SAN FRANCISCO (KCBS) – KCBS has learned that San Francisco water officials warned river-rafting guides about potentially dangerous river flows on Tuesday, the same day a Sausalito woman died on a trip on the Tuolumne River.

Mariati Tani of Sausalito drowned when the guided boat she was in wrapped around a rock during a trip near Yosemite.  All four others in the boat made it to shore safely.

River flows on that stretch of Tuolumne are impacted by releases of water from Hetch-Hetchy reservoir to down stream powerhouses. The water then flows back into the river. The waterway is controlled by San Francisco Public Utilities Commission, which oversees the Hetch Hetchy system.

Officials said a generator failed Tuesday causing the flows to be restricted.

“At 9:15 a.m. on July 31st one hydroelectric generator did go down from the Hetch Hetchy power system, so we immediately proceeded to notify the rafting community via email and also personally went out to talk to each party before they pushed off before their rafting trip.”

That was according to Tyrone Jue of the the SFPUC.

A Tuolumne Sheriff’s spokesman told KCBS that investigators found the lowered river levels exposed rocks and hazards causing the run to go from a tumbling Class 3 to a much more hazardous Class 5 rating.

“A lower flow will definitely change the river conditions and it also affects the window of rafting opportunities because you need a high-flow in order to raft,” Jue said.

Jue added they are working with the Sheriff’s department to determine the exact time line of the accident and to see what role the release played in the accident, if any.

Calls by KCBS to the rafting company Zephyr Whitewater of Columbia have yet to be returned.

(Copyright 2012 by CBS San Francisco. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.)


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