Spanish River Systems: Hydrology and Geographic Characteristics

Characteristics of Spanish River Systems

Atlantic and Mediterranean River Features

Unlike the distinct characteristics of Atlantic and Mediterranean currents, Spanish rivers exhibit unique hydrological patterns:

Atlantic Rivers

• Rivers crossing the Meseta are long.
• Cantabrian and Galician rivers are short and irregular, with very intense dry periods in summer and sometimes in winter.
• The most abundant flows occur in autumn and spring, which are also the times when high water levels concentrate.

Mediterranean Rivers

• Generally short rivers with low streamflow, except for the Ebro.
• Irregular, with intense dry periods and large floods caused by heavy rainfall in spring and autumn.
• Often ephemeral streams or wadis, characterized by channels where water flows intermittently.
• The Ebro River is a notable exception to these general characteristics.

Freshwater Systems: Spanish River Basins

Factors influencing the movement of water in a river basin include:

• Climatic Factors: Rainfall and temperatures.
• Size and Shape of the Watershed: The nature of the rocks.
• Slope: The gradient of the terrain.
• Vegetal Cover: The presence of vegetation.
• Human Action: Anthropogenic influences.

River Regimes

A river regime reflects the change in river flow throughout the year:

• Atlantic River Regime: Maximum flows in winter and minimums in summer.
• Mediterranean River Regime: Very pronounced irregularity and dry periods, with floods in spring and autumn.
• Subtropical River Regime: Marked difference between high water and low water periods.
• Pluvio-Nival Regime: Presents a secondary maximum due to snowmelt.
• Nival Regime: Throughput depends primarily on contributions from spring snowmelt.
• Nivo-Pluvial Regime: The main maximum is due to thaw, and a secondary maximum is due to precipitation.

Hydrographic Slopes

A hydrographic slope is formed by all the basins whose waters flow into the same sea. In Spain, there are two main slopes: the Atlantic and the Mediterranean, separated by mountain ranges that include the Baetic System, the Iberian System, and the Cantabrian Mountains.

Mediterranean Slope

• Characterized by many short, irregular rivers with low flow, though the Ebro is an exception.
• Presence of ephemeral streams and ravines is common.

Atlantic Slope

This slope has two distinct sectors:

• Rivers Crossing the Meseta: These are long and irregular.
• Cantabrian and Galician Rivers: These are short and plentiful, with more regular flows.
• The Canary Islands have regular watercourses.
• The Balearic Islands have intermittent watercourses.