NEWS NOTES ON SUSTAINABLE WATER RESOURCES Oroville Dam Crisis For basic information on the Oroville Dam see https://en.wikipedia.org/wiki/Orovil...

NEWS NOTES ON SUSTAINABLE WATER RESOURCES Oroville Dam Crisis For basic information on the Oroville Dam see https://en.wikipedia.org/wiki/Oroville_DamThe 2017 Oroville Dam crisis is a major and ongoing threat to lives and property in Northern California. At 770 feet (235 m), Oroville Dam is the tallest dam in the United States. Located in Butte County about 70 miles (110 km) north of Sacramento, the dam impounds Lake Oroville, and controls the flow of the Feather River. Storms in early February 2017 caused heavy damage to the dam's spillways, hindering the safe release of floodwater. The prospect of uncontrolled release of water from the lake forced the evacuation of more than 180,000 people living downstream along the Feather River. https://en.wikipedia.org/wiki/2017_Oroville_Dam_crisisIn early February, high inflows to Lake Oroville caused dam operators to start using the concrete main spillway to control the lake level.[6]. While water was being released on February 7, 2017, a crater unexpectedly developed about halfway down the spillway, allowing water to escape the channel and erode the earth beneath.[7] More of the spillway washed away, sending large volumes of water into the earth underneath and alongside the spillway, so engineers closed the main spillway for inspection. During two test flows on February 8–9, the length of the crater increased from 250 ft (76 m) to 300 ft (91 m).[7] Management was then confronted with two choices: continue to use the main spillway, knowing it would likely be further damaged, or allow the reservoir to rise until it overtopped the emergency spillway.[7]Engineers reopened the main spillway. They had hoped that using the damaged spillway with a limited flow could drain the lake enough to avoid use of the emergency spillway, which would potentially damage power lines servicing the hydroelectric plant.[8] They reduced its discharge from 65,000 cu ft/s (1,800 m3/s) to 55,000 cu ft/s (1,600 m3/s),[9][10] but this flow was not enough to prevent the lake from rising.[9] The rising water eventually crested the weir along the front of the dam, cascading over the weir (as designed, as the last resort) and onto the emergency spillway (below the weir), for the first time since the dam was constructed in 1968.[5]Shortly after 8:00 am on February 11, 2017, the emergency spillway began carrying water for the first time since the dam's construction in 1968.[12] Because the spillway was a separate structure from the dam, officials stated that there was no danger of the main embankment being breached, and evacuation of Oroville was not considered at that time, as officials stated that there was no threat to public safety. Once the lake rose to the level of the emergency spillway top, an uncontrolled overflow began that topped out at 12,600 cu ft/s (360 m3/s)[13][14], and water flowed directly onto the earthen channel below the concrete crest of the emergency spillway. Erosion of the emergency spillway threatened to undermine and collapse the concrete weir. If the weir collapsed, it would send a 30-foot (9 m) wall of water into the Feather River below and flood communities downstream.[5] Fearing a collapse, officials issued an evacuation order.[5]The immediate harm from the damage is limited to the area downstream of the breach, eroding the hillside to form a canyon. However, a major danger is that the spillway can erode back up toward the gate due to being undercut by the water falling into the crater. Eventually, this would threaten the spillway gate, in close proximity to the actual abutment of the dam.[9]  This information will also be linked on the 2017 Actions and Activities Page of the Sustainable Water Resources Site at https://sites.google.com/site/sustainablewaterresources/  Tim Smith Sustainable Water Resources Coordinator Government Web Site, https://acwi.gov/Sustainable Water Resources Site, https://sites.google.com/site/sustainablewaterresources/