enough silt to plug a narrow man-made channel in mere days, if not hours.
The Americans’ solution was to build an aquatic staircase fashioned by three locks on either end, rising in watery steps to a lake formed by the dammed Chagres in the middle—a liquid bridge over which boats could float across the hills that the French failed to cut through. The locks use 52,000 gallons of water to lift every ship that passes through—freshwater fed by gravity from the trapped river, which drains to the sea as each vessel exits. Although gravity is always available, the electricity that opens and closes the doors of each lock depends on human operators who maintain hydroelectric generators that also tap the Chagres.
There are also auxiliary steam power and a diesel plant, but, says Perez, “without people, the electricity wouldn’t last a day. Someone in control must decide where the power’s coming from, whether to open or close turbines, et cetera. With no human in the system, it doesn’t work.”
What particularly wouldn’t work are the 7-foot-thick hollow, floating steel doors, 80 feet high and 65 feet wide. Each lock has a double set as backup, pivoting on plastic bearings that, during the 1980s, replaced the original brass hinges that corroded every few decades. What if power were cut, and the doors opened and stayed that way?
“Then it’s all over. The highest lock is 137 feet above sea level. Even if they were left closed, once their seals went, so would the water.” The seals are steel plates overlapping each door’s leading edge, which need replacing every 15 to 20 years. Perez glances up as the shadow of a frigate bird speeds past, then resumes watching the double doors close behind the departing Chinese freighter.
“The whole lake could empty through the locks.”
Gatun Lake sprawls over what was once the course of the Rio Chagres as it emptied into the Caribbean. Reaching it from the Pacific side required cutting through the 12 miles of terrestrial spine that bisects Panama lengthwise at La Culebra, the lowest saddle in the continental divide. Slicing through that much soil, iron oxide, clay, and basalt would have been daunting anywhere, but even after the French disaster, no one really understood how truly unstable the waterlogged Panamanian earth was.
The Culebra Cut initially was to be 300 feet wide. As one gigantic mudslide after another undid months of digging, sometimes burying boxcars and steam shovels as it refilled the trench, engineers had to keep widening the slope. In the end, the mountain range that runs from Alaska to Tierra del Fuego was separated in Panama by a man-made valley, its gap about six times as broad as its floor. To dig it required the labor of 6,000 men every day for seven years. The 100 million-plus cubic yards of dirt they moved, if compacted together, would form an asteroid one-third of a mile across. More than a century since its completion, work on Culebra Cut has never entirely ceased. With silt constantly accumulating, and frequent small landslides, each day dredging rigs with suction pumps and shovels work up one side of the canal as ships come down the other.
In the green mountains 20 miles northeast of the Culebra Cut, two Panama Canal hydrologists, Modesto Echevers and Johnny Cuevas, stand on a concrete abutment above Lake Alajuela, created by yet another dam, one that had to be built upriver on the Chagres in 1935. The Chagres watershed is one of the rainiest places on Earth, and during the Canal’s first two decades, several floods slammed into it. Boat traffic halted for hours while floodgates were opened, lest the pounding of the river cave in its banks. The flood of 1923, which carried entire uprooted mahogany trunks, created a surge on Lake Gatun powerful enough to tip over ships.
Madden Dam, the wall of concrete that holds back the river to form Lake Alajuela, also sends electricity and drinking water to Panama City. But to keep its reservoir from leaking out the sides, engineers had to fill 14 dips in the terrain with earth to create its rim. Down below, massive Lake Gatun is also surrounded by earthen saddle dams. Some are so overgrown with rain forest that an untrained eye can’t see that they are artificial— which is why Echevers and Cuevas must come up here every day: to try to stay ahead of nature.
“Everything grows so fast,” explains Echevers, a burly man in a blue rain jacket. “When I started doing this, I came here looking for Dam Number 10, and I couldn’t find it. Nature had eaten it.”
Cuevas nods, eyes closed, recalling many battles with roots that can tear an earthen dam apart. The other enemy is the trapped water itself. During a rainstorm, these men are often here all night, fighting to maintain a balance between holding the Chagres at bay and releasing enough water through the concrete wall’s four floodgates to assure that nothing bursts.
But if one day there were no people around to do that?
Echevers shudders at the thought, because he’s seen how the Chagres reacts to rain: “Like a zoo animal that has never accepted its cage. The water loses control. If it was allowed to rise, it would top the dam.”
He stops to watch a pickup truck roll across the raised roadway that runs along the top of the dam. “If no one were here to open the floodgates, the lake would fill up with branches, tree trunks, and garbage, and at some point all that stuff would hit the dam and take the road with it.”
Cuevas, his quiet colleague, has been mentally calculating. “The head of the river would be huge when it goes over the top. Like a waterfall, it would erode away the river bottom in front of the dam. One really big flood could collapse the dam.”
Even if that never happened, they agree, eventually the spillway gates would rust away. “At that point,” says Echevers, “a 20-foot head of water would break free. Drastically.”
They look down at the lake where, 20 feet below, an eight-foot alligator floats motionless in the dam’s shadow, then streaks through the teal blue water as an unlucky terrapin surfaces. Madden Dam’s concrete wedge looks too solid to go anywhere. Yet one rainy day, it will likely flop over.
“Even if it survives,” says Echevers, “with no one here the Chagres will fill the lake with sediment. At that point, the dam won’t matter.”
In a chain-link compound where Panama City now spills into the former Canal Zone, Port Captain Bill Huff sits in jeans and a golf shirt before a wall of maps and monitors, guiding evening traffic through the Canal. A U.S. citizen born and raised here—his grandfather, a Canal Zone shipping agent, arrived in the 1920s—he moved to Florida after sovereignty over the Canal passed from the United States to Panama as the clock ticked off the first second of the new millennium. But his 30 years of experience were still in demand, and, now in the employ of Panama, he returns every few months to take a shift.
He switches a screen to a view of Lake Gatun’s dam, a low mound of earth 100 feet wide. Its submerged base is 20 times thicker. To the casual observer, there’s not much to see. But someone has to be looking all the time.
“There are springs underneath the dam. A couple of small ones have pierced through. If water runs clear, no problem. Clear water means it’s coming up through the bedrock.” Huff pushes back in his chair and rubs the dark beard circling his chin. “But if water starts bringing dirt with it, then the dam is doomed. In just a matter of hours.”
It’s hard to imagine. Gatun Dam has a 1,200-foot-thick, theoretically impermeable central core of rock and gravel cemented with liquid clays that are known as fines, sluiced up from the dredged channel below and tamped between two buried rock walls.
“The fines hold the gravel and everything together. They’re what starts coming out first. Then the gravel follows, and the dam loses its adhesion.”
He opens a long drawer in an old pine desk and pulls out a map tube. Unrolling a yellowed, laminated chart of the isthmus, he points to Gatun Dam, just six miles from the Caribbean. On the ground, it’s an impressive mile- and-a-half long, but on the map it’s clearly just a narrow gap compared to the tremendous expanse of water dammed behind it.
The hydrologists Cuevas and Echevers are right, he says. “If not during the first rainy season, within just a few years it would be the end of Madden Dam.
Gatun Lake would then start spilling over the locks on both sides, toward the Atlantic and the Pacific. For a while a casual observer might not notice much, “except maybe unkept grass.” The Canal’s prim landscaping, still maintained to American military standards, would start to turn lush. But before any palms or figs moved in, a flood would take over.
