|
Résumé :
|
In planning and designing an irrigation system,a major problem is to decide what water use efficiency to apply in the calculations.Since basic knowledge on this subject is lacking,it is common practice that this efficiency is either conjectured or derived from existing irrigation systems.Obviously,the efficiency thus obtained is unlikely to suit the conditions of the project area in its future state.Because water use efficiency is usually the "guess" factor in the design of an irrigation system,engineers are facing the problem of uncertainty in their calculations.To cover this uncertainty,canals,structures,and reservoirs are being given a greater capacity than would be necessary if objective efficiency standards were available and could be applied.Apart from harmful side-effects, this way of doing things leads to investments that may be considerably higher than would otherwise be necessary.Obviously,there is an urgent need for more basic knowledge of irrigation efficiencies under different climatological,topographical,soil,agricultural,and socio-economic conditions.In an attempt to shed some light on the matter,an inquiry was organized to find out what methods of water distribution are applied in irrigated areas throughout the world.A carefully planned questionnaire was prepared and tested in close cooperation with a number of National Committees of the ICID.The answers to this inquiry have revealed a number of interesting features about irrigation efficiencies which were unknown until now.This publication describes the approach that was applied in the inquiry,the results obtained from it,and the conclusions that could be drawn.These conclusions can be used as a guide in planning and designing new irrigation systems and in studying deficiencies in existing systems.In the following pages we shall first define the problem more precisely and then describe the method of data collection.Next a brief description of the data processing will be given,followed by a detailed discussion of the results.A sample of the questionnaire,forms used for calculating the various efficiencies,and tables of basic data are given in appendices.
|
