The combination of wind blowing in from the south across Mississippi River water rushing toward the Gulf of Mexico made for a rough ride Friday afternoon as two U.S. Geological Survey hydrologists took out their small boat to get water movement readings at Baton Rouge.

Twice a week as the river water levels remain high, teams from USGS measure the flow of the river to get data that will help U.S. Army Corps of Engineers officials decide how many bays on spillways on the river need to be opened to prevent flooding.

On Friday, it was Scott Perrien, USGS hydrologist, and Todd Baumann, hydrologist and data chief in the USGS Baton Rouge office, who battled the heavy current to get across the river in more or less a straight line to measure just how much water was coming down the river.

The trigger of water flow to open the Bonnet Carre Spillway was reached on Jan. 10, with additional bays being opened all week. On Friday, the Corps opened an additional 24 bays at the spillway, resulting in 124 of the 350 bays now being used to divert water toward Lake Pontchartrain.

The goal of this opening is to keep the river flow past New Orleans at or below 1.25 million cubic feet per second. At the Morganza Spillway near Angola, the trigger for opening is a flow rate of 1.5 million cubic feet per second or more at Baton Rouge. The Morganza structure puts water into the Atchafalaya River Basin.

The Corps announced earlier this week that it is unlikely the flow at Baton Rouge would get high enough to force the opening of the Morganza structure.

To determine that flow, the USGS uses historical data about the river and actual measurements to determine the flow rate. The USGS takes periodic measurements throughout the year to make sure changes in the river don’t influence historical data.

“Out here, it’s so huge, it doesn’t change all that much,” Baumann said.

On Friday morning, the USGS staff made their way carefully across the river, dodging large branches, barges and at one point a very large, and probably confused, water moccasin floating down the river.

With 42.9 feet on the height gauge, USGS anticipated the flow at Baton Rouge to be about 1.315 million cubic feet per second.

The crew usually takes a couple of trips across the river to gather the measurements, but sometimes it can take a few more just to confirm the readings, Baumann said. When the colonel of the Corps of Engineers says we’re pulling pins at Bonnet Carre based on your numbers, he said, you’d better be sure.

After four passes Friday morning, the crew came up with a flow of 1.329 million cubic feet per second, very close to what the water height indicated it would be, Baumann said.

“So far,” Baumann said, “the measurements out here have been confirming (the expected flow).”

The Mississippi River will crest in Baton Rouge on Monday at 43.5 feet. Flood stage in Baton Rouge is 35 feet, but levees protect to at least 47 feet.

Follow Amy Wold on Twitter, @awold10.