The story of the Central Arizona Project (CAP) is lengthy and has been told far better than I could provide here, but my goal is not to tell sordid tales of legislative and financial dealings that led to the project's authorization, funding, construction and eventual delivery of central and southern Arizona from a dry death. There is plenty of criticism of the project's enabling legislation in the Colorado River Basin Project Act, the original benefit-cost analysis, how much the water it carries would need to be priced in order to pay off the original funding on the original terms, how heavily the price of that water is subsidized and who benefits most from the discount; I have not done those calculations. There is plenty of rumor about who knew about the project and directed construction contracts to friends, about family fortunes made from land acquisition on the path of the aqueduct before the government set about acquiring the project easement at inflated values for previously worthless desert tracts; I have not researched those claims. There are (finally) a few emerging studies on how much energy it takes to move the water through the CAP aqueduct, how much water is consumed in the process of generating that energy, how much more water is lost to evaporation from an open-channel in the arid Arizona environment, and how much of the water carried by the aqueduct is used for "beneficial" purposes to support the state's continued right to take its full Compact share of the Colorado River every year.
So I figure that I don't need to cover all of that here for you. There are plenty of resources for your reading pleasure if you're interested in CAP history: books (A River No More, Rivers of Empire, Cadillac Desert, Arizona Water Policy), articles in numerous science/engineering/law journals (search Google Scholar for examples), official websites (The Central Arizona Project and the Arizona Department of Water Resources), and an exceptionally instructive legal review on the origination and operation of CAP. I especially recommend that last link, developed by a graduate student at the University of Arizona College of Law for a course in Advanced Legal Research--those resources will keep you busy for a very long time. Unfortunately the author is no longer available at the e-mail address provided, else we might already be working together to bring that resource up-to-date. Ms. Streatfeild, if you're out there, drop me an e-mail!
|from the Arizona Water Map, UA WRRC|
And yet, more groundwater is used in Arizona than all of Arizona's allocation of surface waters under the Colorado River Compact. For one thing, Arizona has only limited surface waters of its own in tributaries to the Colorado, on which basis a reduction in the state's water allocation from the Colorado River was actually reduced in the negotiations of the Compact way back in the early 1920s. From that graphic we can calculate that Arizona uses ~3.00M acre-feet of groundwater per year, that surface waters such as the Little Colorado River (on the northeastern Arizona Plateau) and the Salt and Verde Rivers (upstream of Phoenix) provide an aggregate total of only ~820K acre-feet, which varies significantly from year-to-year, and that effluent (wastewater) recycling used principally in agricultural applications provides another ~205K acre-feet, for a total state usage of ~6.83M acre-feet of water per year. The total water use varies year-to-year with weather and climate fluctuations, of course, with a quoted value generally near 7M acre-feet per year across the entire state of Arizona.
We might say that Phoenix is at the center of the system, in more ways than just the politics of the state: the Salt River passes through the city after its confluence with the Verde River, and the CAP aqueduct enters the city from the northwest and there turns south toward Tucson. A conceptual system map is offered on the CAP website:
It is in Phoenix and its suburbs that much of the CAP purpose and management are oriented, though that is not to suggest that CAP is not also vitally important to Tucson as well. CAP is legally managed by the Central Arizona Water Conservation District (CAWCD) with a focus on conservation and allocation activities in the Phoenix metropolitan area. There the CAP infrastructure and management also crosses paths with the older Salt River Project, under which the Roosevelt Dam upstream of Phoenix on the Salt and Verde River was commissioned just over 100 years ago. Technically, CAP waters do not commingle with natural surface waters except at the point of origin, Lake Havasu on the Colorado River, before distribution to customers at various locations along the aqueduct between Phoenix and the present system terminus in Tucson. So, then, why doesn't all of the CAP-conveyed water reach these customers?
There are clues in the system map above, those little blue dots that indicate CAP-managed "recharge projects." In 1993, the Arizona Legislature created the Central Arizona Groundwater Replenishment District (CAGRD) with the purpose of restoring groundwater levels by managed recharge (pumping and infiltration) projects within the CAP service area. An excellent overview of the CAGRD and its purposes and methods is given in a paper released in 2006 through the state Water Resources Research Center (WRRC) and the Water Sustainability Program (WSP) at UA. Overall, the mechanics of the state's various aquifer storage and recovery (ASR) project efforts (including but not limited to the CAGRD) are explained well in an infographic from the Arizona Republic on the subject:
The realities and politics of ASR are, however, far more complicated. As reporter (and blogger) Shaun McKinnon noted in a 2 August 2009 article on the CAGRD:
"The Central Arizona Groundwater Replenishment District was meant to help a few outlying communities and subdivisions meet the 100-year water-supply rule until infrastructure, such as pipelines or smaller canals, reached far enough to deliver renewable supplies to them.
"Homes in the district use local groundwater as they would have before the 1980 laws were adopted. The homeowners pay monthly water-use charges to a water utility. Then once a year, the homeowners also pay a replenishment fee to the district, which buys surface water equal to the groundwater used. That water goes into recharge basins."It is, essentially, a swap that allows sub- and ex-urban groundwater use to proceed unabated, wherever that may occur, in exchange for groundwater recharge by surface infiltration at designated sites scattered along the CAP aqueduct in some very strange and far-flung places. By these methods, the CAWCD short-changes itself. First, many of the suburban wells are small enough to remain exempt from registration with the Arizona Department of Water Resources (ADWR), so their actual pumping volumes can only be estimated (presumably) up to the limit for exemption: 50,400 gallons per day per pump, as discussed in part 2 of this series. The volume of water, while still in the aquifer, is protected from evaporation and may be so deep as to be considered fossil water, that carried through the ages from long-ago infiltration and slow percolation and collection in the deep sandstones and gravels of the Basin and Range Province. Once the water is pumped out, open pore spaces in the rock allow aquifer compaction because of the weight of materials above, ultimately leading to surface subsidence that has been recorded and measured in many areas where groundwater mining is a common practice. To pump water right back into the same aquifer, albeit with reduced capacity after vertical compaction, would be fruitless. So the water is reintroduced to the subsurface elsewhere.
However, the problems are that the recharge method is not as rapid or efficient in delivering the same volume of water to the subsurface as was extracted, and that the mined aquifer body is not the same reservoir that is "recharged." Water poured into a surface infiltration basin (as shown above in the infographic) is akin to flood irrigation in agricultural fields, a practice now intensively discouraged in arid and semi-arid regions for the massive loss of applied water to simple evaporation, not to mention the inefficiency in getting water to deeper plant roots. To expect infiltration and then deep percolation from the surface all the way to a water table, in an already arid environment, is tantamount to an expectation of little-to-no effective aquifer recharge. If anything, the time that process takes would be more than long enough for aquifer compaction to have occurred since extraction, providing a false sense of aquifer refilling after the original withdrawal. The alternative, direct pumping of water to the subsurface, is an option that has been explored and is in operation in many places, especially for the recycling of treated wastewater. This process is limited only by the rate at which the aquifer material (sandstone, gravel, etc.) can convey the introduced water (under pressure from the pumps at the surface) away from the injection well.
But, again, it's not necessarily the same aquifer receiving recharge water as that being pumped dry in the suburban zone. The distance between the two is much too far to anticipate that the recharge will feed back to the mined aquifer in anyone's lifetime, based on how slowly groundwater moves in even the most porous of geologic formations, which may be measured in meters per year in fast-flowing groundwater plumes. The issues of time and space scales for groundwater movement are not properly accounted in the design of ASR programs such as these. There is, however, another oddly named CAWCD program that does recognize the value of groundwater where it already lies. In the early 1990s, CAWCD began to develop Groundwater Savings Facilities (GSF), often operated by irrigation districts as the largest users of groundwater, to encourage the use of CAP water instead of continued and unsustainable mining of groundwater supplies. This was viewed as an "in-lieu" or "indirect" means of recharge, if by "recharge" we mean that those pumping groundwater simply stop. That, however, was a time at which CAP deliveries were not fully allocated, and CAP was itself operating at full capacity for preservation of Arizona's allocation right from the Colorado River. By 1999, the CAWCD Recharge Program had helped replace more than 600K acre-feet of cumulative groundwater extraction with available surface supplies, which count as water volume credits toward CAWCD allocations should they be needed at some time in the future to supplement low availability of CAP water. In these cases, it must be recognized that groundwater pumping is not nearly the same as surface water in terms of rights. Groundwater may be pumped at a rate limited by the aquifer availability and the capacity of the pump, and corresponding fees (for non-exempt wells) are paid to the ADWR on the basis of reported pumping volumes. However, the groundwater user need not pump at a capacity rate if the need is not as large as the aquifer and pump can deliver.
For surface water, it's much different. Under the doctrine of prior appropriation and the Colorado River Compact, the rule for interannual preservation of a water right simplifies to the colloquial "use it or lose it." If you hold a proven claim to 10 acre-feet of water, you must take that much water from the river every year unless told otherwise by a higher authority because of a shortage condition. If no shortage is declared, but one season it rains a little more and you only take 9 acre-feet of water from the river to meet your irrigation needs that year, a junior rights-holder can challenge your claim to 10 acre-feet because you didn't use it all. After a couple years in a water court (which are established throughout the US West) during which your requirements somehow remain less than your original claim, your water right may be reduced by a judge to 9 acre-feet per year. The next year, you can only take 9 acre-feet of water from the river, even if your requirements increase because it rains less or the weather is warmer. What to do? Buy that acre-foot of water you need from someone else on the same river, usually a more senior rights-holder who can just about name their price (despite their likely small or even zero payment for the right in the first place), since no formal water market exists... So, if Arizona does not take it's full Colorado River allocation every year, it could very well lose the portion not taken forever, not just for the year that less is used. This simple but paradoxical rule has motivated Arizona to find places to put extra water in years that the allocation is greater than the need, as during wet years. It has turned out that one of the best places to bank extra water is in the ground. So, instead of pumping it downward under high pressure, the GSF is one way that the state can get farmers to turn off their groundwater pumps and use the extra surface water that was found to be available instead. The groundwater is conserved for later, when there isn't so much extra surface water to meet customer obligations.
To be continued...