In water year 2018, a below normal year, 15.45 MAF of river water entered the Sacramento-San Joaquin Delta; the State Water Project and Central Valley Project pumps exported 4.61 MAF of it, 30 percent, and 5.99 MAF flowed to San Francisco Bay above the outflow floor that Water Right Decision 1641 sets for the month and the kind of year. The Delta’s own farms and channels used 1.05 MAF, and net outflow to the Bay was 9.79 MAF, of which 3.82 MAF was the floor itself.
How does 2018 compare with the ten water years before it?
Over water years 2008 to 2017, exports averaged 4.21 MAF a year, 26 percent of inflow. In 2018 the share was 30 percent. On 353 days of the year a standing rule, permit term, or biological opinion held exports below pump capacity while surplus water existed; on 12 days outflow sat at or below the floor, so there was nothing to take without breaking the rule. The most common condition across the year was a rule or permit held exports.
Month by month
| Month | Inflow (MAF) | Exports (MAF) | In-Delta use (MAF) | Net outflow (MAF) | Floor (MAF) | Exports, percent of inflow | Most common condition |
|---|---|---|---|---|---|---|---|
| Oct 2017 | 1.05 | 0.37 | 0.10 | 0.57 | 0.25 | 35.3 | a rule or permit held exports |
| Nov 2017 | 1.03 | 0.45 | 0.04 | 0.54 | 0.27 | 43.8 | a rule or permit held exports |
| Dec 2017 | 1.06 | 0.52 | 0.12 | 0.42 | 0.28 | 48.9 | a rule or permit held exports |
| Jan 2018 | 1.31 | 0.40 | -0.13 | 1.04 | 0.28 | 30.5 | a rule or permit held exports |
| Feb 2018 | 0.91 | 0.23 | 0.04 | 0.64 | 0.39 | 25.0 | a rule or permit held exports |
| Mar 2018 | 2.01 | 0.40 | -0.12 | 1.73 | 0.44 | 19.8 | a rule or permit held exports |
| Apr 2018 | 2.73 | 0.24 | 0.00 | 2.49 | 0.42 | 8.7 | a rule or permit held exports |
| May 2018 | 1.09 | 0.17 | 0.13 | 0.78 | 0.44 | 16.0 | a rule or permit held exports |
| Jun 2018 | 0.88 | 0.23 | 0.22 | 0.44 | 0.24 | 25.7 | a rule or permit held exports |
| Jul 2018 | 1.03 | 0.36 | 0.26 | 0.41 | 0.40 | 34.7 | a rule or permit held exports |
| Aug 2018 | 1.22 | 0.63 | 0.23 | 0.35 | 0.25 | 52.0 | a rule or permit held exports |
| Sep 2018 | 1.13 | 0.61 | 0.15 | 0.36 | 0.18 | 54.2 | a rule or permit held exports |
MAF = million acre-feet.
What contractors were told to expect
| Contractor class | Final allocation, 2018 | Final allocation, 2017 |
|---|---|---|
| SWP Table A | 35 percent | 85 percent |
| CVP south-of-Delta agriculture | 50 percent | 100 percent |
| CVP south-of-Delta cities | 70 percent | 100 percent |
| CVP north-of-Delta agriculture | 100 percent | 100 percent |
| CVP north-of-Delta cities | 100 percent | 100 percent |
| Settlement Contractors | 100 percent | 100 percent |
| Exchange Contractors | 100 percent | 100 percent |
| Friant Class 1 | 88 percent | 100 percent |
| Friant Class 2 | 9 percent | 100 percent |
| South-of-Delta refuges | 100 percent | 100 percent |
Allocations are percentages of contract supply.
How 2018 measures against other supplies
The 4.61 MAF exported in 2018 is 1.0 times California's 4.4 million acre-foot basic apportionment of the Colorado River under the Boulder Canyon Project Act of 1928, the state's other large imported supply. The 5.99 MAF that left the Delta above the floor is 1.3 times the 4.55 million acre-foot capacity of Shasta Lake, the largest reservoir in the state; 69 percent of it passed in three months (Jan, Mar, Apr).
Frequently asked questions
How much water did the Delta pumps export in water year 2018?
4.61 MAF: 2.29 MAF at the Central Valley Project's Jones plant and 2.15 MAF at the State Water Project's Banks plant, which together serve cities and farms on both projects. That was 30 percent of the 15.45 MAF that entered the Delta in a below normal year.
How much Delta water flowed to the ocean in 2018?
Net Delta outflow was 9.79 MAF. Of that, 3.82 MAF was the minimum that Water Right Decision 1641 requires to keep salt water out of the Delta and its intakes, and 5.99 MAF was above that floor, 61 percent of the outflow.
What did project contractors receive in 2018?
The State Water Project's final Table A allocation was 35 percent of contract supply. Central Valley Project south-of-Delta agricultural contractors were told 50 percent and south-of-Delta cities 70 percent. An allocation is an announcement of the share of contract supply to expect, not a delivered volume.
Explore the year on the toolkit: Delta diversions by month, the constraint calendar, allocation history.