The Colorado River, as many Southwesterners know, quenches the thirst of millions of people in several states. Many also are aware that the river is over-allocated, with more water designated to each of the Southwest states and Mexico than is the long-term average flow of the river. What’s more, streamflow over the past decade (2001-2010) has been substantially lower than the 20th-century average, and the latest projections show this trend continuing into the mid- to late-21st century (Southwest Climate Assessment Summary for Decision Makers and the 2013 draft of the National Climate Assessment).
These issues pose serious problems for water resource managers. With demand increasing (population in the Southwest is projected to grow to 94 million people by 2050, up from 56 million in 2010), and supply projected to decrease—from drought, warmer temperatures, decreased snowpack, and earlier snowmelt—water managers will need to be innovative to avoid serious consequences.
A recent study by the Bureau of Reclamation may be able to help. The authors of the report, entitled Colorado River Basin Water Supply and Demand Study, solicited study participants, interested stakeholders, and the general public for approaches to resolve imbalances between water supply and demand. They received over 150 proposals, which they categorized according to how they addressed imbalances: through increasing supply, decreasing demand, modifying operations, or changing governance/facilitating implementation. The options representative of the first three categories were then assessed for cost, potential yield, and years before available, as well as a host of other criteria including technical feasibility, energy needs, and long-term viability (see figure 1 for an example). The fourth category, implementation, was not evaluated because doing so would require significant legal and policy considerations.
Figure 1. A portion of the table from Colorado River Basin Water Supply and Demand Study, showing representative options to increase water supply, their estimated cost, years before available, and potential yield.
Some options for increasing supply are: desalination of both seawater and groundwater (in Southern California and near Yuma, Arizona), reuse, local-scale rainwater harvesting or treatment of coal bed methane-produced water, watershed management through such actions as dust control or forest management, and water importation. Of these, the options that would take the least time to implement (10 years or less) are desalination of groundwater (also one of the cheapest supply alternatives), reuse of wastewater, and expanding local supplies. Options with the highest potential yield by 2060 are desalination in the Gulf of California, reuse of municipal wastewater, and weather modification. These options, however, could take 30 to 45 years to become operational.
Far fewer options were proposed for reducing demand and modifying operations. Suggestions for reducing demand included water conservation (municipal, industrial, and agricultural) and improved water-use efficiency in the energy sector. Neither would take very long to implement (about 10-20 years), and water conservation has a very high potential yield and is considered relatively inexpensive to implement. Proposals for modifying operations included changing system operations—such as covering canals and reservoirs to control evaporation, modifying reservoir operations, and constructing new storage—and implementing water transfers, exchanges, and banking in the upper basin. These options also wouldn’t take very long to implement (about 15 years), but vary in their potential yield and cost. For example, controlling evaporation by installing physical canal and reservoir covers would be expensive and wouldn’t save very much water, whereas controlling evaporation using chemical covers and water transfers and exchanges would be less expensive and have very high potential yields.
After considering all of the options, the authors calculated an overall potential yield of 5.7 million acre-feet per year (mafy) by 2035 and more than 11 mafy by 2060 if all of the options were implemented. Some of them, however, have significant technical feasibility challenges or wouldn’t be very reliable in the long-term (such as importing water to southern California via submarine pipelines or icebergs, or controlling dust). Eliminating the infeasible options produced a potential yield of about 3.7 mafy by 2035 and about 7 mafy by 2060.
Hoover Dam at Lake Mead along the Colorado River, showing the notorious “bathtub ring” of low reservoir levels.
How significant are these figures? Is 3.7 mafy enough? Would it “solve” our water problem? Yes, according to the authors. They projected both Colorado River supply and demand through 2060 and found that, based on the middle-of-the-road projections, demand will exceed supply by about 3.2 mafy (not taking into account reservoir storage). So if the feasible options described above were implemented, we could potentially avoid a water crisis.
Some of these options, however, may not be worth the effort. For example, the reuse of grey water would cost an estimated $4,200 per acre-foot of water and would only yield 178,000 acre-feet per year. In contrast, agricultural water conservation would yield 1 mafy and only cost $150-$750 per acre-foot. Obviously water conservation is a much more viable option for saving water than grey water reuse.
Water managers weigh costs versus benefits when making decisions about whether or not to move forward with an idea, and if some of these options aren’t worth the effort they won’t move ahead with them. This means that the 3.7 mafy of potential yield the authors calculated could potentially be a lot less. What’s more, this number doesn’t take into account issues such as legal considerations, who will bear the cost of implementing these options, and societal acceptance. Existing policy on many different scales (federal, state, or local) may put a wrench in implementing some of these options. Maybe even a bigger wrench is finding someone to pay for these large costs. For example, will the energy industry be willing to bear the cost of implementing more water efficient equipment in their power plants? Will cities and states be willing to pay for canal and reservoir covers? And maybe cities will be willing to pay for wastewater reuse, but will citizens be willing to use the treated water, or say “no way”? All of these questions, and many more, will play a role in which options are implemented and which are not.
Don’t get me wrong, this report was a huge step in the right direction for “solving” our looming water crisis here in the Southwest. And a lot of the options suggested in the report are worth implementing. But we need to keep brainstorming and coming up with even more ideas on how to increase supply or decrease demand, and we need to start trying to implement some of the options outlined in this report, because as we Southwesterners know, some areas are already experiencing water shortages, and it’s only a matter of time before more and more regions are facing the same problems.