Understanding Hydrological Features and River Terminology

Watershed / River System

A watershed, also known as a river basin or drainage basin, is the territory drained by a main river and its tributaries. It is bounded by watersheds (divides). A basin is considered symmetrical if the structure and number of its tributaries are similar in both areas. In Spain, the largest basin is that of the Douro River.

Fluvial Regime

A fluvial regime refers to the variation of river flow throughout the year. It depends on rainfall distribution and the importance of snowmelt. Accordingly, we can speak of pluvial, nival, or mixed fluvial regimes.

Rambla

A rambla is a watercourse, generally dry, which theoretically carries a river current. Ramblas appear in rivers that have a torrential regime, meaning they have no flow for most of the year. This phenomenon is common in the Mediterranean basin.

Delta

A delta is a fluvial landform, generally triangular in shape, generated by the accumulation of sediment at the mouth of a river. These materials fill the river mouth, forming a penetration of land into the sea. In Spain, the most remarkable delta for its breadth is the Ebro Delta.

Estuary

An estuary is a coastal landform at the mouth of a river. It occurs when the bottom of the river valley is flooded by the sea. When the tide is rising, it pushes river water inland; at low tide, both fluvial and marine waters are evacuated.

Endorheic Area

An endorheic area is a type of drainage basin where waters, even if permanent, do not reach the sea. Instead, they accumulate in depressed areas, forming lakes and wetlands. This relief may result from climate and rocky terrain.

Head of a River

The head of a river refers to its birth and early stages. It is the steepest area of its course, where the water flows with significant strength and speed. This section is where the river has its highest erosive capacity, wearing down, transporting rocks, and carving out valleys.

Flowrate of a River

The flowrate of a river is the amount of water, measured in cubic meters, evacuated by a river over a period of time; it is typically expressed in cubic meters per second (m³/s). Flowrate is the item that best characterizes the flow regime. The Duero River stands out in this regard.

Low Water of a River

The low water of a river is the period during which the river reaches its lowest flow. In Spain, particularly severe low water periods occur in summer, coinciding with the summer drought, and have their greatest influence on the Mediterranean rivers of the southern half of the Iberian Peninsula.

Torrente

A torrente (or wadi) is an intermittent watercourse that only carries water when it rains. For much of the year, their beds are dry. They are characteristic of areas with low and erratic rainfall.

Ria

A ria is a river valley that has been invaded by the sea. The largest rias in Spain are found in Galicia, in relation to the structure of the Galician massif.

River Diversion

River diversion refers to the moving of water by artificial channels from one river to another. In Spain, notable examples include the Turia-Júcar and Tajo-Segura water transfers.