HELP!!!! what does this meann!!?!?

It sounds like an account of flood abatement. A diversion channel would be a ditch going away from a house or something, that would divert water away from something. Blast away the debris means there is stuff from the flood. like wood, parts of cars, etc, damming the way the water could flow if the debris were removed. So the soldiers will use dynamite or special guns to cause the debris--trash--to be moved.