Ok mate I'll try just for you
Whoever told you lives on another planet.
The river Dour flows into the sea, the sea does not flow into the Dour,the last section between the subway and the Nelson is far too steep for water to come inland.
There are 5 waterfalls between the Dours exit and it's source of which 3 of them are 8 foot plus drops, so no matter what state Wellington dock is in makes no difference.
The water is disappearing from somewhere up stream and my feeling it's Drelingore pumping station.
Does that help at all matey.
