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An East Baton Rouge Parish Sheriff's Office vehicle with high clearance goes down Hooper Road to help extract residents from Central and surrounding areas of north Baton Rouge, during flooding, Sunday Aug. 14, 2016.

Advocate staff photo by TRAVIS SPRADLING

When more than 20 inches fell in parts of East Baton Rouge and nearby parishes Thursday to Saturday, all that water tried to start its journey south, swelling rivers, flooding thousands of homes. This slow-moving disaster continues as water makes its way along the meandering route to Lake Pontchartrain.

Not only did the river levels rise in the Comite and Amite rivers, but all the creeks and waterways that feed into those the rivers filled up as well. Like rush hour traffic, numerous creeks and bayous all trying to flow in the same direction as the traffic jam, leading to widespread flooding in the northern part of East Baton Rouge and Livingston parishes.

And the water kept heading south.

“Typically, that north and south flow is via Amite and Comite and tributaries leading to them,” explained Carey Chauvin, assistant chief administrative officer with East Baton Rouge City-Parish Department of Public Works. “As the crest moves down stream, that’s where you see the flooding we’re seeing.”

The large rainfall amounts joined up with water trying to drain into areas already saturated with rainfall and higher water levels. Traveling down the Comite River, which joins with the Amite River at Florida Boulevard, high water in the rivers had nowhere to go but over their banks.

On Saturday, Central Mayor Jr. Sheldon said there wasn’t a road in the city that wasn’t impacted by floodwater in some way. The water rose quickly leaving some people stranded in their homes which lead to rescue operations that continued through the evening and into Sunday morning primarily in areas around Baker, Zachary, Central, Denham Springs.

By Sunday morning, the water in the northern part of East Baton Rouge Parish had started to recede, but the bulge of water started spilling over into North Sherwood Forest Boulevard, Choctaw Drive, O’Neal Lane and places south.

“Tributaries being full and water having nowhere to go,” Chauvin explained.

By Sunday night, the water was still working its way down through the system and causing record-breaking river flood levels. The Amite River at Port Vincent was still on the rise, expected to ultimately reach a record-breaking level of 17.5 feet Monday morning. Farther downstream, the Amite River at French Settlement was expected to crest at 8.7 feet either Monday evening or Tuesday morning.

As the water moves closer Lake Pontchartrain, northern sections of the Amite and Comite begen to fall, but it will take some time before they reach normal levels for this time of year.

“It’s going to take days for that water to come down,” Chauvin said.

In the meantime, as rain is expected to continue throughout the week, local tributaries like Bayou Fountain, Bayou Duplantier or Ward Creek will have little room to accept more water. All of these, as well as most waterways in south Baton Rouge, flow into Bayou Manchac and then into the Amite River. As long as the Amite River remains high, any additional water trying to drain out of these areas will have no place to go.

Although the additional rain isn’t expected to have much impact on river levels, it could still add to localized flooding.

“The biggest problem is going to be for the backwater areas because the rivers won’t allow it to drain,” said Jeff Grashel, National Weather Service hydrologist. Because this is such a historic event, it’s going to be difficult to see how this extra water might move over the land.

“It’s unprecedented and it’s not anything, anyone will know for sure,” Grashel said.

This backwater flooding occurs as water overflows the banks and works its way through the landscape, also called backwater flooding. Where that could end up is almost impossible to tell at this point because of the sheer amount of water involved and no history of how the water would move.

“We’re so far above what is normal flood stage,” Chauvin said, adding that some stream gauges aren’t even registering a rise anymore because they’re already under water. “We’re urging extreme caution to all residents.”

If someone lives along Bayou Manchac or one of the many tributaries to the bayou, be careful, he said.

“We know we will have a backwater condition there,” he said.

Follow Amy Wold on Twitter, @awold10.