The Egyptian claim that there are no weapons coming from Egypt to Gaza, due their “fantastic” ability to seal 1500 tunnels is ludicrous because beneath or parallel to every “sealed” tunnel there is another tunnel. There are at least 28,000 houses within tunnel distance in the Egyptian side of the border. The smuggling business is a very profitable business and to say that there is no soldier or police that is not complicit or profiteering from the tunnel business is like saying there is no corrupt government official or politician. Tunnels are used to move merchandise, weapons, people and generate huge profits that no one can account for. It is pathetic to listen to Israeli generals saying they are astonished time and time again with each network of tunnel they discover. Tunnel use and tunnel excavation in Gaza are the most profitable businesses to local entrepreneurs in Gaza or Sinai. Relief funds that pays labor and merchandise is converted to money or weapons even during the war and specially during the war. Those generals have no clue on how the symbiosis of economy of smuggling and the economy of terror work together.
If we take three to one ratio of tunnels and weapon stashing per building/house in viable ratio of a tunnel exit to three houses gives an estimate of 9000 tunnel entrances and about 130 miles of tunnels that Egyptians are ignoring or closing an eye in their Refah side.
There can’t be a 100% solution against tunnel warfare under civilian population because under each uncovered tunnel there might be another tunnel. A new tunnel can be excavated a short time under the house or rubble next door. In the Kurdish and Vietnamese war zones there are reports of 5 levels of tunnel diggings. The use of sea water is futile because it doesn’t solve the problem of undiscovered tunnels and iron or impermeable doors of siphon excavation which is a technique of slopping up a section and making a draining tunnel extension.
Mitigating the danger of tunnel warfare in the Gaza area may involve having a 50 meter deep dry canal along side a wet canal that can flood the other whenever a seismic activity is detected and further excavation is done in that area. In the battle of the Somme in WW1, the British used a huge amount of explosives underground which led to an earthquake that collapsed all German tunnels into themselves in a 10 KM radius.Another mitigation option would be a 5 KM uninhabited belt which makes tunnel excavation easier to deal with with constant digging and bombing of that area making it a classic DMZ zone. As wide the belt is, the longer time it takes to build a tunnel across it. Tunnels have all the facilities and storage capacities the enable the stashing, and manufacturing weapons and as launching pads for terrorism for months.