On any planning application like this starting works is contingent on a whole host of ore-conditions. They will have to agree plans, methods of working, carry out additional surveying (Archaeological, munitions, contamination etc.), repair works. Etc. before they are allowed to get stuck into the main works. It's completely normal for them not to just turn up on day one and start digging...
As well the initial works will be of lower value, at least for the first few months. Dredging isn't a particularly expensive operation so there is every chance that it starts without even having the funding in place.