Analysis of design criteria for vineyard terraces in the Mediterranean area of North East Spain

The Penedes and Anoia regions in NE Spain are important areas for the cultivation of grapes used in the production of high quality wines. The Mediterranean climatic conditions define a xeric soil moisture regime. Rainfall are concentrated in spring and autumn while the summer is warm and dry. The climate is characterized by high rainfall intensities, being one of the main factors responsible for soil erosion in the area. Since grape quality depends on the availability of water for the vineyards and since soil erosion is an important parameter dictating the sustainability of vineyards, soil and water conservation can not be forgotten in the area. The most widely used measure for soil conservation in the area is terracing (hillside ditches, local name rases). Local technical solutions have been studied and in this paper different types of terraces are described and analysed in terms of its effectiveness for runoff control. Mean potential soil losses are evaluated according to the USLE and compared with field measurements in experimental plots. The distances between terraces have been calculated using the criteria proposed by several authors. Owing to the wide diversity of results, an acceptable value for 'soil loss tolerance' (T-value) has been used in order to establish some criteria to make recommendations, taking the values of soil loss measures in the field as a reference. According to these preliminary results based on measurements taken over a period of two years, some advisable distance between terraces (rases) in vineyards can be proposed in view to improve local criteria. With a slope of 6%, a distance of is 28 m would be advisable, and in fields with a slope of 8% the distance should be 20 m. Bennett's criteria to calculate distances between terraces are the more advisable being closely related with experimental results in the area.