LAKEPORT >> Phil Moy, Water Resource Director for Lake County, said he would be looking into trying to reducing the Grigsby Riffle back to historic levels in order to help prevent future long periods of flooding. He made the statement during an update to the Lakeport City Council on the Cache Creek Dam and the water levels of Clear Lake this week.
Cache Creek Dam is operated by Yolo County Flood Control and Water Conservation District. The gates of the dam have been open at maximum capacity since the second week of January with only brief closures to remove debris.
However, even though they are open, lake levels continue to fall extremely slowly. This is because the dam is not able to discharge as much water as it would under ideal circumstances. During the month of February, the dam was only able to drain about one tenth of a foot per day. The location of the structure, downstream from the Grigsby Riffle in a narrow stretch slows the process.
“It’s sort of like a clog in your artery,” Moy said. “You could have an open artery with a wide-open flow, and the Grigsby Riffle comes along and it’s this rock sill and constrains how much water can get past that and that’s what controls how much water can get out.”
Currently the lake is being drained at around 3200 cfs (cubic feet per second). Moy added that, depending on the lake level, it can vary between 3500 to 4700 cfs. Some days it can be higher due to inflow of other creeks such as Copsey and Herndon Creeks.
From the slow outflow and the riffle, the lake levels will likely stay high through March, Moy said. Still, he had asked to reopen the lake for economic benefits because the lake brings in a lot of money to the county through boating permits and fishing tournaments.
“While it’s a little bit better than it might have been in the 1890s and early 1900s it is still a constraint,” Moy said of the water flow.
Lakeport City Council member Kenneth Parlet said after being in a drought for the past several years, removing the riffle would not be a high priority. However, looking at it now this should be looked into further.
“Due to siltation and infill we are over what the original free flowing level would have been,” Parlet said. “So we would be in our rights to go in and remove some of that.”
City Council member George Spurr said the riffle has since increased in size since early 20th century legal battles over the location.
“Looking at those figures we could at least take it down another foot because we’ve come up a foot and a half from what it was from when those laws were passed,” Spurr said.
