EDINBURG — With the threat of more rain Tuesday night, Hidalgo County officials raced to bolster the drainage system that reached capacity following the Monday night storms that dropped more than a foot of water in less than six hours.

More than 12.2 inches of rain fell Monday night as a front clashed with a hot air mass and 4- to 5-inches more were expected Tuesday night, Hidalgo County Emergency Management Coordinator Ricardo Saldaña said Tuesday afternoon.

Monday’s rain caused major flooding along the Hidalgo-Cameron county line — especially in Harlingen, Mercedes, Weslaco, Monte Alto and the Delta area — and maxed out the county’s capacity to retain water.

Hidalgo County Drainage District 1 began releasing water into the International Boundary and Water Commission floodway on Tuesday, District Manager Raul Sesin said. But because of the amount of water in the system, he estimated it would take up to 24 hours to create 20% capacity.

“ Our system is full. However, we have seen a lot of drops in areas — up to 4 feet in some. Water is moving,” he said, noting all of it had positive flow. “The system is flowing very well. We have not seen any obstructions.”

All of the IBWC floodgates were also open.

“ They have never been closed,” Sesin said.

Crews also placed pumps to help move water faster from the county’s system over the levee and into the IBWC floodway, the district manager said.

Still, many homes were flooded throughout the eastern portion of the county because of the large amount of rain that fell there in a relatively short amount of time.

“ It’s just something that the system is not able to handle,” Sesin said about the heavy downpour.

Fortunately, the west side of the county did not receive as much rain as the east, because it would only have added to the flooding there as the water flows naturally from east to west, he said.

Early estimates indicate the weather event might be classified a 500-year storm because of its intensity, but that designation was not official as of Tuesday. Still, the deluge caught many by surprise.

“ The forecast was 1-to-2 inches,” Sesin said.

Emergency management officials did not release any preliminary figures regarding the number of flooded homes and businesses as they worked Tuesday to assess the damage.

“ I know there was a number of water rescues overnight,” Saldaña said. “I don’t have those numbers, but I can tell you it was probably over 100.”