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Monster Storm Rains in the New Yearby Greg Reis The warm "pineapple connection" storm that hit California on New Year's Eve brought heavy rain to many parts of the Sierra, melted a large low-elevation snowpack, and caused widespread flooding. The Central Valley, Reno, and northern Mono County were a few of the areas hit hard by the storm. To the west, Yosemite National Park suffered approximately $178 million in damage. Here in the Mono Basin the damage was less severe but the high water was still quite eventful. The stage was set when winter storms pounded the Mono Basin from late October through the end of 1996, blanketing the Sierra Nevada with more snow than arrived during the same period of the winter of 1982-83, the wettest on record. The Gem Pass snowpack, at 10,750 feet above sea level in the Rush Creek watershed, tipped the scales with a December 30 water content of 209% of average. Then, over the two days prior to January 1, the temperature stayed warm, night and day. On New Year's Eve it started to rain; by New Year's morning, Tioga Pass Resort reported heavy rain--at well over 9,000 feet above sea level. The warm temperatures and heavy rain continued into January 2, causing Mono Basin creeks to rise dramatically throughout the day. Beartrack Creek flooded old Highway 120 and deposited rocks and sediment on the road after its culvert became plugged. Bohler Creek cut a gully through Aqueduct Road and flooded Cain Ranch Road. South Parker Creek flooded and gullied Parker Lake Road. While Grant Lake Reservoir insulates Rush Creek below Grant Dam from upstream events, Walker and Parker Creeks backed up at their Highway 395 culverts, and contributed their flows to Rush Creek further downstream. I was on Aqueduct Road between Parker and Walker creeks as they were rising on Thursday, January 2, and DWP crews, who were out repairing damage and monitoring the situation, warned me that I would be stuck if Parker Creek washed out the road, and also mentioned that Lee Vining Creek could peak as high as 600 cfs! Lee Vining Creek did indeed give the most impressive show. It quickly rose above the top of the gauge on the flume above the diversion dam, which means it was running at over 400 cfs--well above the average peak runoff for early summer snowmelt. The heavy rain continued into the night; then the temperature finally cooled down, and it snowed several inches by sunrise. Friday, January 3, was a beautiful sunny day. At the Information Center and Bookstore in Lee Vining we recorded 2.33 inches of precipitation (almost all of it rain) between Dec. 31 and Jan. 3. It washed away almost all of the snow on the ground at our elevation. The creeks were still high, and some of the flow of Parker and Walker creeks was being diverted to Grant Reservoir in order to prevent flooding of roads. At the higher elevations, Tioga Pass Resort had suffered water damage when the rainwater began to run on top of the snow and ice, flooding the lodge, instead of flowing at ground level in the creek. Lee Vining Creek had peaked at over 700 cfs at the diversion dam, causing some minor damage to DWP's aqueduct facilities. During peak flows, about 230 cfs had been diverted from Lee Vining Creek to Grant Reservoir due to concerns about subsidence at the Edison substation. On lower Lee Vining Creek, where most vegetation was destroyed by past water diversions and is just beginning to recover, there were significant changes caused by the high flows. The main channel shifted in certain areas, and new pools formed. Some side channels went dry, while the A-4 channel, the most recently rewatered side channel, gained about half of the streamflow. This created new floodplain surfaces and raised the water table between this channel and the main channel. Scientific fieldwork is planned to document the changes, and the implications for restoration remain to be seen. All the high stream flows ultimately added to Mono Lake's surface elevation: the lake rapidly rose three tenths of a foot over a two week period--representing an inflow of approximately 12,600 acre-feet--and on Saturday, January 4, the lake stood at an elevation of 6380.4 feet above sea level. It's even higher now--see Lake Level Watch for details! Greg Reis is the Committee's Information Specialist. He's unnervingly cheerful about chasing down high flows on Mono's creeks in the midst of storms and snow.
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