The hydrology of the park is divided into two great basins: one to the northwest and north, and another to the south and east. Although the main waterways are in the east, between Setúbal, Palmela and the Picheleiros Valley, the ravine of Ajuda is the highest flowing waterway, and results from the confluence of the Ribeiras de Alcube e do Picheleiro, Ribeiras do Almelão and Ribeiras de Pomarinho. This basin includes the valleys of Picheleiro, Alcube and Ajuda, and the western and southern flanks of the Serra de São Luís, as well as the western flanks of the Nico and Viso, in addition to the Ribeira de Melra, Ribeira do Vale de Cavalo and Ribeira de Mareta. Other waterways, such as the Ribeira da Corva, tributary of the Ribeira de Livramento, or the Ribeira do Calhariz, tributary of the Rio Coina, obtain their maximum flow outside the park. Of all these waterways within the park, only the Ribeira da Ajuda maintains its flow throughout the year.
