| Abstract | [Abstract]: The performance of surface irrigation is a function of the field design, infiltration characteristic of the soil, and the irrigation management practice. However, the complexity of the interactions makes it difficult for irrigators to identify optimal
design or management practices. The infiltration characteristic of the soil is the most crucial of all the factors affecting the performance of surface irrigation and both spatial and temporal variations in the infiltration characteristic are a major physical
constraint to achieving higher irrigation application efficiencies. Real-time optimisation and control has the potential to overcome these spatial and temporal
variations and return highly significant improvements in performance. Calculation of the infiltration parameters from irrigation advance data is now the preferred method.
If the process is to be included in a real time control system it must be done accurately, reliably and rapidly, and with a minimum of field data. Substantial work
has been directed towards developing methods to estimate the infiltration characteristics of soil from irrigation advance data. However, none of the existing methods are entirely suitable for use in real time control. The greatest limitation is that they are data intensive and or unreliable and provide soil infiltration properties
after an irrigation event. A simple real-time control system for furrow irrigation is proposed that: predicts the infiltration characteristics of the soil in real-time using data measured during an
irrigation event, simulates the irrigation, and determines the optimum time to cut-off for that irrigation. The basis of the system is a new method for the Real-time
Estimation of the Infiltration Parameters (REIP) under furrow irrigation, developed during this research study, and that uses a model infiltration curve, and a scaling
process to predict the infiltration characteristics for each furrow and each irrigation event. The underlying hypothesis for the method is that the shape of the infiltration characteristic for a particular field or soil is relatively constant (across the field and
with time), despite variations in the magnitude of the infiltration rate or amount. A typical furrow in the field is selected for evaluation (known as the model furrow)
and its infiltration parameters (a, k, fo) in the Kostiakov–Lewis equation are determined by a model such as INFILT or IPARM using inflow, advance and runoff
data. Subsequently the infiltration parameters for this model furrow can be scaled to give the cumulative infiltration curves for the whole field. In this process a scaling factor (F) is formulated from rearrangement of the volume balance equation and is calculated for each furrow/event using the model infiltration parameters and the single advance point. The performance of each furrow can then be simulated and optimised using an appropriate simulation model to determine the preferred time to
cut-off. Using this new method, infiltration parameters were calculated for two different fields T & C. The SIRMOD simulation model was then used to simulate irrigation
performance (application efficiency, requirement efficiency and uniformity) under different model strategies. These strategies were framed to assess the feasibility of and demonstrate the gains from the real-time control strategy. The infiltration evaluation results revealed that the infiltration curves produced by the proposed method were of similar shape and hence gave a distribution of cumulative depths of infiltration for the whole field that was statistically equivalent to that given using the complete set of advance data for each furrow. The advance trajectories produced by
the proposed method also matched favourably to the measured advances. The simulation results showed firstly that the scaled infiltration gave predictions of the irrigation performance similar to the actual performance. They also indicated that by adopting the simple real time control system, irrigation application efficiencies for
the two fields could be improved from 76% for field T and 39% for field C (under usual farm management) to 83% and 70% for the fields T & C, respectively. Savings
of 1239 m3 in the total volume of water applied per irrigation over the area of 7.1 ha of both fields were indicated, which can be used beneficially to grow more crop. The proposed real-time control system is shown to be feasible. It requires few data for its
operation and provides the infiltration characteristics for each furrow without significant loss of accuracy. The irrigation performance is improved greatly from that
achieved under current farmer management and a substantial reduction in the volume of water applied per irrigation is achievable. |
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