Lake Erie’s water level constantly undergoes natural fluctuation. Daily changes, seasonal cycles, and long-term changes in the level of the lake all occur. The water level at any moment is the result of complex interactions between climate, wind, precipitation, bathymetry (the shape of the lake bottom), and the levels of the upper lakes (Superior, Michigan, and Huron). While the interactions themselves are complicated, the key concepts are very simple.
The Great Lakes System
The Great Lakes are comprised of five of the world’s largest lakes, as well as Lake St. Clair, and are connected by a series of rivers. Elevation of the Great Lakes falls from about 600 feet at Lake Superior down to sea level where the St. Lawrence River meets the Atlantic Ocean. The Great Lakes system stretches about 2,000 miles from the west end of Lake Superior to the Gulf of St. Lawrence.
Twenty percent of the world’s fresh water and 95 percent of the fresh water in the United States is contained in the Great Lakes and their interconnecting rivers. The Great Lakes basin (the land surface that drains into the Great Lakes) is about twice the surface area of the Great Lakes themselves.
Why Lake Levels Change
A lake of any size is a dynamic system, subject to constant change. Sometimes slightly more water comes in than goes out, or vice versa, and the lake level changes in response. Some of the factors affecting Great Lake levels are precipitation, evaporation, wind, crustal rebound, dredging, diversions, flood control, and power generation.
Changes in precipitation (rain and snow) are a primary cause of lake level fluctuations. Precipitation anywhere in the Great Lakes basin, whether over water or over land, can end up in the Great Lakes. Sufficient precipitation will raise their levels. However, there is usually a time lag so that increased rainfall or snowfall may not manifest itself as a higher lake level until months later. The following hydrograph (chart of water levels) shows the close relationship between precipitation and lake levels.
With almost 100,000 square miles of surface area, the Great Lakes lose a significant amount of water to evaporation. If Lake Erie's inputs and outlets were blocked off, evaporation alone would cause its level to drop 36 inches in one year. Evaporation is greatest not when the weather is warmest, but when the temperature difference between the water and the air is greatest. Such conditions occur in the fall, when the air has cooled but the water still retains some of the heat gained during the summer. Evaporation continues throughout the winter. Lake Erie, as the shallowest and southernmost lake, is also the warmest and may not always freeze over. If ice cover is insignificant, the open water continues to lose vapor to the dry winter air, dropping water levels.
Precipitation and evaporation together create seasonal cycles in lake levels. Water levels tend to be higher in the spring and summer—a response to winter snowmelt and spring runoff—and lowest in the winter because of summer and fall evaporation. The hydrographs below demonstrate this phenomenon.
Changing trends in precipitation and evaporation can have effects that last beyond one season. In the late 1990s, a pattern of mild winters, with less precipitation and reduced ice cover, resulted in a dramatic lowering of Great Lakes levels that lasted into the early 2000s.
While precipitation and evaporation are the most obvious and most significant factors in changing lake levels, other factors include wind, crustal rebound, and, to a much lesser degree, the human activities of dredging, flow diversion, flood control, and power generation.
Strong winds blowing for an extended period (several hours or more) not only create waves but can also produce wind set-up, the tilting of a lake's surface. A few times each year along Lake Erie, storm winds coincide with the lake’s southwest-to-northeast orientation. Southwesterly winds blowing along the lake’s length can pile water up at one end of the lake (Buffalo), leaving the other end (Toledo) with significantly lower water. The reverse can happen when storms send winds down Lake Erie from the northeast. When the storm winds subside, water at one end of the lake rolls back towards the other end, like a wave created when a tub of water is tilted—a phenomenon known as a seiche. In about twelve hours, this rolling wave has traveled to the opposite end of the lake, raising the level at that end from abnormally low to abnormally high. The cycle of sloshing back and forth continues until the lake’s surface returns to equilibrium.
Glaciers contributed to the creation of the Great Lakes, with ice in Ohio reaching as far south as the Ohio River. When the massive deposits of ice retreated, Earth's crust beneath began to rebound, much as a chair cushion rebounds when you stand up after sitting on it. While initially somewhat quick, rebound continues to this day on the order of only inches per century. But the rebound is unequal. North of Ohio where the ice was thicker, the crust was depressed farther and has therefore rebounded farther. The land surface at the northeastern end of Lake Erie has rebounded over 100 feet higher than land in Ohio that was once at the same elevation. This imparts a tilt to the lake basin that causes water to pile up at the lower (southwestern) end of the basin. Over a century, this factor alone can cause water levels to rise over half a foot at that end.
The effects of human-built structures and activities are described below.
Dredging is the removal of sediment to deepen a channel and make it suitable for navigation. Hydrologists estimate that dredging of the St. Clair River (between Lake Huron and Lake St. Clair), by lowering the outlet from Lake Huron, has lowered the elevation of Lakes Michigan and Huron by 10 inches over the last century.
Diversions are structures that add water to a basin from elsewhere or that bypass a natural outlet from a basin. There are several diversions in the Great Lakes where water is artificially removed from or added to the basin. However, only two diversions exist in the Lake Erie basin—the Welland Canal and the New York State Barge Canal (a successor to the historic Erie Canal). By bypassing the Niagara River, Lake Erie’s natural outlet, these diversions remove water from Lake Erie slightly more quickly than if they did not exist. Hence, the lake is slightly lower than it would be without these outlets. The Welland Canal has lowered Erie's level by about five inches. The mainly-recreational New York State Barge Canal's effect is less because it takes only about 1,000 cubic feet of water per second from the Niagara River, approximately equal to the flow of a small river such as the Cuyahoga. These diversion structures are outlets and do nothing to block the lake’s outflow or raise its level.
Only two of the Great Lakes, Superior and Ontario, have structures on them to expressly control the outflow of water. The St. Mary's River and the St. Lawrence River, outlets of Lakes Superior and Ontario respectively, have structures to regulate lake outflow for flood control and navigation purposes; but they are not designed for regulation of lake levels. The impact of regulation on Lake Superior is to raise that lake’s level about four tenths of a foot, with no effect on the levels of lakes below Superior. The controls on Lake Ontario and the St. Lawrence River obviously can have no effect on Lake Erie because they are at least 325 feet lower than Lake Erie.
Currently, three power generation facilities at Niagara take water from the Niagara River above Niagara Falls and discharge it below the Falls. A popular belief is that these activities have raised Lake Erie's level through damming. However, the power plants at Niagara are unlike hydroelectric plants in the western United States (for example, the Hoover Dam) that use tall dams to impound large amounts of water. The Niagara power facilities use the natural elevation drop of the Niagara River to generate power. Therefore, there are no tall dams on the river.
Taking into account the controls on Lake Superior and the various diversions, the overall effect of artificial controls on Lake Erie's level is ‒0.3 feet. In other words, Lake Erie is about four inches lower than it would be without controls.
Over the Long Term
Lake Erie water levels can change over short periods of time because of winds and can vary seasonally because of precipitation. But what about even longer terms? Geological evidence shows that over the millennia since Lake Erie was formed, its level has varied widely. About 5,000 years ago, the lake stood about 46 feet lower, which would have put the Ohio shoreline 2 to 3 miles farther out than it is today. The other Great Lakes experienced similar "lowstands," evidence for which includes submerged tree trunks—an indicator that forests once stood where water is today. The reasons for these lowstands are not clearly known, but climate was probably responsible.
References & Further Reading
Eckel, P.M., 2002, Botanical evaluation of the Goat Island complex, Niagara Falls, New York: St. Louis, Res Botanica, Missouri Botanical Garden Web site, last accessed June 23, 2009.
Great Lakes Commission, 1986, Water Level Changes-Factors Influencing the Great Lakes: Boyne City, Mich., Harbor House Publishers, 13 p.
National Oceanic and Atmospheric Administration (NOAA), 2002, Water Levels of the Great Lakes: Ann Arbor, Mich., NOAA Great Lakes Environmental Research Laboratory, 1 sheet.
Quinn, F.H., 1999, Anthropogenic Changes to Great Lakes Water Levels, in Great Lakes Update: U.S. Army Corps of Engineers, Detroit District, v. 136, p. 1–4.
Strand, Gail, 2008, Inventing Niagara—Beauty, Power, and Lies: New York, Simon and Schuster, 352 p.
U.S. Army Corps of Engineers, 1987, Fact Sheet-Water Levels of Lake Erie: U.S. Army Corps of Engineers, Buffalo District, 6 p.