Water seepage prompts examination of Lake Ralphine dam
A small amount of water is seeping through the Lake Ralphine dam at Santa Rosa’s Howarth Park, but there is no safety risk to the public, officials said Friday.
Park workers Thursday evening noticed a wet, muddy area at the base of the earthen dam beside the softball field and alerted city officials to a potential problem, Assistant City Manager Chuck Regalia said.
The city’s building inspector, Mark Setterland, contacted a state dam inspector, Jim Lowe, who visited the site Thursday evening.
City parks workers cleared the area of vegetation Friday morning to provide a better view of the dam’s face. It revealed an area of muddy soil near the center of the dam, running down about 40 feet to the bottom of a staircase near an outlet valve.
“This is a typical phenomenon in earthen dams,” said Lowe, a field engineer with the state Department of Water Resources, Division of Safety of Dams.
He estimated the seepage at less than a gallon a minute. Of the approximately 200 dams he inspects, Lowe said about a third have issues with seepage. The integrity of the dam is not in question, he said. The dam likely has been seeping for some time, as evidenced by grasses and berry bushes growing in the area, he said.
It is possible last year’s Napa earthquake created a “minor disturbance” in the interior of the dam that is responsible for the seepage, he said. Repairing the interior of the dam to stop the seeping at the source is not necessary, he said.
“That would be prohibitively expensive and totally unnecessary,” Lowe said.
There was chronic seepage at the southern end of the 700-foot-long dam in 1968, and the solution at that time was to build a drain of perforated pipe that collects the water and disposes of it, according to a city engineering report. A similar solution likely will be needed at the new seepage location, Lowe said.
Lake Ralphine, a popular boating and fishing spot, was created when the earthen dam was built in 1873 by Col. Mark Lindsay McDonald, one of Santa Rosa’s most prominent early citizens, who named the lake after his wife.
The dam was raised 7 feet to its present height in 1994, and the lake now holds 135 million gallons of water, according to a history of the city water system.
The lake served McDonald’s private utility, Santa Rosa Water Works Co., which was purchased by the city and merged with its water system in 1947.
Just a few years later, in December 1951, a large chunk of the vertical upstream face of dam collapsed and slid into the lake. The lake had to be drained and repaired, requiring significant reductions in water usage during 1952, according to city records.
The lake hasn’t been used as a source of drinking water since 1959, when the city began relying primarily upon water from the Russian River.
You can reach Staff Writer Kevin McCallum at 521-5207 or email@example.com. On Twitter @srcitybeat.