Major River Systems of the Iberian Peninsula

Cantabrian Slope Rivers and Climate

The Cantabrian slope is characterized by rivers and a regular, heavy-rain oceanic climate. These rivers are typically short and fast due to the close proximity of the Cantabrian Mountains to the sea. They possess significant erosive power, carving steep slopes, gorges, and ravines before emptying into estuaries.

Notable rivers include the Bidasoa, which forms the border between Spain and Portugal, the Nervión, flowing into the Bilbao estuary, the Sella, emptying near Ribadesella, and the Nalón in Asturias.

Atlantic Coast River Systems

Galician Rivers and the Miño Basin

Galician rivers, particularly within the Miño basin, exhibit significant water volume due to abundant rainfall and low evaporation rates. The region's geological formation has led to coastal subsidence, resulting in the characteristic rías (estuaries).

Key Galician rivers include:

• The Miño (Minho), approximately 350 km long. It originates in the province of Lugo, flows through Ourense, and receives the powerful waters of its main tributary, the Sil, before reaching La Guardia on the border with Portugal.
• The Tambre, which flows into the Ría de Muros y Noia.
• The Ulla river, emptying into the Ría de Arousa.

Duero Basin Characteristics

The Duero (Douro) River, with a length of approximately 900 km, is the third longest river on the Iberian Peninsula. It originates in the Picos de Urbión and forms a significant estuary in Oporto, Portugal.

Its hydrological regime varies:

• Upper course: Nival (snow-fed)
• Middle course: Pluvio-nival (rain and snow-fed)
• Lower course: Predominantly rainfall-fed

In the provinces of Zamora and Salamanca, the river carves the impressive Arribes del Duero, featuring several hydroelectric dams. The Duero Basin covers approximately 100,000 km², with about 80,000 km² located within Spain.

Key tributaries include:

• Right-bank: Pisuerga and Esla (contributing the majority of its flow).
• Left-bank: Tormes.

Tagus Basin and its Significance

The Tagus River is the longest on the Iberian Peninsula, with a length of approximately 1,200 km. It originates in the Sierra de Albarracín and flows into Lisbon, forming the vast Ribatejo estuary, the largest on the entire peninsula.

Its hydrological regime:

• Upper reaches: Nival (snow-fed) regime.
• Rest of the course: Predominantly pluvial (rain-fed) regime.

The Tagus Basin covers approximately 80,000 km², with about 56,000 km² located within Spain. As its name suggests in some regions (e.g., Tajo meaning 'cut' or 'gorge'), it flows through significant cuts and steep banks.

Key right-bank tributaries include the Jarama, Manzanares, and Henares. The river is crucial for hydroelectric power (e.g., dams in the Plan Extremadura) and is highly regulated, notably by the Tagus-Segura Water Transfer System.