We're not waiting, we're currently reinforcing the dikes so they'll be estimated to break only once every 100,000 years instead of every 10,000 years, while taking sea level rise into account.
There's that one dike in Wilnis though that threatens to break every time we have a severe drought, like this year...
It dries out, loses volume and weight, then deforms and tears. There was a dike near Wilnis that actually broke in 2003, leading to half a metre of water in some streets there. Maybe the dike that was in the news a few weeks ago (it didn't quite break, but there was some danger) was a different one; I didn't check, but it was also near that village.
