When looking at the NOPD cars they are clearly missing their yearly inspection sticker on the drivers side. All cars (personnel or city owned) are required to have them in New Orleans.
The exhaled breath of characters speaking to each other outside during the Mardi Gras parade is clearly visible. This almost certainly reveals the location not to be New Orleans in the spring time.
The rescue team that was used in this movie was hired locally. Among the rescuers you can clearly see their actual uniforms displaying the rescue teams patches "OVERT" which stands for "Ontario Volunteer Emergency Response Team".
New Orleans is below sea level resulting in a high water table. If you dig a hole a few feet deep it will likely fill with water. Yet in this movie the tunnels are 60-feet below ground and are bone dry despite being well below the water table.