Major and Minor floods are two stages of Floods :
Minor Flood Stage
Rivers: minor flooding is expected at this level, slightly above flood stage. Few, if any, buildings are expected to be inundated, however, roads may be covered with water, parklands and yards may be inundated and water may go under buildings on stilts or higher elevations.
Coastlines: water will usually run all the way up to the dune in waves during a minor flood. Overwash may occur on shoreline roads. Lifeguard structures and beach concession stands will usually be flooded, and may be damaged by surf.
Major Flood Stage
Rivers: significant to catastrophic, life-threatening flooding is usually expected at this stage. Extensive flooding with some low-lying areas completely inundated is likely. Structures may be completely submerged. Large-scale evacuations may be necessary.
Coastlines: Water surges over not only the dune, but also man-made walls and roads. Large and destructive waves pound weak structures to bits and severely damage well-built homes and businesses. Overwash occurs on high-level seawalls. If major flooding occurs at high tide, impacts may be felt well inland. If cities are at or below sea level, catastrophic flooding can inundate the entire city and cause millions or billions of dollars in damage (such as occurred in New Orleans during Hurricane Katrina).
what/how/why/where the hell?
It is a spoken (not standard English) and impolite phrase used to show that you are very surprised or angry:
• How the hell are we going to do that?