MERCEDES, Texas (Border Report) -- Historic flooding in the Rio Grande Valley border is going down slower on the east side of the region but should now get some help from some gates opened on Monday, Border Report has learned. WATCH: ‘Heartbreaking’: Rescues underway as historic flood ing hits South Texas border The International Boundary and Water Commission opened special diversion gates on Monday after water flows reduced enough to operate the special equipment, Hidalgo County Drainage District Manager Raul Sesin told Border Report. Hidalgo County Drainage District General Manager Raul Sesin said Monday, March 31, 2025, that flatter lands on the eastern part of the Rio Grande Valley are adding to slower draining of flood waters. (Sandra Sanchez/Border Report) "That started today. They started opening some gates to try to divert because our water flows west to east," Sesin said from his offices in Edinburg where his team of drainage engineers and specialists have been working around the clock since historic rains began Thursday afternoon. Some places received over 20 inches of rain in the Rio Grande Valley, and a tornado touched down Thursday near Edcouch-Elsa. Texas Gov. Greg Abbott on Saturday issued a disaster declaration for four counties in the region including: Cameron, Hidalgo, Starr, and Willacy. Municipalities are working with state and federal officials to surge resources to the region. About half of the water has already gone down, Sesin said, but it's not even throughout the Rio Grande Valley. Most of the water has gone down in the western part of the Rio Grande Valley and he attributes that to improved drainage structure that the county has spent millions of dollars to upgrade, as well as the hills in the region that allow the water to move more quickly. Vehicles are submerged as a high-water rescue vehicle maneuvers around stalled cars on Friday, March 28, 2025, in Weslaco, Texas. The area received about 18 inches of rain in a couple hours. (Sandra Sanchez/Border Report) But east of the flood spillway in the mid-Valley city of Mercedes, the water moves surprisingly slow, he said. The elevations vary from 350 feet above sea level in parts of Starr County and 270 feet above sea level in the west part of Hidalgo County, to just 50 feet above sea level in Mercedes. East of that it drops to sea level heading to the Gulf. All that water from the rainfall has to move through the county's main drain system, which also suffered some delays due to debris that caused back ups. But flat lands, he said, have been the most difficult to overcome. “It is challenging to move water out of flat areas or low areas. Very challenging, we have a lot of challenges in that areas because the water tends to stagnate or move very slowly," Sesin said. The opening of the IBWC gates allows some water to be diverted into the Arroyo Colorado, not to the Laguna Madre at the Gulf. Sesin says that should help the water to go down in subdivisions and on roadways in the eastern part of the Valley quicker. "Staff are patrolling levees to ensure gate structures are set to aid in the drainage of localized runoff into the floodways," IBWC U.S. Commissioner Maria-Elena Giner said in a statement. "If necessary, excess flood flows will be diverted into the Mexican floodway at Retamal Dam, upstream of Progreso, Texas." An IBWC official told Border Report on Monday that the waters were receding and teams were working together to help the region. Since 2018, Hidalgo County approved two bonds for drainage improvements totaling $385 million. The second bond was approved in 2023 and some of that work is still ongoing, Sesin says. The drought the region has been in did not enable his crews to test some of the new equipment the county has acquired from these renovation projects. That includes nine new pumps that were put to their first use this past week, he said. The Water District is also working with the Texas Department of Transportation, and it wants to start a new project to help reduce flooding on frontage roads, which caused many cars to stall and sink and residents to flee and abandon their vehicles on the highways on Thursday evening. Sesin says pumps are working overtime, and as long as the rains don't return, he says he believes they will have all of the water cleared in the upcoming days. "The blessing that we've received that we did not get any additional rain, so that it allowed us to continue our operations and move water sufficiently out," he said. Sandra Sanchez can be reached at SSanchez@BorderReport.com. ...read more read less