LUCENA, K. F. M.; http://lattes.cnpq.br/2117359419680710; LUCENA, Kennedy Flávio Meira de.
Résumé:
An optimization model has been developed for minimizing the total costs (investment
and operational) of microirrigation systems for leveled and unleveled areas, considering the
influence of the water demands, the division of the system in subunits, the number of
operational units, the shape of the irrigated area and the operation with changeable tariffs of
energy with the irrigation schedule effects- The model was applied in microsprinkler system,
for a referencial hypothetical area of 34 ha (340000 m2) with the culture of the mango
(Mangifera indica L.), The water demands were computed by the annual climatic water
balance and monthly soil water balance, considering the annua! and monthly average
precipitation with 75% of occurrence probability and the reference évapotranspiration for two
localities in the Northeasteam region of Brazil with climatic diversities, Iguatu (Ceará State)
and João Pessoa (Paraíba State). The otimizatiou technique was based on nonlinear
programming through the Matlab software. The water demand computed by the annual water
balance underestimated the necessities of irrigation in relation to the monthly water balance,
leading to a shorter time of functioning of the system and, consequently, smaller operational
energy cost. However, the investment costs did not suffer important alterations with the two
water balances for the same number of operational units, thus evidencing that there was no
modification in the design for the two situations. In João Pessoa it was possible to increase the
number of operational units, leading to a higher reduction of the investiment costs and the
total costs. As for the application of the energy tariffs, the model allocated the functioning
period to the lower tariffs time, promoting significant saving in the operational costs. The
changeable tariffs did not affect the sizing of the system. Thus, for the currently operation
systems measures of energy saving can be adopted, through modifications in the daily periods
of operations. The investiment costs represented almost the total amount of the costs. The
main costs was those of the lateral polyethylene lines, the emitters, the PVC tubing and the
water treatment system. The factors that most affected the total costs of the system was the
number of subunits and operational units, having lesser effect the shape of the area. The
increase in the number of subunits and operational units of the system reduced the investiment
costs significantly. However, the subunit of minimum cost and bigger number of operational
units did not guarantee the attainment of the minimum cost system. The subunit of minimum
cost for one determined service pressure was that one that uses all the head loss available. The
preestablishment of percentages of head loss in the lateral lines and manifold lines did not
guarantee the attainment of lhe subunit of minimum cost. The system of minimum cost was
achieved with the minimum service pressure of the emitter, lower emission unifonnity and
lower irrigation frequency. The system design without considering the energy cost was
inefficient under the energetic and economic aspects.