Lake Arrowhead Opens Spillway After 6 Years - Mountain News : News

Lake Arrowhead Opens Spillway After 6 Years

By Christian Shepherd, Reporter | Posted: Thursday, March 14, 2019 9:00 am

After several heavy rain and snow storms have hit the mountain in the last few weeks, the Arrowhead Lake Association (ALA) opened Spillway Gate One multiple times during the last week as the lake approached the 6-inch above full mark.

The gate was first opened at Thursday, March 7 at 9:30 a.m. and was closed on Saturday, March 9 at 8:30 a.m. The lake dropped around 1.8 inches during this 47-hour period. It was opened again on Tuesday at 8 a.m.

This is the first time the lake has been full since May 23, 2012, said Ralph Wagner, retired hydrologist and ALA board member.

The decision was made by ALA to open the spillway after taking into consideration current lake levels, forecasted storms and the incoming runoffs from 27 sources of water that flow directly into the lake.

Wagner said the fullness of the lake is due to larger than average rainfall that began in January.

“The mild El Niño arrived in January 2019 with about 12.09 inches of precipitation (162 percent of normal) followed by 20.43 inches in fabulous February (264 percent of normal),” Wagner said in a recent Water Watch report. “All of these precipitation events raised the lake level to 5,105.69 feet on March 1, just 12.12 inches below being full.”

“The total precipitation in that five-month period was about 41 inches (157 percent of normal),” Wagner added.

Wagner said that if the spillway had not been open, many piers on the lake would have been flooded and docks would have floated onto the lake.

“It is estimated that about 415 acre-feet of water had been released from the lake, or about 135.3 million gallons over the 47-hour period at an average rate of about 47,964 gallons per minute,” Wagner said.

Ric Fratus, head of member relations for ALA, said increased snowfall does not necessarily mean more water runoff into the lake.

“If the snow evaporates we get nothing,” Fratus said. “If there is rain right after a snow event the contribution is much more.  It also depends on how packed the snow is as well as the temperature.”

The spillway flows into Willow Creek, which is managed by the Mojave Water Agency.

As of March 11 at 8 a.m., the gates remained closed and the lake level is still 4.5 inches above full.

“The lowest level of the lake was in October of 2004 when the lake level was 5,085.42,” said Fratus.

ALA will continue to observe the lake level and reassess the spillway every 24 hours, added Fratus.

Christian Shepherd can be reached at cshepherd@mountain-news.com.