Traditionally, most irrigation practices in Southern Europe have been based on gravity-fed surface irrigation systems. Currently, these systems remain a relevant typology in the European Union (EU) member states of the Mediterranean areas, where it is often the only sustainable method for farmers due to the small size of agricultural holdings, their reduced capacity and readiness to invest and the low ratio between yield profits and irrigation costs. In the last several years, in response to European and national directives, surface irrigation has garnered increasing attention at the political and bureaucratic levels due to frequent criticisms of its postulated low efficiency and high water wastage. However, these systems commonly provide a number of ecosystem services and nature-based solutions that increase the positive externalities in different rural socio-ecological contexts and often have the potential to extend these services and provide solutions that are compatible with economical sustainability. This study aims to discuss the prospects for new practices and for the rehabilitation and modernization of the gravity-fed surface irrigation systems in EU Mediterranean areas to enhance water efficiency, thus gaining both economic advantages and environmental benefits. The difficulties, stimuli for improvements and peculiarities of the irrigation water management of four rural environments located in Italy, Spain and Portugal were analyzed and compared to the current state of the gravity-fed surface irrigation systems with hypothetical future improvements achievable by innovative technologies and practices. In these different case studies, the current gravity-fed surface irrigation systems have an obsolete regulatory structure; water-use efficiency is not a driving criterion for the management of the conveyance and distribution canal network, and farmers are not yet adequately encouraged to adopt more efficient gravity-fed irrigation practices. A continuous knowledge exchange is thus necessary for the interaction of all irrigation water managers and farmers to improve their eco-efficiency and to preserve and promote their cultural heritage across the entire water supply and delivery chains. We argue that the best way forward will require precisely targeted rehabilitation measures of gravity-fed surface irrigation systems based on the integrated use of decision support services, gate automation, remote and feedback controls and real-time flow optimization.

Micro-irrigation can apply water with high uniformity. However, uniformity alone is not sufficient to achieve the goal of irrigation. Irrigation scheduling is equally important in micro-irrigation systems. The significance of various irrigation schedules and emitter flow uniformities were examined in a system design. Several irrigation schedules were compared with an optimal irrigation schedule. The optimal irrigation schedule can achieve optimal return and also provide water saving compared with the conventional irrigation schedule in which the whole field is fully irrigated at the same time. Deep seepage can be eliminated or minimised by scheduling deficit irrigation. An environmental protection irrigation schedule, where the whole field is in deficit, can save more water but will cause some reduction in total return compared to the optimal irrigation schedule. A simple irrigation schedule, in which the total amount of water applied is the same as the amount required, cannot only produce nearly optimal yield but also achieve increased water saving when high uniformity is also applied in the design. It is important to specify that the differences in total return and water saving between different schedules are reduced when high uniformity is applied in the design. For high uniformity the effects of crop sensitivity to deficit irrigation are not important and result in only limited (or acceptable) yield reduction and over-irrigation. Since a high proportion of water resources are used for agricultural production, micro-irrigation systems designed with high uniformity can be scheduled to achieve water conservation as well as environmental protection

The aim of this article is to determine with real data to what extent the hypotheses on which Clément’s first formula is based are fulfilled, and to compare the results of applying this formula. To this end the flow demand in the peak period was studied in two distribution networks with different irrigation methods and crops located in the Ebro River basin (northeast Spain). The calibration procedure for this formula proposed by the Centre Technique du Génie Rural des Eaux et des Forets (CTGREF) in 1977 was also analyzed. The result was that most of the hypotheses were not fulfilled. Furthermore, the discharge distributions obtained in the period of study did not correspond to a normal distribution. However, comparing the real accumulated probability curve and that calculated by Clément’s formula, it was found that the differences between the two curves for probabilities greater than 90% (a wide range of application of the formula) were lower than 9.4%. The reason for this result was found. It was shown a...

Knowledge of the maximum length for paired drip laterals facilitates the economic optimization of microirrigation systems. The methodologies proposed to date have been based on complicated mathematical procedures that make certain restrictive assumptions, such as fixed pressure head variation, and disregard emitter flow variation; this has limited their application. The methodology presented in this study, which assumes the basic equations for the analysis of a drip lateral based on the energy gradient line, allows evaluation of the maximum length of paired drip laterals with non-pressure-compensating emitters when diameter and slope are known and pipe is laid on a uniformly sloping field. The results show that the maximum length of a paired drip lateral with a given diameter is almost constant for any slope, although there is a maximum slope above which the lateral pipe diameter needs to be reduced. The maximum slope can be obtained when the ratio between the difference in elevation and the head loss due to friction of the downhill lateral exceeds 1. A method is also proposed to determine the lateral pipe diameter for a fixed length.

The crop water production function (WPF), representing the relationship between crop yield and seasonal irrigation water, is a useful tool for irrigation planning purposes. The objective of the paper is to propose a methodology to evaluate the optimal seasonal irrigation depth based on the crop production function, the field distribution uniformity, and economic considerations. An extended unpublished database experimentally obtained on the onion crop on the island of Kula, Hawaii, was initially used to assess the crop WPF. The combination between the crop WPF and the model representing the field distribution uniformity allowed determining the area subjected to underirrigation and overirrigation, as well as the corresponding yield, that were finally averaged across the field. An economic comparison was also carried out in order to evaluate the optimal seasonal water depth aimed at maximizing the farmer’s gross margin under different irrigation system distribution uniformities and water prices. According to the experimental data, it was observed that the onion crop is more sensitive to deficit than overirrigation, as well as that a quadratic model, valid for the entire range of the seasonal applied irrigation depths fitted better than a two-slope linear model, representing separately the conditions of deficit and over-irrigation. Moreover, the maximum yield, as well as maximum gross margin, can be obtained by applying average irrigation depths lower than those which correspond to the maximum yield, with percentages that declined at decreasing of water distribution coefficient and at increasing of water price. The proposed methodology can be applied even for other crops once the corresponding WPFs aree known, thus providing interesting evaluations that are useful for irrigation planning.