2017 Water Supply Outlook

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IMG_3819 small website San Lorenzo River January 22, 2017 flowing high (~10,000 cfs) near Highway 1 Bridge

April 14, 2017

 

As winter gives way to warm, sunny weather, perhaps the image that people will remember longest about this extraordinary water year is the damaged spillway at Oroville Reservoir north of Sacramento. Closer to home, in Santa Cruz County, the forces of nature caused tens of millions in storm damage to local roads, the most in decades. Repairs are still being made to damaged sections of the water system. And, for the first time in years, most of California is finally out of the drought.     

The numbers tell the story. Over four feet of rain has fallen in the City of Santa Cruz. Rainfall now measures 176 percent of normal for the season to date. Near the reservoir, rainfall totals range from 76 to 87 inches. Average stream flow in the San Lorenzo River for the months of January and February, calculated at 1,643 and 1,909 cubic feet per second respectively, were the highest ever recorded for those two months. Cumulative runoff since October 1 has now reached about 239,000 acre-feet and the water year classification is manifestly Wet.There are only two years in the hydrologic record that have been wetter, 1941 (265,000 ac-ft) and 1983 (283,000 ac-ft). And the year isn’t over yet. Loch Lomond Reservoir is full and spilling. (Figures 1-3).  

Figure 1. Cumulative Precipitation 03_26_17 

 Figure 1

 Figure 2. Mean Monthly Runoff 03_26_2017

Figure 2

 Figure 3. Cumulative Runoff 03_26_17

 Figure 3

 

Figure 4. Projected Reservoir Drawdown

Taken together, the water supply outlook for 2017 is healthy. A conservative forecast of supply and demand for 2017 shows Loch Lomond Reservoir remaining above 80 percent of capacity at the end of October (Figure 4). Under the circumstances, there is no reason the City needs to declare a shortage or impose temporarily restrictions on water use for 2017. The forecast for 2017 has numerous uncertainties and assumptions factored in (Table 1). First is that availability of water from the City’s north coast sources will be limited mainly by instream flow requirements, but also by storm damage to the Majors Creek pipeline. Bypass flows on the San Lorenzo River, which vary based on streamflow condition, are expected to be higher than ever experienced before, but don’t begin to affect production from the river until about August. Live Oak wells are assumed to be placed in service again in June. 

Figure 5. System Water Demand mgd

System water demand is conservatively forecast to be slightly higher (+5%) than in 2016, but substantially below where it was in 2013 (Figure 5). There is, however considerable uncertainty about how the actual pattern in demand will evolve as customers gain more experience under the new rate system this summer and see another planned rate increase scheduled for July 1, 2017.   

 

On April 7, 2017, Governor Brown declared California’s drought emergency officially over in most parts of the state. Even though this year water is plentiful, the City of Santa Cruz is committed to ensuring conservation and long-term water efficiency continues as a way of life. The City is actively investing in programs, educations, and incentives to help customers adopt sustainable practices and make changes that result in permanent water savings. While the City of Santa Cruz is not under emergency water use restrictions, the waste of water is always prohibited under the City's Water Waste Regulations (Chapter 16.02 of the Santa Cruz Municipal Code). 

 

 

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