Development and Application of an Irrigation Demand Model Based on Crop Factors

In planning for the operation of Victoria's rural water supply systems, the emphasis has changed from development of new resources to the more efficient use of existing resources with the focus shifting from the headworks towards the user end of the system. In the past the approach to the estimation of irrigation water demands for system simulation studies has been mainly based on the analysis of historic demand data for irrigation supply area. This approach has only limited ability to model the likely impacts of changes to water allocation methods, cropping patterns and on farm water use management. The Program for Regional Irrigation Demand Estimation (PRIDE) was therefore developed as a flexible tool for the prediction of irrigation demands at the level of a supply area. The model is based on estimated irrigation water requirements for the main crop types in an irrigation area using a seasonally varying crop factor and climatic variables. The paper describes the main features of the model and experience gained with its application in a number of supply areas within different mixes of crop types and different levels of water usage. The performance of the model is compared with alternative approaches for irrigation demand estimation. The model is shown to be a reliable and flexible tool to predict historic irrigation demands in supply areas for which cropping patterns and crop demands are well defined and will lend itself to further development.