Final Water Supply Outlook for 2013
(March 27, 2013)
The Water Department will present this report to the Water Commission on April 1st. Staff will recommend City Council adopt a resolution declaring a Stage 1 Water Shortage Alert for 2013, pending an improvement in local water conditions.
This report is the third in a series of three monthly statements summarizing current water conditions and evaluating the City’s water supply outlook for 2013. It covers the water year beginning October 1, 2012 through nearly the end of March 2013.
The dry weather pattern that began in January continued through the month of March. Over the past month, less than one inch of rain fell in the City. The watershed picked up a little under two inches. Rainfall for the season to date now measures 16.00 inches, or 58 percent of normal, in the City of Santa Cruz. In the Newell Creek watershed, total rainfall to date measures 33.29 inches, or 74 percent of normal. Monthly rainfall totals for the Santa Cruz area are presented in Figure 1 (1). While it is not uncommon for more rain to occur in April and even into May, chances of any significant change this late in the season are low.
Stream flow in the San Lorenzo River, the City’s primary source of water supply, continues to decline from its peak in December 2012. Mean flow for the month of March to date measures 47 cubic feet per second (cfs), about 16 percent of the long term average level (Figure 2). As of the date of this report, mean daily flow in the river registered 35 cfs. This level of flow is what one might expect to see in June or July, but not this time of year.
Loch Lomond Reservoir is in good shape and remains filled to capacity. It is no longer spilling, however.
Water Year Classification
Cumulative runoff from the San Lorenzo River for the year to date measures 48,013 acre feet, about 65 percent of average through the month of March, and very close to the 49,000 acre-foot threshold that differentiates a dry year from a normal year (Figure 3). Thus, while the 2013 water year is presently classified as “Dry”, it is only a matter of time, perhaps a few weeks, until the classification for water year 2013 is upgraded to “Normal”.
Projection of Water Supply Availability for 2013
This has been a year of contrasts. The period from October through December was considerably wetter than average. Since then, conditions have remained abnormally dry. Another contrast: the reservoir is filled to its brim, but local stream and river flows are running unusually low for this time of year.
Ordinarily, the combination of a normal water year (even a borderline year like this one) and a full reservoir at the end of winter would translate to no problems meeting full water system deliveries for the season ahead. There are three factors, though, that makes the water supply outlook more ambiguous this year.
• Timing: the bulk of this season’s rainfall fell early this year. As a result, streams and the river will be running lower than they would have given a more consistent rainfall pattern over the winter season. There is no year on record quite like this one going back to the 1930’s in which the water year was designated as normal (or even dry), and the flow in the San Lorenzo River was so low in March. Right now the river is flowing more like what would be seen in a critically dry year. This unusual seasonal rainfall/runoff pattern makes forecasting how the river will flow later this summer more uncertain.
• Last year was dry, too: This is the second consecutive year in which rainfall and runoff have fallen below average. Water year 2012 was designated as Dry. How this extended dry period may affect the yield of the City’s flowing sources going forward is difficult to tell.
• More stringent limitations to protect steelhead and salmon: The Water Department, in accordance with a draft agreement the CA Department of Fish and Wildlife, has operated the North Coast system this winter as would be required under a proposed Habitat Conservation Plan flow regime to protect threatened and endangered fish species. This change has resulted in a severe reduction in otherwise available flow this winter from the City’s north coast sources, and affected service to selected raw water customers. The draft agreement specifically calls for the City to stop diverting from Laguna Creek from June through December 2013. Less water from the coast sources means the system must rely more on water stored in Loch Lomond Reservoir to meet daily demands this summer.
All this is to say that, despite a full reservoir, the City faces, for both hydrologic and regulatory reasons, another marginally low water year ahead.
Table 1 represents an analysis of the City’s water supply and demand situation for the upcoming dry season, assuming no further change in weather conditions. The forecast does call for a 20 to 30 percent chance of rain beginning Wednesday, March 27 through early April, which is not factored in. The weather is still dynamic and any additional rainfall will only improve the supply situation represented in Table 1.
Much like last year, with the combination of below normal water conditions and the ongoing commitment to make operational changes to protect fisheries, it is staff’s recommendation to implement a Stage 1 Water Shortage Alert again beginning May 1, 2013, pending a major improvement in local water conditions. This action would serve as both a precautionary measure in case dry conditions continue into the next year, and to maintain a heightened level of awareness among customers this year, until more normal water conditions are restored. Stage 1 includes both voluntary and mandatory response measures aimed at achieving a 5 percent, or roughly 100 million gallon demand reduction goal for the season.
Table 1 shows forecast reservoir storage at the end of the 2013 dry season given staff’s best estimates of available supply and a level of demand comparable to last year with a Stage 1, five percent use curtailment in place. The table indicates that the reservoir would end the 2013 dry season at about 75 percent of capacity. Last year at this time, the reservoir was projected to end the dry season at near 80 percent full, but it actually ended closer to 90 percent full due to late season rains that improved the water supply. This year’s projection is very conservative given the factors described above. Clearly, one of the tradeoffs of greater instream flow releases will be comparatively lower end of season reservoir levels.
Stage 1 involves the following restrictions:
• Restricting landscape irrigation to early morning and evening
• Prohibition on non-essential uses (serving drinking water except by request, no washing driveways, patios, parking lots, draining and refilling residential pools etc.)
• Hose nozzle required for any purpose
• Stepped up water waste enforcement
The City’s Water Shortage Regulations and Restrictions are contained in the Santa Cruz Municipal Code Chapter 16.01, and are put into effect by a resolution of the City Council for the period of time set forth in the resolution.
(1) From a water supply perspective, rainfall that occurs in the watershed is more important than rain that is reported in the City limits. The Santa Cruz location, however, is used to best illustrate rainfall patterns because it is an official National Weather Service observation station with a long period of record.