accumulation by decreasing the groundwater levels, which makes it more suitable to alleviate the problems...

Irrigation plays an important role in agricultural production, especially in arid and semi-arid regions. However, the conflict between water supply and demand will become more serious with increasing population. This study was to evaluate the effects of limited irrigation on regional-scale water movement and salt accumulation processes in agricultu...

Subsurface drainage systems have been widely used to help manage soil salinization worldwide. However, designing a subsurface drainage system requires predictions of regional groundwater and salt dynamics. While these dynamics can be obtained using MODFLOW’s drain package (DRN), this package requires that the drain conductance be specified, which i...

An increasing number of canals are designed with liners to decrease canal seepage. As the lining material and cracks or holes were previously considered equivalent porous media, few studies have quantified the effects of lining parameters on canal seepage, and the relationships between the reduction factor (β) of the lining and the crack width (df)...

Soil water and salt movement in freezing-thawing periods play an important role in the agricultural ecological environment. Field experiments show a non-synchronized movement of soil water and salt during the freezing-thawing period with no definite mechanism. In this study, the non-synchronization of water and salt movement in the frozen layer (0-...

Soil water in an unsaturated zone is the major source of groundwater recharge, and likewise soil contaminants are the major source of groundwater contamination. It is thus essential to jointly consider soil water movement and solute transport together with groundwater movement and solute transport, which is particularly important when addressing re...

Purpose Monitoring and evaluating spatiotemporal dynamics of soil salinity over large areas for an extended period is important for keeping crop yield in salt-affected areas, but difficult due to its high variability. In this study, measurements of soil salinity with 68 sampling sites at different depth from top soil to 1.8 m were carried out in 20...

The suitable groundwater exploitation scheme in freezing-thawing agricultural areas under the well-canal conjunctive irrigation conditions is confronted with two major challenges, which are computationally expensive local grid refinements along wells, and the model suitability problem in the freezing-thawing period. In this study, an empirical meth...

Concrete and geomembranes are common materials used in canal linings to decrease canal seepage. Current numerical studies focus on concrete linings only by equivalent continuous models and seldom are about geomembrane and are suitable to quantify the seepage loss from canals with damaged linings. In this study, a new model is developed for the coup...

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 wate...

Water storage in unsaturated and saturated zones during the crop non-growing season is one of the important supplementary water resources to meet crop water requirements in arid areas with shallow water table depth. It is necessary to analyze utilization of the soil-ground water storage during the crop growing season and its attribution to irrigati...

Canal lining is commonly used to reduce seepage loss and increase water use efficiency. However, few studies have quantitatively estimated the seepage control effects of different lining materials under different service times. Ponding tests were conducted on the same canal section with four different lining statuses to investigate the canal lining...

Soil salinization has become a widespread problem that seriously affects the sustainable development of agriculture. To deal with the salt accumulation and leaching problems in practical agricultural systems, a new soil water and solute transport model adopting the mass balance scheme is developed in this study. The soil water movement module is ba...

This study investigates the influence of clogging substances on pore characteristics and permeability of geotextile envelopes that were used for 3, 7 and 15 years in irrigated farmlands in Xinjiang region, which is arid and suffers from the soil salinity problem. Results show that the macropores (above 125 μm) of envelopes are evidently clogged, wh...

In arid agricultural areas with shallow water table depth, water exchange between vadose zone and groundwater is intensive during the freezing-thawing period, and thus has a significant impact on crop growth. This study is aimed to develop a one-dimensional model that couples heat and variably saturated water in seasonally freezing-thawing agricult...

For computationally efficient modeling of unsaturated–saturated flow in regional scales, the quasi-three-dimensional (3-D) scheme that considers one-dimensional (1-D) soil water flow and 3-D groundwater flow is an alternative method. However, it is still practically challenging for regional-scale problems due to the highly nonlinear and intensive i...

Long-term and accurate predictions of regional groundwater hydrology are important for maintaining environmental sustainability in arid agricultural areas that experience seasonal freezing and thawing where serious water-saving measurements are used. In this study, we firstly developed a machine-learning method by integrating a multivariate time se...

For computationally efficient modeling of unsaturated-saturated flow systems of regional scale, it is necessary to use Quasi three-dimensional (3-D) schemes that consider one-dimensional (1-D) soil water flow and 3-D groundwater flow. However, it is still practically challenging for regional-scale problems due to the high non-linear and intensive i...

A simple root zone salt balance model was developed for long-term soil salt prediction. A groundwater balance module was integrated to obtain the water flux at the bottom of the root zone, since groundwater level is easily and reliably measured data. An assumption that the net percolation at the bottom of root zone equals to the net recharge from r...

The dry drainage system (DDS) is an alternative technique for controlling salinization. To quantify its role in soil salinity control, a five-year field observation from 2007 to 2011 was completed in a 2900 ha experimental plot in Yonglian Experimental Station, Hetao Irrigation District, China. Results showed that the groundwater table depth in the...

The conjunctive use of groundwater and surface water is a promising measurement to alleviate the water resources shortage in Hetao irrigation district. It can not only decrease the amount of water diversion from the Yellow River but also prevent the deterioration of soil salinization by decreasing the groundwater table and evaporation. However, it...

A three-dimensional groundwater model of Hetao Irrigation District was established. Model parameters were calibrated and validated with datasets from 2006 to 2013. Then, the numerical model was applied to estimate the impacts of conjunctive use of groundwater and surface water under 9 water saving scenarios with 3 different irrigation quotas and 3...

Nitrogen reactive transport modeling is subject to uncertainty in model parameters, structures, and scenarios. By using a new variance-based global sensitivity analysis method, this paper identifies important parameters for nitrogen reactive transport with simultaneous consideration of these three uncertainties. A combination of three scenarios of...

This study is focused on investigating the impacts of organic carbon on the denitrification process of nitrogen transformation and transport. A numerical model, Nitrogen-2D, is modified by considering the impact of organic carbon in the denitrification equation. The modified model is used to simulate the soil nitrogen (including nitrate and ammoniu...

Predicting water table depth over the long-term in agricultural areas presents great challenges because these areas have complex and heterogeneous hydrogeological characteristics, boundary conditions, and human activities; also, nonlinear interactions occur among these factors. Therefore, a new time series model based on Long Short-Term Memory (LST...

Long-term prediction of regional groundwater and salt dynamics is important for the agricultural sustainability in Hetao Irrigation District, where the water resources supply and demand contradiction is prominent. The mulched drip irrigation with the well-canal conjunctive irrigation will be applied to save water and control soil salinity. In this...

This paper assesses the value of multi-scale near-surface (0∼5 cm) soil moisture observations to improve state-only or state-parameter estimation based on the ensemble Kalman filter (EnKF). To the best of our knowledge, studies on assimilating multi-scale soil moisture data into a distributed hydrological model with a series of detailed vertical so...

Multi-scale modeling of the localized groundwater flow problems in a large-scale aquifer has been extensively investigated under the context of cost-benefit controversy. An alternative is to couple the parent and child models with different spatial and temporal scales, which may result in non-trivial sub-model errors in the local areas of interest....

Water resources allocation for agriculture irrigation in the Yellow River basin will be reduced due to water shortage and increasing demand for non-agricultural use. Different measurements should be taken to save water and to ensure the sustainable development of agriculture. The conjunctive use of groundwater and surface water is one of the most p...

Quantitative estimation of soil moisture, nitrogen transformation and transport, and crop growth is important for improving nitrogen use efficiency and decreasing nitrogen pollution in agricultural areas. The objective of this study was to develop a transient soil water and nitrogen dynamics model with the consideration of crop growth. A crop growt...

Simulations of solar radiation have become increasingly common in recent years because of the rapid global development and deployment of solar energy technologies. The effect of air pollution on solar radiation is well known. However, few studies have attempting to evaluate the potential of the air pollution index in estimating solar radiation. In...

The mixing layer theory is not suitable for predicting solute transfer from initially saturated soil to surface runoff water under controlled drainage conditions. By coupling the mixing layer theory model with the numerical model Hydrus-1D, a hybrid solute transfer model has been proposed to predict soil solute transfer from an initially saturated...

Due to the high nonlinearity of the three-dimensional (3-D) unsaturated-saturated water flow equation, using a fully 3-D numerical model is computationally expensive for large scale applications. A new unsaturated-saturated water flow model is developed in this paper based on the vertical/horizontal splitting (VHS) concept to split the 3-D unsatura...

Most popular unsaturated-saturated water flow models were developed based on solving different forms of Richards' equation. Because these models all have their unique applicability and computational accuracy, it is important to select the most reasonable and efficient model for specified problems. This research used a Bayesian Model Averaging (BMA)...

As the amount of water resources that can be utilized for agricultural production is limited, the reuse of treated wastewater (TWW) for irrigation is a practical solution to alleviate the water crisis in China. The process-based models, which estimate nitrogen dynamics under irrigation, are widely used to investigate the best irrigation and fertili...

Onsite sewage treatment and disposal system (OSTDS) or septic systems, is one of the significant sources of nitrogen in groundwater and surface water, poseing serious threats to human health and the environment. The ArcGIS-based Nitrate Load Estimation Toolkit (ArcNLET) has been used to simulate nitrogen transport and estimate nitrogen load from se...

:The non-linearity of unsaturated flow requests small time step and fine grid in the corresponding simulation，and the simulation often suffers from some unfavorable boundary conditions． Therefore，it is time-consuming to simulate the regional unsaturated-saturated flow by traditional numerical methods． In view of this issue，a 1D unsaturated model ba...

The average surface of head gradient in the irregular triangular prism element was proposed to develop a simplified numerical model of solute transport in the irregular groundwater system. The results of the solute mass balance in a triangular prism element were calculated using the hybrid finite element method and the finite difference method basi...

A coupled unsaturated-saturated water flow numerical model was developed. The water flow in the unsaturated zone is considered the one-dimensional vertical flow, which changes in the horizontal direction according to the groundwater table and the atmospheric boundary conditions. The groundwater flow is treated as the three-dimensional water flow. T...

The mean head gradient plane of the irregular triangle column volume was proposed to solve the simplified numerical simulation problem of groundwater in irregular and declining aquifer-aquitard system. According to the results of water balance in a finite volume based on the mean head gradient plane, the net lateral flux and elastic storage of the...

According to the ammonia volatilization principle, a submodel of ammonia volatilization was suggested and coupled with the nitrogen dynamic model Nitrogen-2D to establish a modified model for improving the simulation of nitrogen transformation process. The modified model was used to simulate the distribution of water content, ammonia concentration...

An ammonia volatilization submodel and a crop-growth submodel have been set up and incorporated to the 2D nitrogen transport and transformation simulation model Nitrogen-2D. The coupled model Nitrogen-2D considers all the important nitrogen transformation processes such as mineralization, immobilization, denitrification, nitrification, volatilizati...