I don't mean to sound negative, just giving you some ideas...

The channels that are directly over the GPU will have no flow, because they don't join the water channels. You need to allow water to flow through them to let them help cool the GPU.

Also, don't make the channels deeper. You want the water channel to look as flat as possible, because if you make each channel's cross-section look too much like a pipe, it will act just like a pipe... where the water in the center of the pipe flows freely, but the water at the edges (on the surface of the copper) will not move as quickly... meaning you are just circulating a bunch of cool water around, while the water touching the copper doesn't get nearly as much flow.