With thousands around the globe, dams play an integral part in providing the world with irrigation, hydropower, flood control and water supply.
In tackling water scarcity challenges, the role of dams and the reservoirs they create is intertwined with the broader portfolio of solutions for watershed planning and water management.
Water supply dams create storage for runoff, rain and snow melt and can provide carryover from the wet seasons to the dry even multi-year carryover of supplies to help withstand drought. They can provide flexibility to respond to changing conditions, maximize long-term storage, extend the life of existing water resources and provide emergency backup.
“Given the right circumstances, the role of dams is one that’s very much an integral part of the solution for reliable and sustainable water supply management,” said Faruk Oksuz, Dams Business Line Leader for Black & Veatch’s global water business. “The reservoirs created by dams are an important insurance policy for the quality of life that we have come to expect.”
The construction of new dams on main waterways – main stem dams – is often the most complex to implement because of the wide footprint of impacts that frequently result. “Dam and reservoir schemes can provide a positive impact that can last generations, but they must be thoroughly studied to avoid unintended consequences,” said David Egger, Heavy Civil Business Director for Black & Veatch’s global water business.
In the Sultanate of Oman, the Wadi Dayqah Water Supply Project includes a new, large dam that was completed in 2009. The project features a 75-meter-high main dam to help use and collect valley flows that would otherwise be lost to the sea. In total, the dam delivers 35 million cubic meters of water per year to an extremely arid climate with few permanent surface water supply resources. This helps maintain vital sources of water for drinking, agriculture, livestock, and overall social and economic sustainability.
Throughout the Middle East, Asia, Australia and the U.S., dams have been a key piece of the water resource puzzle. In Australia, surface water from Water Corporation dams contributes 25 to 40 percent of the water for the Integrated Water Supply System. The U.S. Bureau of Reclamation estimates there are approximately 80,000 dams of varying sizes in the United States, where trends surrounding the industry are changing. Globally, the construction of dams has declined since the height of the era in the 1960s and 1970s.
“Many municipalities and government agencies, particularly in water-scarce areas or growing areas, are re-examining all of their existing storage facilities and infrastructure,” Egger said. “They are primarily looking at optimizing the conveyance infrastructure to the storage facility, and they’re looking at optimizing the storage facility itself. There are new ‘greenfield’ dams under construction out there, but optimization is one trend were seeing in the industry.”
California Water Supply
Through optimization, agencies are looking to make their existing facility more efficient. Raising the height of a dam, thereby providing more water storage in the reservoir, is part of the optimization strategy for some. Dam safety – for example, making the structure more seismically robust – is another significant feature of optimization. Also as part of the retrofit, agencies often evaluate the structures for hydropower capability, making these facilities a sustainable power producer, as well as a source of water.
Take the San Vicente Dam Raise Project in San Diego County, California. By adding 117 feet to the existing 220-foot-tall structure, the San Diego County Water Authority (SDCWA) will gain additional flexibility in emergency water storage. The $530 million project will more than double the current capacity of the reservoir.
Since up to 80 percent of the regions water is imported from northern California, a crisis, such as a major earthquake or extended drought, would mean severe water availability problems for San Diego County. By boosting the capacity of the reservoir through this key cog in the Emergency Storage Project, the SDCWA will be in a better position to ensure water availability in support of the regions 3 million residents and $150 billion economy.
Another California dam optimization project is the Calaveras Dam Replacement Project for the San Francisco Public Utilities Commission. In recent years, the Calaveras Reservoir, a critical element in the local storage and water supply for the city and county, has been drawn down to about 40 percent of normal storage due to seismic concerns at the dam. The planned 210-foot-high zoned earth and rockfill dam will better withstand an earthquake and restore full use of the reservoir for water supply and storage.
Constructing new dams on main waterways can be a long cycle, Egger said, and that leads to an additional industry trend – “off stem,” or off-stream, storage. Through this type of scheme, communities seek additional supply and storage located in smaller watersheds that aren’t directly on the main waterway.
“With off-stem storage, the idea is to attempt to locate a more environmentally and socially benign side valley or feature such as a re-engineered quarry that feeds the main waterway,” Egger said. “It’s generally a smaller watershed with fewer environmental impacts.”
The Eastside Reservoir, also known as Diamond Valley Lake, southeast of Los Angeles, is a massive off-stream reservoir created from three dams in Riverside County. It was built to meet seasonal, drought and emergency needs. With a capacity of approximately 260 billion gallons, the reservoir, when full, would be capable of supplying most of Southern California with six months worth of water in an emergency. The facility is one of the largest man-made lakes built in the United States in recent years, according to Oksuz.
That’s a lot of storage at the Eastside Reservoir, and the world will need more similar storage schemes as water scarcity challenges continue to evolve, Egger said. Other large storage plans are being developed around the globe, including U.S. projects in northern and central California, Colorado, Georgia and Florida, among others, Oksuz noted.
“Climate change is like many other changes – slow but continuous,” Egger said. Some areas will see more precipitation, and others will see less. As we understand that better, certainly those areas of the world where theres less precipitation will likely need to change water-use patterns and add more storage.
“There are other buttons you can push – you can conserve water and take other measures, but ultimately, if the population in the area continues to grow, you’re going to need more storage to address and balance the need.”