Resumen de Optimization of irrigation water distribution networks, layout included

P. Planells, José Fernando Ortega Álvarez, José María Tarjuelo Martín-Benito

• The purpose of this paper is to develop a procedure which takes into account both the network layout and the pipe size of an on-demand water branched network in order to obtain the lowest total cost (investment and energy cost). The process begins with a main ring network which is obtained by giving consideration to the possible alternatives of branched irrigation networks, taking into account the limitations imposed by plot boundaries, gravel roads, etc. The optimization process progressively eliminates pipes to obtain the most inexpensive branched irrigation network, verifying the criteria of the economic series methodology for sizing the pipes and the design flow obtained in the pipelines according to Clément's methodology. The dimensioning through the Economic Series Method determines the optimum diameter as a function of flow.

  Three stages are considered in the optimization process. In the first stage, the network layout and the pipe size of the lowest cost are obtained for different K values, as well as the necessary upstream head. In the second stage, the pumping station is dimensioned for each K value and annual costs for investment and energy consumption are obtained, according to the operation hours of the pumping station to satisfy crop water needs. In the third stage, the K value which leads to the lowest total cost (investment and energy cost) is determined.

  In the procedure, the network can be fed by direct injection (i.e. a fixed and a variable speed pump discharge directly into the network) or with a water tank (i.e. placed at an adequate head). The different network layouts and associated cost can be studied depending on the water source or sources in the network. This method can also be used for the layout of the main ring networks, establishing some minimum diameters as a reference to eliminate the pipelines. An interesting case could be the analysis of the network supply from several points.

  The sizing of the pipes that is performed, using the solutions that lead to the optimum network layout, is only a first approximation. Therefore, once the network with the optimum layout is determined, a new procedure for pipe size optimization should be used