Monthly Water Resources and Irrigation Planning: Case Study of Conjunctive Use of Surface and Groundwater Resources

The Tehran metropolitan area is one of the mega cities of the world and has an annual domestic water consumption close to one billion cubic meters. The sewer system mainly consists of traditional absorption wells. Therefore, the return flow from the domestic consumption has been one of the main sources of groundwater recharge. Some part of this sewage is drained into local rivers and drainage channels and partially contaminates the surface runoff and local flows. These polluted surface waters are used in conjunction with groundwater for irrigation purposes in the southern part of the Tehran. In this paper, a systematic approach to surface and groundwater resources modeling in the study area, with its complex system of water supply, groundwater recharge, and discharge, is discussed. A dynamic programming optimization model is developed for conjunctive use planning. The objective function of this model is developed to supply the agricultural water demands, to reduce pumping costs, and to control groundwater table fluctuations. To develop the response function of the aquifers located in the study area, a mathematical model for simulation of the Tehran aquifer water table fluctuations has been developed and calibrated with the available data. Different scenarios are defined to study the long-term impacts of the development projects on conjunctive use policies and water table fluctuations. Comparison of the results showed how significant is the effects of an integrated approach to the surface and groundwater resources allocation in Tehran metropolitan area. The proposed model is a useful tool for irrigation planning in this region.     

Water Table Fluctuation in the Presence of a Time-Varying Exponential Recharge and Depth-Dependent ET in a Two-Dimensional Aquifer System with an Inclined Base

An analytical solution is presented for water table fluctuation between ditch drains in presence of exponential recharge and depth-dependent evapotranspiration (ET) from groundwater table in a two-dimensional gently sloping aquifer. The groundwater head above the drain is small compared to the saturated thickness of the aquifer. A sound mathematical transformation is devised to transform the two-dimensional groundwater flow equation into a simple form, which makes possible to obtain an analytical solution. The transient midpoint water table variations from the proposed solution compare well with the already existing solutions for horizontal aquifer. A numerical example is used to illustrate the combined effect of depth-dependent ET coupled with a time-varying exponential recharge on the water table fluctuation. The inclusion of a depth-dependent ET in the solution results in water table decline at a faster rate as compared to the case when ET is not considered. With an increase in slope of the aquifer base, water table profiles become asymmetric and the water table divide shifts towards the lower drain. The height of the water table profiles increases on moving away from the boundary of the aquifer and the highest level of the ground water table is obtained in the central portion of the aquifer basin due to the presence of drainage ditches on the aquifer boundary. When the effect of ET is incorporated in combination with recharge, the analytical solution results in accurate and reliable estimates of water table fluctuations under situations subjected to a number of controlling factors. This study will be useful for alleviation of drainage problems of the aquifers receiving surface recharge and surrounded by streams.     

甘肃阳山金矿床充水因素分析

阳山金矿床位于甘肃省陇南地区,为一超大型微细浸染型金矿床,主要受安昌河-观音坝断裂带控制,矿区出露岩性主要为千枚岩、灰岩及斜长花岗斑岩。区内地下水及地表水补给、径流和排泄条件较简单,通过分析区内第四系孔隙水、层状岩类基岩裂隙水、块状岩类基岩裂隙水和构造带脉状裂隙水4种类型含水层,初步探讨了大气降水及各类含水层对矿床充水的影响,以及坑道涌水对采矿的影响,对于区内矿床涌水提出采取地表水防治结合矿坑水进行防治的建议,并对区内地下水的合理利用提出了初步建议,为下一步工作提供参考。     

Generalized Analytical Solutions for Groundwater Head in Inclined Aquifers in the Presence of Subsurface Drains

Analytical solutions for groundwater head in the presence of subsurface drains are important in assessing the effectiveness of an existing drainage system under a probable extreme variation in the rate of recharge and designing a new drainage system. Generalized analytical solutions for groundwater head in inclined aquifers in the presence of parallel subsurface drains are obtained considering the transient rate of recharge as a power series (polynomial) function and depth-dependent rate of evapotranspiration. An appropriate function, new to analytical drainage studies, is used for correctly representing the depth-dependent rate of evapotranspiration. The solutions are obtained considering the practical situation of drains placed at shallow depth in a considerable depth of aquifer. Two conditions of large and small saturated thicknesses in comparison to the increase in groundwater head are considered. A mathematical criterion is proposed to distinguish between large and small saturated thicknesses. The analytical equations for discharge to drains for different cases considered are also obtained. The discharge equations used by prior investigators are found inappropriate.     

Quantifying Rainfall and Flooding Impacts on Groundwater Levels in Irrigation Areas: GIS Approach

Landscapes continuously irrigated without proper drainage for a long period of time frequently experience a rise in water-table levels. Waterlogging and salinization of irrigated areas are immediate impacts of this situation in arid areas, especially when groundwater salinity is high. Flooding and heavy rainfall further recharge groundwater and accelerate these impacts. An understanding of regional groundwater dynamics is required to implement land and water management strategies. The purpose of this study is to quantify the impact of flood and rain events on spatial scales using a geographic information system (GIS). This paper presents a case study of shallow water-table levels and salinity problems in the Wakool irrigation district located in the Murray irrigation area with groundwater average electrical conductivity greater than 25,000?μS/cm. This area has experienced several large flood events during the past several decades. Piezometric data are interpolated to generate a water-table surface for each event by applying the Kriging method of spatial interpolation using the linear variogram model. Spatial and temporal analysis of major flood events over the last four decades is conducted using calculated water-table surfaces to quantify the change in groundwater storage and shallow water-table levels. The drainage impact of a subsurface drainage scheme partially covering the area has also been quantified in this paper. The results show that flooding and local rainfall have a significant impact on shallow groundwater. The study also found that postflood climatic conditions (evaporation and rainfall) play a significant role in the groundwater dynamics of the area. The spatial net average groundwater recharge during the flooding events ranges from 0.19 to 0.52?ML/ha. The GIS-based techniques described in this paper can be used for net recharge estimation in semiarid regions where it is important to quantify net recharge impacts of regional flooding and local rainfall. The spatial visualization of the net recharge in a GIS environment can help prioritize management actions by local communities.     

Effects of Stormwater Infiltration on Quality of Groundwater Beneath Retention and Detention Basins

Infiltration of storm water through detention and retention basins may increase the risk of groundwater contamination, especially in areas where the soil is sandy and the water table shallow, and contaminants may not have a chance to degrade or sorb onto soil particles before reaching the saturated zone. Groundwater from 16 monitoring wells installed in basins in southern New Jersey was compared to the quality of shallow groundwater from 30 wells in areas of new-urban land use. Basin groundwater contained much lower levels of dissolved oxygen, which affected concentrations of major ions. Patterns of volatile organic compound and pesticide occurrence in basin groundwater reflected the land use in the drainage areas served by the basins, and differed from patterns in background samples, exhibiting a greater occurrence of petroleum hydrocarbons and certain pesticides. Dilution effects and volatilization likely decrease the concentration and detection frequency of certain compounds commonly found in background groundwater. High recharge rates in storm water basins may cause loading factors to be substantial even when constituent concentrations in infiltrating storm water are relatively low.     

Modeling Evapotranspiration of Two Land Covers Using Integrated Hydrologic Model

Modeling evapotranspiration (ET) distribution in shallow water table environments is of great importance for understanding and reproducing other hydrologic fluxes such as runoff and recharge. Unfortunately, ET distribution can be the most difficult hydrologic process to analyze. The partitioning of ET into upper zone ET, lower zone ET, and groundwater ET is complex because it depends on land cover and subsurface characteristics. One comprehensive distributed parameter model, integrated hydrologic model (IHM), builds on an improved understanding and characterization of ET partitioning between surface storages, vadose zone storage, and saturated groundwater storage. It provides a smooth transition to satisfy ET demand between the vadose zone and the deeper saturated groundwater. In this paper, the IHM was used to analyze ET contribution from different regions of the vadose zone and saturated zone. Rigorous testing was done on two distinct land covers, grass land and forest land, at a study site in West-Central Florida. Sensitivity analysis on the key parameters was investigated and influence of parameters on ET behavior was also discussed. Statistics with the root mean square error and mean bias error for forest total ET were about 1.46 and 0.04 mm/day, respectively, and 1.61 and 1.07 mm/day for grass total ET. Modeling results further proved that ET distributions from the upper and lower soil and water table, while incorporating field-scale variability of soil and land cover properties, can be predicted reasonably well using IHM model.     

Generalized Analytical Solutions for Groundwater Head in a Horizontal Aquifer in the Presence of Subsurface Drains

Generalized analytical solutions for groundwater head in horizontal aquifers in the presence of parallel subsurface drains are obtained considering a transient rate of recharge as a power series (polynomial) function and depth-dependent rate of evapotranspiration. A function, new to analytical drainage studies, is proposed for correctly representing the depth-dependent rate of evapotranspiration. The solutions are obtained considering the practical situation of drains placed at a shallow depth in a considerable depth of aquifer. Two conditions of large and small saturated thicknesses in comparison to the changes in groundwater head are considered. A mathematical criterion is proposed to distinguish between large and small saturated thicknesses.     

Development of a Hydro-Salinity Simulation Model for Colorado’s Arkansas Valley

A model to calculate the quantity and quality of river flows by simulating hydro-chemical processes in soil and the spatial/temporal distribution of irrigation return flows is introduced. By simulating the hydro-chemical processes, the quantity and quality of the deep percolating water can be predicted. The spatial and temporal distribution of the deep percolating water is simulated by constructing a groundwater flow path and calculating the groundwater travel time using response functions. A probabilistic approach was developed to calculate the groundwater travel time taking into account the fact that some irrigated fields have subsurface drainage which shortens travel times. All related hydrological components are integrated into the computation of river flow quantity and quality including groundwater return flow, irrigation tail water, tributary inflow, river diversion, phreatophyte consumption, river channel losses, and river depletion due to pumping. An illustrative example is included to demonstrate the capabilities of the model. The results of this example show that river salinity is lower during the irrigation season and higher during the off season. Due to salts carried by return flows, downstream reaches have higher salinity levels than upstream reaches.     

Applying MODFLOW Model for Drainage Problem Solution: A Case Study from Jahir Irrigated Fields, Israel

High water table and soil salinization processes are common in irrigated fields in Israel. Subsurface drainage systems are a common technique to solve soil salinity problems. Subsurface drainage models can contribute to the efficiency of the drainage system as it can assist in the selection of the proper drainage system and its proper placement in the field. In this study we used the MODFLOW groundwater flow model to simulate groundwater levels in Jahir irrigated fields, the Jordan Valley, Israel. Using a three-layer groundwater flow model, the most efficient drainage system was found to be a combination of deep drains with relief wells and a pump placed in the area with soil salinity problem and upward hydraulic pressure. It was found that simulated drainage system can yield nearly 200,000?m3 of water per year. Given certain information, a spatially distributed groundwater flow model such as MODFLOW can provide more reliable information than different analytical solutions for planning of an effective subsurface drainage system.     

Water Table Profiles and Discharges for an Inclined Ditch-Drained Aquifer under Temporally Variable Recharge

This paper presents the solution of the linearized Boussinesq equation for an inclined, ditch-drained aquifer, with a temporally varying recharge rate. Water-table profiles and flow rates into the ditches are calculated. As an initial condition the steady-state profile for a constant recharge rate is used, and the linearized Boussinesq equation is solved for a different recharge rate. Then, at a specified time, the transient water table profile is used as initial condition for the Boussinesq equation with a new recharge rate. The transient solution at a new specified time is then used as the initial condition for the Boussinesq equation with a different recharge rate, and so on. Using the Darcy equation, analytical expressions for the flow rates into the ditches can be obtained. The solution allows the calculation of the transient behavior of the groundwater table and its flow rates due to temporally variable recharge rates.     

Regional Water Management Modeling for Decision Support in Irrigated Agriculture

Efficient water management is one of the key elements in successful operation of irrigation schemes in arid and semiarid regions. An integrated water management model was developed by combining an unsaturated flow model and a groundwater simulation model. These combined models serve as a tool for decision making in irrigation water management to maintain the water tables at a safe depth. The integrated model was applied on a regional scale in Sirsa Irrigation Circle, covering about a 0.42 million ha area in the northwestern part of Haryana, India, which is faced with serious waterlogging and salinity problems in areas underlain with saline ground irrigated by the canal network. The model was calibrated using the agrohydrologic data for the period 1977–1981 and validated for the period 1982–1990 by keeping the calibrating parameters unchanged. The model was used to study the long-term impact of two water management interventions related to the canal irrigation system—change in pricing system of irrigation water, and water supply according to demand—on the extent of waterlogging risk. Both of these strategies, if implemented, would considerably reduce aquifer recharge and consequently waterlogging risk, compared to the existing practice. The water supply according to demand strategy was slightly more effective in reducing aquifer recharge than the water pricing intervention. The implementation of the proposed water pricing policy would pose no problem in fitting into the existing irrigation system, and thus it would be easier to implement, compared to the water supply according to demand strategy, when taking technical, financial, and social considerations into account.     

Analytical Solution for Transient Water Table Heights and Outflows from Inclined Ditch-Drained Terrains

This paper presents two analytical solutions of the linearized Boussinesq equation for an inclined aquifer, drained by ditches, subjected to a constant recharge rate. These solutions are based on different initial conditions. First, the transient solution is obtained for an initially fully saturated aquifer. Then, an analytical expression is derived for the steady state solution by allowing time to approach infinity. As this solution represents the groundwater table shape more realistically, this water table profile is used as an initial condition in the derivation of the second analytical solution for the groundwater table height, and the in- and outflow into the ditches. The solutions allow the calculation of the transient behavior of the groundwater table, and its ouflow, due to changing percolation rates or water level heights in both ditches.     

Rule-Based Fuzzy System for Assessing Groundwater Vulnerability

Parallel to industrial growth and ever increasing use of agrichemicals, environmental resources have been affected and deteriorated by generated pollutants. Groundwater, an important source of fresh water, has not been immune from contamination. Recognition of groundwater vulnerability to pollution will help in managing groundwater quality conflicts. The DRASTIC model (where D=depth to groundwater; R=net recharge; A=aquifer media; S=soil type; T=topography; I=impact of vadose zone; and C=hydraulic conductivity of the aquifer) has been used extensively for assessing the vulnerability of groundwater. It employs a linear combination of some intrinsic properties of aquifers to develop a vulnerability index. As there is no clear boundary for the set of vulnerable aquifers, groundwater vulnerability can be addressed through fuzzy set theory instead of classical set theory. In this study, benefiting from a fuzzy system and a conscious knowledge base, a regional-scale model is developed for groundwater vulnerability assessment that employs DRASTIC parameters. A comparison between the output of the fuzzy model and the DRASTIC index is accomplished. The ability of the fuzzy system to cope with the modeling of a nonlinear system and presentation of the output of the fuzzy system in the framework of a geographical information system are highlighted.     

Water Table Fluctuation between Drains in the Presence of Exponential Recharge and Depth-Dependent Evapotranspiration

A linearized form of the Boussinesq equation was solved analytically to predict the water table fluctuation in subsurface drained farmland in the presence of recharge and evapotranspiration (ET). The recharge was assumed to be variable with time and the ET considered decreasing linearly with a decrease in the water table height above the drains. The proposed analytical solution was verified for special cases with the existing solutions. There was a close match between the solutions. Applications of the solution in prediction of the water table height in a drainage system are illustrated with the help of physical examples.     

Groundwater Quality Evaluation for Productive Uses— The Afram Plains Area, Ghana

Groundwater is the most widely used water resource in the Afram Plains area, Ghana. The objective of this study was to determine the distribution of fluoride, sodium adsorption ratio (SAR), and salinity (EC) in groundwater from the different aquifers in the Afram Plains area. The distribution of these parameters would enable a determination of the quality of groundwater from the different aquifer units for use in households and irrigation purposes. The inverse distance weighting, interpolator with a power of 2 was applied to 143 data points of each parameter to generate prediction maps for fluoride, SAR, and EC in the area. The distribution maps from this study show that the shale aquifers that underlie the southwestern sections of the area have the highest levels of fluoride, SAR, and EC. A narrow strip of the shale aquifer in the southwestern region produces groundwater whose fluoride level (2.2?mg/L) is higher than the World Health Organization minimum allowable fluoride concentration of 1.5?mg/L in drinking water. The feldsparthic sandstone, arkose, siltstone, and mudstone aquifers in the northeastern sections of the area produce groundwater with fluoride concentration in the range of 0.0–0.3?mg/L, which fall outside the minimum range of 0.7–1.2?mg/L required in drinking water for normal bone and dental health. The highest SAR and EC are also associated with the shale aquifers to the southwestern section of the area. Using the World Food and Agriculture Organization’s guidelines for irrigation water quality, it was determined that groundwater from the Afram Plains area will generally have a mild to moderate effect on the hydraulic properties of soils when used as irrigation water.     

Interactive Effects of Controlled Drainage and Riparian Buffers on Shallow Groundwater Quality

As a result of recent surface water quality problems in North Carolina, riparian buffers and controlled drainage are being used to reduce the loss of nonpoint source nitrogen from agricultural fields. The effect of controlled drainage and riparian buffers as best management practices to reduce the loss of agricultural nonpoint source nitrogen from the middle coastal plain has not been well documented. The middle coastal plain is characterized by intensive agriculture on sandy soils with deeply incised or channelized streams. A 2-year study was conducted to determine the effectiveness of controlled drainage, riparian buffers, and a combination of both in the middle coastal plain of North Carolina. It was hypothesized that raising the water table near the ditch would enhance nitrate-nitrogen reduction through denitrification. On the sandy soils studied, controlled drainage did not effectively raise the water table near the ditch to a greater degree than observed on the free drainage treatment. Due to random treatment location, the free drainage treatment was installed along a ditch with a shallower impermeable layer compared to the impermeable layer on the controlled drainage treatments (2 m versus 3- to 4-m deep). This resulted in a perched or higher water table on the free drainage treatment. Over 17 storm events, the riparian buffer (free drainage) treatment had an average groundwater table depth of 0.92 m compared to 0.96 and 1.45 m for the combination (riparian buffer and controlled drainage) and controlled drainage treatments, respectively. Nitrate concentration decrease between the field wells and ditch edge wells averaged 29% (buffer only), 63% (buffer and controlled drainage), and 73% (controlled drainage only). Although apparently more nitrate was removed from the groundwater on the controlled drainage treatments, the controlled drainage treatment water table near the ditch was not raised closer to the ground surface compared to the free drainage treatment. Nitrate removal effectiveness was attributed to local soil and landscape properties, such as denitrification in deeper reduced zones of the soil profile.     

Groundwater Classification Using Multivariate Statistical Methods: Birimian Basin, Ghana

Groundwater from the aquifers of Birimian system in the northern and southern sections of the country was sampled for the concentrations of the major ions in the area. The objective was to determine the spatial groundwater associations which will in turn be used to infer the position of each groundwater group in the flow system. In addition, this study intended to determine the major sources of variation in the hydrochemistry and the suitability of groundwater from aquifers of the Birimian system for irrigation activities. R-mode factor and Q-mode hierarchical cluster analyses were used together with conventional graphical techniques. This study revealed four groundwater associations (clusters) representing three major groundwater types in the Birimian System: the Ca–HCO3 water types which make up Clusters (groups) 1 and 2 members; the Na-K-Cl water types comprising cluster 3 members, and Mg–HCO3 water types comprising Cluster 4 members. Cluster 2 has the lowest average electrical conductivity of 194 mS/m with total dissolved solids (TDS) ranging between 50 and 250 mg/L. This is the freshest groundwater type in the area and is typical of groundwater in recharge areas of the groundwater flow system. Cluster 1 members range in salinity between 50 and 500 mg/L. The highest average salinity is contained in Cluster 3, with TDS in the range of 300 to 1,000 mg/L, which is characteristic of groundwaters in discharge areas of the groundwater flow system. Members of this group are also characterized by high fluoride concentrations; average fluoride concentration in this group is 4.60 mg/L. Cluster 3 is the least desirable of the four clusters, for domestic water supply. Cluster 4 has TDS in the range of 300 and 1,000 mg/L, with low fluoride content. This study finds that the hydrochemistry of groundwater in the terrain is controlled by three major factors: silicate mineral weathering and cation exchange, carbonate mineral weathering, and chemical fertilizers from farms in the area. All the groundwater clusters have low sodium content and will not pose the sodium hazard when used for irrigation. However, as a result of high permeability indices, all but one of the Cluster 2 members plot within the class III region of the Doneen’s chart and are therefore unsuitable for irrigation on these grounds. Clusters 3 and 4 members are the best water types, while Cluster 1 members are equally distributed between Classes II and III categories.     

Monitoring and Modeling Flow and Salt Transport in a Salinity-Threatened Irrigated Valley

Saline high water tables pose a growing threat to the world’s productive irrigated land. Much of this land lies along arid alluvial plains, where solutions must now be developed in the context of changing constraints on river management. Findings are presented from the preliminary phase of a project aimed at developing, through well-conceived data collection and modeling, strategies to sustain irrigated agriculture in the salinity-threatened lower Arkansas River Basin of Colorado. Extensive field data from a representative subregion of the valley reveal the nature and variability of water table depth and salinity, irrigation efficiency and salt loading, and soil salinity. The shallow water table had an average salinity concentration of 3,100 mg/L and an average depth of 2.1 m, and was less than 1.5 m deep under about 25% of the area. Evidence reveals low irrigation efficiencies and high salt loading under each of six canals serving the subregion. Water table depths less than 2.5–3 m contributed to soil salinity levels that exceed threshold tolerances for crops under about 70% of the area. Preliminary steady-state modeling indicates that only limited improvement can be expected from vertical drainage derived from increased pumping, or from decreased recharge brought about by reduced overirrigation. Investments in canal lining, horizontal subsurface drainage, and improved river conditions also will need consideration.     

阳山金矿床开采技术条件分析

对矿区地下水类型及补给、径流、排泄条件进行分析,确定了矿床水文地质条件和矿山开发用水源地;划分了矿区软弱类工程地质岩组,调查了矿区的环境地质情况,确定了矿区工程地质及环境地质条件。基本阐明了矿床的开采技术条件,为下一步矿山开发提供了参考。