Some beaches change all the time. Or at least you can be pretty sure that if you haven't been there in while, it will be different when you come back. This beach isn't one of those. It has few degrees of freedom - admittedly, that was a key point of its design. It's the beach equivalent of putting a wide-ranging predator in a small enclosure in an old-fashioned zoo. Not very authentic, but much easier to manage.
The sediment is all nicely sorted gravel. Which means the beachface remains the same in both shape and texture. The coarse gravel also tends to stay high on the beach - it has less tendency to want to get lost offshore (ignoring stone-throwing children). The two rock groins assure that no material escapes and therefore the beach volume and position don't change. The groins also constrain the small opening of the beach to Elliott Bay which assures that the wave regime is limited and the beach can't shift back and forth too much in its cage.
I love this little beach and wish we could incorporate beaches into our urban shorelines more often. But I also think it is a good reminder that we shouldn't confuse domesticated beaches for wild ones. On the surface, they may look similar, but the domestic ones are more predictable and as a result, may have a little less character.