In Deserts of Southwestern North America Developers Often Build Houses

In deserts of southwestern North America developers often build houses in dry stream beds and build only minimal subsurface drainage systems to handle a flow of water comparable to the size of the dry stream channel.Is this a reasonable development model in the interest of public safety?

A) Yes,although flash floods can occur,using the channel size is a reasonable estimate of the maximum flood size.
B) No,flash floods can produce high viscosity mudflows that would not be captured by the drainage system and could flow out over the valley,destroying everything in its path.
C) No,giant rock avalanches could come down the valley covering houses.
D) Yes,any potential flooding catastrophe would be a 100 year flood event and would have adequate warning to evacuate people for safety,so the drainage system is adequate.