Madrid Water Reservoirs: The Embalse de Valmayor and El Atazar

Category: Madrid

Like most major metropolitan areas, Madrid, the capital and largest city in Spain, has a number of dams and reservoirs designed to harness the flow of various rivers that flow in and around the region. These structures help to stockpile water for various purposes throughout the city, including hydrology-based energy and drinking water. In the following article we will take a closer look at two of these reservoirs, the Embalse de Valmayor and El Atazar, and provide some background information on each.

Embalse de Valmayor

In the mid 1970s, the growing water needs of the province of Madrid led to various studies designed to harness the flow of the Guadarrama River through the construction of a large reservoir on its track. Ultimately the decision was made to build the reservoir on the Aulencia River instead, a tributary of the Guadarrama, largely due to the favorable geographical conditions of its valley and the virtual absence of any population in this area. The dam was completed and inaugurated with a grand opening in 1976.

The Embalse de Valmayor, or Valmayor Reservoir, is situated to the northwest of Madrid in the municipality of Valdemorillo. It is managed by the Canal de Isabel II, and belongs to the basin of the Guadarrama River. The reservoir, which runs along a length of eight miles upstream of the Aulencia, occupies an area of 755 hectares and also serves the towns of El Escorial and Colmenarejo. In terms of the amount of water stored, the Embalse de Valmayor is the second largest reservoir in the province of Madrid, with a capacity of 124.4 million cubic meters. The largest, which we will describe in more detail in the next section, is the Atazar Reservoir, located in the basin of the Lozoya River and boasting a whopping capacity of 425.3 million cubic meters.

Despite being built on the Aulencia River, Embalse de Valmayor receives its largest contribution of water from the Guadarrama, located several kilometers away and possessing a much higher rate of the flow of than the Aulencia. Water from the Guadarrama reaches the reservoir through a transfer tunnel, about five miles long, which has a small reservoir sensor called Las Nieves, located near La Navata, a residential area near the city of Galapagar.

Embalse del Atazar

El Atazar Dam is an arch dam situated very near Madrid on the Lozoya River, exceedingly close to where the river joins the Jarama River. It is the oldest dome-style dam in the world and is responsible for creating the largest reservoir in the Madrid area. Given the narrow canyon in which it is built, the arched design of El Atazar makes it optimal for retaining water in the reservoir. Arch dams are thin and require less material to construct than any other types of dams.

Construction on El Atazar commenced in 1968 and continued for four years until it was finally completed in 1972. Prior to building the dam, officials of the Community of Madrid made the decision to use the dam solely for the purposes of storing and regulating water and not for providing energy, a role played by several other dams in the region.

El Atazar’s design features a double curvature, concrete arch buttress. At its apex, it has a height of 440 feet (134 meters) and a width of roughly 172 feet (52 meters) at the foundation. As mentioned above, the reservoir formed by the dam has a total capacity of 425.3 cubic meters, or 344,000 acre feet.

Over its short history, El Atazar has played a vital role in the storing and regulating of water for the Community of Madrid, but there have been some problems and issues with the dam that are certainly worthy of note. In the mid-seventies, monitoring of the dam revealed irregular movement. While most dams tend to move slightly, the left side of El Atazar was found to be moving more than the right, largely due to a support built on the dam’s right side that made the sides less flexible. A small crack was noticed in the dam in 1977—a crack that by 1979 had grown to 150 feet (46 meters) and had to be repaired. The year 1983 saw other problems with the dam. Years of abnormal movement and settling into the foundation had caused fracturing in the rock, resulting in a significant increase in the foundation’s permeability. The crack has since been treated and since then the problems have fortunately abated completely.