Human rights lawyer Walid Abu al-Kheir said families of victims of the disaster were supporting the lawsuit, which will allege massive mismanagement of city works construction by the Jeddah government as a key cause for the flooding.
"They didn't make the drainage work. They have told us for three years or more that it has been completed," he said. "Even people from the city government said there were mistakes."
Waleed said he planned to file his lawsuit next Saturday, when government offices and courts reopen after the two-week Eid al-Adha holiday.
A huge rainstorm sparked the flash floods, with many victims caught in their cars and drowning in two metres (6.5 feet) or more of water.
Roads were destroyed and cars and trucks left in piles after the waters receded on Thursday.
Electricity is still out in some of the worst hit parts of the city, the country's second largest after Riyadh.
With public protests banned in Saudi Arabia, Jeddah residents have taken to the Internet to attack the government.
More than 11,000 people joined a Facebook page created three days ago to complain about the floods, saying the city government and contractors were at fault for not building adequate infrastructure.
"We've been talking about this issue for years. Everybody knew this disaster was coming. We've seen something like this on a smaller scale," Saud Kateb, a media technology professor and one of the Internet protesters, told AFP.
"There's only one reason: it's corruption," he said. "The government is putting a lot of budget into this, and the budget just disappears."
Many posters to the Facebook page "Popular Campaign to Save the City of Jeddah" called for officials to be tried or at least be fired, although few were willing to name names.
"In Saudi Arabia, it is very difficult to point your finger in certain ways," said Kateb.
He said many Jeddah residents were outraged as well that the official state news agency SPA had reported after the storm that Jeddah residents appreciated the rain and the city's infrastructure was working well to handle the water.
"SPA wrote something unbelievable," Kateb said.
After complaints were made to his own popular Facebook page, Information Minister Aziz Khoja subsequently criticised the agency as being insensitive to the victims.
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