Israel first informed the U.S. of the option early last month, prompting a discussion weighing its feasibility and effect on the environment against the military value of disabling the tunnels, officials said.
U.S. officials said they didn’t know how close the Israeli government was to carrying out the plan. Israel hasn’t made a final decision to move ahead, nor has it ruled the plan out, officials said.
Sentiment inside the U.S. was mixed. Some U.S. officials privately expressed concern about the plan, while other officials said the U.S. supports the disabling of the tunnels and said there wasn’t necessarily any U.S. opposition to the plan. The Israelis have identified about 800 tunnels so far, though they acknowledge the network is bigger than that.
The weekslong process of flooding the tunnels would enable Hamas fighters, and potentially hostages, to move out, a person familiar with the plan said. It isn’t clear whether Israel would even consider using the pumps before all the hostages are released from Gaza. The Palestinian militants who attacked Israel on Oct. 7 took more than 200 hostages and brought them back to the Gaza Strip.
“We are not sure how successful pumping will be since nobody knows the details of the tunnels and the ground around them,” the person said. “It’s impossible to know if that will be effective because we don’t know how seawater will drain in tunnels no one has been in before.”
The deliberation over the plan to flood the tunnels illustrates the balance Israel’s forces must make between pursuing their war aims and the intense international pressure they face to protect civilians. The Israeli military campaign has flattened neighborhoods and the fighting has displaced more than a million Gazans from their homes in the crowded strip of territory.
An Israel Defense Forces official declined to comment on the flooding plan, but said: “The IDF is operating to dismantle Hamas’s terror capabilities in various ways, using different military and technological tools.”
Hamas has used the extensive tunnel system to hide, move undetected between houses in Gaza and hold hostages. Some of the more sophisticated tunnels were built with reinforced concrete, contain power and communication lines, and are tall enough for an average-size man to stand up in them.
Most Gazans don’t currently have access to clean water. Among the sources for drinking water in Gaza are purification plants that have been recently disabled. Before Oct. 7, three Israeli pipelines sent water into Gaza. Of those, one has shut down and the other two operate at sharply reduced levels.
At its peak, the system provided 83 liters of water per person a day. Now Palestinians receive no more than three liters a day, according to the United Nations. The U.N. says the minimum should be 15 liters a day.
Because it isn’t clear how permeable the tunnels are or how much seawater would seep into the soil and to what effect, it is hard to fully assess the impact of pumping seawater into the tunnels, said Jon Alterman, senior vice president at the Washington-based Center for Strategic and International Studies.
“It’s hard to tell what pumping seawater will do to the existing water and sewage infrastructure. It is hard to tell what it will do to groundwater reserves. And it’s hard to tell the impact on the stability of nearby buildings,” Alterman said.
Former U.S. officials familiar with the issue confirmed that Israeli and U.S. officials had discussed flooding the tunnels with seawater but said they didn’t know the current status of the plan.
The former officials acknowledged such an operation would put the Biden administration in a tough position and perhaps bring global condemnation, but said it was one of the few effective options for permanently disabling a Hamas tunnel system estimated to stretch for about 300 miles.
One of the former officials said Gaza’s water and sanitation systems are badly damaged and heavily polluted, and would need to be reconstructed with international assistance after the war.
Wim Zwijnenburg, who has studied the impact of war on the environment in the Middle East, said that assuming that about one-third of the tunnel network is already damaged, Israel would have to pump roughly 1 million cubic meters of seawater to disable the rest.
Gaza’s aquifer, from which the population draws for drinking water and other uses, is already becoming saltier with a rise in the sea level, requiring more energy to fuel the desalination plants on which the population depends, said Zwijnenburg, who works for PAX, a Netherlands-based peace organization.
Flooding could affect Gaza’s already polluted soil, and hazardous substances stored in the tunnels could seep into the ground, he said in an email.
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Egypt in 2015 used seawater to flood tunnels operated by smugglers under the Rafah border crossing with Gaza, prompting complaints from nearby farmers about damaged crops.
Typically, militaries charged with clearing tunnels, including Israel, use dogs and robots to check for threats or to search for hostages before sending ground troops in, said Mick Mulroy, a former deputy assistant secretary of defense and officer in the Marine Corps and CIA.
“Dogs are most effective,” he said, but need to be followed by troops to clear the tunnels. “Robots move slow and break. And using humans is risky.”
Using water over a long period would force Hamas fighters out, Mulroy said.
But “if you salted the water, it could compound the humanitarian crisis,” he said.