From CNN's Soledad O'Brien in New Orleans
The concrete is so clean on the Inner Harbor Navigation Canal/Surge Barrier that it looks like they poured it yesterday. But the roiling clouds above it made it clear why its completion in May was critical. It's about to face its first test
They call it "the wall" - a two-mile long stretch of concrete that's designed to keep the waters of the Gulf from flooding into Lake Borgne then inundating New Orleans neighborhoods like the Lower Ninth Ward, a surge that destroyed homes and left a trail of dead during Hurricane Katrina.
This massive post-Katrina effort by the Army Corps of Engineers with three 150-foot-wide gates began in 2009. At 10:30am on Tuesday, the two doors were closed for the first time in anticipation of Hurricane Isaac.
"It will keep water from coming from the Gulf of Mexico through Lake Borgne. Last time the surge went into Lake Borgne and into the heart of the city, " said Col. Edward Fleming of the US Army Corps of Engineers. "This wall is built to 26 feet high and we expect to see surges of eight to 10, maybe 15, feet."
We walked along the top of the wall of this surge barrier as peaceful small waves rippled along the lake on one side and a swelling, choppier Gulf rose on the other.
"The Wall" is what has kept Jackie Grosch, from packing up and leaving town. Jackie, who lives in St. Bernard Parish has spent the last 7 years rebuilding her home that was destroyed by Hurricane Katrina.
"The upstairs was spared," said Jackie - but the first floor practically disintigrated. Seven years ago I was doing liveshots by Jackie's exposed spiral staircase.. The lower walls of her home were gone.
Today she's riding out the storm because she's confident in that wall.
In Plaquemines Parish there was less confidence in the levee system. Several backhoes and a tractor and a dozen trucks full of gravel worked through the light rain trying to lay a gravel road over a massive pile of sandbags - five feet tall and three feet wide - that were brought in at the last minute to replace a failing floodgate.
The parish had a mandatory evacuation order, and by early Tuesday afternoon the parish announced a curfew. About 300 people had settled in to cots and chairs in three shelters - including a church and a high school.
The parish sits just southwest of the mouth of the Mississippi River and it went under during Hurricane Katrina. This storm, said the parish president is no Katrina, but his deputies were keeping a close watch.
"The parish is inside the levee system," said Sheriff Lonnie Grieco, Sr. " We're hoping we can make it through this wave here. You never know what Mother Nature's gonna bring us."
Donald Taylor, who came to the shelter with his parents, sister-in-law and nephew, amused himself by playing videogames.
He was a teenager when Katrina hit.
"During Katrina, I slept through it. It did a lot of damage to our house. I don't think Isaac is gonna do a lot of damage."
Evacuee Wilma Taylor was surrounded by her grandchildren. She was resigned to a long haul.
" I aint nervous - long as I'm around a lot of people chit-chattin' I won't be nervous."
The storm hit just before 7 p.m. Â local time and we felt the strong irregular gusts and occassional sheets of rain, the tell-tale signs of an unpredictable storm. At that time, the water had not risen much, but there was a lot of rain still to come.