During a large rainfall event, a stream will fill up with water and possibly overflows its banks causing a flood

During a large rainfall event, a stream will fill up with water and possibly overflows its banks causing a flood.

• During this event, when is velocity of water in the stream the highest (half bankfull, bankfull, flood stage)?
• When is total volume the highest (see previous 3 options)?
• If the probability of a particular sized flood in any given year is 0.1%, what is the recurrence interval of this size flood? Show your calculations and explain.
• Finally, explain why paved areas tend to have more issues with flooding than areas surrounded by natural wetlands?