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Aquifer Recharge, Storage and Recovery
November 04, 2008
The rapid depletion of pristine aquifers during the twentieth century was a miscalculation for water managers in the arid lands of the Southwest. As a consequence, vital springs and streambeds dried up, land surfaces began to fissure and subside, pumping costs increased, water quality deteriorated, and emergency water reserves to endure conditions of persistent drought were compromised.
However, this miscalculation is now an opportunity for water managers of the twenty-first century, because depleted aquifers can now serve as safe, underground reservoirs for storing surface water. Managers can thus avoid the huge costs, insecurities and trade-offs associated with traditional dam construction.
Additionally, in the case of the Colorado River system of dams, which is overbuilt by a factor of two, aquifer storage can minimize water loss to evaporation in hot desert climes. Since the filling of Lake Mead in 1935 (73 years of operation) and the filling of Lake Powell (45 years) in 1963, a combined total of 84 million acre-feet (maf) has been lost to evaporation at these two reservoirs.
In the southwestern United States, the practice of refilling an underground aquifer with water for retrieval later is commonly called "Aquifer Storage and Recovery," or ASR. The concept of recharging an aquifer is quite simple and achieved by meeting four prerequisites: 1) locating a feasible aquifer of known character; 2) deciding which recharging method to use; 3) providing water of suitable quality; 4) building a conveyance system to deliver and recover that water.
The expertise to add reliable aquifer recharge programs to a managers water portfolio is world-wide, with over four decades of knowledge and experience to work upon. ASR programs also enjoy a growing public acceptance similar to the support for developing renewable energy alternatives, such as wind and solar. Millions of people are currently tapped into ASR programs across the country and its full potential is yet to be fully utilized.
The benefits of ASR programs include: reduced overall operation costs, increased water yields by minimizing evaporation losses, improved water quality, and reducing impacts from long-term drought. Incidentally, ASR programs will arrest subsidence and saltwater intrusion problems, and revive springs and river beds for human enjoyment and wildlife habitat.
Once ASR programs are fully operational, managers can effectively start to work on their long-term challenges from the previous 100 years of dam-building, such as the removal of sediment and removing dams that serve no function. In so doing, efficiencies can be maximized and critical habitat for endangered species enlarged and restored.
There are two ways to refill an aquifer: indirect and direct. Indirect recharging is accomplished by placing the water in confined basins, which allows the water to percolate down into the aquifer below and at rates that range from one foot to twelve feet per day. Direct recharging is done instananeoulsy with mechanical pumps that phyically inject water into the aquifer. Direct injection is usually required where layers underneath include fine clays, which slow or impede percolation rates.
Click here to view examples of aquifer recharge methods.
A good primer about ASR programs is available from this issue of Southwest Hydrology.
A groundwater glossary can be found here.
Discussion of Arizona Groundwater depletion and the Central Arizona Project: 2003 - Cadillac Desert Revisisted (Central Arizona Project). Holland et al.
Building more surface reservoirs is a direction for managers to move away from, because maintaining, repairing and eventual removal of the existing 79,000 dams in the United States, is already a considerable budget item. Not to mention the maintenance and repairs of ancillary projects such as power plants, substations, aqueducts, canals, levees, quagga mussel control, and habitat restoration.
Aging infrastructure issues are discussed in this issue of Southwest Hydrology.
An example of new and expensive dam construction is the reservoir created by the Metropolitan Water District (MWD) called Diamond Valley Lake, which was finished in 2002 at a price tag of $2 billion. The reservoir stores 800,000 acre-feet of Colorado River water via aqueduct and primarilly to ensure that there would be no interupption of water deliveries during an emergency situation. In comparison, MWD's ASR program at Hayfield can also store 800,000 acre-feet of Colorado River water underground via aqueduct for emergencies and for a price tag of $68 million.
The cost of repairing a dam is two to five times the cost of original construction. Funding mechanisms to pay for serious repairs or the removal of unsafe dams simply do not exist. Managers need to start focusing and organizing on this future financial burden right now. Should a major repair, removal, or even dam failure occur, ASR programs will provide managers with a strategy to deliver water during any interruption of traditional services.
This is truly a management alternative whose time has arrived if the leadership embraces the opportunity. The loss of water in surface reservoirs to evaporation and seepage, which is not recoverable, should no longer be considered as "the price of doing business." Getting more water for less money, and with less impact to the environment is reasonable course of action.
The annual yield of the Colorado River has dropped 2 million acre-feet (maf) in the last 100 years, and this trend is expected to continue since Rocky Mountain snowpacks are increasingly debilitated by evaporation from a warming atmosphere, caused by the human consumption of fossil fuels.
The water managers in the basin states are responding cooperatively, so far, by creating internal guidelines for managing potential shortages and preparing for the implications of lowering reservoir. For example, extending the length of pipeline intakes at Lake Powell for Navajo Generating Station, and at Lake Mead for water delivery to Las Vegas.
Obviously, lower cost/impact management schemes, such as ASR programs, should be implemented as soon as possible since the reservoirs will likely empty by 2026. If not by 2026, assuredly by 2036. Water quality will plummet when the reservoirs bottom out and major lawsuits will result.
Increasing the carrying capacity of existing aqueducts and canals may be one of the more pressing issues to overcome in creating a reliable ASR system in the Colorado River service area, but this is not an insurmountable obstacle. Once ASR systems are in place and fully operational, managers can then objectively deal with the other pressing issues that presently are overlooked, such as sediment removal from existing reservoirs to increase the storage capacity of exisitng surface reservoirs. This would also include dismantling Glen Canyon Dam, which represents unnecessary storage in the system that needlessly compromises water quality for downstream users, and the biological integrity of Grand Canyon National Park.
With these problems solved, the management will eliminate contentious litigation over noncompliance with the Law of the River, the Clean Water Act, and the Endangered Species Act.
The annual consumption of groundwater in the the Basin and Range province of Utah, Nevada, California and Arizona is currently about 6.3 million acre-feet per year. On average, only half this amount will naturally and incidentally be recharged back into the system. This practice of overdrafting groundwater supplies during the last century has created considerable storage capacity in the Basin and Range Province. In fact, the capacity exceeds the combined storage capacity of Lakes Mead and Powell, which is 52 million acre-feet (maf).
Estimated use of water in the United States. US Geological Survey. 2000.
From 1915 to 1980 Arizona withdrew 184 maf from their aquifers and 90 maf was naturally and incidentlly recharged back into the system. This means there is at least 94 maf of aquifer storage in Arizona alone. Unfortunately, some of this available space has been lost to the subsidence and the intrusion of poor quality water.
In 1980 the Arizona Ground Water Management Code was passed by the state legislature. The Code has three primary goals. The first is to control the severe overdraft currently occurring in many parts of the state. The second goal is to provide a means to allocate the state's limited ground water resources. The third goal is to augment Arizona's groundwater through artificial recharge programs. Arizona water managers have already recharged their aquifers with about 5 maf of water, so far.
The Arizona Department of Water Resources (ADWR) estimates there is a range of 15 - 20 million acre-feet of underground storage available right now in basins directly adjacent to the aqueduct of the Central Arizona Project. There is even more capacity available in basins within a reasonable distance to the aqueduct.
In 1985, the counties in California's Mojave Desert withdrew about 1.74 maf from their groundwater reserves and, unlike Arizona, not all service providers in California have uniform codes to protect their groundwater resources for further degradation. The Association of Groundwater Agencies of California (AGWA) estimates that over 21.5 maf of groundwater storage is available for recharge in the groundwater basins of southern California.
Coachella Valley near Palm Springs has overdrafted their groundwater supplies by 150,000 acre-feet each year. From 1973 to 2005, about 2 maf has been recharged into the Whitewater River sub-basin. The Coachella Valley is an ideal candidate for intensive aquifer recharge programs because of the San Andreas Fault system. This fault system acts as natural barriers to keep groundwater from migrating to other basins. Basically the Coachella Valley is compartmentalized into four distinct ground-water subbasins that have storage capacity in millions of acre-feet. Additionally, there are two Colorado River water delivery conduits that can deliver Colorado River water to the Coachchella Valley, the Colorado River Aqueduct and the Coachella Canal.
Another reason why California is ideal for ASR programs is their ability to pull water from other state water projects, such as the western and eastern slopes of the Sierra Nevada Mountains, and from the local mountains surrounding the Los Angeles basin. This vast network of aqueducts and canals in California gives great potential for transferring water between the various service districts for maximizing the potential of ASR programs.Other aquifers with ample capacity adjacent to the Colorado River Aqueduct in California's Mojave Desert include Cadiz (972,856 acre-feet), Upper Chuckwalla (500,210 acre-feet) and Hayfield (800,174 acre-feet).
Maps: List of California basins; Colorado River Basin;
The capacity for groundwater storage in the immediate Los Angeles metro area ranges from 3 to 7 million acre-feet.
MWD's assessment of ASR programs
Water Replenishment District of Southern California
Even though Las Vegas was once totally dependent on local groundwater resources, it is now entirely dependent on Colorado River surface water. The city has been seriously engaged in ASR programs for two decades now and have comfortably refilled their aquifers with surplus Colorado River water. The city uses electric pumps to recharge their aquifers in the winter time when demand is low and then recovers that water in the summer time when the demand is high.
Nevada has made legal agreements with Arizona and California to store surplus water in their aquifers. This program will serve as an exchange mechanism for Nevada to withdraw water from Lake Mead when needed. This mechanism is called water banking. Because Las Vegas has committed to continue their urban growth beyond their fixed entitlement to Colorado River water, they will exhaust this water banking account of 1.4 maf in the very near future.
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