Damaged Oroville Dam spillway may reopen as water levels rise

March 10 (UPI) -- Officials in northern California said they will likely have to reopen the heavily damaged Oroville Dam spillway as water continues to rise in its reservoir.

The spillway has been shut off since Feb. 27, when officials with the California Department of Water Resources closed it off to begin repairs and remove debris that had built up after a series of massive water releases into the Feather River below the dam.

The hole in the main concrete spillway combined with the huge buildup of runoff into Lake Oroville forced officials to use a never-attempted emergency spillway to release water. Erosion caused by the spectacular waterfall along the unpaved emergency spillway prompted emergency officials to order the hasty evacuation of some 180,000 people in three counties amid fear of mass flooding if the emergency spillway gave way.

The Los Angeles Times reported Thursday officials are planning to reopen the partially repaired spillway after water levels in Lake Oroville have risen 21 feet due to rain and melting snow in the area.

Officials said the water levels in the lake are nowhere near as high as they were at the height of the crisis a month ago, but said intermittent releases along the damaged spillway will prevent the need to use the emergency spillway again.

The Sacramento Bee reported the water release could being as soon as March 17, by which point the water levels in the lake are expected to rise another 5 feet.

Still, officials continued to work to repair the spillway after a gaping 300-foot hole formed in the concrete, exposing the ground below. After experimenting with various rates of releases in late February, engineers determined allowing a slower flow of water down the spillway was actually causing more erosion to the ground beneath the concrete. That erosion could further compromise the spillway and, eventually, the Oroville Dam itself if it continues. In response, workers dumped large rocks and concrete slurry into the eroded areas to help shore up the spillway.

In another bit of news officials said will prove helpful in regulating water levels, enough debris has been removed from the base of the dam to allow the hydroelectric power plant there to resume operation. Its water outflows became clogged from the mud and debris unleashed when the emergency spillway was pressed into service. The power plant began operating at 50 percent capacity on Thursday, and will contribute to efforts to regulate the levels of Lake Oroville as the spring snow melting continues, officials said.