By Nicole Osorio
Most people in California receive some of their drinking water supply from the State Water Project (SWP). The SWP also supplies water to over 10% of California’s irrigated agriculture. The SWP and its service area span much of California, delivering water to 29 wholesale contractors shown in Figure 1.
Each year, the Department of Water Resources announces SWP Table A allocations which inform water contractors’ SWP deliveries: “Table A”, “Carryover”, and “Article 21.” What are these different SWP delivery categories and how do they work?
Table A, Carryover, and Article 21 are three types of SWP deliveries described in this post. Some additional, more minor, deliveries are made as: transfer and exchange Table A, and Pool Water deliveries.
The 2020 water year is dry, but the recent May storms led to the increased 2020 SWP Allocation from 15% to 20% of SWP contractors requested “Table A” delivery amounts. Figure 2 compares the initial and final SWP allocations from 1996-2020. Some lessons from this graph include:
- 2006 was the last 100% allocation year, 14 years ago.
- Final allocations usually increase significantly from the initial allocation estimate sent to SWP contractors (usually in October). However, final allocations (usually in May) could be less than initial allocation estimates in extreme dry years.
- Drought years tend to have little or no increases from initial to final SWP allocations (such as 2007-2009 and 2012-2015).
- It is likely that 2020’s final allocation will be 20%. The last 20% final allocation year was in 2015, one of the driest years on record.
Figure 3 shows Table A, Carryover, and Article 21 deliveries from 2000-2017. Minimum, average, and Maximum Table A and carryover statistics were combined because both are categorized under Table A water while Article 21 deliveries are made above the approved Table A amounts. 2014 had the least Table A and carryover deliveries at 475 TAF while 2003 contained the most at 3202 TAF.
What is Table A?
Table A allocations represent “a portion or all of the annual Table A amount requested by SWP water contractors and approved for delivery by DWR (CA DWR 2019).” DWR and the public water agencies and local water districts developed the SWP’s long-term water supply contracts in the 1960s. Table A contract amounts originated from these long-term contracts and have been amended. The 1994 Monterey Agreements significantly revised the long-term water supply contracts. Table 1 presents each contractor’s maximum Table A contract delivery amount, adding up to 4.17 million AF, anticipated to be the SWP’s ultimate delivery capability in the 1960s (an amount rarely actually available). As a wet year example, the last column indicates how much each water contractor utilized their Max Table A amount in 2006, a 100% allocation year. San Joaquin contractors were more likely to take their full Table A and supplement water supplies with Article 21 water, described later.
What is Carryover water?
Carryover water is a portion of Table A water that contractors may save for next year’s delivery. Carryover requests allow SWP contractors to store some of their annual allocation for the next year, and not lose undelivered allocation at the end of the SWP contract year, December 31. When contractors request carryover for next year’s delivery, that water is stored in the SWP’s share of San Luis reservoir in Merced County.
However, storing carryover water in San Luis reservoir has a low operating priority and so brings a risk. SWP contractors can lose this stored carryover water when San Luis Reservoir fills. In the 2017 wet year, some contractors (Santa Barbara County , Crestline Lake Arrowhead Water Agency and San Gorgonio Pass Water Agency) needed to transfer their carryover water from San Luis to another non-SWP facility to prevent losing their carryover storage. Figure 4 shows how San Luis filled in 2017 for the first time since 2011, following the 2012-2016 drought.
Overall, San Luis carryover water provides water contractors with a safety net in dry years, like 2020. During the 2012-2016 drought, contractors almost exclusively relied on only Table A and carryover. 2014 was the only year when carryover deliveries (383 TAF) exceeded those of Table A (92 TAF) (Figure 3). Carryover storage acts as a “savings bank account” which water agencies can draw on in dry conditions, but at some risk in very wet years.
What is Article 21 water?
Article 21 (described in water contracts) allows water contractors to take deliveries above approved and scheduled Table A amounts (CA DWR 2019). Article 21 is sometimes called interruptible, unscheduled, or surplus water. It is offered predominantly in wet years (2005, 2006, 2011, and 2017) (Figure 5).
As an ephemeral surplus supply, contractors cannot “request” and schedule Article 21 deliveries in advance. DWR can only offer Article 21 deliveries when (CA DWR 2018, 2019; CA WATER COMMISSION: Article 21 water, explained):
- Article 21 deliveries do not interfere with SWP allocations.
- Excess water is available in the Delta.
- Conveyance is not being used for SWP purposes or scheduled SWP deliveries.
- Article 21 water may not become Carryover water, stored in SWP facilities.
The different types of SWP deliveries are akin to managing household finances. Table A deliveries are like a monthly paycheck for fixed recurring expenses. Carryover requests let you save part of your “Table A paycheck” for the future. Lastly, Article 21 deliveries are like an unusual annual bonus. You could splurge your “Article 21 water” bonus for direct retail delivery, or save it in an aquifer or reservoir outside the SWP.
In California’s highly variable climate, each water contractor must match these SWP water supplies, other local and regional water resources, and water demands for this year’s water use and in preparing for future droughts. In this dry 2020 year, SWP contractors are likely aware that the next drought could be just around the corner.
Nicole Osorio is a first year Master’s student of Water Resources Civil Engineering at the University of California, Davis.
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