they may not dig that out, the water may swoosh it from where it is built up and eventually may all settle spread out across the bottom of the channel. It'll only add a few inches across the whole channelNorth West part of the channel you mean? Yeah it is a head scratcher. They must be able to dig the remaining out whilst it is filling up with water. All logic would tell you it would have been better to dig out it all, except a small bank right at the mouth just to hold it back. Be interesting to see how they finish it.