Aspects agronomiques, hydrologiques et économiques de l'assainissement agricole

Agronomical, hydrological and economic aspects of surface drainage in agriculture

Ingénieur en Chef du Génie Rural, des Eaux et des Forêts, Chef de la Section Technique Centrale des Travaux d'Hydraulique

Résumé

Water is essential for plant life and orten is a limiting factor for plant growth. Air is just as essential, however, and given a certain climate and soil types, may also represent an appreciable agricultural yield-reducing factor. These two factors are frequently contradictory and the prodominance of one or the other is an obstacle to rational farming. Optimum air/water equilibrium should be aimed at, therefore, by making arrangements for the following: (i) Disposal of excess water and its replacement with air, which is achieved by surface drainage; (ii) Disposal of excess air and its replacement with water, which is achieved by irrigation. A number of conditions are attached to surface drainage, which determine the type of work and structures required and their operating capacity. These are as follows:- (i) Agronomical conditions, which determine the minimum melioration requirements ensuring that aeration of the root zone is sufficient to give an O/C02 ratio consistent with the growth of aerobic fermentations providing the necessary food for the plants; (ii) Hydrological conditions, which it is necessary to allow for in order to facilitate surface water runoff, deep infiltration and disposaI of this water in drains and outfalls, alheit whilst avoiding excessive acceleration of shower concentration times liable to displace the flooding problem and risk of submersion; (iii) Economie conditions governing the choice of technical solutions which are both effective and the least costly it is possible to achieve, for the profitability of surface drainage works is always limited and often deferred, resulting in a reduction in investment costs.