In a race against the clock and the clouds, East Ascension drainage officials have opened the once-closed Frog Bayou floodgate and kicked on two powerful, portable pumps to lower water levels in Bluff Swamp in double time, parish officials said Tuesday.
East Ascension Drainage Director Bill Roux said parish officials are trying to lower high water in the Bluff Swamp before the next major rainfall to avoid possible house flooding along the swamp’s perimeter in the northwestern part of Ascension Parish.
Heavy rain in December and early January drove up water levels in Bluff Swamp, Frog Bayou and Bayou Manchac and before that water could be drained, a major storm front in mid-January pushed levels up further, dumping more than 10 inches of rain on Gonzales alone.
“What’s really scary is having that big (water) elevation in there and not being able to bring it down and have another rain event like we had two weeks ago on top of that elevation (in the Bluff Swamp), then we would have house flooding,” Roux said.
The low-lying Bluff Swamp acts as a rainfall runoff storage area for an upper section of East Ascension and is drained by Frog Bayou into Bayou Manchac.
Floodgates at the junction of Frog Bayou and Bayou Manchac — operated by Ascension Parish government — normally control drainage through gravity flow.
The pumps needed to expedite draining excess water from the swamp were installed next to the Frog Bayou floodgates on the Bluff Swamp side of Alligator Bayou Road. The pumps’ two 42-inch discharge pipes are now in place across Alligator Bayou Road to carry water pushed by the pumps into Bayou Manchac, parish officials have said.
Roux said the two pumps, which began running early Friday afternoon, were being operated virtually nonstop at a combined rate of 120,000 gallons per minute, more than double the capacity of the Frog Bayou floodgate.
The floodgate, which drains about 100,000 gallons per minute by gravity flow from the swamp, also was reopened Friday, Roux said.
The Frog Bayou floodgate cannot be opened and also serve to prevent high water in Bayou Manchac from backing up into Frog Bayou and the Bluff Swamp when the water elevation in Bayou Manchac is higher than the elevation in Frog Bayou and the swamp, however.
Roux said that was happening periodically in late December and early January and again in mid-January. This resulted in a situation in which not only were the Frog Bayou floodgates kept closed, but also the nearby floodgates at Alligator Bayou had to stay shut.
Spanish Lake drains through Alligator Bayou into Bayou Manchac.
Manchac’s water level at the Alligator Bayou floodgate gauge peaked at more than 13 feet on Jan. 15, for example, the U.S. Geological Survey says. At the same time, water elevations in Alligator Bayou had reached a little more than 9 feet.
Roux said officials were not sure at that point whether the Bluff Swamp could be drained through the Frog Bayou floodgate quickly enough, so officials rented the two big pumps.
Roux said parish officials want to lower the water elevation of Bluff Swamp and Frog Bayou about 4 feet, a process that would take 22 days by using the floodgates alone.
He said with pumps running and the Frog Bayou gates open, the 4-foot elevation drop is expected to take 11 days.
Frog Bayou does not have a depth gauge but its water level is now a few inches below the level in nearby Alligator Bayou, Roux said. A gauge showed the water elevation in Alligator Bayou at the Bayou Manchac floodgate standing at 8.74 feet about 1 p.m. Tuesday, USGS says.
The Frog Bayou pumps and their installation, however, have forced the closure of Alligator Bayou Road since Friday, parish officials have said.
The floodgate at Alligator Bayou, which Iberville Parish government controls, also was opened Friday, Roux said.