Journal of Irrigation and Drainage Engineering

Abstract

Conventional flood irrigation is the common irrigation system practiced in many developing countries. Under this regime, a large quantity of water is used to irrigate a variety of crops, such as banana, which consumes about 1,200–2,200 mm of water per year. Using the example of Yemen, the main objective of this study was to explore how to save as much of groundwater as possible and select the most suitable irrigation depth that does not affect the quantity and quality of banana production in the Al Mahwit governorate. Two models were used in this investigation. The BROOK90 (B90) hydrological model was employed to examine the banana field under existing water depth ($\mathrm{1,500}\mathrm{mm}{\mathrm{year}}^{-1}$) and under two irrigation-reduction scenarios (1,000 and $500\mathrm{mm}{\mathrm{year}}^{-1}$), and CROPWAT was applied to validate the findings of the B90 model, taking advantage of the monthly climate data in the CROPWAT package. Climate data were collected and field measurements of water consumption rates, plant characteristics, and soil properties were taken. The results show that the current irrigation depth with a quantity of $\mathrm{1,500}\mathrm{mm}{\mathrm{year}}^{-1}$ is more than the banana water requirements and most of the irrigation water is lost to seepage. The irrigation scenario with $500\mathrm{mm}{\mathrm{year}}^{-1}$ appeared to be less than the banana water requirement, and water stress was observed. The scenario of $\mathrm{1,000}\mathrm{mm}{\mathrm{year}}^{-1}$ was found to be appropriate. Actual evapotranspiration (ET), soil water content (SWC), and seepage (SEE) had standard rates, and there was no stress in the soil. Most importantly, following the suggested irrigation schedule of $\mathrm{1,000}\mathrm{mm}{\mathrm{year}}^{-1}$ will save as much as $500\mathrm{mm}{\mathrm{year}}^{-1}$ of groundwater compared with current water use. Furthermore, evaluation of effective rainfall and the tested irrigation depths to meet the amount of water required by banana indicated a strong correlation between CROPWAT and the B90 model with an average percentage bias of 13.2. Overall, both models yielded identical results, confirming the finding of an optimal irrigation depth.

Practical Applications

Agriculture consumes a great amount of freshwater resources, making efficient water management imperative. This research from Yemen presents a universally applicable solution for optimizing irrigation practices and emphasizes the importance of calculating the actual water input for high-demand crops such as banana. The BROOK90 and CROPWAT models can be used in any region of the world to address water scarcity challenges. Furthermore, the strong agreement between the CROPWAT and B90 models in the validation of the proposed optimal irrigation depth makes the study findings more sensible and applicable, with no effect on banana productivity. The research introduces an innovative strategy to improve water-use efficiency in agriculture. In arid and semiarid regions, the irrigation depth of 1,000 mm for banana cultivation is proven to be sufficient, and would result in a considerable saving of groundwater for other uses. From a farmer’s perspective, saving water will result in a great reduction of the fuel required for operating water wells and also will save time and labor. Moreover, conflicts among water users over limited water resources are expected to diminish. Therefore, supplying banana with the actual irrigation input, based on intensive field research, is essential, and promises a significant conservation of groundwater resources on a larger scale.

Lake Urmia in the northwest of Iran is one of the largest vanishing lakes in the world. Several water-saving strategies have been implemented in the lake basin over the last decade, but they are not producing efficient results. This study employed a modified version of the Soil and Water Assessment Tool (SWAT), an agrohydrological model, to investigate the basin-scale effectiveness of some water-saving plans implemented at the farm scale. Data collected from 301 monitoring sites in the Lake Urmia basin were applied to the modified SWAT model. The modified SWAT model was used to estimate water balance components and was coupled with the Water Accounting Plus framework (WA+). Six discharge stations, crop yields, evapotranspiration, and groundwater level tables were calibrated and validated from 1987 to 2015 within the Zarrineh Rud Basin (ZRB), the most crucial subbasin in the Lake Urmia basin. Next, four individual water-saving plans—changes in irrigation management and developments in irrigation systems, changes in fertilizer type and regime, changes in the type and method of cultivation, and farm size and shape adjustments—as well as seven combinations of the water-saving plans, were applied to the agrohydrological model. The results reveal that assessing restoration plans for Lake Urmia without considering both farm and basin scales provides no reliable results. With changes in management and the development of irrigation systems, considerable differences in water withdrawal were observed. Developing irrigation systems leads to enhanced water consumption and evapotranspiration, which is expected to improve water yield and crop productivity. However, individual plans such as developments in irrigation systems cannot increase the inflow to Urmia Lake, and combined water-saving strategies can help restore the lake only to a limited extent, because the changes in inflow are not substantial.

A new analytical solution is developed to calculate the hydraulic emission uniformity ($E{U}_h$) of horizontal tapered drip laterals. Our methodology builds upon normalizing the pressure head profiles along each segment of the lateral. Results indicated that the $E{U}_h$ remains fairly consistent regardless of the total lateral length if a fixed pressure head tolerance ($\delta$) is assigned in the design process. Instead, the $E{U}_h$ is primarily influenced by the number of emitters on each segment, their diameter ratio, and the emitter exponent $x$. Employing tapered laterals for any given values of $\delta$ and $x$ enhances energy conservation compared to using single diameter laterals. However, it may lead to a reduction in the $E{U}_h$, particularly when the number of emitters in the smaller diameter segment is low relative to the total number of outlets. It was concluded that the coefficient of variation in emitter pressure heads $CV$ and $E{U}_h$ exhibit a nonlinear behavior in the case of tapered laterals, whereas it has been previously established as linear for single diameter laterals. Interestingly, when applying the newly formulated relationships for $E{U}_h$ and $CV$ while keeping the same diameter for both segments, the results align with those previously obtained for single diameter laterals. Validation of the proposed $E{U}_h$ model against the precise stepwise solution revealed a maximum absolute relative error of $\approx 1\%$. When excluding the fully laminar flow condition ($x=1$), relative errors typically remained below 0.5%. The proposed model could serve as a foundational framework for designing tapered laterals to achieve a targeted uniformity level in future studies.

Sensitive irrigation programming requires both a good knowledge of plant physiology regarding water use and the monitoring of the effect of water stress on plant physiology. In this study, the effect of different irrigation strategies on full-grown olive trees of the Memecik variety irrigated by the drip irrigation method was investigated over three crop seasons (2012–2013, 2013–2014, and 2014–2015), and the possibility of using these strategies in forming an irrigation program was examined. The experiment consisted of five irrigation treatments with three replications in a random block design. One significant finding after the three years of observation in the study was that it was possible to determine in a simple and sensitive way the temporal responses of olive trees under conditions of water stress with predawn plant water potential, stomatal conductance, and plant water stress index but not chlorophyll content (SPAD value). Statistically significant differences were found between the treatments in the measurements made. Taking into account the three-year averages of treatment values for water applications, acceptable threshold values for predawn plant water potential, stomatal conductance, and plant water stress index are $-1.64\mathrm{MPa}$, $330\mathrm{mmol}{\mathrm{m}}^{-2}{\mathrm{s}}^{-1}$, and 0.37, respectively. It is easy to put these measurements into practice, and doing so will enable very significant water savings in Mediterranean climate conditions.

Furrow infiltration interference results from the merging of the wetting plumes of neighboring furrows and reduces infiltration rates. Simulation models and computational procedures used to analyze furrow irrigation flows currently ignore this effect. An understanding of this process and its impact on infiltration is needed, and infiltration modeling approaches must be modified to account for interference effects, if those effects are substantial. A simulation study was conducted to characterize the transverse spread of furrow infiltration plumes subject to interference (i.e., constrained plumes) relative to unconstrained ones and its impact on infiltration rates. Constrained and unconstrained plumes were computed for the same furrow geometry, soil hydraulic properties, initial conditions, and boundary conditions and different combinations of these variables were tested. A relatively wide computational domain was used to compute the unconstrained plumes, whereas a relative narrow domain was used for the constrained plumes. Moment analysis was used to evaluate spread and fraction of infiltrated water contained within elliptical different regions of the plume. For any set of conditions, when a plume ceases to expand horizontally, its final horizontal standard deviation is approximately equal to the semiwidth of the constraining furrow divided by 1.7. This constant, and the resulting standard deviation, define an ellipse of an unconstrained infiltration plume that, at some point in time, matches the width of the constraining furrow. The onset of interference, and the resulting decrease in infiltration rate, can be predicted from the evolution of the standard deviation of the unfettered plume relative to the ultimate standard deviation of the constrained plume. These concepts were used to modify the lateral flow component of an existing semiphysical furrow infiltration model. The modified model predicts infiltration with reasonable accuracy in comparison with solutions computed with the two-dimensional Richards equation. Results suggest conditions under which interference is likely.

Quantification of basin characteristics from morphometric analysis helps understand the physical process of erosion. This study performed morphometric analysis and uses the revised universal soil loss equation (RUSLE) on a pixel basis to estimate the space–time variability of soil loss in order to prioritize erosion-prone areas. The morphometric factors considered in the study included linear, areal, and relief aspects of the basin. Average annual soil loss was estimated using the RUSLE model for 21 years (1995–2005) and then used to correlate with morphometric parameters to find out the prioritization criteria for the Sutlej catchment. The Sutlej basin, covering an area of $\mathrm{21,595}{\mathrm{km}}^2$, is a fifth-order dendritic drainage basin. Its mean bifurcation ratio is 4.06. Based on the values of morphological parameters, prioritization was being done for eight subwatersheds of the Sutlej basin. It was found that the average annual soil loss was strongly correlated with the time of concentration, drainage density, and texture ratio, but not with other morphological characteristics. The study suggested that indices based on morphometric parameters should not be preferred alone for prioritizing catchments prone to erosion. This research works shows the nexus between morphological parameters and their direct relationship with the erosion to prioritize the Sutlej catchment and its subwatersheds. Unlike previous applications, this integrated methodology not only enhances the accuracy of erosion risk evaluation but also addresses the limitations of relying solely on morphometric factors. The results reveal significant correlations between certain morphometric factors and soil loss, emphasizing the need for a multifactorial approach. Additionally, the present study contributes new insights into subwatershed prioritization for targeted erosion control efforts. These innovative findings advance the field by providing a more comprehensive and effective strategy for predicting and managing soil erosion in diverse geographical contexts. Correlation of morphological parameters with erosion rate based on RUSLE can play a significant role to prioritize the watersheds, which is not enough single handedly to demarcate the erosion-prone areas in the catchment for further treatment to conserve the soil loss in the respective region.