Hydrography
The spanish hydrographycal system presents has many peculiarities and strong constrasts. The variety of regimes of runoff is due to a rich and diverse waterways, environmental and landscape.
The feature can best define the Spanish rivers is irregular, the asymmetry of the slopes and the limited importance of endorheic and lakes.
DISTRICT RIVER BASIN
"The term river basin is the marine and land consisting of one or more neighboring river basins and associated coastal waters and groundwater to these basins." The river basins are the main unit of watershed management (article 16 of the Water Act drafted by Law 62/2003).
For each river are considered to fall all groundwater located below the limits of the watershed dividing the corresponding demarcation.
In the case of the shared aquifers between different river basins, each river basin manage his part of the aquifer and should ensure coordination between the two sides. The shared aquifers are defined by the National Hydrologic Plan.
There is a clear relationship between autonomous communities and river basins territory. The territory of the river basins that covers more than one autonomous communities have been definied by royal decree 125/2011.
In Júcar River Basin case have been excluded of its territory the intra-community basins and the transitional waters associated. Also have been excluded coastal waters associated the coastline of the basins, intra-Valencia.
The Norhtern River Basin have been divided in Miño-Sil River Basin, Cantábrico Occidental River Basin and Cantabrico Oriental River Basin. You can see the limits of the spanish river basins in the following map:
Figure 2. Land boundary of river basins. Source: Sistema Integrado de Información del Agua. SIA
Regarding to basins managment it can be said there is two modalities in Spain:
- River Basins: managment the basins that covers more than one Autonomous Community (Cantábrico oriental, Cantábrico occidental, Miño-Sil, Duero, Ebro, Tajo, Júcar, Guadiana, Guadalquivir y Segura).
- Autonomius community: manage river basins that only covers one autonomous community, they are called intra-community basins (Cuencas Atlántica y Mediterránea Andaluzas, Internas Catalanas, Baleares, Canarias, Galicia-Costa e Internas del País Vasco.)
In each inter-community basin exists a cooperation organ called "Appropriate Competent Authorities Committee", which function is to guarantee the cooperation in the application of the protection water rules. In this organs are represented the State General Administration, Autonomous Comunities and Local Entities.
WATERSHED
According to Article 16 of the revised Water Law basin means the area of land whose runoff flows entirely through a series of streams, rivers and, possibly, lakes into the sea at a single river mouth, estuary or delta. The watershed and resource management unit is considered indivisible.
Watersheds are divided in turn into sub-basins, which are the land surface that sheds a particular point in a water course (normally a lake or a river confluence).
The following pictures show the basins of major rivers and Spanish sub-basins of the Spanish part of the peninsula.
Figure 3. Spain rivers basins. Source: Sistema Integrado de Información del Agua. SIA
Figure 4. Sub-basins. Source: Sistema Integrado de Información del Agua. SIA
The following table reflects the characteristics of the watershed basins Spanish.
| Slope | Expanse | Location | Rivers |
| Atlantic | 285000 km2 | Planteau rivers/Guadalquivir depression | Duero, Tajo, Guadiana |
| Mediterranean | 181000 km2 | Mediterranean coastal rivers/ Ebro depression | Ebro |
| Cantabrian | 25000km2 | Cantabrian Mountains | Bidasoa |
Table 1. Characteristics of the basins slopes. Source: Sistema Integrado de Información del Agua. SIA
RIVERS
The major rivers run Spanish in the same direction of the parallels, except for the rivers of the Cantabrian and the southern peninsular which born in mountains near the sea and follow the direction of the meridians.
The river Douro, Tagus and Guadiana sit on the plateau, closed by the Cantabrian and Iberian and Sierra Morena, and find their outlet to the sea in its western part, on the border with Portugal.
The Catalan Coastal Range, the termination of the Mediterranean Iberian and Betic mountain ranges, all near the coast, resulting in small watersheds, with the exception of those for rivers that have a very active remontante action.
The channels Balearic and Canary islands are characterized by their intermittent nature and steep slopes. The presence of karst areas makes much of the water to percolate before reaching the lower reaches and springs appear. In the case of the steep slopes of ravines and the abundance of underground deposits, leading to the absence of surface currents.
Another peculiar feature of the hydrography Spanish is the frequent presence of ephemeral streams, giving the case of continuous lengths coexist with other permanent and intermittent streams with ephemeral flow in a river.
Moreover, not all runoff flowing into the river network, as there are numerous character enclosed areas or semiendorréico endorheic, where the water is retained until lost through evaporation or seepage.
Figure 5. Spanish rivers. Source: Sistema Integrado de Información del Agua. SIA
It develops and publishes weekly from data of the river basin, the Water Authorities in intercommunity basins, the National Institute of Meteorology and Red Electrica of Spain. The information obtained can be used as decision support in water management.
More information. Sistema de Información del Agua. SIA
To carry out the measurement of river flows have been established gauging stations. The following map we can see the distribution of gauging stations in Spain.
Figure 6. Gauging stations in Spain. Source: Sistema Integrado de Información del Agua. SIA
In the longitudinal profiles of the main Spanish rivers, there are three sections:
Header: In this zone the river between steep advances that favor its erosive capacity.- Middle section, whose length is considerably larger, has uniform slope along the channel, whose action is the transport property.
- The final section or mouth: this is where the river swept material settles in the basin, reaching to form deltas and coastal deposits.
The combination of erosion and sediment transport tends to mold a smooth longitudinal profile between birth and the level of mouth.
Below are the longitudinal profiles of the longest rivers
Source: Environmental Profile of Spain
LAKES
According to Water Framework Directive, a lake is a "body of standing inland surface water" whose area exceeds 50 Ha.
In Spain there isn´t large lakes- However, due to climate and geological diversity the lakes have different typologies. Most of them are in endorreicas areas, where there are shallow lagoons with reduced extension. These lagoons can appear in gropus, like in "Mancha Húmeda". The topography in this area is set by ephemeral streams that flow to encharcadizas plains, lakes and wetlands.
Figure 7. More representative lakes in Spain. Source: Sistema de Información del Agua. SIA
The following map also reflects those lakes with an area larger than 8 ha and exceeding 3 m deep and Basin Organizations that have considered be defined as water bodies in this category because of its special significance.
Figure 8. Spain lakes. Source: Sistema Integrado de Información del Agua. SIA
In Spain there are 2474 lakes and ponds. The lakes in Spain are small compared with the rest of Europe. However, if we have lakes from many sources, as shown in the table.
| Type of lake | Origin/ Features | Location |
| Glacier | Formed by the geological action of glaciers | Sanabria |
| Endorreico | Formed by the low area where water accumulates | Sariñena |
| Tectonic | Origien tectonic features | Janda |
| Volcanic | Formed in the crater of an extinct volcano | Fuentilleja |
| Karst | They occupy depressions formed in the limestone soils of karst | Ruidera |
| Lagoons | They originate in the mouth of the rivers | Albufera, Mar Menor |
Table 2. Types of lakes
In many cases, 70% of the annual contribution to the rivers is concentrated during a few months, and even in one, leading to flood events.
The irregular basin in Spain is defined by the following three conditions: Irregularity in the spatial, temporal irregularity, both seasonal and interannual occurrence of huge volumes avenues in relation to average values.
RESERVOIRS
In Spain there are over a thousand dams that regulate water surface, allowing sufficient water to meet water demands.
The total storage capacity is about 60,000 hm ³.
Table 3. Main data of reservoirs in operation. Source: Sistema Integrado de Información del Agua. SIA
Are 347, the reservoirs with a capacity exceeding 10 hm ³, (which is un98, 2% of total reservoir capacity). The geographic distribution of these reservoirs is shown in the figure below.
Table 4. Geographic distribution of the reservoirs. Source: Sistema Integrado de Información del Agua. SIA
CONCEPTS
- Inland waters means all standing or flowing water on the soil surface and all groundwater on the landward side the line that forms the basis for measuring the breadth of territorial waters.
- Coastal waters: surface waters landward side of a line whose points are all located at a distance of one nautical mile offshore from the nearest point of the baseline used to measure the width of territorial waters and that extended, if necessary, to the outer limit of transitional waters.
- Transitional waters are bodies of surface water near the river mouths which are partly saline as a result of their proximity to coastal waters but which are substantially influenced by freshwater flows.
- Surface water: inland waters, except groundwater, transitional waters and coastal waters, and in respect of chemical status for the territorial waters.
- Flow: The amount of water flowing in a river at a point, measured at gauging stations. It is measured in cubic meters per second
- Watershed: land area whose runoff flows entirely through a series of streams, rivers and, possibly, lakes into the sea at a single river mouth, estuary or delta.
- Floods and droughts: data volume compared to dates, frequency and probability
- River basin: marine and land area composed of one or more neighboring river basins and associated coastal waters and groundwater to these watersheds.
- Irregularity: The ratio of mean flows of year and the less mighty mighty
- Lake: mass of standing inland surface water.
- River: body of inland water flowing for the most part on the soil surface, but which may flow underground for part of their course.
- System of a river flowing in the same way and is defined by the following
- Sub-basin area of land from which surface runoff flows entirely through a series of streams, rivers and, possibly, lakes to a particular point in a water course (normally a lake or a river confluence).