When 58% of California is currently in a state of “exceptional drought”, water is on many people’s minds. As Lake Tahoe approaches its natural rim, leaving boat ramps and rafters high and dry, it’s hard to imagine there really is enough water available to support much more development in the Tahoe basin. But the Water Supply Assessment released by the Squaw Valley Public Utility District last month suggested that there is enough water to support the needs of several proposed developments within Olympic Valley over the next 25 years. This unexpected conclusion drew the attention of local environmental groups and several local scientists that have been studying Tahoe hydrology for years.
Hatchett does some field testing in Tahoe
One of them, Benjamin Hatchett, approached us with his concerns. Hatchett is no stranger to weather and precipitation. Hatchett has earned degrees in Physical Geography (B.S.) and Atmospheric Sciences (M.S.) and is currently working on a Ph.D. in Geography studying climate dynamics and paleohydrology in the Great Basin. Over the last 12 years he has been keen observer and reporter of weather in the Tahoe Basin and eastern Sierra.
Hatchett’s concerns focus on the narrow range of data used in completing the WSA, an 18 year period spanning 1993 through 2011. You really don’t need a scientific degree to figure out that 18 years is not a long enough time period to get an accurate picture of what sort of precipitation is “normal” for the Tahoe Basin. Hatchett’s alternative analysis looks at 90 years of data, from 1922 through 2013. It leads to a significantly different conclusion than the WSA.
The graph above represents data from Central Sierra 5 Station Index, a widely recognized data set used in water planning that correlates well with Squaw Valley data. Hatchett points out that it does not match exactly with the Squaw Valley data used in the WSA.
• The water years used in the Squaw Valley WSA are colored in red
• The twenty wettest years during the longer study period are green
• The twenty driest years during the longer study period are brown
Hatchett makes a point of noting that the shorter study period used in the WSA includes 7 of the wettest years, but includes only 1 of the driest years. This leads to what may be an artificially inflated “average precipitation” in the WSA study. Using the shorter WSA time period, the estimated average precipitation is 42.7 inches, while the longer study period produces an estimated average precipitation of only 36.6 inches. The difference is significant, as the WSA number is roughly 117% of the longer term average.
Hatchett is not suggesting that the WSA was designed to intentionally mislead anyone. He only suggests that the study would be far more robust using the longer study period. Hatchett is also concerned that the WSA does not look at the potential affects of a longer term drought scenario. Although we are currently in a third very dry year, there are far drier years in the historical record, and much longer lasting megadroughts.
According to Hatchett, local scientists Scott Stine, Scott Mensing, John Kleppe, and Larry Benson have all studied the megadrought occurrences in the Tahoe area. Stine wrote a paper in the journal Nature in 1994 (Stine1994) that first published the ages of tree stumps found in Walker Lake, Mono Lake, and Tenaya Lake. The ages of the trees found in Fallen Leaf lake (from John Kleppe and Scott Mensing) correlate very well with Stine’s work. The data shows these droughts lasted 100-150 years, interspersed by a 90 year wet period, and took place during Medieval times.
Lastly, Hatchett notes the WSA fails to address any future climate scenarios adequately. He suggests that “many millions of dollars have been spent getting global climate model data into forms easily digested by hydrologic models for impact analysis.” Hatchett wrote about the use of the models in studying the Incline Creek watershed in 2012.
We showed the numbers from Hatchett’s study to Tom Mooers, Executive Director of Sierra Watch. Sierra Watch has kept a keen eye on the development proposals in Olympic Valley, especially as it might relate to water demands. Here was his comment on the WSA:
It looks like it answered a very narrow question, as required by law, with a severely limited set of assumptions. But it left many more unanswered. – Tom Mooers, Executive Director, Sierra Watch
Updated 8/19/14: We also ran the data set by Mike Geary, General Manager of the Squaw Valley Public Services District. Geary countered by saying that the calibrated numerical groundwater model relies on data specifically from Squaw Valley. The model also requires data on groundwater elevation, pumping and stream flows. According to Geary, that data is not available prior to 1993. Geary felt that using the complete suite of information in their model gave them the best possible answer.
The question of water availability within Olympic Valley is an important one. The alternative water supply identified by SVPSD is the widely unpopular and expensive “8 Mile Pipe” proposal to bring water from Martis Valley to Olympic Valley. The last estimated cost of the project exceeded $30 million and the project would create a serious disruption in the Martis Valley, the town of Truckee, the Highway 89 corridor and Olympic Valley during pipeline construction. It would be unfortunate if entitlements for new construction in Olympic Valley were granted before the completion of a more robust water supply assessment, forcing the “8 Mile Pipe” as the only solution.
Updated 8/25/14: Tom Mooers released a more specific editorial piece to Moonshine Ink that stated Sierra Watch’s position on water in Olympic Valley. Here’s the link to Moonshine Ink.