The National Weather Service began sending flash flood warnings that should have triggered cellphone alerts a little after 1 a.m., while local officials began posting on Facebook about four hours later.

Survivors have described the floods along the Guadalupe River as a “pitch black wall of death” and said they received no emergency warnings.

As Central Texas reels from flash floods that killed over 100 people this weekend, questions are sharpening about whether officials could have done more to avert the tragedy – both in the decades leading up to the disaster,