NEW ORLEANS — The catastrophic flooding that has partially filled the bowl that is New Orleans may worsen in coming days because rainfall from Hurricane Katrina continues to flow into Lake Pontchartrain from north-shore rivers and streams, and east winds and a 17.5-foot storm crest on the Pearl River block the water's outflow.

The lake normally is 1 foot above sea level, while the adjoining metropolitan New Orleans is an average of 6 feet below sea level. But a combination of storm surge and rainfall from Katrina has raised the lake's surface to 6 feet above sea level, or more.

That water has found several holes in the lake's banks — all pouring into New Orleans.

A 500-foot breach in the eastern wall of the 17th Street Canal separating New Orleans from Metairie had poured hundreds of thousands of gallons of lake water per second into the New Orleans area before easing up yesterday. Two more levee breaches along the Industrial Canal had created a flood in the Lower Ninth Ward on Monday that spread south into the French Quarter and other parts of the city.

That break might last no longer than the next high tide. New Orleans Mayor Ray Nagin said the water in his city could reach as high as 3 feet above sea level.

Louisiana State University Hurricane Center researcher Ivor van Heerden warned that Nagin's estimates could be too low.

"We don't have the weather conditions to drive the water out of Lake Pontchartrain, and at the same time, all the rivers on the north shore are in flood," he said. "That water is just going to keep rising in the city until it's equal to the level of the lake.

"Unless they can use sandbags to compartmentalize the flooded areas, the water in the city will rise everywhere to the same level as the lake."

This isn't the first time that the 17th Street Canal has proved to be a hurricane-flooding Achilles' heel. After a 1947 hurricane that made a direct hit on New Orleans and Metairie, officials were unable to clear floodwaters from Metairie through the canal for two weeks.

Sewage from a treatment plant that stagnated in the canal created enough sulfuric-acid fumes that nearby homes in Lakeview painted with lead-based paint turned black.

Van Heerden said water that flowed through New Orleans' back door used a weakness that he and many others have been concerned about for years: a V-shaped funnel formed by the joining of the Mississippi River-Gulf Outlet and the Inner Harbor Navigation Channel. Storm surge as high as 18 feet pushed through the funnel, into the Industrial Canal and on to the lake. That surge water is believed to have caused breaks in the Industrial Canal levees that sent lake water flowing through into the Ninth Ward.

Water entering that funnel also is thought to have topped levees surrounding Chalmette and eastern New Orleans, causing flooding in both places.

If there's a silver lining to this disastrous event, van Heerden said, it's that the eye of Katrina didn't go directly over or to the west of the city. If that had happened, the storm surge could have been much higher and would have directly topped levees all along the lake and much more rapidly filled the bowl, which would have meant an even higher death toll than is anticipated from this slow-moving event, he said.

The problems caused by floodwaters will only worsen, according to van Heerden. For one, if the water in the city does rise to the height of levees along the lakefront, it may be difficult to open floodgates designed to keep the lake out that would now be needed to allow the lake to leave. Van Heerden said the rising floodwaters also would cause major pollution problems in coming days, as they float dozens of fuel and chemical storage tanks off their fittings, severing pipelines and allowing the material to seep into the floodwaters.

"In our surveys of the parish, a lot of the storage tanks we looked at weren't bolted down with big bolts," he said. "They rely on gravity to hold them down. If an industrial property is 5 feet below sea level and the water gets to 5 feet above sea level, that's 10 feet of water, and I'm certain many we looked at will float free.

"You'll see a lot of highly volatile stuff on the surface, and one spark and we'll have a major fire," he said.