SANTA CRUZ, Calif. (KGO) --The Bay Area's recent El Nino-fueled storms have helped rivers and creeks rise to levels we haven't seen in years.
"So once we lower it down it makes contact with the water surface," Santa Cruz County Redwoods State park Henry Cowell said.
Technology from 1938 was being used on the side of a bridge over the San Lorenzo River.
In a little redwood building, the modern equipment uses satellite, radar and tiny bubbles of nitrogen. "It's extremely accurate, we measure water surface to .01 of a foot," USGS Hyrdologic Technician Anthony Guerriero said.
The city of Santa Cruz needs that precision. "This gauge is fundamental, it's the foundation of all of our water supply planning," Santa Cruz Watershed Manager Chris Berry said.
And thanks to El Nino, that planning is cautiously optimistic.
But all that water can be a double-edged sword and that's the other purpose of these measurements: To know when the communities downstream need to prepare for flooding.
Knowing how high the water is only paints part of the picture because you have to know how fast it's moving.
The US Geological Survey calibrates stream gauges with tools or the more modern replacement. "Using sound waves and measuring the time it takes for those sound waves to return to the sensor," US Geological Survery Bruce Cyr said.
Measuring currents at all different depths, makes a map of the ever-changing world beneath the surface. "Vegetation grows, trees fall into the channel, things like that, so it takes regular calibration to know that the data we're producing is correct," Berry said.
With careful measurements and a lot of math, they boil it down to a single number reported every 15 minutes day and night. "That data is then gone to the decision makers who decide when to activate the emergency alert system to warn people that flooding is imminent," Guerriero said.
The rivers have risen several feet since the rain began, but so far it's all smiles. "We've had good gentle rain, which his good for recharging the aquifers and we don't have flooding problems when we have gentle rain which is a good thing," Berry said.
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