Optimization of basic irrigation controlling area network for micro-irrigation based on maximum control area and minimum cost models

Abstract: System allowable pressure beforehand distribution between laterals and branch pipes, and the location analysis of the maximum and minimum water pressure points are often involved in the traditional optimization way of irrigation network for micro-irrigation. However, the study of maximum control area of basic irrigation controlling area network is inadequate. In this paper, in order to expand the control area, simplify the structure and lower the cost of basic irrigation controlling area network system, the objective functions of basic irrigation controlling area network were established. The function was modeled by taking some typical commercial pipes for branch and lateral pipe as the research object. The network's laterals were unidirectional or bidirectional for micro-irrigation. There were two models including maximum control area model and the minimum cost per area model, respectively. According to the actual engineering requirements and taking practical types of pipes in the market into consideration, we selected seven pipes. These pipes had different types of diameter as branch pipes and same type lateral pipes. The branch pipes were connected together in the order of diameter from large pipe diameter to the small one. In addition, same diameter lateral pipes were connected to the outlets of branch pipes. Considering planting characteristics and the pattern of water requirements of crop, distance between two adjacent outlets of branch pipes or lateral pipes could be set as the constant standard length. In order to facilitate the optimal design of the micro-irrigation network, every type of pipes, including branch pipes or lateral pipes, was considered as being composed of integral units of constant standard length and a unique allowance (less than the constant standard length) that was located in front of branch pipes or lateral pipes. There were two lateral layouts in the system, unidirectional and bidirectional. Then pipeline network arrangement of basic irrigation controlling area was accomplished. First, we supposed that flow of every lateral outlet was in the condition of the design flow and maximum pressure drop of all outlets in the basic irrigation controlling area network system for micro-irrigation should be less than allowable pressure; then the optimal combinations of pipelines were given based on matlab genetic algorithm toolbox (GA toolbox). The pipelines met the pressure condition in accordance with irrigation uniformity. The network was considered as a whole in this method. Practically, the paper simulated water pressure factors such as the surface slope, and the hydraulic gradient for value of every outlet including all laterals and branch pipes. In the method, the system allowable pressure, and the location discussion of the maximum and minimum water pressure points could be ignored. Pipe diameter adjusting based on the optimal combinations result was not necessary. Nevertheless, the optimal combinations result could be applied to engineering design directly. The results showed that based on maximum control area model，the control area of the network with bidirectional laterals was significantly higher than unidirectional one. The number was increased by about 23%-24% and the cost per area was reduced by about 23%-36%；In the model of minimum cost per hectare, compared with unidirectional laterals, the control area of bidirectional was improved by about 105%-200%. Meanwhile, the cost was decreased by about 7%-10%. The optimization results indicated that the network with bidirectional laterals was superior to unidirectional one in all respects. Optimization design results can be improved continuously by adjusting system parameters such as pipe diameter and length. This design method has practical meaning and theory value in optimization of micro-irrigation network.