Channel capacity under arranged demand irrigation

To date, arranged demand irrigation and on-demand irrigation were considered as two distinct types of systems. This paper presents the hypothesis that arranged demand is a continuous function with on-demand as one extreme and fully arranged demand as the other. This paper introduces the index of relative timeliness to capture this semantic. This index assumes a value of 1 for an on-demand system and 0 for a fully arranged demand system. This paper then demonstrates that how this index can be incorporated in mathematical modelling. An earlier integer programme is modified to include the concept of relative timeliness. As a case study an existing tertiary unit is simulated using this tool to investigate whether, given its current capacity, the tertiary unit can be operated on an arranged demand basis, and if so what level of service can be expected. The model also indicates what capacity is required if the tertiary unit were to be operated on an on-demand basis. The capacity requirements as predicted by the model developed in this work relate well to earlier empirical/experience guidelines. The model developed is useful for investigating and simulating existing tertiary units, but in its current form cannot be used for general design guidelines for new designs. Some recommendations for further developments are made.