Journal of Irrigation and Drainage Engineering

An improved understanding of the water budget components in floodplain aquifers is necessary to implement and support water accounting requirements for use of river water. Of critical importance is the groundwater return flow as a result of recharge from irrigated water in a typical irrigation district near a river, which is the most uncertain and difficult component to be estimated. The objectives of this study are to (1) develop an effective but simple approach to estimate the amount of groundwater return flow to the river because of irrigation recharge; and (2) conduct uncertainty and sensitivity analyses of groundwater return flow to various recharge scenarios. The approach takes advantage of comprehensive drainage network typical in irrigation districts. The approach is evaluated and tested against numerical model results. It is found that the approach is accurate in calculating groundwater return flow for practical purposes of water accounting for less than 10% error. The authors further examine how groundwater return flow may change in response to variations in recharge distributions using the proposed approach. As long as information about river stage, drain stage, and distributions of irrigation water is available, the approach could predict changes in the amount of return flows.

A mathematical model for a field-scale hydraulic characterization and simulation of solid set sprinkler systems with single-line and double-line lateral layout configurations is developed. This paper describes the hydraulic equations, numerical solution algorithms, and the hydraulic characterization functionality of the model for a system with single-line laterals. Numerical solutions of the lateral and mainline hydraulic equations are based on standard manifold hydraulics. A rigorous and flexible formulation of the sprinkler hydraulic problem is obtained by coupling the energy equation for each lateral and mainline segment with the continuity equation at a node. The resulting set of equations is then solved iteratively, starting from the distal end sprinkler or mainline outlet and moving sequentially upstream. The hydraulic characteristics of the sprinklers is defined based on manufacture’s pressure head and discharge data, and the hydraulic characteristics of each mainline outlet are computed by the system hydraulic characterization functionality of the model. The cubic spline method is used to interpolate mainline outlet discharges from the respective hydraulic characteristics curves as a function of total heads, effectively providing the interface for coupling the numerical solutions of the laterals and the mainline hydraulic equations. Evaluation of the hydraulic model with field data suggests that the hydraulic model is accurate. A companion paper describes the formulation of the hydraulic equations and numerical solutions for sprinkler systems with double-line laterals and the system simulation functionality of the model.

This paper describes a mathematical model for the hydraulic characterization of a field-scale solid set sprinkler irrigation system with a double-line lateral layout configuration. Formulation of the basic hydraulic equations along the mainline and laterals is based on manifold hydraulics. Lateral hydraulics remains the same as that described in a previously published paper, for systems with single-line laterals. A description of the mainline hydraulics of systems with a double-line lateral layout configuration, which requires the formulation and iterative solution of a system of nonlinear equations, is presented here. The hydraulic characterization functionality of the model, described in a previously published paper, serves as an interface for coupling the numerical solutions of the lateral and mainline hydraulic equations. In addition, this paper presents a description of the simulation functionality of the sprinkler hydraulic model and a related numerical algorithm, which is based on one-dimensional optimization. A comparison of model output with field data suggests that model performance is satisfactory. Example problems, consisting of field-scale solid set sprinkler systems with single-line and double-line laterals, are used to highlight the practical application of the hydraulic model.

With an increase of population, agriculture, and industry, the demand for water has increased gradually across the world. Currently, agricultural crops have been damaged by drought severity due to climate changes that contribute to water scarcity. Policy/decision makers need to be prepared for reducing damages to crops due to severe droughts. For this reason, a genetic algorithm (GA)-based irrigation water management model (IWMM) adapting a hydrological model [soil water atmosphere plant (SWAP)] was developed. This approach is linked with a noisy Monte Carlo genetic algorithm (NMCGA) that can estimate effective soil hydraulic properties from in situ/remotely sensed (RS) soil moisture data. Based on the estimated soil parameters, vegetation information, and historical weather forcings, long-term root zone soil moisture (SM) and evapotranspiration (ET) dynamics were reproduced at fields using SWAP in a forward mode. This approach incorporates a soil moisture deficit index (SMDI) that can estimate the weekly drought severity using the daily estimated soil moisture dynamics. The irrigation schedules, intervals, and amounts were determined by the degree of drought based on the SMDI values (below 0 indicating drought). The Lubbock and Walnut Creek (WC) $11/14$ sites in Texas and Iowa were selected for testing the applicability of the studied approach using in situ (point scale) and RS (airborne sensing scale) soil moisture products. As this approach irrigates the appropriate/minimum water amounts (yearly average 65.5–136.1 mm) to the agricultural fields, one could prevent the drought-driven crop damages with the positive SMDI values. Thus, the newly developed model could be helpful for improving agricultural water management and reducing drought severity efficiently in irrigated agriculture.

Rice and wheat are very important grain crops and are heavily grown in lands between the Ravi and Chenab Rivers in Pakistan. Because rice is generally cultivated under standing water conditions, careful estimation of actual water consumption and crop water productivity (CWP) is key for proper water management. In the current study, an effort is made to estimate actual evapotranspiration (${\mathrm{ET}}_a$) by using the soil and energy balance algorithm (SEBAL), which used the moderate-resolution imaging spectroradiometer (MODIS) satellite with a spatial resolution of 1,000 m. Rice and wheat crop dominance areas were identified by using the ISODATA crop classification technique by utilizing MODIS normalized difference vegetation index (NDVI) 250 m resolution data. Crop-specific ${\mathrm{ET}}_a$ was masked out both for rice and wheat, and this information was utilized with crop yield for estimation of CWP. Tehsil administrative-level crop-yield data were collected and extrapolated to model crop yield on a pixel basis by benefiting from crop yields and specific NDVI empirical relationships. Study results showed a variation of ${\mathrm{ET}}_a$ (402–780 and 244–328 mm), yield (823–2,596 and $\mathrm{1,287}–\mathrm{3,646}\mathrm{kg}/\mathrm{ha}$), and CWP (0.14–0.56 and $0.54–1.44\mathrm{kg}/{\mathrm{m}}^3$) for rice and wheat, respectively. Best results were attained for rice in tehsil Hafizabad with a coefficient of variation in CWP of 7.94%. Most of the other tehsils showed higher variability of approximately 16%. The primary cause of lower CWP for rice crop in these tehsils is higher values of ${\mathrm{ET}}_a$ (i.e., greater than 600 mm), which is ideal for maximizing CWP in the study region. For the wheat crop, because water consumption is almost similar in all parts and CWP is primarily variable owing to yield differences, this suggested minimum scope for CWP improvement by water management for wheat. Crop cultivation expenditures can be reduced both for rice and wheat by proper application and management of water and fertilizer.

Tropical home gardens in developing countries are a traditional land-use system, which contributes to the basic food requirements of the farming families, as well as providing a small but important income throughout the year. Most of these home gardens rely on rain for survival, i.e., rainfed systems. At present home gardens are being neglected due to social and environmental problems. Among these issues, the scarcity of water during cropping seasons is the most important issue that adversely affects crop production from home gardens. This is mainly due to the occurrence of unexpected dry periods during the cropping seasons, and the requirement to have a water source at the farmer’s residence to irrigate the home garden during the dry spells (to capture and conserve roof runoff in the home gardens for subsequent use) is an appropriate green option to mitigate this situation. Microlevel rainwater tanks are promoted to be used to collect roof runoff water during wet periods enabling the farmer to irrigate his home garden crops during dry periods. Field experiments were carried out at Mapalana Research Farm in Sri Lanka to obtain the roof runoff coefficients from commonly used roof types; namely: asbestos, tiles, and thatched (either straw or woven coconut leaves). The objective of the case study is to develop a methodology to estimate the optimum size of a rainwater tank based on the roof size, roof cover, climatic conditions, and the irrigation requirement for home garden irrigation. This paper presents the experimental setup, the runoff coefficients obtained from different types of roof materials, and the methodology used to calculate the optimum storage capacity of the tank for home garden irrigation. In designing the rainwater tank sizes, microirrigation systems with both drip and pot irrigation systems were assessed. The water-use efficiency of drip systems was comparatively small compared to the subsurface pot irrigation. Based on the tank sizes obtained in the study, roof runoff water from the farmer’s own roof is sufficient and recommended to be used as the irrigation source for home gardens.

Drip irrigation may be used to deliver water and air to plant root systems, although uniformity of air bubble delivery along the irrigation line is an issue. Use of 1.2 ppm of a nonionic surfactant (alcohol alkoxylate) in an open-end drip irrigation system increased the Christiansen uniformity coefficient (CUC) of the emitter air flow rates to 80%, compared to 20% without surfactant. In a closed-end irrigation system, addition of 32 ppm surfactant raised the CUC of the emitter air flow rates from 1 to 23% for the symmetric connectors and from $-83$ to 37% for the asymmetric connectors, respectively, over the controls without surfactant. In the absence of the surfactant, insertion of turbulence-inducing sealing plugs before the 9.5-mm-long symmetric and asymmetric connectors raised the CUC of the emitter air flow rates from 1 to 18% for the symmetric and from $-82$ to $-64\%$ for the asymmetric connectors, respectively. Regardless of the type of the connectors, the highest CUC for emitter air flow rates in the closed-end system was obtained when both sealing plugs and surfactant were used.