Initial Water Supply Outlook for 2014
(January 29, 2014)
The Water Department will present this report to the Water Commission on February 3rd. The public is invited to attend.
This report provides an overview of current water conditions and presents the Water Department’s first formal outlook covering the City’s water supply situation for water year 2014. It will be updated at the end of February as the season progresses and a final water supply outlook will be prepared in the month of March, when the bulk of the winter wet season has passed and the water supply situation becomes more certain.
Given the extraordinary and very serious circumstances that the City potentially faces this year, we begin with a summary of recent actions at the state level.
On Friday, January 17, 2014, Governor Brown officially declared a drought emergency in California. He asked California residents and businesses to voluntarily reduce their water consumption 20 percent and directed state agencies to take a range of steps to ease the effects of water shortages on agriculture, communities, and fish and wildlife. Earlier in December, the Governor convened an Interagency Drought Task Force to coordinate state efforts with Federal and local agencies. These actions follow the designation of 2013 as being the driest calendar year on record, which has left many of the state’s largest reservoirs, river systems, and Sierra snowpack at dangerously low levels and has contributed to unseasonable winter wildfires. The U.S. Drought Monitor, as of January 21, 2014, now classifies over 60 percent of California, including all of the San Francisco Bay Area and Central Coast regions, in a condition of “extreme drought”, one stage below the most severe designation, “exceptional”.
At roughly halfway through the winter “wet” season, the City of Santa Cruz, like the rest of California, is experiencing unprecedented dry conditions. It would be an understatement to say that 2014 is shaping up to be the third straight dry year. Normal rainfall for this time of year is about 16.4 inches. So far this year, the Santa Cruz area has received only 1.3 inches of rain, scarcely eight percent of average. Most notably, there has been no measureable rainfall detected this January, which is historically the wettest month of the year. During the 1976-77 drought, the worst drought on record for the City, rainfall totals, by comparison, measured 8.6 inches at the end of January 1977. The extraordinary lack of rain this year is being attributed to persistent high atmospheric pressure centered over the eastern Pacific Ocean, which has forced weather systems far to the north and shows no signs of abating in the near future.
In the Newell Creek watershed, only 2.26 inches of rain has been recorded this year, and, like the City, there has been no measureable rainfall so far in January. Normal rainfall for this time of year in the watershed is about 24 inches. In 1977, the Ben Lomond area had received about 10 inches of rain by the end of January.
The short-term weather outlook indicates a chance of rain later this week, the first possibility of rain since December 7, 2013. Long-term, the National Weather Service Climate Prediction Center is showing the probability of below normal precipitation and above normal temperatures across California in its winter outlook over next three months.
Figure 1 shows monthly rainfall amounts in Santa Cruz for the year to date through January 24, 2014.
Like many other rivers across California, stream flow in the San Lorenzo River is at a record low level for this time of year. The flow in the river measured at the U.S. geological Survey gauge in Felton is currently running 12 cubic feet per second (cfs). The previous record low, 13 cfs, was set in 1991 in what was then the 5th year of a six-year drought. The mean monthly flow for January is 351 cfs, meaning that the river currently is running at a tiny fraction of normal, about four percent. It is even lower than would be expected late in summer or early fall. Without any rainfall to help replenish the watershed, flow in the San Lorenzo River is expected to continue dropping gradually over time.
Figure 2 shows mean monthly stream flows in the San Lorenzo River for the season to date, along with the long-term average values, and the 2013 water year for comparison. Figure 3 shows mean monthly stream flow this year compared with flows recorded during the 1976/77 drought. The level of flow in the river now is an astonishing 37 to 43 percent lower than it was in that critically dry period.
Loch Lomond Reservoir presently stands at about 65 percent of capacity, holding 1.85 billion gallons of its 2.83 billion gallon capacity. Although this percent of storage is significantly better than many large reservoirs statewide, its capacity is relatively small. Even when full, the reservoir holds the equivalent of less than one year’s supply. Right now, the water level in the reservoir is down nearly 20 feet below the spillway elevation.
While Stage 1 water restrictions instituted last May and extended this October helped to reduce system water demand and to preserve reservoir storage for the possibility (now a probability) of a third dry year, the lack of rain this past fall meant that plant operators had rely more on its reserves than expected in the months of October and November 2013. Since then, operators have been able to meet daily demands without having to draw further on the reservoir. However, with extended dry conditions, warmer than average weather, extremely low river flows, we are now at the point once again of having to tap Loch Lomond to meet the community’s wintertime daily water needs. It is not unusual for the City water system to need lake water in the winter season. What is extraordinary is the reason. In most years, the reservoir serves as a backup source of supply when winter storms make the river and coast sources untreatable at the Graham Hill Water Treatment Plant due to high turbidity. This year, it is simply that the yield from the City’s flowing sources is close to a level that cannot sustain even seasonally low winter water needs, which are currently averaging about 7.8 million gallons per day (mgd).
One major difference between this time in 1977 and 2014 is that reservoir storage today is in comparatively better shape. In 1977, reservoir storage was at only 35 percent of capacity at the end of January, heading into the second year of that drought.
Water Year Classification
The Water Department uses a water year classification system to characterize the City’s overall annual water supply condition. Under this classification system, the water year beginning October 1 is designated as one of four types – Wet, Normal, Dry, or Critically Dry - depending on the total annual discharge of the San Lorenzo River, measured at the stream gage in Felton, and expressed in acre-feet (1).
Water Year 2014 is so far shaping up to be a Critically Dry year. Cumulative discharge for the water year to date measures only 3,089 acre-feet , less than one-tenth of the 33,000 acre-foot long-term average discharge for this time of year. Annual discharge from the San Lorenzo River must reach a threshold of 29,000 acre-feet for the year to be reclassified as Dry and 49,000 acre-feet to be upgraded to Normal.
Figure 4 shows the cumulative discharge from October 1, 2013 through January 24, 2014, along with the long term average, and two prior years for comparison. It illustrates how local runoff patterns can differ from year to year. In water year 2012, the bulk of seasonal runoff occurred early in late November and December, while in water year 2011, runoff did not develop until much later in the season. How this year will ultimately develop cannot be predicted. What is known is that it typically takes about 12 inches of rain in the watershed before soils become saturated and significant runoff develops. The two inches of rain that fell in the watershed earlier in the year have long since been lost to evaporation, so the preconditions for runoff to occur this year are basically the same as if there had been no rainfall at all. Each additional day without rain makes it that much harder to catch up.
Figure 5 shows the tiny amount of discharge measured this season compared to the historical record going back to 1921. While a not a complete year, it is another visualization of how unprecedented and scarce the water supply could be if conditions do not improve in the second half of the wet season.
Initial Estimate of Water Supply Availability
At this time, the water supply outlook for 2014 is dire. Three months have gone by with virtually no rain. Unless there is a dramatic change in weather in the second half of the season, the City potentially faces the very real threat of a devastating, critical water shortage emergency that is unprecedented in the City’s history.
Experience tells that winter weather can change suddenly, and with a few major storms, the outlook can improve quickly. There have been years when winter got off to a late start, but came on strong later in the season. But the opposite has also occurred when the second half of the winter season was almost completely dry, like last year.
The situation underscores how vulnerable the City is to water shortage in extended and or critically dry years when available supply runs low. Unfortunately, there is very little that the City can do in the short run to increase its supply. The Water Department is in the process of preparing a petition, in coordination with state regulatory agencies, to potentially cut instream fish releases temporarily below Loch Lomond Reservoir, and to reduce the amount of water the City has been bypassing at its diversion facilities. Water Production staff is looking at the possibility of changing its standard for treating turbid water to help preserve storage. These measures would all help but only to a small degree. Ultimately, the only option in lieu of a supplemental water supply during times of shortage is to put in place measures to curtail water use.
One key decision concerning supply that will need to be made, assuming conditions remain dry, will be how much reservoir water should be made available for use in 2014 and how much should be banked as a safeguard against the possibility of another dry year. The considerations and guidance to help inform that decision are contained in Chapter 2 of the City’s Water Shortage Contingency Plan.
The Stage 1 Water Shortage Alert adopted in May 2013 and extended last October still remains in force. Normally, any recommendation to change the level of shortage would be brought forward to City Council in the April timeframe. Doing so beforehand would be premature, for two reasons. One, there are too many uncertainties trying to project available supplies for the season ahead any earlier than March. Two, the measures to curtail water use are geared around reducing peak season demands. Nevertheless, given the extraordinary circumstances, and to honor the Governor’s emergency proclamation, staff will be recommending that City Council in the meantime adopt a resolution that echoes the Governor’s call for a voluntary 20 percent reduction in water use by all City water customers.
The Water Department will continue to monitor water supply conditions and reevaluate the water supply outlook at the end of February, and again in late March. At that time, we should have enough information on which to make a monthly projection of the City’s water supply availability and evaluate the adequacy of this supply to meet expected water demands within the City’s water service area for the rest of 2014.
At the same time, staff is working hard on a variety of related communications and internal operating actions, which include the following:
• Launching a web page dedicated to ongoing drought information,
• Implementing a major advertising campaign,
• Creating signage for key gateway locations throughout the City service, and
• Making modifications to the City’s utility billing system, billing frequency, and billing format in order to implement water rationing, should it be needed in 2014.
Finally it is worth mentioning that the City of Santa Cruz has a Local Hazard Mitigation Plan, updated in 2013, that has passed its initial review by the California Office of Emergency Services. The LHMP Update is currently under final review by FEMA. Once the plan is approved by FEMA and adopted by the City Council, the City becomes eligible to compete for funds through FEMA’s Pre-Disaster Mitigation (PDM) Grant Program. These funds are awarded annually on a competitive basis for hazard mitigation planning as well as for the implementation of mitigation projects prior to a disaster event.
(1) Discharge refers to the accumulated volume of runoff. One acre-foot of water is equal to 325,851 gallons. 3.07 acre-feet equals one million gallons.
Annual discharge of the San Lorenzo River is regarded as the best individual benchmark of the City’s water supply condition for two reasons. First, the river is the city’s single largest source of drinking water, providing about half the normal annual supply. Second, about three quarters of all the water used by city water customers is obtained from a flowing source of supply. In general, the higher the volume discharged from the San Lorenzo River means that:
• the local watersheds in the Santa Cruz mountains are more saturated;
• the stream sources will flow at higher levels later into the dry season; and
• there is more water available from all surface water sources, including the reservoir, to meet system demands over the course of the year.
The converse is also generally true; the lower the volume discharged by the San Lorenzo River means less water is available from all surface sources to meet system demands.