gmhTODAY 14 gmhToday May June 2017 - Page 14

jurisdictions. The cost to move water is higher than the cost of the water itself. THE CURRENT STATE OF OUR DAMS SCVWD District 1 includes five reservoirs (see chart below) that are managed by the water district under the regulatory authority of the California Division of Safety of Dams. Anderson Dam is also under the Federal Energy Regulatory Commission because it has a hydroelectric generating facility. Our dams were built 50 to 80 years ago primarily for water storage and eco- system support. A prolonged drought depletes these surface water resources. They also provide incidental flood protection (all but Uvas are operated according to a “flood rule curve,” which restricts storage capacity). Aging dams such as Anderson need improvements in order to be safe and effective resources, at capacity, during periods of flooding or in the event of an earthquake. According to the water district, one acre-foot of water (325,851 gallons) is enough to serve two households of five for a year, on average. South County reservoirs (excluding Calero, which serves North County) have a current combined storage of over 104,700 acre feet. ANDERSON RETROFIT Anderson Dam was built in the 1950s when knowledge of local geologic and seismic characteristics was quite limited. What we now know is that a significant earthquake could cause the dam to fail, releasing a wall of water that would reach downtown Morgan Hill in about 15 minutes, and parts of San Jose within a few hours. The dam needs a seismic retrofit and SCVWD is taking steps to make that happen. The goal is to remove, rebuild, and replace all of the dam embankment, modify the spillway, and increase draw- down capacity, among othe r improve- ments. Construction is slated for 2020- 2024 with a price tag around $400 million. South County will pay about 20 percent. The other 80 percent will be paid by North County, which derives a greater benefit from the dam. The winter’s fierce storms filled Anderson beyond capacity-level restric- tions set by the Division of Safety of Dams. Emergency measures to draw down excess capacity were exacerbated by the fact that the Coyote Valley area was already saturated. The Coyote Creek system overflowed its banks, flooding a number of San Jose neighborhoods. DAM LEVELS AS OF APRIL 13, 2017 Description Reservoir Storage (acre-feet) Reservoir Capacity (acre-feet) % of Reservoir Capacity COYOTE VALLEY Coyote Reservoir 23,317.9 23,244 100.6 (restricted capacity=53%) Anderson Reservoir 63,386.4 90,373 70.1 (restricted capacity=68%) UVAS/LLAGAS Chesbro Reservoir 8009.2 7,945 100.8 Uvas Reservoir 9,950.2 9,835 101.2 GUADALUPE WATERSHED Calero Reservoir 4,220.6 9,934 (supplies North County, not South County) 41.5 (restricted capacity=46%) Source: Santa Clara Valley Water District 14 GILROY • MORGAN HILL • SAN MARTIN MAY/JUNE 2017 gmhtoday.com