Journal of Irrigation and Drainage Engineering

Design methods for agricultural drainage denitrification bioreactors must be optimized for these novel systems to provide maximized water quality improvement. The objective of this paper was to further develop science-based bioreactor sizing guidelines by calibrating an existing design procedure with multiple years of drainage flow data collected at two sites in Iowa. The models created for the two hypothetical bioreactor sites showed the original design criteria (use of a design flow rate one-fifth of the peak flow rate) generally allowed simulated bioreactor treatment of the majority of total annual drainage volume, but treatment of this majority was not necessary to maximize nitrate removal. Larger bioreactors resulting from use of either increased design flow rate or higher design retention time increased the extent of nitrate removal, but had lower nitrate removal rates. This modeled simulation analysis informs that bioreactor design procedures considering flow rate and retention time should use design flow rates of 10 to 20% of the anticipated peak flow rate at design retention times of 6 to 8 h, thus updating and refining the original design procedure. This approach produces bioreactors of increased length to width ratios, with improved performance based on nitrate removal extent and removal rate. Further field-scale validation is suggested for this drainage bioreactor design procedure.

Continuous seepage from earthen canals creates a serious water-management problem in Pakistan. Efficient water management through a properly designed drainage system is therefore indispensable and imperative not only for the control of waterlogging, but also to provide a favorable environment for crop root development that ultimately enhances crop growth and increases yield potential. This paper discusses the effectiveness of different remedial measures adopted to intercept seepage from the Rohri canal and control the rising water table on 1,000 ha of agricultural land near the Gambat railway station in the district of Khairpur in the Sindh Province of Pakistan. A three-dimensional (3D) finite-element model for groundwater flow and solute transport (FEMGWST), developed at Universiti Putra Malaysia, has been used to evaluate the performance of horizontal and vertical drainage systems, operating either independently or simultaneously, for different flow levels in the Rohri canal. Simulation results have revealed that an increase in tube-well discharge from 20 to $24\mathrm{L}/\mathrm{s}$ can result in about 5.02% more reclaimed area, and an 8.68% additional reclaimed area can be achieved when the well discharge was increased from 20 to $28\mathrm{L}/\mathrm{s}$; however, waterlogging still prevailed along the canal embankment. About 196.35 ha of agricultural land had water-table depth below 0.5 m when the well was discharging at $20\mathrm{L}/\mathrm{s}$, followed by 146.14 ha and 109.59 ha of land for the well discharges of 24 and $28\mathrm{L}/\mathrm{s}$, respectively. Thus it was obvious that the vertical drainage system alone cannot maintain the water table below the root zone adjacent to the canal embankments. Results revealed that managing waterlogging with the horizontal tile drainage system is only effective up to a distance of 300 m away from the canal, beyond which the effectiveness of this system gradually diminishes. A combined drainage system (tube wells plus a horizontal drainage system) is more effective and beneficial in maintaining the water table within desirable depths, and more land could be cultivated. Under the combined drainage system only 91.98 ha of land was still considered waterlogged as compared to 236.38 ha when only the vertical drainage system was operating.

Procedures that can characterize spatial correlation and interpolate values at unknown locations can be valuable in capturing spatial trends, may increase sampling accuracy, and reduce error. This study sought to compare three common methods of measuring infiltration, the double ring (DR), sprinkler (SPR), and frame (FRM) methods, on a hillslope to characterize the spatial structure of the infiltration measurements. All infiltration method measurements were log normally distributed; therefore, universal kriging estimators were developed in conjunction with semivariogram analysis and an error model to interpolate infiltration rates under wet and dry antecedent soil conditions. Variability in measured infiltration rates were greatest from the DR and SPR methods, coefficients of variation (CV) ranged from 42–53%, whereas the CV of the FRM method was 27%. This, however, is not unexpected, as the DR and SPR methods had highly significant directional trends and captured a much larger range in infiltration rates on the hillslope. After removing the directional trend in the data, the semivariograms were able to characterize the spatial correlation reassuringly well. Nugget variance was low for most methods/antecedent conditions, indicating that there was little unexplained variation in the semivariogram model. The range of autocorrelation between measurements varied from 17 m for the SPR method to 33 m for the FRM method. Using the modeled correlation, infiltration rates were interpolated at 284 unsampled locations with an average error of 7.8%. These results indicate that methods of measuring the infiltration rate of a soil differ in first order statistical measures (mean and variance), but not substantially in second order statistical measures (spatial structure). This information can be used to characterize physical or environmental phenomenon not easily modeled with deterministic equations.

Leaf temperature has long been recognized as an indicator of water availability. The stress level in a plant can be quantified from leaf temperature by using the crop water stress index (CWSI). In this study, it was investigated whether infrared thermometer measurements and accordingly CWSI could be used to create irrigation schedules for olive trees (cultivated variety Memecik). The research was conducted at the olive tree plantation of the Olive Research Station between 2009 and 2010. In the study, the effects of different irrigation treatments on the yield, canopy temperature, and CWSI of olive trees were investigated, and the optimum irrigation schedule was determined according to the findings. Seven different water application treatments were created using the drip irrigation method. Five treatments consisted of irrigating at a rate equivalent to 25% (S-0.25), 50% (S-0.50), 75% (S-0.75), 100% (S-1.00), and 125% (S-1.25) of the cumulative evaporation in 5 days from a Class A evaporation pan. The other two treatments consisted of a treatment in which the humidity lost at a soil depth of 0–90 cm was replenished each time to the field capacity (Control, S-C) and a treatment in which no irrigation was performed and cultivation was carried out under completely rain-based conditions (Stress, S-0). In the study, the amounts of irrigation water applied to the treatments ranged from 0 to 809 mm, and the crop water consumption values varied from 127 to 853 mm according to the average of both years. The highest water-use efficiency was obtained in the S-0 treatment, whereas the highest irrigation water–use efficiency was obtained from the S-0.50 treatment. One of the important findings of this study was that handheld infrared thermometer can be used for stress detection and irrigation scheduling of olive trees. When the mean CWSI values in the experimental years were examined in terms of the irrigation treatments, the CWSI values ranged from 0 to 0.68 in 2009 and from 0.02 to 0.71 in 2010. In both years, the highest values were recorded in the S-0 treatment, and the lowest values in the S-1.25 treatment. When water-use efficiency is evaluated along with CWSI values, irrigation can be recommended at half of the evaporation from a Class A evaporation pan (S-0.50, when CWSI values reach 0.39). In conditions in which water sources are insufficient, it can be recommended that irrigation be started when evaporation is a quarter (S-0.25), that is, when CWSI values reach 0.49.

A lumped hydrologic model (ACRU2K.1), developed from ACRU2000, was extended and evaluated to simulate water dynamics in a plastic mulch bedded system for vegetable production under high water table environments. The updated model (ACRU2K.2) and ACRU2K.1 were calibrated using data collected during the fall 2005 and spring 2006 crop seasons of a field study for a vegetable production system in south Florida. Both model versions were evaluated using data from the fall 2006 crop season. Graphical and statistical methods were applied to evaluate and compare the performance of ACRU2K.1 and ACRU2K.2 using observed and simulated water table depths (WTD). Graphical analyses showed no added advantage in using ACRU2K.2 with its new irrigation process. However, the introduction of a drainage process for ACRU2K.2 showed some improvement over ACRU2K.1 in simulating changes in the water table. For the calibration period, Nash-Sutcliffe coefficient (NS) values for ACRU2K.1 and ACRU2K.2 were 0.73 and 0.65, respectively. However, for the evaluation period NS values for ACRU2K.1 and ACRU2K.2 were $-0.60$ and $-0.67$, respectively. In general, ACRU2K.1 and ACRU2K.2 underperformed when simulating the WTD for plastic mulch bedded systems under high water table environments. This was the result of ACRU2000’s inability to respond correctly to sharp water table fluctuations (within 12 h) and is a fundamental limitation in its hydrological response time.

A simple model was developed to explore the effect of water saving technologies by simulating the soil water balance in a lawn turfgrass system based on site-specific soil characteristics, irrigation schedule, real-time weather data, and irrigation technology (i.e., time-based irrigation, time-based irrigation with rain sensor, time-based irrigation with soil water sensor, and evapotranspiration controller). The model has been integrated into an interactive tool for homeowners and landscape professionals to evaluate and improve irrigation scheduling. Model coding was tested by using two software programs and verified by using a field data set. Average absolute differences between measured and simulated irrigation and deep percolation by event were different among irrigation technologies, ranging from 0 to 0.46 and 0.19 to 2.03 cm, respectively. The model is available as an online tool through the Florida Automated Weather Network using Google technology. The free tool requires minimum user input, offers default values, and generates an updated e-mail by using the input data and real-time weather on a weekly basis.

Agricultural soils of southern New Mexico, especially sand and sandy loams receiving numerous nitrogen (N) fertilizations, are prone to leaching large amounts of N to shallow groundwater. Adsorption and leaching experiments were conducted to investigate the use of clinoptilolite zeolite (CZ) as an amendment to sandy soils to increase N retention and reduce nitrate (${\mathrm{NO}}_3^{-}$) leaching. Urea-ammonium-nitrate (UAN 32) fertilizer was applied to four soil treatments to simulate crop irrigation. The treatments were composed of 100% CZ, 100% loamy sand (LS), a mixture of $80:20\%$ (LS:CZ), and a mixture $60:40\%$ (LS:CZ) by mass, respectively. Results from the experiments showed an inverse relationship between nitrate-nitrogen (${\mathrm{NO}}_3^{-}\text{-}\mathrm{N}$) adsorption and the amount of CZ added to soil caused by anion exclusion and a direct relationship between ammonium-nitrogen (${\mathrm{NH}}_4^{+}\text{-}\mathrm{N}$) adsorption and the amount of CZ mixed with LS due to ${\mathrm{NH}}_4^{+}\text{-}\mathrm{N}$ entrapment by the CZ molecules. It is therefore recommended to use other types of fertilizers that do not include ${\mathrm{NO}}_3^{–}$ to LS soils amended with CZ in order to reduce the risk of leaching. Otherwise, it is suggested to apply fertilizers containing ammonium nitrate in LS soils amended with CZ at reduced rates but at higher frequencies to meet plant demands.

In canal irrigated areas, where interactions between surface water and groundwater are high, the conjunctive management of surface water and groundwater can play a significant role in improving water availability in time and space, thereby promoting more equitable distribution of water while maintaining long-term availability of groundwater resources. Achieving a harmonious balance between the use of surface water and groundwater requires careful consideration of the associated benefits, impacts, and trade-offs. In this study, a simple, integrated framework was developed and implemented to characterize and quantify interactions between surface water and groundwater in a canal irrigated area; this framework was used to evaluate the impacts of alternative levels of conjunctive use under varying climate and cropping conditions. Applying the model to a case study area of the Srisailam Right Branch Canal project in Andhra Pradesh, India, indicated that regulating canal supplies to optimum levels can prompt sustainable groundwater use and save up to 48% of allocated canal water; these water savings could be reallocated elsewhere within the irrigated area to promote equity.

The Yellow River Basin is a closed basin under serious stress with dense population, intensive agriculture, and excess water withdrawals. Low water use efficiency and groundwater overexploitation are threatening the sustainable development of the basin. This paper describes a coupled modeling approach to analyze sustainable management strategies in surface–groundwater conjunctive use irrigation districts in the lower Yellow River Basin. An appropriate irrigation schedule and an optimal range of groundwater levels are first established using the soil water atmosphere plant (SWAP) model with data from an irrigation experiment station. The integrated surface water and groundwater model was then set up using modified soil and water assessment tool (SWAT2000) and modular three-dimensional groundwater flow model (MODFLOW) models. The two models were connected through standardized simulation grids and calibrated using field measurements. Five scenarios that were designed according to different well-canal irrigation supply ratios and the irrigation schedule determined by SWAP were tested using the integrated modeling approach. It is proved that conjunctive management strategies of canal diversions and tube-well pumps can effectively reduce phreatic evaporation losses, increase water use efficiency, and sustain groundwater levels while maintaining crop yields at current levels.