flood is the water that overflows the river bank & a riverbank is made of soil -> when it floods, land will underflow the sand on the stream under_mattress when it floods, water will overflow the soil on the river bank  when it floods, water will overflow the soil on the river bank & a drain is a mean of moving land & soil erosion is when moving water moves soil from fields / environments -> a flood overflowing the riverbank will cause soil erosion