Well, "Duh!". Tunnels are wonderful, they keep stuff from getting in the way on the surface. But, in most places, they sit below the water table, or below acce

Well, "Duh!". Tunnels are wonderful, they keep stuff from getting in the way on the surface. But, in most places, they sit below the water table, or below access from sea, rivers, or storm water and naturally they tend to fill up. Usually the pumps, that are working away on an continuous basis, can keep in front of water ingress so we don't notice that the tunnels would normally be flooded all the time. It's only when the pumps break down, or they get swamped by sudden water flows, that we suddenly get to scream about the normal state of affairs.