Since the crackdown began, thousands of Palestinians have been thrown out of work, contributing to soaring poverty in the territory. Already long power cuts have gotten worse, as tunnels supplying one million liters (about 260,000 gallons) of diesel each day have been shut down. Thousands of tons of merchandise no longer get in.

Mr. Sisi has put even more pressure on Gaza through prolonged closings of the Rafah border crossing. The 20 tunnels that remain in operation are able to move only small items like cellphones and cigarettes.

During the summer, the Egyptians dug a trench on the Sinai side of the border and then laid pipes parallel to the dusty buffer-zone road, known as the Philadelphia route. Water from the nearby sea was pumped in, creating an overnight canal, said Abu Ibrahim, a Palestinian border guard. The water channel flooded two tunnels, causing them to collapse, smugglers said.

In early October, it happened again, this time flooding 10 tunnels.

Abu Khalil, 34, said he was working on repairs to his 2,000-foot tunnel when he heard the water rushing in.

“We saw the water,” he said. “We could have been washed away.”

He returned with 15 workers and a pump. For two days, they pumped water out of the tunnel, trying to keep the walls from collapsing. Abu Khalil said that once all the water was pumped out he would shore up the walls with pieces of wood.

“God willing, we’ll take control,” he said.

If the recent episodes of flooding were a trial run, as many Palestinians here suspect, a more sustained flooding would be a disaster, because Gaza officials could not pump the water out fast enough into the sea.