HYDRIC RESOURCES. FLUVIAL COURSES: RIVER BASIN OF LOZOYA RIVER

Most of the courses that drain the sector of Sierra del Rincón belong to the river basin of the Lozoya River, articulating themshelves in two great subriver basins:

• The Nava River: it drains all the North sector of Sierra del Rincón, with a general disposition NNW-SSE. In its majority, they are courses of nonpermanent volume and certain length. The middle and low sections of subsidiary streams of the Nava River excavate their channel forming sometimes important streams beds.
• The Puebla and the Riato streams: this subriver basin is organized around the valley of Puebla de la Sierra. The disposition of the drainage network is conditioned by the relief, which rises in this sector of Sierra del Rincón. The main channel follows a direction NNW-SSE in the high part to bend in the most southern sections towards the south and later towards the west. This configuration is due to the importance that the relief acquires in this scope, constituting the valley of La Puebla as a closed unit. The course of La Puebla River after passing the urban centre is fitted with a spectacular form in the place known as El Tormo. The channels of near streams have to cover an important difference in height to spill their waters to La Puebla river, generating cascades and rapids own of high river sections.

The rivers and streams of this sector are characterized to present acidophilic black willow groves (Salix atrocinerea) in the high river sections and interesting black alder groves (Alnus glutinosa) in the low sections of La Puebla River.