The last 18 000 years

Almost 18 000 years ago, very soon after the last glacial maximum, the sea level was a few dozen metres under the present day level. The glaciers that covered the uppermost areas of the Pyrenees disappeared little by little and, in some cirques and some hollows of the longitudinal profile of the valleys, small lacustrine basins were formed, sometimes contained by the old moraines.

The progressive decrease of the extension of the polar ice caps provoked a sea transgression that flooded the coastal lowlands and the ancient deltaic plains.

11 500 years ago when the Holocene started, the current geological period, the sea level had been stabilizing and was about 2 metres above the present one. The greater part of the plains of Empordà, the Besòs, the Llobregat Delta and the Ebre Delta were submerged. They were shallow bays, surrounded by alluvial lowlands, from which some small islands emerged. Towards the year 1000 BC, the accumulation of sediments contributed by the rivers had considerably increased the emerged areas and their landscape consisted of bogs and marshy lowlands. In the human settlements, located in the periphery of these plains and also on some small islands, agriculture and stockbreeding started to developed; the remains of Iberian villages are a good witness to this fact.

In historical times, the coastal plains of the Empordà, the Baix Llobregat and the Ebre had continued to grow with the alluvia contributed by the rivers, so that towards the year 50, the coastline was already quite close to the actual one (figure 19).

Figure 19: Reconstruction of the coastline, in blue, towards the year 50, with the situation of the main Roman cities on the Catalan coast

Durant l'Edat Mitjana, a causa de conflictes polítics i militars entre nobles veïns, alguns rius, com el curs baix del Ter, foren repetidament desviats. A les zones de muntanya, de forts pendents, l'activitat antròpica va deixar la seva empremta en el paisatge en forma de bancals i terrasses de conreu.

Més tard, al segle XVII, la desforestació de grans àrees de bosc es traduí en un augment considerable de les aportacions dels rius i, en conseqüència, en un increment de la superfície emergida de les planes deltaiques i costeres. El delta de I'Ebre assolí la seva extensió màxima cap a finals dels anys 10 del segle XX. Des de llavors, per raó de la retenció de sediments en els embassaments de la seva conca, el volum de materials del delta roman pràcticament constant. Els sediments disponibles ara són redistribuïts per l'acció dels corrents de deriva litoral, per les onades i, en menor mesura, per les marees, de manera que la silueta del delta de l'Ebre tendeix a ser arrodonida, a l'estil de la del delta del Llobregat. Durant la resta del segle XX el paisatge de Catalunya ha anat evolucionant amb pocs canvis, gairebé tots deguts a l'acció antròpica fins a assolir l'aspecte que podem percebre actualment.