Harbor Vista - best in Large!

I went to a place today from where you can see the Siuslaw River Mouth. It is called Harbor Vista because the flat on the right of the black dam(called North Jetty) that is holding back the river must have been a former harbor. (That's where some people are digging for clams) The river had a different bed in the old days and with these two jetties it is channeled into its actual bed. The waves often go into the river and make it really wild. I don't understand how these Jetties , consisting of these enormous black lava blocks, can hold the water inside of the bed and do not allow it to flow over the sides. Often the water in the river is clearly higher than the sand in the former harbor. That area gets flooded with the tides, but not very high. On the left side , next to the so called south Jetty, you can see a little piece of the beach with rolling waves. The Kite surfers love that spot. You cannot see more of the beach here because there are high dunes, but it goes in a straight line 30 miles south. A great place for long walks, unfortunately also for a lot of dune buggies.