On-farm irrigation methods


Analysis of hydraulic performance

During the last decades pressurized distribution systems have been developed with considerable advantages over open canals as they guarantee better services to the user and higher distribution efficiency.  In order to meet farmers’ requirements, designers and managers are often oriented to on-demand delivery schedules allowing a greater freedom in user’s decisions. Discharges flowing in such networks strongly vary over time depending on the cropping pattern, the meteorological conditions, on-farm irrigation efficiency and farmers’ behaviour, as well as on the number of hydrants simultaneously open. Such variation in discharges causes notable variation in pressure at the hydrants serving the on-farm sprinkler networks (Lamaddalena & Sagardoy, 2000).

In the design of sprinkler irrigation networks, droplet size formation, mainly affected by pressure, is of concern to designers for two reasons. Firstly, the small droplets resulting from a high-pressure head are subject to wind drift and evaporation and can distort the application pattern. Secondly, larger droplets, resulting from low-pressure head, possess greater kinetic energy, which is transferred to the soil surface causing particle dislodgment and pounding that may result in surface crusting, runoff and erosion (Jiusheng, 1997).

During the peak demand period, hydrant pressure head may drop to unacceptable values, causing a decline in the uniformity and the amount of water applied by the sprinkler network (Tizaoui et al., 1997).

Due to the lack of water distribution uniformity, parts of the surface area may result to be over-irrigated while others might be under-irrigated. In the former case the irrigated area may result in poor soil aeration, leaching of mineral nutrients and lower yields. In the latter case, a drop in yield is expected due to the inadequate supply of water to the crop (Francisco, 1998). This non-uniformity causes havoc with irrigation scheduling. If the farmer applies enough water to adequately dampen the dry spots, he/she might place too much water on the wet spots; on the other hand, if he/she manages the wet spots, the dry spots most likely turn to “dead” spots. Both of these two scenarios make healthy plants and efficient water use a difficult proposition (Wilson and Zoldoske, 1997). For that reason, Sepaskhah & Ghahraman 2004 found that relative yield analysis with combined effects of irrigation efficiency and distribution uniformity on deficit irrigation is more realistic (Sepaskhah, 2004).

Timing:
Starting: 8.01.2000
Scheduled ending: 23.09.2019
Real ending: 23.09.2019
Objectives:

The purpose of this research is then to analyse the effect of the pressure head variation at a given hydrant on the performance of an on-farm sprinkler network served by the latter. The characteristic curve of the hydrant and the water distribution pattern of a typical sprinkler are studied in the hydraulic laboratory, while the characteristic curve of the on-farm network is generated, through using a simulation model developed for the purposes of this research.

The pressure head variation at the hydrants under different operating conditions is assessed by using a stochastic simulation model, called AKLA (Lamaddalena & Sagardoy, 2000).  The on-farm network performance is evaluated by using the classical performance indicators: Uniformity Coefficient (CU), Distribution Uniformity (DU) and Distribution Efficiency (DE). 

Wind effects will be also taken into consideration in the framework of such a research line. All the above research will allow better defining design criteria aiming at maximizing the performance of the on-farm sprinkler system.

The same approach can be also used in the case of trickle irrigation methods.

Justification:

This research allows creating an important linkage between the on-farm network and the collective network that has never been studied so far. In fact, the pressure at the hydrant, which represents an important input data for the application of the above said model, depends on the configuration of hydrants simultaneously operating on the collective network. Furthermore, also the characteristic curve of the hydrant is taken into consideration to assure that the hydrant delivers the discharge demanded by the on-farm network.

This research line was officially demanded by all the Mediterranean partners, members of the networking activities coordinated by the IAM-B L&W Division, as described in the background.

Potential:

This research will allow defining new design criteria aiming at maximizing the performance of the on-farm sprinkler system and taking into consideration also the technical characteristics of the delivery devices, which are not usually considered by designers and managers. In addition, the software packages that are currently under development will give great visibility to the MAIB L&W activities.

Results:
Notes:
  • Strengths

The activities carried out for more than 15 years within the framework of the MAIB Cooperative research networks (WUE-Net, CIS-Net, UWRM-Net) have created the conditions for the continuation of the above research in the Mediterranean region, as requested by all the Mediterranean partners. In the research strategy of the L&W Division, this is considered only as a step in the whole integrated water system. This approach implies a strong interaction among engineering, agronomic and socio-economic aspects, which produces real innovations.

  • Weaknesses

The weakness is mainly related to the complexity in model calibration in the Mediterranean countries where data are scarce, difficult to access and, often, not reliable.

Reference person/s: Lamaddalena Nicola /
Collaborators: Zaccaria Daniele /
Thesis: Hydraulic interface between distribution network and on-farm irrigation system
Hydraulic interface between on-farm and distribution network
The rough set theory applied to the evaluation irrigation systems design and management
A procedure to develop an expert system for micro irrigation systems design
Institutions involved: Politecnico di Bari
Technical University of Lisbon
 
 
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