One of the problems we have encountered in Spain is that the charts do not show drying heights, nor do they show (generally, at least) clearance heights under bridges. As devoted creek crawlers this is a nuisance, especially as it is very difficult indeed even to get an estimation of the height of a bridge.
The idea is to survey first in the dinghy and then (allowing a safety margin, of course!) to make a call on whether we go up to anchor. I'll report later on how we get on with it!