Simulation of irrigation water requirement

Nyameche, Isaac Kwame (1978) Simulation of irrigation water requirement. University of Southampton, Doctoral Thesis.

Abstract

Deciding whether irrigation is necessary, and how often to irrigate, is not an easy problem in semi-arid climates. Mathematical methods have been presented in this work for assessing theme parameters, and their limitations have been stressed. The need to generate synthetic data to improve upon design parameters was identified, and a computer simulation model was developed to evaluate crop water requirement. Because of good correlations with evapotranspiration, panevaporation data formed the basis of the evapotranspiration model. The evaporation data was modeled as an A8 1) series by the Box-Jenkins method. The monthly averages showed marked variation, and they were represented by a Fourier series. By generating daily pan evaporation as a stochastic series, estimates of evapotranspiration were obtained. Soil moisture was considered as influencing daily evapotranspiration, thus the necessity for generating daily rainfall values. Each day of the growing season was considered as belonging to a dry-spell or a wet-spell. Both wet and dry spells were modelled by an exponential distribution function and the daily precipitation was generated by a log-normal distribution. The generated evapotranspiration values were analysed was average irrigation water requirement for several time intervals far given probability levels of acceptance. Even though the data used is from Accra, the model is suitable for other climatic conditions. The results are useful for design or planning of irrigation systems.

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