Feb 9, 20173 min read

Archive: SFAR Water Year Forecast February 2017

tl;dr: Wet. Very Very Wet.

South Fork American River water year forecast as of February 8, 2017

The February Water Report was released Tuesday afternoon February 8th, with the Water-Year forecast expectedly solidly in the Wet range. Specifically it’s forecasting the American River below Folsom at 5.610 million acre-feet (MAF), with 3.500 or greater being considered Wet. The 80% probability range of 4.615-7.450 MAF gives great comfort that the forecast will likely remain within the Wet category through the final May forecast.

October through January we’ve already seen 2.384 MAF of runoff, as compared to the 2.595 MAF we saw for the entire Oct 2015-Sep 2016 water year. Oct16-Jan17 recorded more runoff than we recieved in all of 2015 (0.843 MAF) and 2014 (0.918 MAF) water year’s combined. January 2017 alone recorded 1.420 MAF, besting the 2015 and 2014 water years.

Guaranteed Minimum Flows

While the February forecast is technically only valid until around March 10th, it’s a reasonable assumption that the following will not change barring an act of God or congress (I’m not intending to be flippant. I really do mean a literal act of God or a literal act of Federal Congress).

It’s also worth noting that depending on how quickly/slowly the snowpack melts, there is a strong probability for significantly higher flows (especially between now and mid to late June and even into July) than the minimums stated below.

February Flows

No guaranteed rafting flows: Monday – Friday
Saturday & Sunday: 1,500 cfs 9am-12pm
Minimum Fish Flow: 250 cfs

March-May

Monday – Friday: 1,500 cfs 9am-12pm
Saturday & Sunday: 1,750 cfs 7am-1pm
Minimum Flow: 250 cfs March, 300 cfs April, 500 cfs May

Summer Flows – May 27th through September 4th

Monday – Friday: 1,500 cfs 8am-12pm
Saturday & Sunday: 1,750 cfs 7am-1pm
Minimum Flow: 500 cfs May & June, 350 cfs July, 300 cfs August, 250 cfs September

September 5-30, 2017

No guaranteed raftable flows Monday, Tuesday, Wednesday
Thursday, Friday, Saturday, Sunday: 1,500 cfs 9am-12pm
Minimum Flow: 250 cfs

October Flows

No guaranteed raftable flows Tuesday, Wednesday, Thursday
Mondays & Fridays: 1,300 cfs 9am-12pm
Saturdays & Sundays: 1,500 cfs 9am-12pm
Minimum Flow: 250 cfs

November through early February

No guaranteed raftable flows Monday-Friday
Saturdays & Sundays: 1,500 cfs 9am-12pm
Minimum Flow: 250 cfs

The next water year forecast should be released around March 8th, with it taking effect 3 days after issuance.

Reservoir Storage – Of Interest

With a high snow pack and reservoirs on the Upper American River Project (UARP) filling up, here are some (There are many more reservoirs in the system, these are just the most impactful) quick water storage related numbers (For reservoir storage, current elevation is a hard number, while current storage is a rough calculation based on estimated capacity at that elevation. Natural sediment deposits over time, and from high runoff/melt conditions, can modify (sometimes greatly) actual capacities) that might be of interest.

As of February 9, 2017 – 6 AM

Loon Lake – 6,405 ft (spills at 6,418 ft) with 62,598 AF (spills at ~76,500 AF)
Ice House – 5,438 ft (spills at 5,454 ft) with 35,972 AF (spills at ~37,120 AF (But some data says 43,496 AF))
Union Valley – 4,863 ft (spills at 4,855 ft (an Ogee gate can be lowered from May 1-Sept 30 raising the spill elevation to 4870 ft. Though when the gate is down they typically will raise it for a controlled spill at around 4,868 ft)) with 245,717 AF (spills at 230,000 AF (Again, May 1-Sept 30 the capacity can be increased to about 277,300 AF))
Slab Creek – 1857 ft (spills at 1,850 ft) with 14,780 AF (spills at ~13,350 AF) ( Official data claims 1,870 ft for spill and 16,600 AF of storage, but historical data shows 1,850 ft and 13,350 AF to be more realistic – I’m looking into it.)
Chili Bar – 1,009 ft (spills at 997.5 ft) with a max capacity of just 1,340 AF.