The Army Corps of Engineers began a controlled release of the reservoirs around 1 a.m., in an effort to protect the city from further flooding.
Bear Creek Village, near Addicks Reservoir, started seeing a gradual rise in floodwater levels around 4 a.m., said Jeff Lindner, with Harris County Flood Control District.
By noon today, the Canyon Gate subdivision near Barker Reservoir is expected to see more water spilling into roadways, flooding homes.
Roadways around the reservoirs are expected to be underwater, and officials said houses will flood in at least these two neighborhoods.
The reservoir water levels increased dramatically late Sunday night, prompting the need for the release.
Dr. Edmund Russo, with the Corps of Engineers, said 25 inches of rain had already been added to the reservoir. The National Weather Service warned another 25 inches could be coming over the next several days.
Even with the controlled release, the reservoirs are rising at a rate of four inches per hour, Russo said.
"This event has the potential to exceed a 1,000 year flood plain threshold," Russo said, in a press conference on Monday morning.
Lindner explained there is more floodwater flowing into the reservoirs from Waller, Ft. Bend and west Harris counties than is being released.
Addicks Reservoir is already slightly above the levels seen during the Tax Day floods in 2016, Lindner said.
About 812 cubic feet of floodwater is being released per second at both dams. By noon, that number could increase to about 8,000 cubic feet of water per second.
While a number of mandatory and voluntary evacuations have been called, Lindner did not expect the need for additional evacuations.
To download the maps, visit Harris County Flood Control District's website.