Exercise 1 solution

1 Sv = 1,000,000 m3/s.
20,000 m3/s = 20,000 / 1,000,000 = 0.02 Sv.

Number of such rivers for 30 Sv: 30 / 0.02 = 1,500 rivers (equivalently 30,000,000 / 20,000 = 1,500).

So the Gulf Stream at Florida carries as much water as about 1,500 rivers of that size, a very large river by any standard.