dc.description.abstract |
Runoff from agricultural areas under sprinkler irrigation systems is a big
problem. This is because runoff not only reduces water use efficiency (WUE),
but also reduces soil fertility through depletion of fertilisers and pesticides,
causes non uniformity of soil water content along the field slopes and
ultimately reduces crop production and causes environmental pollution.
Although sprinkler irrigation systems are usually designed so that the water
application rate is less than the soil infiltration rate to avoid runoff, there are a
growing number of sprinkler systems where runoff has become a serious
problem. Large mobile single sprinklers (rainguns) which can irrigate large
areas in a relatively short time are prone to severe runoff problems, because
of the high application rates. Modern centre pivot and linear systems, which
have now been designed to run at low energy saving pressures also produce
high application rates and potential runoff. Most runoff problems are dealt with
in the field on a trial and error basis. Being able to predict runoff under
sprinkler irrigation would enable water application rate to be recommended
and cultivation practices to be ‘designed’ rather than guessed on a trial and
error basis in order to store surface water and avoid runoff.
The objective of this study was to develop a mathematical model that can
predict surface runoff from a small watershed area using sprinkler irrigation
systems in either a stationary or moving condition. The objective was met in
two ways: a mathematical model was developed from first principles called
Overland Flow (OLF) and an existing model, KINEROS modified to
EUROSEM, but designed for overland flow and soil erosion from hydrological watersheds was adapted to suit micro-catchment conditions for both stationary
and moving sprinklers. Both models are based on kinematic wave theory.
Both models were validated by laboratory and field experiments using
stationary and moving sprinklers on simple plane and ridge and furrow
cultivation practices. The validation results showed that the model predicts
well the shape of the runoff hydrograph but also the key points for practical
application. For example, time to start runoff, time to peak, peak flow rate,
volume of runoff and time to end which are important when designing a
cultivation practice in the field. The performance of the EUROSEM-KINEROS
model was further evaluated by statistical techniques. There was good
agreement between observed and model results.
The EUROSEM-KINEROS model was also used to examine the best practical
techniques to minimise the surface runoff. The application of this model to
sprinkler irrigation design and management was also assessed. The
evaluation results showed that the hydrograph parameters can be used to
recommend water application rate, water application time and / or to design
soil and water conservation structures to avoid critical situation in the field.
Model validation for a moving sprinkler is recommended to be undertaken for
different moving irrigators such as rainguns, centre pivot, side move systems
and low energy precision application (LEPA) systems. Further investigations
are also required to evaluate the use of the model to predict the effects of soil
and water conservation techniques on runoff prevention for a cultivated land
for different crops. |
en_UK |