The crescendo comes at the end, with the roar of a waterfall so loud that rafters on the Chattahoochee River whitewater course can hardly hear the orders their guides are shouting.
The rafts drop and buck, drop and buck, like a bull ride upon the plunging river channel, which cuts just feet away from a rock island below the old Eagle & Phenix Mill's powerhouse, near the Chattahoochee RiverWalk's 12th Street access.
That rapid, engineered with a mechanical "wave-shaper," is the crowning glory of the whitewater course, even more of an adventure than "Cut Bait," long the name of the companion rapid paralleling it on the river's Phenix City side.
Rick McLaughlin of The McLaughlin Group that designed the course, thinks nothing beats it at high water -- say around 13,000 cubic feet per second -- the upper limit for rafting.
"Personally, I think the Georgia channel's just awesome at 13,000," he said this week. "It's the funnest thing I've ever been in. It reminds me a lot of the Grand Canyon, except it doesn't have the consequences. One guy in it when I was out there last said, 'You just can't come out of this channel without smiling.' He's right."
After running the rapid, guides sometimes turn their rafts around and have clients paddle hard back into it from downstream. If they can hit it just right, with gravity and human weight pressing the raft down in equilibrium with the force of the water beneath it, they can "surf" the rapid, the raft maintaining its position atop the waves.
That's usually the climax of the trip, unless rafters decide on a second run, and instead of taking the eastern route through the wave-shaper -- a rapid named "Heaven's Gate" -- they instead go west to Cut Bait.
But on excursions booked through outfitter Whitewater Express, they won't do that without first "scouting the rapid," the way people running wild rivers do, said owner Dan Gilbert.
It's a chance for customers to talk about how they tackle the rapid. They stand on the rocks over Cut Bait and with their guide discuss their approach and strategy.
Cut Bait can be unforgiving, pitching people out hither and yon, but it's not the monster it used to be before construction crews opened the Georgia channel.
Most of the water now flows to the wave-shaper on the Georgia side, but Cut Bait remains a challenge.
And no matter what the river's flow, from the minimum 800 cubic feet per second to the upper range of 13,000, Cut Bait and Heaven's Gate are always there, always a rush to run. They change according to the river's flow, but it would take a flood to drown them out and submerge them entirely.
Upstream, the rapids may change drastically by flow, some disappearing under high water.
But that constant change is one thing Gilbert finds so attractive about the Chattahoochee. Often over the past few weeks, as Columbus geared up for whitewater's opening day Saturday, he remarked that the Chattahoochee is a different river almost every day. Even small changes in flow create new features to explore.
The course that opens this weekend will not be the finished product. At its head, work continues on a weir, or smaller dam, that Georgia Power's building below the North Highlands Dam to create pool that keeps water pressing against the North Highlands Dam's downstream face. That standing water is to keep the dam's turbines operating efficiently.
Because that work isn't finished, an adjacent Georgia-side put-in or launching point for rafters can't be completed yet, either. Because rafters cannot yet launch from there, they won't get to experience a rapid being engineered just below that point. It's to be called "Ambush."
"Ambush is going to be one of the nicest rapids on the river, particularly at normal flow," Gilbert said. "Ambush is a house-sized boulder that is directly centered in the river . The water will rush directly into this enormous boulder, and all the water divides and goes right or left. The McLaughlin Group has been working on the rapid on each side."
Whitewater rapids are rated by difficulty: Class I, the lowest, being no danger at all, and Class VI, the highest, being lethal.
Of Ambush, Gilbert said: "My guess is we'll have a good Class III rapid."
It will be about 50 yards from the put-in, he said.
Because the put-in isn't open yet, Whitewater Express launches from the Phenix City side, at a level spot on the bank at 33rd Place off 5th Avenue, about even with 29th Street on the Georgia side. From there, on relatively level water, rafts drift south toward City Mills, off 18th Street in Columbus.
The guides make customers practice their moves and paddle in synch.
The first rapid is right below where the City Mills Dam used to be. "Gooder n' Grits," it's named, partly because City Mills was a grist mill grinding grains. The rapid is centered in the river, a wide, long set of waves.
Gooder n' Grits would be rated around Class II, Gilbert said. It's about a 6-foot drop, a sudden decline in elevation once bordered by the dam's downstream face.
Were rafters to turn toward the Alabama riverbank, they instead would run the rapid "Cascades," also right below where the dam used to be. The river there flows over a set of rocks, and at high flows of 9,000 to 13,000 cfs, it's a good ride, Gilbert said.
From there rafters continue downstream, under the railroad trestle just south of Columbus' 17th Street, to a Class II rapid named "Turner's Tumbler," which Gilbert calls "a fun little run with a few standing waves."
Then there's a break.
Gilbert has guides pull into an eddy to the east, to a beach where customers disembark. They hike from there over to the "habitat pools," including a channel around the island in front of the TSYS complex. The island is home to a heron rookery.
There guides show clients how to swim a rapid -- feet pointed downstream, head up to see where they're going -- as they float through the channel cut 8 feet wide through granite. It's a relaxing float that takes about 15 minutes, Gilbert said. Because of its resemblance to a logging flume, it has been named "Log Jam."
Said Gilbert: "As you're floating through there -- when the water's clear, which is most of the time -- you look below you, and there are turtles swimming upstream. You're totally immersed in nature."
Log Jam has an alternative, called "Surprise." Rafts may take a route that is not as long as Log Jam, but has a drop of about a foot that no one sees coming.
From there rafters back in the main channel cross under the 14th Street bridge -- Whitewater Express calls it "Battle Bridge" because of its significance in the Civil War battle of Columbus -- and just south of it come to one of the most attractive rapids, named "Wilson's Run" for Union Gen. James Wilson, the Union commander who captured Columbus.
"It and the wave-shaper are the two best rapids," Gilbert said.
Wilson's Run is where rafters get a true feeling for what's to come. Gilbert estimates the low-flow drop at 8 feet. In a raft you feel a burst of speed, and sense the power of the water's volume and force. Its quickening tempo signals the growing crescendo.
"It is a powerful rapid," Gilbert said. "That water comes together at that spot, shoots through that drop, and it is moving. That I would say is a Class III."
It is among the rapids made more dramatic by a lower river flow, as high water tends to fill in the drop.
From there rafters pass under the 13th Street bridge, and then comes the finale.
It starts with "The Flume," the central channel racing toward the split where one branch goes west to Cut Bait, the other east to Heaven's Gate, the wave-shaper.
"Now at that point, at high flow, from 13th Street down, it's essentially one rapid," Gilbert said. "You're in a rapid for a quarter of a mile We call it 'The Flume' because you're flying. You're moving as fast in that water as I think a raft goes anywhere."
Then comes "Staircase," marking the descent toward the final rapids. From there the raft must go either left or right, to Cut Bait or to Heaven's Gate.
At high water, that decision must be made back at the 13th Street bridge, Gilbert said: "If you wait, and you're making those turns down at Staircase, you're committed one way or the other."
Staircase has three or four "enormous" waves, up to maybe 10 feet, so high that from the perspective of those watching from the bank, the 13½-foot-long raft disappears behind walls of water.
If the guide by then has not prepared to maneuver toward the wave-shaper, the river chooses, and the raft goes to Cut Bait.
"If you don't put much effort into it, you're in the middle of Cut Bait before you know it," Gilbert said. "In Cut Bait, you have a strong possibility of turning over . We like to do the wave-shaper side first, so you can get some experience, go through those rapids, and then come over and scout Cut Bait."
The wave-shaper's marked by a steep drop that drives the raft head-on into a giant wave, with a series of other waves to follow, up to six or eight at low water, four or five when the water's up. Below that, water backs up from Lake Eufaula, and when that lake level rises, it sucks energy from the standing waves, reducing their height and power.
Should customers choose to try Cut Bait, that requires a second run, starting from the put-in, but that run is directly to the rapid -- no stopping at Log Jam for a swim.
Cut Bait is more challenging at low water than high, Gilbert said: "The most difficult rapid on the river is Cut Bait. I think it's tougher at 9,000 than 13,000. It's a bigger drop."
High water tends to fill in the drop, reducing the drama. "You've got several major drops you've got to go through as you go through Cut Bait," he said.
That's the end of the whitewater. From there rafters go to the take-out, either the concrete dock behind the Iron Works in Columbus or the low, sandy bank along the Phenix City side north of the amphitheater.
Those headed west to Phenix City pass through a flatwater pass called "Hanging Tree Flats," so named because of a nearby historic marker noting six Indians once were hanged there.
"What we're trying to do over time is link to history here on the river -- the grist mill, the Hanging Tree Flats, the battle," Gilbert said.
Whitewater Express for this opening season is charging $32.50 an individual for a one-way trip at low flow and $48.50 for a double-run at high flow.
For reservations call 1-800-676-7238 or visit www.whitewaterexpress.com.