Swollen Texas rivers prompt evacuations, severe weather kills 21

DALLAS (Reuters) - More heavy rain caused Texas rivers to overflow their banks and prompted widespread evacuations on Friday after a week of historic storms flooded Houston, killed at least 21 people and damaged more than 4,000 buildings.

Thousands of cars were trapped for about six hours on a suburban freeway blocked by floodwaters near Dallas, where rainfall reached about seven inches (17.8 cm) between Thursday night and Friday. The Red Cross distributed Girl Scout cookies and water to stranded motorists.

"The back roads are all blocked by high water crossing barricades, so we're just kinda stuck." Vanessa Paterson, who was trapped on the highway with her 6-month-old son, told TV station WFAA.

The National Weather Service issued a flash flood watch from Central Texas into Missouri, with the additional rain swelling Texas rivers already at dangerously high levels.

Texas Governor Greg Abbott has declared 70 counties disaster areas and called on Texans to heed severe weather warnings.

The mayor of Wharton, about 60 miles (100 kms) southwest of Houston, issued a mandatory evacuation order for about 900 people living near the Colorado River, which began flooding into the city on Thursday and has been rising steadily since.

Across Texas, people spent the night in shelters as this week's floods turned streets into rivers, ripped homes off their foundations and swept over thousands of vehicles.

The Brazos River began overflowing its banks on Wednesday in Parker County about 30 miles (50 kms) west of Fort Worth, forcing people out of homes in low-lying areas. County officials said after the storms overnight, another surge is coming.

"This situation will get worse before it gets better," said Parker County Emergency Management Coordinator George Teague.

The rushing water trapped people in cars and houses, prompting hundreds of calls for help in North Texas. Near Austin, firefighters rescued 21 people from a drifting houseboat overnight.

The rainfall for May across the state has already set a new record and more storms were on tap for large parts of Texas over the weekend.

In Wimberley, near where at least seven people have been killed in floods, residents took time out from searches and clean-up for a high school graduation ceremony.

"Watching our kids for the past three days come and pick up shovels and go to neighborhoods and step in and help with clean up has just been awesome," said school district superintendent Dwain York.

(Writing by Jon Herskovitz in Austin, Texas; Reporting by Lisa Maria Garza in Dallas and Jim Forsyth in San Antonio; Additional reporting by Marice Richter in Dallas and Heide Brandes in Oklahoma City; Editing by Lisa Lambert and Doina Chiacu)