After burning nearly 4,600 acres and destroying nearly 70 homes, the Hidden Pines Fire remains at 80 percent containment. As people in fire-damaged areas of Bastrop County take more steps toward the recovering, officials and residents are preparing for expected flooding this weekend as investigators determine the cause of the fire.

Rain ahead

The rain that started falling on Central Texas today is expected to be followed by heavier rainfall in the days ahead. Larry Hopper, a meteorologist with the National Weather Service, says a number of ingredients are coming together to produce the most rain this area has had in months. Hopper says moisture from the Gulf, a cold front and a tropical system in the Pacific, all headed this way.

“Getting all those things to find out when specifically the greatest threat is, is still a bit of a challenge at this point,” he says. “But certainly we do believe that sometime between Thursday evening and early Sunday morning there’s going to be at least one fairly heavy rain event somewhere over our area, and there could be possibly more than one.”

The Weather Service forecasts a 70 percent chance of rain for the Austin area today, with Friday and Saturday chances at 80 percent.

Increased flood risk

The areas in Bastrop County scorched by the blaze could see a lot more runoff and potential for flash flooding if heavy rains in the forecast materialize. University of Texas hydrology professor Bayani Cardenas says it’s because of a thin waterproof layer that forms when organic material is burned.

“I would say expect a lot of runoff and erosion. And we saw that with the fires of a few years ago,” he says. “Bastrop State Park lost a lot of its topsoil cover because of that same reason.”

Cardenas compares the occurrence — called hydrophobicity — to pouring water on a rain jacket.

Adding to the likelihood of flooding is the lack of a tree canopy to capture rainwater. But, he says after that waterproof layer washes away, the ground can absorb even more water than it could before the wildfire.

Investigating the fire’s origin

While the cause was initially attributed to malfunctioning farm equipment, officials are also examining the possibility that the Hidden Pines Fire was started by a burn ban violation. That investigation is ongoing, but the fire's so-called burn scar could help investigators discern the fire's epicenter.

So, when the rain passes and the wildfire’s eventually all been put out, what does the burn scar pattern look like?

Captain Andy Reardon with the Austin Fire Department says a fire’s footprint, strangely enough, often looks like a hand. The wrist is typically the fire’s point of origin, and it’s typically going to be the most heavily burned part of the wildfire. The fingers are small, strong fires sparked by fuel or heavy winds. They are small origin points branching out from the main one. Finding your way back to that main point – or, if you’re still with me, your wrist – helps if there are burnt objects to study. As troubling as it is, scorched homes, vehicles and farm equipment also provide vital clues.

“We can look at them also and see if, given the damage they have going on, those are anywhere near the origin and then we can start doing a little bit more investigation. Who owns them? Were they running at the time? Those kind of things that happened.”

Reardon says they’ll also look at burn patterns on trees, and in which direction the grass flipped when it burned. It should all point back to the ignition spot. Again, like tracing each finger, or small fire, back to where it came from: the wrist.