by Jody Argo Schroath
The Conowingo Dam is the Chesapeake Bay's 800-pound gorilla in the room, and it's time we talked about it. So for the next two issues, that's what we're going to do. We're going to get acquainted with our own gorilla. We're going to learn how our gorilla got there in the first place, how it does its job, why it's the best thing that ever happened to the Bay, and why it may very well turn out to be the worst. We'll learn why it's still a force for good, yet holds a ticking time bomb that could virtually destroy the Bay at just about any time. It's a time bomb that nobody wants to do anything about it. Why? We'll see. But first, let's meet our gorilla.
The Conowingo Dam, owned by Exelon Energy Corporation of Chicago, lies across the Susquehanna River between Harford and Cecil counties in Maryland, a mere ten miles upstream from the river's mouth at Havre de Grace. Ten miles? That would seem too far downstream to barricade such a mighty river. And the Susquehanna is nothing if not mighty. Each day, the Susquehanna pours an average of three billion gallons of fresh water into the Chesapeake Bay. It furnishes 90 percent of the upper Bay's fresh water, and 50 percent of the entire Bay's supply. It is, in point of fact, the longest river on the East Coast, covering 448 miles from its origins at the south end of Otsego Lake near Cooperstown, N.Y., to Havre de Grace at its mouth. To barricade a river at mile 10, not to belabor the point too much, would be like building a dam across the Potomac River between St. Marys River and the Yeocomico. Yes, certainly, 10 miles would be too soon . . . if the Susquehanna were a navigable river. But it isn't. Not really. Even the peripatetic Captain John Smith was halted 10 miles upriver by shallow water and a roadblock of boulders that he named Smith Falls (okay, specifically "Smyths fales").
Not that people haven't found ways of negotiating vast stretches of the Susquehanna one way or another. Native Americans in canoes came and went by river, leaving behind them in some unmeasured past rock carvings, or petroglyphs, of yet undetermined meaning. A couple of centuries after Smith was brought up short at the fall line, entrepreneurs stripped Pennsylvania's forests of timber and then gouged millions of tons of coal from its mountains. They moved the raw materials downriver to waiting ships at Port Deposit and Havre de Grace using great arks of newly harvested logs, which were piled with cargo and floated downstream, often shepherding great flocks of floating logs as they went. Later, canals were constructed to bypass the worst of the Susquehanna's rocky barricades. But these proved to be economic train wrecks and were abandoned as railroads and eventually highways shouldered the responsibility of hauling cargo. Life on the river got pretty quiet.
Then came the age of cheaply produced hydroelectric power, and everything on the river changed forever. Early in the 20th century millions of people living in rural areas throughout the United States were still without electricity. Water-generated power seemed to be the solution. Late in the preceding century, engineers had learned how to couple hydraulics with electric generators to produce low-cost power. In 1881, Schoelkopf Power Station No. 1 near Niagara Falls began producing electricity. By 1886, there were 45 hydroelectric power plants in North America; by 1889 there were about 200 in the United States alone; and by 1920 some 40 percent of the power produced in this country was hydroelectric.
Hydroelectric power has a lot to be said for it, even now. Once constructed, a hydroelectric plant needs no fuel--no coal, no uranium, no petroleum. It needs only the force of water to sustain its production of electricity. Nor does it emit harmful byproducts. It pollutes neither air nor water. In addition, it needs only basic and consistent maintenance to sustain its operations. The Conowingo Dam, for example, continues to use nearly all of its original equipment more than 80 years later.
It's little wonder then that bigger and bigger dams were constructed. In 1936 Hoover Dam's 1,345 megawatt plant became the largest in the world, but that was soon surpassed in 1942 by the Grand Coulee Dam. In 2008 China's Three Gorges Dam project became the largest in the world, producing a staggering 22,500 megawatts of power. (How big is a megawatt? The common example is that one megawatt can power a thousand homes.)
When the Conowingo Dam came online in 1928, it was no spider monkey among hydroelectric gorillas. Producing 252 megawatts of power, it was then the second largest hydroelectric project in the country after Niagara Falls. In the 1970s, four more generators were added and production rose. The dam currently generates 572 megawatts of power, enough to qualify it as a major-league hydroelectric dam.
A Band of Brother Dams
The Conowingo, however, was not the first dam to span the lower Susquehanna River. That distinction belongs to the Holtwood Dam, which opened in 1910 as the McCalls Ferry Dam and which is now owned by Pennsylvania Power & Light (PPL). (As an example of the longevity of hydroelectric equipment, one particular part in the Holtwood Dam's No. 5 generator--specifically the Kingsbury thrust bearing--has been designated an International Historic Mechanical Engineering Landmark because it has been in use since 1912!) At 55 feet in height and 2,392 feet in length, the Holtwood is about half the size of the Conowingo and produces commensurate wattage. After a century of operation, work began last year to increase Holtwood's production to 230 megawatts by 2013.
The newest of the three hydroelectric dams on the lower Susquehanna is Safe Harbor Dam, which was completed in 1931. The dam is co-owned and operated by PPL and Constellation Energy and generates 417 megawatts. Exelon also owns two nuclear power plants on the Susquehanna: Peach Bottom Atomic Power Station (which it co-owns with Public Service and Gas of New Jersey) and Three Mile Island Nuclear Generating Station.
You can see that the Susquehanna is a very busy place. And these facilities account for only what's on the lower Susquehanna. The entire river is practically chock-a-block with dams and generating stations, from Goodyear Lake dam in upstate New York to the Conowingo in the south. But our subject is the Conwingo. So let's get back to business and meet Earl Hopkins.
Birth of a Gorilla
Earl Hopkins played only a minor role in the massive undertaking of men and machinery to construct the Conwingo Dam. But, years after the fact, it is Earl Hopkins whose name survives, having captured the imagination of the press, not once but twice. The first time was in 1928 when he drove the first car across the newly completed dam. The second was half-a-century later, when he was first across once more, this time as a passenger in a 1928 Lincoln, with Maryland Governor Harry Hughes at his side. The occasion was the rededication of the dam following a major renovation and expansion in the 1970s. Oddly enough, Earl Hopkins was just a regular Joe, one of the thousands of workers hired to work on the dam, and not a major player--like, for instance, the president of the Susquehanna Water Power and Paper Company of Harford County, or the CEO of Philadelphia Electric Company (PECO), both of whom certainly had a lot more to do with the building of the dam.
It was Susquehanna Water Power that initially acquired the thousands of acres of land necessary for the project and then built a small wing dam at the Conowingo site in 1905, before selling out to Susquehanna Power Company. That company tried to construct a major dam on the site, but didn't have the economic clout to push the deal through. That was left to PECO, a much larger and wealthier corporation, which purchased the Conowingo site and the notion of a large hydroelectric dam 20 years later. PECO set about putting the plan into action and began building our gorilla. Yes, the town of Conowingo would be drowned in the 14-mile-long lake that would be formed behind the dam. Yes, the petroglyphs would be lost as well (though some were ultimately removed from the rock and preserved). The railroad tracks, too, would have to be relocated to higher ground.
And what about the millions of shad that swim up the Bay from the Atlantic Ocean each year to spawn in the Susquehanna's tributaries? Yes, they would be butting their heads against a mile-wide wall of poured concrete. Too bad. This was declared the right spot for the dam, so this is where it would be.
With its plans drawn up, PECO awarded contracts for the $50-million project to Arundel Corporation, a Maryland construction company, and to Stone & Webster, a Boston engineering firm. In 1926, 3,800 people were signed on as temporary employees and work finally got under way. One of those 3,800 people was Earl Hopkins, who was 15 years old when he was hired by Stone & Webster as an office boy and later a driver. For the next two years he ran errands for the company . . . and for the workers. He drove trucks carrying construction materials and he drove a kind of informal taxi to fetch food and cigarettes, as well as less legal provender such as bootleg liquor--this was Prohibition after all. The story is told that one of Earl's tasks was to drive a busload of French-Canadian woodcutters to the brothels of Havre de Grace on Saturday, then get them all back onto the bus later that night for the trip back to Conowingo.
For two years, Hopkins and the thousands of other employees labored on the dam. Materials were brought to the site by train. A town was built to house the laborers, and a smaller, finer town was built for the loftier job-holders, like engineers, foremen and executives. Teams of mules were brought in to haul out trees and rocks and then smooth the land for the soon-to-be relocated rail line. Meanwhile, huge cofferdams, constructed of eight million feet of timber, were built to part the river and allow construction of the dam.
At last, the work was done. As news photographers snapped pictures and a raft of reporters took notes, Earl Hopkins drove down U.S. Route 1 and over the brand new Conowingo Dam. Why Earl? He just happened to be there making a delivery. "Earl Hopkins drives first car across the Conowingo Dam," the headlines read the following day. It was, in fact, a truck rather than a car, loaded with lampposts--and, just perhaps, a couple of gallons of illegally distilled whiskey stowed safely under the seat. No matter. The dam was done and the new gorilla was ready to roar.
Anatomy of a Gorilla
The Conowingo was built as a gravity dam--that is, it was held in place by its weight alone--using from 435,000 to 660,000 cubic yards of poured concrete (the number is given variously) on a solid rock formation of granite and diorite. It was built as a gravity dam, but in 1978, the dam was upgraded after it was nearly shaken loose in 1972 by the catastrophic event known as Hurricane Agnes (we'll have much more to say about this catastrophic event later on).The dam was anchored to the bedrock by 537 stranded wire tendons that were snaked 105 feet through the dam and then 60 feet into the bedrock below.
When it was completed the new dam spanned the river with a latitudinal run of nearly a mile--4,648 feet to be exact--and an average height of 94 feet. It has four distinct sections, which are, east to west: (1) the 1,190-foot-long non-overflow section; (2) the 2,385-foot spillway; (3) the 950-foot-long intake powerhouse section; (4) and the 100-foot long abutment section. (You can see the Conwingo's four sections on the diagram at left.)
Generally, the water level of the forebay is (theoretically) never going to be allowed to reach the top of the 115.7-foot-high non-overflow section. Instead, most of river's flow and the forebay's rise can be dealt with in times of high water by opening up to 50 of the crest gates (aka flood gates) located at the 87-foot level of the spillway section. If necessary, two higher gates, at the 99-foot level of the spillway, can be opened as well. These impressively heavy crest gates, each of which is 22.5 feet high by 38 feet wide, are hauled open by gantry cranes--one 90-ton and two 60-ton cranes--that slide ponderously along rails from gate to gate.
The opening of crest gates is a subject of great interest to the people who live downstream from the dam, especially those in nearby Port Deposit. Five, 10 or even 15 open gates cause little or no concern, but when the number pushes beyond 30, the likelihood of flooding grows to a near certainty. In January 1996, for example, PECO opened 39 gates to relieve pressure from colossal mountains of ice that had built up behind the dam, but gave little advance warning to Port Deposit residents. Most of the townspeople managed to evacuate, but the town's 100 new condominiums suffered extensive ice and water damage, and a number of boats were smashed, sunk or washed out into the Bay. Happily, warning systems have improved, and Exelon has been conscientious about alerting residents before it opens the crest gates.
But let's complete our tour of the dam. Inside the powerhouse section, the heart and soul of the Conowingo Dam, lie the seven original turbine/generating units; outside the powerhouse there are four additional units that were added half-a-century later and after the dam had been anchored into the bedrock. The inside turbines produce from 54,000 to 64,000 hp each at best efficiency, while the outside turbines produce a considerably more robust 85,000 hp each. The original turbines are housed in an immensely tall, immensely cavernous, immensely impressive room, known as Turbine Hall. With its palisade of 16 floor-to-ceiling windows (which can be opened to cool the hall in summer), its finely wrought, meticulously cared-for 80-year-old machinery, its 1920s sensibility of fine detail, Turbine Hall is hard to compare with anything we see on a regular basis. Imagine Willy Wonka's Chocolate Factory (either version), by way of Fritz Lang's Metropolis and you'll begin to get the idea.
At the east end of Turbine Hall is the control room, where a controller sits behind a bank of computer screens that give a second-by-second accounting of all the turbine measurements, the water levels on both sides of the dam (five points if you automatically thought "forebay" and "tail race"), the water temperatures on both sides and the amount of oxygen in the water in the forebay. (That fairly stagnant water is kept sufficiently oxygenated by blowing air into it if necessary so the fish don't die while waiting to shoot through the turbines or floodgates.) The controller also monitors the flow rate and--here is the raison d'etre of the whole shebang--how much electricity the dam has been assigned to produce at any given time, depending on demand and a hundred other factors. The electricity is produced, sent off for storage and then sold to willing buyers. On the walls opposite the bank of computers are two earlier sets of controls. On the left is a wall of black-faced gauges used by the earliest controllers, who had to memorize 400 individual procedures before they could be control-room qualified, a learning curve that commonly spanned 25 years. On the right is an array of more modern instruments, set into a wall painted in that popular institutional color of the more enlightened 1960s known as "eye-rest green."
Leaving the dam itself, we come, finally, to Conowingo Pond, the dam's 14-mile-long forebay, which was created by water backed up as the dam was constructed. As predicted, the rising water took with it all trace of that area's long history, including farms, inns, the entire town of Conowingo and many of those ancient rock carvings. In their place, the pond has come to provide a number of useful services. First, of course, it provides the fall necessary to produce the electricity the dam was put there for in the first place. In addition, It provides cooling water for Peach Bottom Atomic Power Station seven miles upstream and serves as a lower reservoir for Muddy Run Pumped Storage Project 12 miles upstream. It serves as a water source for the City of Baltimore and the Chester Water Authority. And it offers recreation for boaters and fishermen--as does the tailrace on the dam's downriver side. In addition, the tailrace in particular has become a popular spot for bald eagles, who gather sometimes by the dozens to pick off fish attracted by the dam's out-flowing water.
The Dark Side of the Gorilla
Well, that's our gorilla, from forebay to tailrace and from powerhouse to crest gate. He's a fine looking fellow . . . big, powerful, useful. And eminently dangerous. Yes, it's time to move on to the "scary gorilla" part of our story. Next month, we'll take a good look at why the best thing the Conowingo Dam ever did for the Bay is going to turn out to be the worst.
What is the best thing the Conowingo has done for us? From the very beginning, the dam has trapped behind it an average of 3.5 million pounds of phosphorus and 2 million tons of dirt every year. That's about a third of the phosphorus and half the sediment moving down the Susquehanna toward the Chesapeake. But instead of finding its way into the Bay, these millions of pounds of dirt and millions of tons of phosphorus are stopped by the dam and then settle onto the bottom of Conowingo Pond. And that's a good thing. In fact, it's a great thing! So what's the problem? The problem is one of multiplication. If you take 2 million tons of dirt and 3.5 million pounds of phosphorus (and a lot of miscellaneous stuff like coal dust and PCPs) and multiply that by the number of years it has been piling up behind the dam, you get a very big figure. A figure so large that within a few years it will equal the storage capacity of the pond. In other words, the pond is going to be full. So what will happen when the pond runneth over? That's what we're going to look at next month . . . and the picture is not a pretty one.
Consider Hurricane Agnes. In 1972, Hurricane Agnes dumped so much water on the northeast U.S., and ultimately into the Susquehanna River, that the Conowingo was forced to open all of its crest gates. Along with the great torrent of water that flooded through--in addition to the debris and cows, cars and fuel tanks--came years' worth of trapped sediment. So much sediment poured into the Bay that it took years for the grasses and marine life in the northern Bay to recover. So what would happen to the Bay if we were to get another Agnes, now that there is 30 years more sediment built up behind the dam? That's our gorilla's ticking time bomb.
But there's a human side to this story as well. You'll be pleased to know that Earl Hopkins will be back. And we'll meet Earl's son, Mark Smith. Mark was working in the dam during Hurricane Agnes, and he has a harrowing tale to tell. There will be others too. But we'll save all that for next month in the second part of our series.