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.     

Hydrologic Impacts due to Changes in Conveyance and Conversion from Flood to Sprinkler Irrigation Practices

Improvements in irrigation efficiency are well documented when changing from flood to sprinkler irrigation methods; however, other impacts to the watershed associated with this change are not well known. The resulting impacts to a river basin hydrology when irrigation and conveyance methods are changed are the focus of this study. In an attempt to improve water application and conveyance efficiencies in the Salt River Basin of western Wyoming, irrigation practices were changed from flood irrigation to sprinkler irrigation beginning in the late 1960s, with completion by the mid-1970s. Based upon a water balance, flow in the Salt River increased an average of 65.62 MCM/year. Return flow timing was also impacted by the conversion to sprinkler irrigation. Flows increased 34% in May and 50% in June, while decreasing 15 and 14% in August and September. These changes may have coincided with decreases in groundwater storage. However, analysis of changes in groundwater levels with time was inconclusive. Surface water total dissolved solids (TDS) appears unaffected by the conversion in irrigation practices, while limited groundwater quality data indicate that TDS values are lower in sprinkler irrigated areas.     

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.     

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.     

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.     

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.     

Describing Near Surface, Transient Flow Processes in Unconfined Aquifers below Irrigated Lands: Model Application in the Western San Joaquin Valley, California

In order to rigorously examine near surface, field to field interactions between irrigation management regimes and a shallow fluctuating water table, an enhanced deforming finite element (DFE) model was recently developed. The enhanced DFE model, through a process of iteration within each time step, avoids making common assumptions regarding the changing geometry of an aquifer free surface. This paper demonstrates the usefulness and effectiveness of the model by employing it to an irrigated region in the western San Joaquin Valley, Calif., where shallow subsurface tile drains have been installed to control shallow water tables. By virtue of the problems created by the need to dispose off the drainage water, this region has been the focus of several important regional scale modeling exercises, which have evaluated the utility of management strategies, such as source control, groundwater pumping, and land retirement. By refining the focus of the analysis, the enhanced DFE model is found to be able to show that both sources control and managed pumping could be more effective drainage control strategies than predicted based on the results of regional models.     

Allocation of Scarce Water Resources Using Deficit Irrigation in Rotational Systems

On irrigation schemes with rotational irrigation systems in semiarid tropics, the existing rules for water allocation are based on applying a fixed depth of water with every irrigation irrespective of the crops, their growth stages, and soils on which these crops are grown. However, when water resources are scarce, it is necessary to allocate water optimally to different crops grown in the irrigation scheme taking account of different soils in the command area. Allocating water optimally may lead to applying less water to crops than is needed to obtain the maximum yield. In this paper, a three stage approach is proposed for allocating water from a reservoir optimally based on a deficit irrigation approach, using a simulation-optimization model. The allocation results with a deficit irrigation approach are compared for a single crop (wheat) in an irrigation scheme in India, first with full irrigation (irrigation to fill the root zone to field capacity) and second with the existing rule. The full irrigation with a small irrigation interval was equivalent to adequate irrigation (no stress to the crop). It is found that practicing deficit irrigation enables the irrigated area and the total crop production in the irrigation scheme used for the case study to be increased by about 30–45% and 20–40%, respectively, over the existing rule and by 50 and 45%, respectively, over the adequate irrigation. Allocation of resources also varied with soil types.     

Residential Irrigation Water Use in Central Florida

Automatic inground irrigation is a common option for residential homeowners desiring high-quality landscapes in Florida. However, rapid growth is straining water supplies in some areas of the state. The first objective of this study was to document residential irrigation water use in the Central Florida ridge region on typical residential landscapes (T1). The second objective was to determine if scheduling irrigation by setting controllers based on historical evapotranspiration (ET) (T2) and reducing the percentage of turf area combined with setting the controllers based on historical ET (T3) would lead to reductions in irrigation water use. The time frame of this study was 30?months beginning in January 2003. Irrigation accounted for 64% of the residential water use volume over all homes monitored during this project. The T1 homes had an average monthly water use of 149?mm/month. Compared to the T1 homes, T2 resulted in a 30% reduction (105?mm/month), and T3 had a 50% reduction (74?mm/month) in average monthly water use. Average monthly water use was significantly different (p<0.001) across the three irrigation treatments. Setting the irrigation controllers to apply water according to seasonal demand resulted in significantly less irrigation water applied. In addition, increasing the proportion of landscape area from 23% (T1 and T2) ornamental plants irrigated with sprinklers to 62% and irrigated with micro-irrigation (T3) resulted in the largest reduction in irrigation water applied. Compared to T2 where only the irrigation controllers were adjusted, this additional decrease in irrigation water applied was a result of low volume application on only a portion of the landscaped beds where irrigation is only applied to the root zone of plants.     

Pond Water Source for Irrigation on Steep Slopes

Existing technologies have been tailored to deliver cost-effective irrigation on a railway embankment and excavated steep slopes (referred to as batters) within a semiarid environment. Irrigation is to aid the establishment of 100% grass cover within a few weeks to mitigate soil erosion problems. It is based on water sourced from a temporary excavated pond plus the use of a solar powered pump and a drip irrigation system. Railway batter erosion remediation is timed for the wet summer season when irrigation can be used to supplement natural rainfall. For a given irrigation demand and catchment area, critical (minimum) pond volume is estimated from regional charts developed for ungauged catchments. About 20% of the critical volume is added to account for evaporation losses and dead storage. Also, seepage losses need to be considered if the soil is medium to coarse textured and if the pond is not lined with an impermeable material. Initial results are very encouraging with a cost estimate of AU$2.74/m2 of batter area treated (irrigated). Irrigation unit cost is expected to decrease with a larger scale irrigated batter area and the refinement of technologies and installation procedures. Although irrigation methodologies were developed for railway embankments and excavated slopes, they can also be used for erosion control on steep slopes such as road embankments or excavated slopes and earth dam side slopes.     

Survey of Irrigation Methods in California in 2001

Reliable information on irrigation methods is important for determining agricultural water demand trends. Therefore, a study was conducted during 2002 to collect information on irrigation methods that were used by growers to irrigate their crops in 2001. The results were compared to earlier surveys to assess trends in cropping and irrigation methods. A one-page questionnaire was developed to collect information on irrigated land by crop and irrigation methods. The questionnaire was mailed to 10,000 growers in California that were randomly selected from a list of 58,000 growers by the California Department of Food and Agriculture, excluding rice, dry-land, and livestock producers. From 1972 to 2002, the area planted has increased from 15 to 31% for orchards and from 6 to 16% for vineyards. The area planted to vegetables has remained relatively static, while that planted to field crops has declined from 67 to 42% of the irrigated area. The land irrigated by low-volume (drip and microsprinkler) irrigation has increased by about 33%, while the amount of land irrigated by surface methods has decreased by about 31%. Sprinkler usage has decreased in orchards and vineyards, but it has increased in vegetable crops.     

Knowledge-Based Model for Supplementary Irrigation Assessment in Agricultural Watersheds

In this paper a knowledge-based model for supplementary irrigation assessment in rainfed agricultural watersheds is presented. The supplementary irrigation assessment problem is divided into different components and is modeled separately. Geographic Information System (GIS) is used to aggregate spatially varying attributes required for the modeling. A graphical user interface is developed in a GIS platform by using the ERDAS macro language tools. The model was applied to two case study areas in India: a subwatershed of Gandheshwari area (West Bengal), and Harsul watershed (Maharashtra). In the Gandheshwari subwatershed, the water availability was found to be inadequate to meet the irrigation requirement and hence the model identified the areas that can be irrigated with different outsource water supply. On the other hand, surface runoff generated in the Harsul watershed was found to be sufficient to meet the supplementary irrigation requirement, thereby showing the feasibility for supplementary irrigation in the area. Using the model, the effect of any rainfall condition can be simulated and hence appropriate measures can be taken in advance to reduce the risk of crop failure.     

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.     

Optimal Reservoir Operation for Irrigation of Multiple Crops Using Genetic Algorithms

This paper presents a genetic algorithm (GA) model for obtaining an optimal operating policy and optimal crop water allocations from an irrigation reservoir. The objective is to maximize the sum of the relative yields from all crops in the irrigated area. The model takes into account reservoir inflow, rainfall on the irrigated area, intraseasonal competition for water among multiple crops, the soil moisture dynamics in each cropped area, the heterogeneous nature of soils, and crop response to the level of irrigation applied. The model is applied to the Malaprabha single-purpose irrigation reservoir in Karnataka State, India. The optimal operating policy obtained using the GA is similar to that obtained by linear programming. This model can be used for optimal utilization of the available water resources of any reservoir system to obtain maximum benefits.     

River Hydrograph Retransmission Functions of Irrigated Valley Surface Water–Groundwater Interactions

Storage and release functions of western U.S. traditional river valley irrigation systems may counteract early and rapid spring river runoff associated with climate variation. Along the Rio Grande in northern New Mexico, we instrumented a 20-km-long irrigated valley to measure water balance components from 2005 to 2007. Hydrologic processes of the system were incorporated into a system dynamics model to test scenarios of changed water use. Of river water diverted into an earthen irrigation canal system, some was consumed by crop evapotranspiration (7.4%), the rest returned to the river as surface return flow (59.3%) and shallow groundwater return flow that originated as seepage from canals (12.1%) and fields (21.2%). The modeled simulations showed that the coupled surface water irrigation system and shallow aquifer act together to store water underground and then release it to the river, effectively retransmitting river flow until later in the year. Water use conversion to nonirrigation purposes and reduced seepage from canals and fields will likely result in higher spring runoff and lower fall and winter river flow.     

Integrated Water Management for the 21st Century: Problems and Solutions

Most of the projected global population increases will take place in third world countries that already suffer from water, food, and health problems. Increasingly, the various water uses (municipal, industrial, and agricultural) must be coordinated with, and integrated into, the overall water management of the region. Sustainability, public health, environmental protection, and economics are key factors. More storage of water behind dams and especially in aquifers via artificial recharge is necessary to save water in times of water surplus for use in times of water shortage. Municipal wastewater can be an important water resource but its use must be carefully planned and regulated to prevent adverse health effects and, in the case of irrigation, undue contamination of groundwater. While almost all liquid fresh water of the planet occurs underground as groundwater, its long-term suitability as a source of water is threatened by nonpoint source pollution from agriculture and other sources and by aquifer depletion due to groundwater withdrawals in excess of groundwater recharge. In irrigated areas, groundwater levels may have to be controlled with drainage or pumped well systems to prevent waterlogging and salinization of soil. Salty drainage waters must then be handled in an ecologically responsible way. Water short countries can save water by importing most of their food and electric power from other countries with more water, so that in essence they also get the water that was necessary to produce these commodities and, hence, is virtually embedded in the commodities. This “virtual” water tends to be a lot cheaper for the receiving country than developing its own water resources. Local water can then be used for purposes with higher social, ecological, or economic returns or saved for the future. Climate changes in response to global warming caused by carbon dioxide emission are difficult to predict in space and time. Resulting uncertainties require flexible and integrated water management to handle water surpluses, water shortages, and weather extremes. Long-term storage behind dams and in aquifers may be required. Rising sea levels will present problems in coastal areas.     

Impact of Irrigation Management Transfer on Land and Water Productivity and Water Supply in the Gediz Basin, Turkey

In the 1990s, Turkey started a fast transfer program in which a large proportion of government-managed irrigation systems were put into the hands of Water Users’ Associations (WUAs) in a very short space of time. One of the first systems to be handed over was the Gediz Basin. This study aims to set out the effects of the transfer of irrigation management in this basin on water and land productivity and water supply. For this purpose, the indicators of productivity and water supply proposed by the International Water Management Institute have been used to show changes between the pretransfer, transfer, and post-transfer periods. WUA averages for the post-transfer period calculated from the results ranged $2,076–$2,898?ha?1 for output per command area, $2,747–$4,585?ha?1 for output per irrigated area, $0.26–$0.68?m?3 for output per irrigation supply, $0.30–$0.63?m?3 for output per unit water consumed, 0.88–1.49 for relative water supply, and 0.99–1.99 for relative irrigation supply. During the period evaluated by the study, there was a decline in water supply indicators, as against a steady increase in the productivity of water and land use. The basic reason for this decrease in supply is the long-lasting and ongoing drought in the region.     

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.     

Methodology for Estimating Specific Yield in Shallow Water Environment Using Continuous Soil Moisture Data

A methodology for estimating specific yield in shallow water environments using continuous soil moisture data is introduced. An accurate estimate of specific yield is critical for management of water resources affecting well yields, water levels, and rates of water level decline. The study area is located in an intensive small-scale hydrologic monitoring field site in Hillsborough County, Florida. Data from four soil moisture monitoring stations were studied. The objectives of this paper are to describe a methodology to obtain precise estimates of the specific yield that can be obtained by a fitting procedure and to determine functional relationships between measured soil parameters and soil moisture storage variability. Estimated specific yield values varied from zero, when the water table was near land surface, to a maximum that was close to drainable porosity consistent with a humid shallow water environment, where sensitive ecosystems and wetlands are dependent on a seasonal hydroperiod of water table fluctuations. The results will be incorporated into regional integrated surface and ground water models that are being applied successfully in West-Central Florida.     

Predicting Soil Salinity under Various Strategies in Irrigation Systems

This paper presents a model to estimate the soil salinity for different on-farm management strategies under irrigated conditions. It is based on research in the Mani?oba irrigation scheme in northeast Brazil, where upward flow from the shallow water table is the main cause of soil salinization. The model calculates soil water and salt balances for the topsoil. It is calibrated for the topsoil of abandoned plots and for the root zone (0.9?m) of mango trees. Simulating the effect of different management scenarios on soil salinity may help to organize the switch from intensive surface irrigation to more efficient irrigation practices.