NOW is the time for Israel to declare nuclear status by peacefully detonating a 100kt nuclear weapon below Gaza, OR, alternatively, several 10-30kt nuclear weapons to:
1) prove nuclear status and send warning,
2) destroy most of the tunnels,
3) create untunnelable barrier between Israel and Gaza (if Israel is dumb enough to keep them as neighbors.
Lots of studies done during Operation Plowshares for peaceful nuclear engineering. It would destroy most, if not all tunnels under Gaza City, and little release of radiation, unless you dig down to the detonation chamber 1000m down.
Sedan crater, above, proof that you need to drill deeper unless you want to nuclear engineer a ditch/lake/harbor/ canal THAT deep.