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Reservoirs

El Moro Reservoir

Territorial Framework and Management.

Physical Characteristics of the Basin

The surface of the reservoir basin catchment area is 379.77 km². The volume of the reservoir at the height of the threshold of the lower spillway, hereinafter, NAI, is 4.36 million cubic metres and the surface at the same height is 47.41 hectares. Below a picture of the catchment basin can be seen.

Volume of the Basin
Volume of the Basin

Here is a summary of the main characteristics of Rambla del Moro reservoir and catchment basin:

Surface area of the catchment basin : 379,775 km²
Height of lower spillway (N.A.I.) 226,52 m.s.n.m.
Reservoir volume (N.A.I.) 4,36 hm³
Reservoir surface area (N.A.I.) 47,41 ha
Height of upper spillway (N.A.S.) 230,52 m.s.n.m.
Reservoir volume (N.A.S.) 6,70 hm³
Reservoir surface area (N.A.S.) 71,31 ha
Max. inflow standard project flood level 726,95 m³/s (T- 1.000 años)
Max. inflow maximum flood level 1.236,2 m³/s (T- 10.000 años)
Standard project flood level (N.A.P.) 231,04 m.s.n.m.
Reservoir volume (N.A.P.) 7,07 hm³
Reservoir surface area (N.A.P.) 74,33 ha
Maximum flood level (N.A.E.) 232,39 m.s.n.m.
Reservoir volume (N.A.E.) 8,13 hm³
Reservoir surface area (N.A.E.) 81,91 ha
Dead storage level 202,67 m.s.n.m.
Maximum daily rainfall registered (April 1946) 118,5 mm
 

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In the initial project for the Rambla del Moro Reservoir dated 3/84, there is no environmental impact assessment or annex related with this issue.

However, an environmental impact assessment is included in the project "Urgent Conditioning of the Rambla del Moro Reservoir". The actions contained in this project which were potentially harmful for the environment were:

  • Elimination of the Keuper clay and loam outcrop downstream from the dam
  • Extension of the spillway basin
  • Construction of the jetty
  • Waterproofing injections, consolidation of foundations and opening of the chimney drain

Although it does not directly affect the dam, an environmental impact assessment was also made regarding the works carried out in the project for the hydrological correction of El Moro basin.

As for its use, the Regulations for the environmental integration of the dam are included in the Regulations for the Use of the Rambla del Moro reservoir published in this Technical Assistance.

In these integration regulations, the current environmental legislation that may affect its use is analyzed, there not being any measure worth mentioning basically due to the fact that the normal mode of use is an empty reservoir.

On the other hand, the dam and reservoir are not situated in any area of environmental protection.

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Geology and Seismology

Regional Geology

Rambla del Moro reservoir is located in the north-eastern area of the Baetic Mountains, which, in turn, form the north-western segment of the peri-Mediterranean Alpine Orogenic belt (alignment of mountain ridges with structure on shifting strata formed during the Cretaceous and Tertiary periods and which present a centrifugal layout regarding the area occupied by the sea; Martín Algarra, 1987).

Within the Baetic Mountains, the area in question forms part of the external zones, right on the boundary between the Internal Pre-Baetic and the Internal Sub-Baetic.

The environment of the reservoir is located between the Geological Unit known as Frontal Internal Sub-Baetic and its Tertiary post-mantle materials. These materials are discordant in this area over the Geological Unit known as Internal Pre-Baetic.

The reservoir ravine is located on Mesozoic material corresponding to the Frontal Internal Sub-Baetic, whereas the reservoir basin area is located on Tertiary post-mantle material. The contact between both types of rock is due to the overthrusting belt, made up of the northern line of the advancing overthrusting event formed by the Frontal Internal Sub-Baetic on the materials of the Internal Pre-Baetic. For this overthrusting, originated with a horizontal anticline, the Internal Sub-Baetic unit would have run over the External Sub-Baetic (Jurassic to Tertiary). This overthrusting belt is located 30 m upstream from the dam.

General Geological Map of the Baetic Mountains
General Geological Map of the Baetic Mountains

The materials of the Internal Sub-Baetic Front that appear in the ravine make up the allochthonous unit that is formed by a sequence going from the Triassic period, in its Germanic facies, to the Lower Cretaceous one, made up of dolomitic limestones from the Muschelkalk (on which the dam foundations are directly built) and of loams with gypsum from the Keuper.

The overthrusting belt puts the Triassic material in contact with a detritic formation, made up of conglomerates and sandstones with calcareous cement that form the base of the post-mantle materials (Lower Tortonian age). These materials are visible 40 metres upstream from the ravine. On the right bank of the wadi there is a very characteristic outcrop.

Between the Muschelkalk and the Tortonian (substratum of the overthrusting) there is another Keuper layer in an inverse order to that of normal stratification.

Downstream from the dam, there is an olitostromic unit that was formed as a result of several stages in which movement took place toward the North of the Internal Sub-Baetic Front, and it became interstratified between layers dated as belonging to the Upper Tortonian age. Due to the tilting of the Neogene basin, there is no concordance of the olitostrome with the Miocene covering material. The olitostrome was formed during this movement and it was checked by the Miocene substratum related with the overthrusting belt of the Triassic on the Neogene.

Geology and Geotechniques of the Storage Area Upstream of the Dam.

The bottom of the reservoir and the areas near the bed are made up of alluvial deposits, recent or old. In the upper parts, there are post-mantle Miocene soils corresponding to the Tortonian age in the intermediate area (conglomerates and sandstones with calcareous cement in the area nearest to the ravine, and loams and loamy limestones in the most distant part), and to the Andaluciense age (yellowish-white loams) in the upper part, both from the Upper Miocene. Most of the reservoir basin is made up of loams and loamy limestones from the Upper Tortonian.

It is formed by impervious soils (except for an area of limestone) in its entire visible surface or concealed beneath the wadi sediments.

The hillsides formed by the Miocene materials do not seem prone to landslides, but they are easily eroded.

However, the left hillside of dolomitic limestones, in the area of the left abutment, did show some signs of instability when the dam was being built.

Geology and Geotechniques of the downstream boundary for the storage area.

The dam is built on the Muschelkalk limestones that form part of the overthrusting belt. These limestones lie on in a layer of approximately 10 m of Keuper that has been a plastic support over which the limestones have slidden on the Miocene sandstones.

Beneath this layer of Keuper are conglomerates with carbonated cement and rounded stones from the Upper Tortonian age (Miocene). These conglomerates are folded next to the overthrusting belt (to the north of the dam), there being here a stratification dipping 40-50º to the south, and passing sub-horizontally to the north, far from the overthrusting belt.

Both the left and the right dam abutments are formed by Muschelkalk limestones.

This area is highly tectonized, as a result of which some faults can be detected in the two abutments, at the same time as the limestone is much brecciated, being fractured into blocks whose spacing can be a few centimetres and whose discontinuities are occupied by yellowish clay-silts and fragments of dolomites whose opening can sometimes be centimetres.

The dip in the right abutment is the same as the one that the rocky massif follows (except for the abutment on the left riverbank), which in this area specifically has an E-W dip 25º to the south.

Seismology

Seismic hazard varies depending on the place and it has been a habitual practice to grade territories in accordance with that hazard. Taking into account the recommended guidelines contained in the Technical Guide on Dam Safety. Technical Guide on Dam Safety. Material Prospecting and Geological Studies (published by the Spanish National Committee on Large Dams, CNEGP), in Section 3.3., a classification is made in three groups:

a) Areas of low seismicity: ab < 0,04g

b) Areas of medium seismicity 0,04g < ab < 0,13g

c) Areas of high seismicity 0,13g < ab

ba: basic acceleration

In accordance with this classification, the Rambla del Moro Reservoir is located in an area that we could classify as being of medium seismicity, since the “basic acceleration” for the municipal district of Abarán is 0.1 g.

In accordance with the Technical Guide on Dam Safety. Material Prospecting and Geological Studies, and bearing in mind the land factor (using the seismo-resistant regulations NCSE-2002), the acceleration calculated for the design earthquake would be 0.13·g, and for the maximum considered earthquake it would be 0.21·g.

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