Do recent Trinity River flood warnings mean homes are at risk?

The rainy weather that has been dousing North Texas is expected to continue into early next week, prompting flood warnings.

The National Weather Service issued a warning for the Trinity River in Dallas until Thursday morning — one of multiple warnings issued for the river over the last month.

Monitoring and managing the water levels of the Trinity River is an intricate process that requires coordinated efforts of multiple agencies. Here’s what you need to know.

How much water causes the river to flood?

The flood stage of the Trinity River at Dallas is 30 feet, according to the Weather Service. The river was already seeing minor flooding when the warning was issued Wednesday, with levels at 34.6 feet by 8 a.m. By 5 p.m., the levels were at 33.1 feet.

There are minor and major flood stages that can happen in the river, said Sarah Standifer, assistant director of Dallas Water Utilities. But even crossing a major flood stage doesn’t necessarily mean a widespread threat to the neighborhoods along the river.

“We are in a minor river flood right now,” she said. “That level would indicate that we’re just right above the bank of the Trinity itself. When we get into major flood stages, that means that it’s coming up onto the levees, [but] it doesn’t necessarily mean it will overtop the levees.”

Minor flooding can affect some low areas, crossings and agricultural lands, according to the Weather Service.

Water levels above 40 feet would produce major flooding, which has happened six times in the last 20 years, according to Weather Service figures. It happened most recently in May 2015, when storms caused the river to rise to nearly 42 feet in parts of Dallas.

How do officials manage flood risk?

The Trinity River is monitored and maintained by the city of Dallas and the U.S. Army Corps of Engineers in Fort Worth.

The city has a levee system that’s regulated by the corps, which is responsible for managing the flood risk, Standifer said.

“We have different man-made features, whether they’re levees or pump stations or natural features. … the Trinity Forest is actually the floodway, so those different features all work together,” she said. “The city maintains those features, the corps regulates them, inspects them [and] provides assistance as needed.”

The U.S. Army Corps also mitigates the risk of the Trinity River through reservoirs. The corps controls eight in North Texas: Benbrook Lake, Joe Pool Lake, Ray Roberts Lake, Lewisville Lake, Grapevine Lake, Lavon Lake, Navarro Mills Lake and Bardwell Lake.

During heavy rain or flooding, water is held in the reservoirs until the river is at a safe level for it to be released downstream, said Clay Church, a public affairs specialist for the corps.

There are 11 control points along the river that the corps monitors to determine when and where to release water from the reservoirs, Church said. Six of those control points were above the flood stage Wednesday evening.

“It just depends on which fork of the river you’re on, and what’s going on upstream and downstream of the river,” he said.

The city of Dallas also runs a 24-hour operation with more than 200 staff members who monitor and respond to conditions in neighborhoods and local areas, Standifer said.

The team responds to 311 calls for flooding and monitors things including inlets, which are storm water pipes that carry water from neighborhoods to creeks or the Trinity River.

Standifer said the city has responded to more than 400 calls related to flooding over the last month. Most of those came in during the same week after heavy rain in mid-May, Standifer said.

“Many are in known low-lying areas, we have low water crossing bridges throughout Dallas, and we have thousands of acres that abut adjacent to creeks and channels,” she said, adding that it’s not unheard of for the city to get that many calls after heavy rain. “Some are known areas and some are areas where there has been a blockage or something that created a scenario that is not typical.”

Standifer said that if the Trinity River were to flood, it doesn’t mean the neighborhoods surrounding it will, too.

A common blockage problem the city sees this time of year is a result of residents blowing their grass clippings and leaves into an inlet after mowing, Standifer said.

Will major flooding happen in the river this year?

The recent downpours across North Texas follow a wetter-than-usual May, with a total of about 7.8 inches of rain across 19 of the 31 days of the month, according to KXAS-TV (NBC5). Dallas-Fort Worth usually gets about 4.8 inches in May.

While meteorologists say the multi-day rains throughout May have pulled Dallas-Fort Worth out of a drought, those storms have caused the water level of the Trinity River to rise so high that even a small amount of additional rain could cause flooding in some areas.

“This is the highest all of the lakes have been all year,” said Greg Waller, a service coordination hydrologist at the Weather Service. “We’re in a persistent rain pattern, and we’re to a point that a thunderstorm that produces an inch of rain is producing flooding.”

He said he has been referring to the recent rainfall as “May 2015-lite.’”

During the 2015 storms, the rainfall was greater and the affected areas were larger.

“We’re getting enough breaks for some of the water to drain downstream,” he said.

Standifer and Church said they don’t expect major problems with the river this year.

Church said each of the eight reservoirs has plenty of capacity to hold more flood water.

“The rivers and streams and the lakes are doing what they’re designed to do,” he said. “There’s not a real big concern at this point on capacity or on the capabilities of the lakes and floodways to do their jobs.”

What are the risks if the river does flood?

Church said one of main risks in major flooding events are the effects on wildlife.

“The thing that we caution people on, especially if they’re going to be out at our lakes in a recreation-type environment, is with those high [water] levels, the fire ants and other animals and snakes will follow the water line up,” he said. “A lot of times there might be some wildlife or other creatures that may show up where they normally aren’t seen.”

He said boaters also should be cautious going out on the lakes during heavy rainfall. Lake Worth in Fort Worth, for example, is already above flood levels.

“Picnic tables, grills, things of that nature may be underwater now,” Church said. “Boaters need to be really conscious about where the shoreline is in relation to some of these things that normally are out of the water.”