The biggest problem confronting Israel in its war on Hamas is how to destroy the Gaza tunnel networks and the terrorist operations therein.  Bombing works—mostly—but there’s a better way.  Not only would it dramatically reduce Israeli military and Gazan civilian casualties, but it would effectively destroy the tunnel systems for the long term.  That solution is to flood the tunnels with seawater from the adjacent Mediterranean.

I worked on the Gaza Strip back in the 1990s.  The U.S. government was pouring tens of millions of tax dollars into development assistance there on engineering infrastructure, housing, and related projects.  Part of reviewing that work on the ground involved tramping over much of the small territory on foot.

Gaza consists of a strip of beach, back beach, and coastal plain that’s flat to slightly rolling.  The territory stretches for about twenty-five miles along the eastern Mediterranean.  At its widest, in the south, it’s about seven and a half miles wide; most of it is far narrower, about half of that.

The Gaza tunnel system, mostly constructed over the last forty years, provides Hamas with offensive access to Israel.  It also constitutes the terrorist organization’s most formidable defensive redoubt.  The tunnels present by far the most difficult logistical problem for Israel in eliminating enemy targets.  Open-source maps show at least eleven independent tunnel networks, some nearly adjacent to the sea.  The number of independent networks, however, could far exceed that.  Hamas claims that the total length of the tunnels is about three hundred miles.    

The geography of Gaza argues strongly for the stratagem of flooding the tunnels.  It would force the enemy above ground where they can more easily be destroyed, dramatically reduce the Israeli casualties required to accomplish that task and resolve the problem of dealing with parts of the tunnels that are too deep to destroy through bombing.  Most importantly, flooding is a permanent or near-permanent solution to the Gaza tunnel problem.  Once accomplished, pumping them out enough to be usable again would be both extremely costly and—especially in conjunction with bombing—exceptionally difficult.  The timing of executing a flooding strategy is flexible; some could be flooded now, others later, and still others once they’re discovered. 

The engineering is straightforward.  Egypt flooded thirty-seven cross-border tunnels in southern Gaza back in 2015 in what stands as a practical proof of concept in this location.  Seawater from the Mediterranean would be pumped directly into the tunnel openings through short pipelines.  While there’s little hydrological head, there is also little topographical relief to deal with in laying the pipe.  Large volumes of water are pumped long distances every day, and Israeli water technology is world class. 

The shortest and most direct route to the tunnel entrances would be directly from the Mediterranean.  This would require kinetic clearing of the construction sites and holding them for the duration of the operation to protect the temporary water transmission lines.  The distance that would need to be cleared and held could be minimized on the northernmost and eastern tunnels by running a trunk line through adjacent Israeli territory and feeding water distribution lines to the tunnel entrances off that. 

Flooding doesn’t have to be slow.  A six-by-five-foot tunnel that runs 300 miles is a huge volume to fill, but how fast it fills depends on how fast the water is pumped.  Rough calculations indicate that if a single pipe were used for each of eleven tunnels, with each pipe pumping at a very conservative 100 gallons per minute, it would take about seven and a half months for all eleven tunnel networks to fill.  Pumping water at ten times that rate, however, is routinely done today everywhere from wastewater treatment plants to oil field operations.  Also, the tunnels wouldn’t have to be filled to capacity to generate the desired effect.  The effect would begin as soon as water started to flow; by the time a tunnel has two or three feet of water it would be effectively unusable.  

The collateral damage to infrastructure should be minimal.  The distances are short, the diameter of the required pipe is small, and the pipelines would run very close to the surface.  As with the Egyptian tunnel operations, the impact of flooding on groundwater salinization would no doubt be raised.  The extent of saltwater leakage through the tunnels into local groundwater would depend on the depth and construction of the tunnels and the configuration of the local aquifer.  Gaza’s shallow aquifer is already over-depleted, however, and ninety-five percent of its groundwater was considered unfit for public consumption as far back as 2017.  The reason is that it’s extensively contaminated with chemicals and sewage, as well as saltwater intrusion from the Mediterranean due to a long history of over pumping.  Because of that, Gaza relies heavily on desalinization for potable water.    

In the short term, think of flooding Gaza’s tunnels as humanitarian assistance.  By eliminating the need to keep bombing them, flooding would reduce civilian casualties and other collateral damage.  In the long term, think of denying Hamas access to the tunnels as an A2AD stratagem.  At the end of the war, there can be no complete destruction of Hamas, nor long-term peace out of Gaza, unless and until the Gaza tunnels are taken out.

Jeff Goodson is a retired U.S. Foreign Service officer. In 29 years with the U.S. Agency for International Development, he worked on the ground in 49 countries in Africa, Asia, Latin America, Eastern Europe, and the Middle East, including the Gaza Strip. He served 31 months during three tours in Afghanistan. From 2006-2007 he was Chief of Staff and Head of Civil-Military Planning and Operations at USAID/Kabul, and from 2010-2012 he served as the DCOS/Stability Director of Development at ISAF Headquarters.

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