HOUSTON -- The search resumed in Dayton, Liberty County, for a man believed to have been swept away by floodwaters from the Trinity River, KPRC Local 2 reported.

Dayton police, firefighters and volunteers have been looking for Gene Roberts, 45, since Sunday night.

Roberts and three friends were on horseback herding cattle to higher ground when water rose to their horses' chests.

The friends got separated. Roberts' horse was later found unharmed, but tangled in brush.

Searchers have been using small boats, all-terrain vehicles and horses to look for Roberts.

Volunteers with Texas EquuSearch are also providing manpower.

Roberts is a truck driver by trade who loves to rope calves on weekends.

Roberts' family said they are surprised something happened because he was an experienced horse rider.

"He loves to rodeo. He loves horses and that's why he was out here, because he does this all the time," Roberts' wife, Linda, said.

They have been married for 20 years.

"(I'm just) hoping that he comes back," Linda Roberts said. "I know that God does everything for a reason."

She said that is the only thing that is keeping her going.

"We're exhausting every means possible in order to locate him. But with the water being as high as it is, there's still places that's hard to get to," a searcher said.

"The water -- it's very muddy. The terrain is terrible," said Alvin Tipps, with Texas EquuSearch.

"You see this happen to other people all the time, but you never expect it to be you," Linda Roberts said.

The search will continue Monday until dark and will resume at sunrise on Tuesday.

More volunteers are needed. For more information on how to help with the search, call Texas EquuSearch at 281-309-9500.