Action Lab: Baix Llobregat
The lower basin of the Llobregat river (approximately 120 km2) is located near Barcelona (NE Spain). It includes numerous wells for the extraction of groundwater and two points of surface water collection for the production of drinking water.
Geomorfology and climatology
The lower basin of the Llobregat River is a fluvial plain oriented in the N-NW / S-SE direction, where the Llobregat River divides the mountain ridges located parallel to the coastline and generates a delta at its mouth. This geographical arrangement is associated with a predominance of winds throughout the basin. During the winter, cold north winds penetrate, while in summer, the sea wind provokes, winds of S-SW component in the delta zone and component S or S-SE in areas more interior of the basin. On the other hand, its orientation S-SE (solana) allows it to receive a high irradiation, which contributes to the achievement of a privileged median temperature. This, together with the regulatory influence of the sea and the physical protection of the mountain ridge lines and the exposure to the S-SE ensure mild winters and extend the warm season until two months of autumn (September-October). The average rainfall is 583 mm, with maximum rainfall during the months of September and October (autumn) and minimum during the months of June and July (summer), and precipitacones in the form of snow exceptionally. These climatic conditions are very indicated for the crops that are produced mainly in the delta and the lower basin: orchard and fruit trees in the open air and in greenhouses.
The deltaic plain and the river terraces belong to the Quaternary period and include the Llobregat fluvial deposits and tributaries, the dunes of the dunes, now fixed with pine trees, and the deposits that cover the slopes. These sediments are of very good quality as farmland because of their high permeability and of interest to the aquifer. The use of sands and gravel as a construction material led to its extraction in agricultural lands and in the river bed itself, generating serious problems later due to the filling of the extracted areas with unknown materials, as well as the waterproofing of the shore of the river. River. The danger of flooding of the lower lands meant that the old urban centers were built, except El Prat, in higher areas, safe from floods
The aquifer is the basic hydrological unit. The location of the aquifers and their importance are a consequence of the characteristics of the materials and their disposition in the space, which make them more or less apt to contain and circulate infiltrated water, fact that has allowed to originate the most important aquifer of the Cuenca del Llobregat and one of the most important in Catalonia. The number of wells in the lower basin is above 700. Most of them are located in the delta area, exploiting the deep aquifer with an average volume of extraction of 105 hm3 / year. From the set of extractions the industrial and urban supply represents more than 85 percent and agricultural irrigation, around 15 percent.
The agricultural area used (SAU) in this region is 4,708 hectares that are divided, approximately, into two halves, one irrigated and the other dry. 43% are land under cultivation. Practically all the surface of cultivation of irrigated land corresponds to the scope of the Agrarian Park with an area of 2,938 hectares of which 67% (1,969 hectares) is considered SAU.