Soil survey for drainage projects [articol]

Abstract

For a proper diagnosis of drainage problems one must have the appropriate soils information. The required soil data have to be of morphological, physical and chemical nature to relate to the hydrological problems. Soil mechanical interpretations and civil engineering aspects must also be kept. A survey of the water table is one of the most important parts of any drainage investigation. For a well-balanced drainage plan, the soil data will be include active gley phenomena, which give a reasonable idea of the fluctuations in groundwater levels. Reduced soil materials, Gr, that are permanently saturated have a characteristic gleyic colour and the horizon Gr must be present in the first 50 cm of the soil profile. Gleysols can be used for arable cropping, provided the groundwater table is lowered or groundwater seepage from the uplands is intercepted. A common soil survey offers soil data only for a depth of 1 to 1.5 meter. For hydrological calculations it is necessary to know the composition of the subsoil, even to depths of 50 to 100m. For tile drainage, it is necessary to know the characteristics, to a depth of at least 4 to 5 meters. For a drainage plan, the following soil data will be required: active gley phenomena, permeability, available water, salinisation and sodication problems, rippening; maturation. The drainage specialist will find the sensitivity analysis a useful tool in guiding the required soil and geohydrogeological investigations, which differ from project to project, and in working out alternative solutions regarding the use of pipe drains or ditches, drain depth, etc.