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Bayco Reservoir

Territorial frameworkwork.

Physical features of the basin.

The Bayco riverbed begins at the confluence of different watercourses, such as the Cepero and the Jaraba; such a confluence takes place near Sainetes, a village located 3 km to the west of Fuente Álamo.

The catchment basin, up to the dam enclosure, has a surface of 245 km2. It is fan-shaped, and its section are defined by a series of small mountains, hills and minor mounds.

To the north, it limits with the Júcar basin. This Northern divide is marked by a series of small mountains, among which is possible to highlight, from east to west, the Arabinejo mountain (1,051 a.m.s.l.), Miralcampo, the Muela mountain(1,021 a.m.s.l.) and the Romeral hill.

To the northwest, the Pinilla mountain separated it from the Charcos basin; and to the southeast, it runs through the Conejeros mountains and the high Madroño, and it limits with by the middle basin of the Tobarra stream.

To the south, the foothills of the upper Madroño and the Parda mountain separate it from the semi-endorheic plains of Ontur and Albatana. Although in these plains the Bayco riverbed flow is negligible, topographically, these lands are tributaries of the lower basin of the Tobarra stream or to the Minateda riverbed, as it has become obvious during important floods.

To the southeast, the basin shares a boundary with the Cañada de Albatana stream, which is also included in the Tobarra stream catchment basin.

In general, the basin is almost flat,the soil is made up of Plio-Quaternary clays and silt, apart from the Jurassic limestone and dolomite crests that shape the small mountains that create the divide.

The length of the largest riverbed is 18.8 km, beginning at an elevation of 970 m and ending at 670 m in the dam enclosure. Therefore, the average slope is 1.6 %.

The basin time of concentration is 4.8 hours.

The basin pluviometry is scarce and erratic. An average yearly rainfall of 366 mm is estimated, alternating long periods of drought with sporadic, short-lasting, heavy rains, and very intense rainfall.

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Environmental information.

The area of the Bayco reservoir is characterized by a tempered continental Mediterranean climate.

Based on all of these parameters, it is clear that its climate favors physical erosion processes of certain intensity (torrential rains, frost, etc.), thus, creating certain typical morphological features.

The area's water network does not have important hydrographic arteries but is limited instead to just seasonal watercourses, ravines and streams.

The hydro-geological features of this area are associated to the water conditions of the materials.

Erosion is an important factor in this area, given considerable soil losses as a consequence of external processes (rains, weathering, etc). During the rain season, erosion is intense, and it is favored by the scarcity of vegetation which implies significant material hauling.

Bayco dam construction commemorative monolith
Bayco dam construction commemorative monolith

It has been estimated that soil depletion due to laminal hydric erosion and irrigation channels is approximately 57 t/ha, which places this area within the sub-desert zone of the south-eastern part of Spain.

The potential of these soils is based on their physiographic location and erodability; the firmest slopes are used for forestry and the softer slopes for grains and grapevines, representing a potential reserve in the expansion of district irrigation.

The Rivas-Martínez agro-climatic classification places the Bayco basin in the meso-Mediterranean floor, Manchegan section of the Castellano-Maestrazgo-Manchega province. The natural vegetation belongs to the sclerophyllus formations of leathery, evergreen leaves, a defense mechanism against the arid environmental conditions of the area.

Potential vegetation would be made up of holm oaks (Quercus rotundifolia), with a shrub border of groves. The current vegetation is grouped in three natural units: fields, thickets and trees.

The fields are grassy areas made up of leguminous and grassy plants, associated with different shrubs: thyme, rosemary, etc. They frequently grow on old esparto fields, currently abandoned, creating the esparto-fields unit.

Thyme, gorse and rosemary thickets occupy a large area of the basin, especially on sharp slopes which are not suitable for agricultural exploitation. Cattle feeds there.

Holm oak and pine forests appear at the highest basin elevations, generally surrounded by thicket and representing the basis for development of the animal community.

On cultivated land, it is possible to find groups of larks, passerines and finches, as well as many corvids.

The plant units support an important bird wildlife, as well as many mammals common in Spain: rabbits, hare, etc.; nevertheless, the predominance of cultivated land over natural vegetation translates into the wildlife characteristics of that unit.

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Geology and seismology.


The area occupied by the Bayco reservoir is the link between the Baetic and Iberian Systems.

Downstream dam shoulder, crops and irrigation systems
Downstream dam shoulder, crops and irrigation systems

Southwards from the reservoir, from east to west, we find structures clearly belonging to the Pre-Baetic domain, as the northernmost and external part of the Baetic System, whereas northwards, structures are Iberian, in a north-south direction.

In this area, it is possible to observe Baetic structures, i.e. east-west, such as the thrust and

the folds of the Madroño Mountain and the upfold of the Parda mountain. To the north, towards the tail end of the reservoir, it is possible to observe folds in the north-south axis, and formations lying to the west, typical Iberian features. The Morras, which make up the dam's left abutment, have a dome structure, possibly due to the impact of two upfolds: one is Iberian in a north-south axis, while the other is Baetic, in the ENE-WSW axis.

In the reservoir area, the following stratigraphic soils are found:

  • Jurassic:
    Jurassic soils emerge in the reservoir basin and the surrounding mountains, such as the Madroño and the Parda mountains, as well as in the small isolated hills, surrounded by recent soil covers (alluvial and colluvial).
    The lithological types observed in the reservoir area are dolomites, groups of dolomites and limestone, and alternate layers of limestone and silty marl.
    Dolomites practically make up the entire left abutment of the dam.
    Groups of limestone and dolomites make up the right abutment of the dam. The limestone emerges on the left margin of the enclosure, downstream from the dam axis and in isolated hills of the reservoir's tail end. Limestone and marly limestone make up the small ravine surrounding the Morras hills on the south and southeast.
  • Cretaceous:
    Thet appear next to the right abutment of the dam and, generally, over the entire northern watershed of Madroño mountains, under the Jurassic dolomites and limestone and in mechanical contact with them. They appear as a set of detritic materials particularly tectonized and laminated.
    Grey, green and red clays, white sand, red grit, conglomerates of round stones and black gypsum have been observed.
  • Continental Tertiary:
    Formed by fluvial deposits and alluvial fans, made up of conglomerates and, to a lesser extent, red grit and clay.
    The conglomerate appears as a compact rock, made up of rounded and sub-rounded calcareous stones, cemented by a red calcareous matrix.
  • Quaternary:
    It makes up most of the reservoir basin soil, covering the most ancient land. It is made up of slope and fluvial deposits, clayey-lime lithology with lots of sand, also containing gravel and some blocks.
    In the geological cartography, it has been possible to distinguish the alluvial deposits occupying the middle of the valley and are made up of brown clays or beige lime clays with layers of abundant lime-clayey gravel and sand lenses, not too consolidated and highly waterproof.
    It has also been possible to distinguish colluvial fan-shaped deposits, with a thin lens-like section. They are made up of whitish or light pink fine sand and marly lime, including angular and sub-angular marl stones and dolomites. Their vertex is on the sides of the mountains and its bottom in the centre of the valley, as its origin is in layers of diffuse runoff. They are quite waterproof.
    The alluvial-colluvial deposit present in the area is a mixed, heterogeneous deposit of anything from clayey alluvial to limey colluvial. They have a characteristic pink color.
    Eluvial deposits have also been found, which have been essentially formed by alteration of the substrate with little movement. Eluvial deposits over red calcareous rocks are scree and decalcification clays, while the Cretaceous sands and clays produce loose sandy clays.


The Bayco basin reservoir is located, according to the Seismic Resistance Construction Regulation (NCSE-02), in an area with a basic seismic acceleration of 0.07 g in the Ontur municipality, which is the nearest town to the reservoir.

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