Manual - Participatory rapid diagnosis and action ... - FAO.org

PRDA Manual 13Water resource and abstraction relates to the type of water source (river, dam,lake, etc) and the technical means used to abstract water (diversion weir,pumps, etc). It determines the:• amount of water available and its variation year-round;• reliability of the water source and possibilities for water storage;• extent to which water supply to the scheme may be adjusted.The site relates to the location of the irrigation system:• total size of the command area;• soil type and distribution in relation to the type of crops and irrigationmethods;• topography.These two sub-constituents are closely linked and should be coherent witheach other.Let us now go to the other end of the irrigation scheme where the two subconstituentsare the plots and water use.Plots: Main characteristics:• size;• shape (length and width);• internal layout and quality of levelling.Water application: Main characteristics:• on-farm irrigation depth (m 3 /ha or mm);• on-farm irrigation technology;• “main d’eau” or discharge at plot gate;• irrigation scheduling: frequency and duration of water application;• reliability.Plots and water use are closely linked. At the design stage, decisions regardingone of them have a strong influence on the other.It is possible to identify two sub-constituents that make the link between siteand water source on the one hand and plots and water use on the other to givecohesion to the irrigation scheme.