In water year 1998, a wet year, 48.01 MAF of river water entered the Sacramento-San Joaquin Delta; the State Water Project and Central Valley Project pumps exported 4.81 MAF of it, 10 percent, and 38.89 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 0.24 MAF, and net outflow to the Bay was 42.96 MAF, of which 4.10 MAF was the floor itself.
How does 1998 compare with the ten water years before it?
Over water years 1988 to 1997, exports averaged 5.21 MAF a year, 15 percent of inflow. In 1998 the share was 10 percent. On 346 days of the year a standing rule, permit term, or biological opinion held exports below pump capacity while surplus water existed; on 19 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 1997 | 0.94 | 0.54 | 0.10 | 0.30 | 0.25 | 58.0 | a rule or permit held exports |
| Nov 1997 | 1.03 | 0.55 | -0.11 | 0.60 | 0.27 | 53.5 | a rule or permit held exports |
| Dec 1997 | 1.56 | 0.68 | -0.02 | 0.90 | 0.28 | 43.5 | a rule or permit held exports |
| Jan 1998 | 4.50 | 0.45 | -0.19 | 4.23 | 0.28 | 9.9 | a rule or permit held exports |
| Feb 1998 | 12.28 | 0.18 | -0.38 | 12.48 | 0.39 | 1.5 | a rule or permit held exports |
| Mar 1998 | 6.52 | 0.14 | -0.05 | 6.43 | 0.44 | 2.1 | a rule or permit held exports |
| Apr 1998 | 5.40 | 0.10 | 0.02 | 5.28 | 0.42 | 1.9 | a rule or permit held exports |
| May 1998 | 4.38 | 0.22 | 0.03 | 4.13 | 0.44 | 5.0 | a rule or permit held exports |
| Jun 1998 | 4.79 | 0.32 | 0.20 | 4.26 | 0.42 | 6.7 | a rule or permit held exports |
| Jul 1998 | 2.69 | 0.50 | 0.26 | 1.93 | 0.49 | 18.5 | a rule or permit held exports |
| Aug 1998 | 2.03 | 0.57 | 0.23 | 1.23 | 0.25 | 28.2 | a rule or permit held exports |
| Sep 1998 | 1.90 | 0.55 | 0.15 | 1.20 | 0.18 | 29.0 | a rule or permit held exports |
MAF = million acre-feet.
What contractors were told to expect
| Contractor class | Final allocation, 1998 | Final allocation, 1997 |
|---|---|---|
| SWP Table A | 100 percent | 100 percent |
Allocations are percentages of contract supply.
How 1998 measures against other supplies
The 4.81 MAF exported in 1998 is 1.1 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 38.89 MAF that left the Delta above the floor is 8.5 times the 4.55 million acre-foot capacity of Shasta Lake, the largest reservoir in the state; 59 percent of it passed in three months (Feb, Mar, Apr).
Frequently asked questions
How much water did the Delta pumps export in water year 1998?
4.81 MAF: 2.47 MAF at the Central Valley Project's Jones plant and 2.13 MAF at the State Water Project's Banks plant, which together serve cities and farms on both projects. That was 10 percent of the 48.01 MAF that entered the Delta in a wet year.
How much Delta water flowed to the ocean in 1998?
Net Delta outflow was 42.96 MAF. Of that, 4.10 MAF was the minimum that Water Right Decision 1641 requires to keep salt water out of the Delta and its intakes, and 38.89 MAF was above that floor, 90 percent of the outflow.
What did project contractors receive in 1998?
The State Water Project's final Table A allocation was 100 percent of contract supply. 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.