San Lorenzo River January 22, 2017 flowing high (~10,000 cfs) near Highway 1 Bridge
February 2, 2017
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 2017. The end of January represents the mid-point of the winter wet season. The outlook will be updated as the 2017 wet season progresses and a final water supply outlook will be prepared toward the end of March. Given how much rain has fallen so far this year, though, the water supply outlook is not expected to change significantly between now and then.
Rainfall The winter weather pattern this year has been very active, to say the least. The wet season started with a bang in mid-October when a remnant of a tropical typhoon swept through the central coast region bringing several inches of rain.
It has continued into late January with multiple atmospheric river-type storm systems. Recent storms generated wide spread, heavy rainfall that caused localized flooding, landslides, and road closures throughout the county. As of January 30, 2017, the Santa Cruz area had received 31.32 inches of rain, or 184 percent of normal precipitation for this time of year. In fact, rainfall to date measures about one-half inch short of the annual average rainfall amount for the City.
Cumulative rainfall for the year to date is shown in Figure 1. A total of 15.66 inches of rain fell in January alone, two and a half times the average monthly total. According to the Western Regional Climate Center, January 2017 ranks as the fourth wettest January in Santa Cruz on record since 1893.
In the City’s watershed around Loch Lomond Reservoir, rainfall has measured between 48 and 56 inches for the season to date, with nearly 32 inches recorded at the recreation area in January alone.
The short term forecast has more rain returning to California in early February. Long-term, the National Weather Service Climate Prediction Center is showing equal chances of normal precipitation across California in its 3-month outlook for the period February through April 2017.
Figure 2 shows mean monthly amount of stream flow in the San Lorenzo River for the season to date, along with the long-term average monthly values for comparison. The extraordinarily high flow in January 2017 is the result of seven distinct, major storm systems that produced very significant peak flows some of which registered higher than 10,000 cubic feet per second at times. The highest event on January 10 resulted in minor flooding of the coast pump station and of Tait Well No. 4. As reported in the local news, these strong storms in January also damaged other critical water system infrastructure, which is discussed further below.
Loch Lomond Reservoir filled to capacity on January 4, 2017, and has been spilling over into Newell Creek since then. At one point in January, the lake level reached almost two feet over the spillway elevation. The lake water now is uniformly more turbid and brown in color than has been seen in many years from all the recent storm runoff.
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.
At this point, there is no question that the 2017 Water Year will be classified as Wet. Cumulative discharge currently measures 117,496 acre-feet. The threshold to be classified as wet is 119,000 acre-feet. It will only be a matter of a few more days’ time, even without any more rain, before that threshold is reached. This will be the first Water Year since 2011 that is classified as Wet. Cumulative discharge From October 1, 2016, through January 30, 2017, is shown in Figure 3. The long-term average discharge for this time of year is about 33,000 acre-feet. Last year at this time, the river had generated only about 18,000 acre-feet, following a succession of dry and critically dry years.
Figure 4 shows the drought monitor map as of January 25, 2017, along with last year’s map at this same time for contrast. It is acknowledged, however, that local groundwater supplies, including the Santa Cruz Mid-County Groundwater Basin from which the City and others pump, have been depleted over a long period of time and will not recover so quickly compared to surface water supplies.
Initial Outlook for 2017 Even with winter only halfway through, the water supply outlook for the City of Santa Cruz is more positive than it has been in a long time. In water years like this, surface water supplies tend to flow stronger and the lake tends to stay full longer into the dry season. Exactly how much stronger will depend on how weather shapes up in the second half of the wet season. Aside from the possibility of continuing state-mandated water conservation targets and ongoing water waste prohibitions, staff foresees no reason at this time for instituting restrictions on water use this summer. This is especially true in light of the low level of demand experienced in 2016. Even with no restrictions in place, total system demand in 2016 amounted to only 2.56 billion gallons, 23 percent less than in 2013 and almost exactly the same as in 2014, when rationing was in place. It is uncertain how long water sales will continue to lag. Changes to water rates that took effect last October, and are scheduled to take effect again in July, will likely reinforce ongoing conservation behavior.
The State Water Resources Control Board is scheduled to consider readopting its drought related emergency regulation on February 8, 2017. In the meantime, the City continues to meet its state mandated 8 percent reduction in total water production compared to same months in 2013 that is in effect through February 28, 2017. The Water Department will continue to monitor water supply conditions and will reevaluate the water supply outlook again in mid-March.
Storm Related Damage to Water System As mentioned above, the water system experienced significant damage during the January storms. The most critical loss was a break in the Newell Creek pipeline within Henry Cowell State Park that occurred during the overnight hours of January 8/9. This pipeline is used to bring lake water to the plant when the San Lorenzo River is too turbid to treat. While the line was temporarily out of service, operators were just able to balance demand and maintain treated water storage using the limited north coast supplies, Beltz wells, Tait wells, and about one mgd of water from the intertie with Soquel Creek Water District. Water Department crews and contractors eventually repaired the leak, rebuilt Pipeline Road, and partially restored service. Another leak on the same line has since been discovered nearby and is in the process of being repaired.
The full scope of the damage to the water system caused by these storms is still being assessed. Staff is currently working with State OES and FEMA to pursue possible reimbursement.