5. OPERATIVE CONSIDERATIONS
The present version of the model (on a monthly basis) does not take into consideration the initial and final soil water reserve nor a possible water table.
As concerns the estimation of crop water requirements, the following must be taken into consideration. The water deficits mapped basically correspond to the net irrigation requirements of the various crops in an unlimited irrigation regime. In planning and designing irrigation systems, the losses that occur during water conveyance, delivery and distribution to the farms and on account of imperfect field application must also be taken into consideration:
Def = CWRnet
CWRgross = CWRnet / Etot
|CWRnet||=||crop water requirements net of losses due to conveyance, delivery and distribution to the field|
|CWRgross||=||crop water requirements gross of losses|
|E tot||=||overall effectiveness of the irrigation system|
Quantatively speaking one must consider that overall losses greater than 50% are not at all rare also in modern sprinkling irrigation systems.
It is the task of the designer of irrigation systems to define the value of efficiency to take as a basis for his calculations. This value should be chosen within a range having, at one end, the maximum potential value and, at the other, a lower, even much lower, value in the case of a poor response by the system administrator and by the users on account of an incorrect use of the water. It is clearly necessary therefore that, especially in the case of public intervention in areas lacking a valid tradition of irrigation, the technical-agronomic design be associated with an effective programme for the training of system administrators and for extension services for the farmers.