HYDRIC RESOURCES. FLUVIAL COURSES: RIVER BASIN OF JARAMA RIVER

Jarama River has its beginning in the southern slopes of Peña Cebollera. This course acts as an administrative limit for the communities of Castilla-La Mancha and Madrid from its birth to the Dehesa Boyal de La Hiruela (Boyal Meadow). Streams and channels that spill their waters on the slopes of Hayedo de Montejo and La Hiruela valley drain towards this river basin.

All the channels maintain an E-W and SE-NW direction, cross shade side slopes and conserve the freshest places of the Central System. These channels display the typical characteristics of the high river sections: rocky beds, strong slopes saved by small rapids, high water quality, narrow groves, fitted topographic profile, intense erosive activity, absence of sedimentation, winding and meander courses adapted to the topography, etc.

In this sector two types of courses are possible to be differenciated:

• High sections streams: short sections with pluvionival regime, sometimes they do not maintain the permanent volume, undergoing an ebb tide until autumnal rains. The riverside vegetation is scarce. Due to the geomorphologic characteristics and its volume fluctuations, solely arbustive hydrophilic species and some units of Salix atrocinerea colonize it.
  
  
• High section of the Jarama River: this course is characterized for maintaining a permanent water volume. The water quality is very good and the course maintains an arboreal, well conserved canopy on its margins. The regime, to just as high sections streams, is pluvionival.

This river basin displays a great difference with the Lozoya river basin. The drainage network has in this occasion a role of relief division, fitting itself in slopes and favouring the formation of narrow valleys with strong slope. The orography, much wilder than the one in the slopes of the Lozoya river basin, is segmented and eroded by the described courses.