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【Background and Objective】 Gravity-driven pipelines have low impact on geological environment, low leakage, simple construction and low operation cost. They have been widely used in irrigation and water supply projects. When the end valve is suddenly turn off under unpredicted circumstances, however, it could result in water hammer and pressure vibration in the pipelines, threating safe operation of the system. Considering water hammer is more likely to occur in long-distance gravity flow pipeline in hilly areas, this paper explore efficacy of different methods to ameliorate the damaging effect of water hammer on gravity flow pipeline in hilly areas. 【Method】 The study is based on the gravity pipeline project in Qianyang County, Shaanxi province. Numerical simulation combined with inclined straight pipes and fitted equivalent short straight pipe is used to simulate the protective effect of setting inlet and exhaust valve in each hump section and an overpressure relief valve in the front of the end control valve section. We analyzed the simulation results to determine the effect of these methods in alleviating water hammer at specific locations in the pipelines. 【Result】 Without the water hammer protection measure, when the control valve at the end of the pipeline is turn off quickly, there is no noticeable negative pressure along the pipeline; the maximum negative pressure head reaches - 20.06 m, and the maximum positive pressure at the section of the control valve at the end of the pipeline reaches 87.58 m. Installation of the water hammer protection measures eliminates the occurrence of negative pressure in the pipeline and reduces the maximum positive pressure head in the pipeline to 70.88 m, which is lower than the critical pressure for occurrence of water hammer in the pipelines. 【Conclusion】 For the gravity-driven water transmission pipeline in hilly areas, combination of inlet and exhaust valve and an over-pressure relief valve can effectively alleviate the occurrence of water hammer and ensure that the pressure in the pipeline is less than the critical pressure required in the design of the pipelines.

【Background and objective】 Gravity-driven drip irrigation is a technology using water pressure drop generated by natural terrain to deliver water from its source to emitters. The multi-level drip irrigation system uses its first-level pivot as the water source to deliver water to each head pivot in the subsystems by a pipe network. Optimizing the pipe network is hence critical to reducing project cost without compromising its operation. The objective of this paper is to present a new optimization method. 【Method】 We took minimization of the comprehensive cost per unit area of the project as the objective function, and the layout of pipe network, pipe diameter, emitter-flow rate and water pressure as constraints. The optimization model was solved using the atom search optimization. We applied the method to a two-level gravity-drive drip irrigation project in Xinjiang to demonstrate its reliability. 【Result】 The cost per unit area is least when construction area of the pipe network project is 89 hm2, and excellent when the construction area is in the range of 74 to 98 hm2. Optimization of the construction area under different combinations of emitter spacing, capillary pipe spacing, and emitter-flow rate shows that the optimal results vary with their combinations. For length-width ratio of the construction field in the range of 1.00 to 1.30, the minimized cost per unit area decreases with the increase in emitter spacing and capillary-pipe spacing and increases with the increase in emitter-flow rate. 【Conclusion】 The proposed optimization method is able to optimize pipe network for multi-level gravity-driven drip irrigation systems. The method is computationally stable and efficient. It is applicable for designing gravity-driven drip irrigation network systems.

【Background】Micro-irrigation, including drip irrigation, micro-sprinkler irrigation and small-tube discharge irrigation, is a technology using pipe network to convey water to fields and then to root zones via orifice or emitter capillary tubes. Current design of the pipe network relies on empirical experiences and follows traditional references, and it is hence unlikely to be optimal. Developing optimal design method is required to improve efficiency of the micro-irrigation system and reduce its costs. 【Objective】This paper presents an optimization method to calculate the pipeline layout and pipe diameters for micro-irrigation network operated under self-regulated pressure. 【Method】The length and diameters of the pipes were used as decision variables; the allowable water head difference between the branch pipes and the lateral pipes, the working pressure, the pipe diameter, water flow rates were used as constraints. With minimizing the total costs of the network as objective, an optimization model was derived to design the two-way capillary, self-pressure micro-irrigation pipe network, as well as the one-way capillary, self-pressure micro-irrigation pipe network, respectively. We applied the method to an irrigation project in Xinjiang with the optimization solved by the shuffled frog-leaping algorithm. 【Result】The model was capable of optimizing the pipeline layout and pipe diameters simultaneously for the micro-irrigation pipe network operated under self-regulated pressure. Implementation of the optimal results could noticeably save costs by reducing the numbers of section-pipes and the diameter of part of the section-pipes while in the meantime increasing the length of each section-pipes and the branch-pipes. Overall, it reduced the total costs by 21.5% to 469 129.3 yuan, compared to the results calculated by traditional design method. 【Conclusion】The shuffled frog-leaping algorithm was stable, efficient and accurate, and the optimization results calculated by it from our proposed model could reduce costs significantly. The method has implications for designing micro-irrigation pipe networks operated by self-regulated pressure in areas with relatively flatten surface and sufficient water source.

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