The development of a mathematical model to predict runoff from a micro-catchment under high water application rates
Current trends in sprinkler irrigation to improve
application uniformity and reduce energy requirements haste led to
problems of water application and potential surface runoff, which
in turn have highlighted the importance of the soil and
cultivation practice in making best use of irrigation water.
The objective of this study was to begin the development of
a mathematical model, which will simulate the operation of
current sprinkler-soil-crop system, in order to provide a means
of predicting surface runoff and so provide a more effective
approach to system design.
A model has now been developed which will predict runoff from
a small simple agricultural catchment in the form of a ridge and
furrow cultivation system. The model is based on the kinematic
wave theory involving the continuity equation and the simplified
momentum equation. A four-point implicit finite difference
scheme is used to solve numerically the kinematic wave equations.
The model (SROFF) may be used to predict the runoff at various
times from a simple catchment with different slopes, water
application rates and soil infiltration rate. A further
development of the model was made by the introduction of the
interception loss model (INCEPT) to predict the amount of water
intercepted by the crop canopy during irrigation.
The validity of the model was tested and supported by the
results of laboratory experiments conducted on two soil samples
with different infiltration rates, using three different
application rates. The performance of the model was also
evaluated by statistical test. There was good agreement between
experiment and model results.
The results indicated that this model can provide valuable
information for the effective design of sprinkler systems,
particularly where runoff may be a potential problem. This is
particularly the case with current low pressure irrigation
systems but equally the problem is common with high pressure
systems when applied to soils with low infiltration rates.