the drainage system being installed in egypt is a composite system. its main features are: the laterals are 8 cm in diameter and some 200 m long. they are laid at supplemented of between 1. 20 and 1. 50 m and at spacings of between 40 and 60 m; the collectors are concrete pipes with diameters of between 15 and 40 cm; the maximum depth of their outlets is 2. 5 m; collectors can be up to 2 km long; concrete manholes, 0. 75 to 1 m in diameter, are placed in the collectors at every third or fourth lateral. where the land is properly drained, soil salinity is much lower than in non-drained land; in the properly drained areas, yields of rice were considerably higher than in the non-drained areas (up to 61 percent higher). the same applied for berseem (up to 34 percent higher) yields of cotton, wheat and maize were also higher, but less significantly so; the gross value added to crops on drained land varies on the average from $pound$ e 110/feddan for wheat, $pound$ e 20/feddan for berseem, $pound$ e 30/feddan for rice, to as much as $pound$ e 110/feddan for cotton. rough calculations show that investments in drainage are economically justified if the annual benefit per feddan exceeds $pound$ e 20-25. the panel has suggested that any further economic evaluation of drainage be based on a 'before-and-after' approach, supplemented by studies on production functions under the controlled conditions of pilot areas