Minimising the Earthwork Cost in the Construction of Irrigation Offstream Reservoirs

In the majority of agricultural areas it is necessary to construct irrigation offstream reservoirs to store the required amount of water to be available at any time. In this type of projects, the earthwork can represent up to 80% of the total budget, therefore, one of the criteria in their design is minimising this cost. Due to the fact that the minimising process is carried out by the trial and error method, calculating the cost in different locations and devoting a great deal of time and effort to these calculations, finding the definite location for the lowest earthwork cost is very complicated and difficult to achieve. In this study a computer application which carries out this process is presented. Once the geometry of the offstream reservoir has been defined, as well as that of the land where it will be located and the cut and fill surfaces slopes, a boundary can be fixed within which it will be constructed, and the computer application will perform automatically the calculation of the cost of the earthwork in a series of locations. The different locations within the defined limit are obtained by moving the offstream reservoir along West-East and South-North directions, changing the crown elevation, and even making it rotate with regard to a vertical axis. The range of values for these movements and the increase in variation as they go from one to the next will determine the number of places where the cost of the earthwork will be calculated. The cost function incorporated to the programme allows to take into account the types of materials that will be excavated and the disposition of the soil layers. In the first place, a series of algorithms are detailed which have been developed to do the calculations, then the computer application is described which integrates these algorithms, and finally an application of the programme is explained in which the minimum cost is sought for an offstream reservoir with a capacity of 100000 m<Superscript>3</Superscript>. Copyright Springer Science+Business Media, Inc. 2007