L'irrigation du périmètre du Massa au Maroc

Abstract

Implementation of the Massa irrigation scheme at a site roughly 60 kilometres from Agadir, South Morocco, started in 1971 and was completed in 1975. In view of the local climate, with rainfall of only 230 mm unevenly distributed over the year, moderate temperatures owing to proximity of the ocean, and an abundance of sunshine, production was concentrated on off-season market produce (truck crops) for export, based on the results of an economic model study. Irrigation supplies are drawn from the Youssef ben Tachfine control dam on the river Massa, which has a total storage capacity of 310 million cubic metres. Operating schedules established by simulation of reservoir operation (in which provision was made for adjustment of arable land areas and water application according to storage level) will ensure distribution of roughly 90 million cubic metres of water annually; at a rate of 4670 m3/ hectare, this will provide supplies for traditional and modern service areas of 2000 and 18000 hectares respectively. Water distribution is ensured by the following : a) A pump station (SP1) at the foot of the dam, supplying a concrete-lined 18 km head canal comprising eight raised reinforced-concrete tanks, square canal sections and a covered section (see photograph, Fig. 4). b) A standard trapezoidal main canal with longitudinally prestressed concrete siphons totalling 884 m conveying supplies to the four irrigation sectors. The downstream-control system for this canal is computer-designed to meet the 18/24 hour peak demand (8 m3/sec) of the irrigation sectors by supplying the mean daily 6 m3/sec flow to the head of the system. The main canal comprises nine reaches with eight automatic gates controlling downstream water level. c) Four irrigation sectors each fed by an outdoor pump station drawing supplies from the main canal via raised regulating tanks. The pumps supply water at 9 bars to a system comprising large-diameter reinforced-concrete pipes and smaller (< 500 mm dia.) asbestos-concrete pipes to the irrigation hydrants. Each hydrant supplies sprinklers covering an irrigation unit of 8.3 hectares, at a pressure of at least 3.5 bars via portable pipes. Each of these pipes has nine sprinklers spaced 12 m apart and is transferred 12 m at a time during irrigation.