Irrigation management and investment under saline, limited drainage conditions: 1. Model formulation

A dynamic optimization model for irrigation management and investment of an individual field is formulated. The model is applicable to situations where soil salinity is a current or potential problem and where drainage flows incur costs. The crop rotation is prespecified and several alternate irrigation systems are available for investment. These differ in application uniformity and cost. The field is assumed to be spatially variable in soil salinity and infiltrated water. The joint distribution of these two variables evolves over time in response to annual volumes of irrigation water and type of irrigation system. Social net benefits are defined as crop revenue net of irrigation costs, production costs, and environmental/disposal costs associated with percolation of water below the root zone. The optimization problem is to choose annual applied water volumes and investment in irrigation systems to maximize the present value of social net benefits.