OHL Presa del Val

Overview of the Tarazona Water Management Project

Introduction to Tarazona and Its Geography

• The city of Tarazona is located in a rich region of Zaragoza, near Soria, Rioja, and Navarra, characterized by the iconic silhouette of Moncayo Mountain.

• The area features a natural valley where the Queiles River flows into the Vall River, with local settlements like Los Fallos situated along its banks.

Water Supply Challenges

• A dense network of irrigation ditches exists in the valley; however, water supply is only reliable upstream during rainy seasons.

• Initial requests for regulating both rivers' flow date back to 1934 due to inconsistent water availability.

Key Infrastructure Developments

• The project includes three main components: a diversion weir on the Queiles River, a water transfer tunnel to Vall River Valley, and a reservoir dam utilizing existing natural formations.

• The diversion weir is made from conventional concrete measuring 70 meters long and 13 meters high, equipped with two counterweighted gates.

Construction Details

• Construction began simultaneously at both ends of the transfer tunnel; excavation was completed six months later using drilling and blasting techniques.

• The tunnel measures 720 meters in length with a consistent slope of 0.62%, leading into a trapezoidal channel that extends another 110 meters before discharging into the reservoir.

Auxiliary Facilities and Environmental Considerations

• An auxiliary platform covering eight hectares was created for construction materials storage while ensuring minimal environmental disruption.

• A clay core dam was built to manage up to 100 cubic meters per second flow through a mini concrete block structure.

Reservoir Capacity and Material Sourcing

• The dam's excavation involved moving approximately 597,000 cubic meters of earth entirely through mechanical means for safety reasons.

• Concrete production utilized limestone sourced from a nearby quarry; an aggregate processing plant produced significant quantities needed for construction over two years.

Environmental Impact Mitigation Strategies

• Environmental concerns were addressed by implementing dust control measures such as specialized separators and covered transport systems.

• Post-extraction restoration efforts included replanting native tree species after quarry operations concluded.

Concrete Composition and Transportation Logistics

• The concrete mix consisted primarily of fly ash (65%) combined with cement (35%), while different ratios were used for various applications within the project.

Construction Process of the Dam

Concrete Placement and Compaction Techniques

• The extended placement of compacted concrete was executed using tractors, applying layers of 30 cm thickness leveled by a laser-equipped machine. Vibrating rollers weighing 10 tons were used for compaction.

• Vibrated concrete was also laid in 30 cm layers immediately after the compacted concrete layer was finished, ensuring a perfect bond between both types.

Formwork Systems Used

• Vertical formwork for the upstream face utilized traditional climbing systems with metallic forms measuring 2.45 meters high and 5 meters long, equipped with climbing consoles and safety railings.

• For the stepped downstream formwork, similar metallic forms were employed, anchored to transmit forces to the lower step being concreted.

Construction Workflow and Surface Treatment

• Continuous pouring occurred in blocks of 60 meters length until reaching a height of 2.40 meters; ramps up to 1.20 meters were formed between blocks for machinery access.

• After completing each block's last layer, surface cleaning was performed with high-pressure water several hours post-compaction to avoid dislodging surface aggregates.

Quality Control Measures

• A nuclear density gauge checked the achieved density on-site while laboratory tests monitored material quality, fresh concrete consistency, and hardened strength and impermeability.

Overall Project Timeline and Specifications

• The entire construction process spanned over 24 months, involving a total volume of 740,000 cubic meters of concrete for a dam standing at 90 meters tall on its foundation.

Dam Design Features

Spillway and Structural Elements

• The dam features a fixed lip spillway measuring 20 meters wide with a central pier acting as a weir at an elevation of 620 meters above sea level.

• A stepped design mirrors the downstream slope profile; it includes two three-meter-high side channels leading into a buffer basin that connects to river channels upstream from potential failures.

Drainage System Implementation

• A drainage screen constructed through drilling penetrates at least five meters into rock from the crown downwards to manage seepage effectively.

Gallery Access Points

• Inside the dam are three galleries:

• The upper gallery facilitates inspection.

• The middle gallery provides access to bottom outlet gates.

• The perimeter gallery connects back to other sections at higher elevations.

Monitoring Systems Established

Instrumentation for Performance Assessment

• A comprehensive monitoring system was established focusing on thermal control via thermoresistances embedded in concrete along with extensive use of vibrating wire gauges for deformation measurements.

Overview of the Ebro River Basin Management

Control and Monitoring Systems

• The topographic control is conducted from bases located on the slopes of the dam, ensuring they are sufficiently distanced from its area of influence. Data collected is transmitted via three data acquisition stations to a computer in the control building.

• Continuous monitoring informs about the safety and stability of both the installations and the dam as a whole. This is crucial for maintaining operational integrity.

Impact of the Val Dam Construction

• The construction of the Val Dam, part of Aragón's water pact, represents Spain's largest roller-compacted concrete dam. It aims to secure water supply for approximately 52,000 residents in nearby towns.

• The project will enhance irrigation capabilities over 12,885 hectares across various municipalities in Zaragoza and Navarra while mitigating flood risks along the Queiles River.

Environmental and Community Benefits

• The reservoir created by this infrastructure not only serves agricultural needs but also promotes recreational and tourism opportunities within its surroundings.