When the Water Rises . . .

Q What happens to your car if you drive into a flooded area? Will it be permanently damaged?

AWater could get into the tailpipe, reach the engine and mix with oil or transmission fluid to ruin the motor, according to John Townsend, spokesman for AAA Mid-Atlantic. Wet belts could slip off, or water could kill the battery. Water seeping through doors could short out electrical components in the floor. Unprotected metal in the trunk or around doors could rust. Damage might not show up right away, so have a mechanic check the vehicle.

What water level is safe to drive through?

There is no "safe" water level to drive through, authorities say. Whether a car can safely navigate a flooded road depends on the height of the car, the speed of the water, the condition of the roadway and other factors. As a general rule of thumb, U.S. Park Police advise that if you can't see the roadway, you should not try to drive through the water.

What if your car got wet inside because of an open window or sunroof?

If only a little water got in, wipe off the cushions and hope that's enough. But if the upholstery is soaked, mildew and mold will grow quickly. Cushions should be removed as quickly as possible.

What should you do if your basement gets wet?

If it's a major flood, call in a professional cleaner. For less serious damage, click on the "water damage" icon at the Web site of the Institute for Business and Home Safety ( http://www.ibhs.org/ ) and look at the Water Damage Recovery Guide. Among its advice: Act within two days to dry carpeting with a wet-vac or commercial carpet cleaner. Speed the drying-out by running a dehumidifier or a fan. Carpet padding will probably have to be replaced. Unfortunately, most basement flooding is not covered by insurance.

Why is it that creeks flood right after a rainstorm, but it takes two or three days for the Potomac River to reach flood stage?

The Potomac River rolls down more than 300 miles from its starting point in West Virginia, gathering water from creeks flowing in over its 14,000-square-mile drainage area, before it reaches the Washington area and crests. Creeks pull in water from smaller areas, perhaps 100 square miles. It's like the difference between a bucket and a bathtub, suggests Rich Hitchens, a National Weather Service hydrologist: It takes longer to drain the tub.

Why do trees fall over in a big rainstorm, even without much wind?

Trees can fall for many reasons. Among them, according to David Vismara, director of Brookside Gardens in Wheaton, are that their roots lose support when rain erodes stream banks or the ground becomes so boggy that shallow-rooted trees cannot stay upright, especially if their roots are rotted. Even the weight of rainwater could be enough to topple some weaker trees, he said.