Journal of Irrigation and Drainage Engineering

The present study analyses the effect of sodicity on unsaturated soil hydraulic properties. Permeameter and pressure plate experiments were conducted on six texturally different soils at varying sodicity levels to obtain saturated hydraulic conductivity and van Genuchten soil–water retention parameters. The results show that soils retain less water with high soil–water sodicity relative to low sodicity at the same matric suction. The van Genuchten water retention parameter $\alpha$ obtained from the experimental water retention curves increased in fine-textured soils with an increase in sodicity. In coarse-textured soils, no significant trend was observed. However, the value of parameter $n$ increased in all soil samples. Hydraulic conductivity reduced in fine-textured soils and increased in coarse-textured soils with an increase in sodicity. The simulation of a hypothetical infiltration event at different sodicity levels indicated that the wetting front movement slows down with an increase in the sodicity level for fine-textured soils, whereas the wetting front moves at a faster rate in coarse-textured soils with an increase in sodicity level. Gravity drainage simulations indicate that there is a buildup of soil moisture storage in fine-textured soils with an increase in soil–water sodicity due to reduced gravity drainage and drying of the soil profile in coarse-textured soils due to increased gravity drainage. This study is useful to better manage irrigation scheduling in saline conditions.

In microirrigation systems, start connectors are used at lateral-manifold or microtube-lateral junctions, and minor losses occur when water flows through the start connectors. The connector’s geometry may cause contractions and/or expansions in the flow section, inducing local head losses that should be considered when designing irrigation subunits. The objective of this research was to analyze the experimental datasets available from previous studies in order to develop and validate mathematical models to estimate local head losses through start connectors using dimensional analysis and artificial neural networks. A dataset with 55,331 records of local head loss as a function of flow rate through several geometries of start connectors was evaluated. Four models based on dimensional analysis and artificial neural networks were developed and validated. The local head losses through start connectors depended on the fluid properties, operating hydraulic conditions, and geometric characteristics of the start connectors. For the full and simplified models based on dimensional analysis, 95% of discharge predictions had relative errors less than 13.0% and 14.3%, respectively. For the full and simplified models based on neural networks, 95% of discharge predictions had relative errors less than 12.2% and 12.7%, respectively. A web application was developed to facilitate the discharge predictions. Depending on the connector’s geometry, the minor losses through start connectors represent a significant percentage of the total head loss along the lateral.

To maximize the benefits of an interbasin water diversion system (IBWD), an aggregation model and improved NSGA-II algorithm were constructed to establish operation strategies for water diversion and water supply. An aggregation model was constructed to aggregate multiple reservoirs into an equivalent reservoir which made the operation strategies for water diversion and supply easy to define. Then an improved nondominated sorting genetic algorithm II (NSGA-II) algorithm was developed by considering variables’ sensitivity to improve its search efficiency. Finally, the IBWD subsystem for water supply in China’s Shenzhen city was taken as a case study, and its operation strategies for different water supply scenarios were optimized by the improved algorithm. Simulation results demonstrated that the equivalent reservoir is an effective method to reduce the complexity of operational strategies, and improved NSGA-II algorithm has a higher search efficiency.

This study presents a conceptual model to obtain the shape of the unit hydrograph in a small rectangular basin with a collecting channel on one side of the flow plane. In classical hydrology, flows are classified as linear, convergent, and divergent. In the proposed model, a rainfall of constant intensity is assumed, with the duration equal to the time of concentration of the basin, as in the rational method. The shape of the plane is simplified in order to obtain an analytical solution. It is observed that in the plane of diffuse flow, the flow begins as a convergent of repletion, then passes to divergent of repletion, and finishes as a convergent of depletion. The applied theory allows the development of a classic bell-shaped unit hydrograph, a very common form of the theoretical hydrographs found in the literature. The proposed methodology was also applied to a practical flood damping problem in an urban watershed.