|National Water Availability and Use Program|
U.S. Geological Survey Circular 1311
By Douglas A. Wilcox, Todd A. Thompson, Robert K. Booth, and J.R. Nicholas
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In this report, we present recorded and reconstructed (pre-historical) changes in water levels in the Great Lakes, relate them to climate changes of the past, and highlight major water-availability implications for storage, coastal ecosystems, and human activities. “Water availability,” as conceptualized herein, includes a recognition that water must be available for human and natural uses, but the balancing of how much should be set aside for which use is not discussed.
The Great Lakes Basin covers a large area of North America. The lakes capture and store great volumes of water that are critical in maintaining human activities and natural ecosystems. Water enters the lakes mostly in the form of precipitation and streamflow. Although flow through the connecting channels is a primary output from the lakes, evaporation is also a major output. Water levels in the lakes vary naturally on timescales that range from hours to millennia; storage of water in the lakes changes at the seasonal to millennial scales in response to lake-level changes. Short-term changes result from storm surges and seiches and do not affect storage. Seasonal changes are driven by differences in net basin supply during the year related to snowmelt, precipitation, and evaporation. Annual to millennial changes are driven by subtle to major climatic changes affecting both precipitation (and resulting streamflow) and evaporation. Rebounding of the Earth’s surface in response to loss of the weight of melted glaciers has differentially affected water levels. Rebound rates have not been uniform across the basin, causing the hydrologic outlet of each lake to rise in elevation more rapidly than some parts of the coastlines. The result is a long-term change in lake level with respect to shoreline features that differs from site to site.
The reconstructed water-level history of Lake Michigan-Huron over the past 4,700 years shows three major high phases from 2,300 to 3,300, 1,100 to 2,000, and 0 to 800 years ago. Within that record is a quasi-periodic rise and fall of about 160 ± 40 years in duration and a shorter fluctuation of 32 ± 6 years that is superimposed on the 160-year fluctuation. Recorded lake-level history from 1860 to the present falls within the longer-term pattern and appears to be a single 160-year quasi-periodic fluctuation. Independent investigations of past climate change in the basin over the long-term period of record confirm that most of these changes in lake level were responses to climatically driven changes in water balance, including lake-level highstands commonly associated with cooler climatic conditions and lows with warm climate periods. The mechanisms underlying these large hydroclimatic anomalies are not clear, but they may be related to internal dynamics of the ocean-atmosphere system or dynamical responses of the ocean-atmosphere system to variability in solar radiation or volcanic activity.
The large capacities of the Great Lakes allow them to store great volumes of water. As calculated at chart datum, Lake Superior stores more water (2,900 mi3) than all the other lakes combined (2,539 mi3). Lake Michigan’s storage is 1,180 mi3; Lake Huron’s, 850 mi3; Lake Ontario’s, 393 mi3; and Lake Erie’s, 116 mi3. Seasonal lake-level changes alter storage by as much as 6 mi3 in Lake Superior and as little as 2.1 mi3 in Lake Erie. The extreme high and low lake levels measured in recorded lake-level history have altered storage by as much as 31 mi3 in Lake Michigan-Huron and as little as 9 mi3 in Lake Ontario. Diversions of water into and out of the lakes are very small compared to the total volume of water stored in the lakes.
The water level of Lake Superior has been regulated since about 1914 and levels of Lake Ontario since about 1960. The range of Lake Superior water-level fluctuations and storage has not been altered greatly by regulation. However, fluctuations on Lake Ontario have been reduced from 6.6 ft preregulation to 4.3 ft over the past three decades postregulation, and storage changes have been reduced from 9 mi3 to 6 mi3. Regulation affects shoreline property owners and industries that have structures in the flood-hazard zone; they generally desire lower lake levels. Higher lake levels are preferred by recreational boaters and marinas concerned about lake access in shallow areas, as well as by municipal and industrial water-supply facilities concerned about water-intake structures. The shipping industry and hydropower industry prefer increased flow through the connecting channels and lower St. Lawrence River.
Regulation of lake levels has created problems for wetlands of Lakes Superior and Ontario. Periodic high lake levels are needed to kill trees, shrubs, and canopy-dominating emergent plants in Great Lakes wetlands, and low water levels following the highs are needed to promote seed germination and growth of a multitude of species. Occasional low water levels are also needed to restrict growth of plants that require very wet conditions, such as cattails, at higher elevations in wetlands that are typically colonized by sedges and grasses. The diversity of wetland plant communities and the habitats they provide for fish and wildlife in Great Lakes wetlands are dependent on water-level fluctuations. The effects of regulation have been most severe in Lake Ontario, where the natural pattern of high and low lake levels has largely been eliminated. As a result, extensive stands of cattails have become established in nearly all wetlands in Lake Ontario, mostly at the expense of the sedge/grass community, and diversity of habitats has been reduced substantially.
Great Lakes Water Levels
Recorded Water-Level History
Reconstructed Water-Level History
Relation to Climate
Relation to Storage
Relation to Coastal Ecosystems
Relation to Human Activities
|1. Map of the Great Lakes showing the extent of the drainage basin.|
|2–6. Graphs showing:|
|2. Volume and land and lake area for each of the Great Lakes.|
|3. Water inflow to the lakes.|
|4. Water outflow to the lakes.|
|5. Water balance for the Great Lakes, including types of input to and output from the lakes.|
|6. Historical lake levels for the Great Lakes, 1860–2005.|
|7. Oblique aerial photograph of a strandplain of beach ridges near Manistique, Michigan.|
|8. Hydrograph of late Holocene lake level and historical lake level for Lake Michigan-Huron.|
|9. Graph showing late Holocene lake level interpreted from beach-ridge studies in relation to surface moisture interpreted from testate
amoeba studies in peatlands.
|10. Graph showing water storage for the Great Lakes, 1860–2005.|
|11. Simplified diagram of the effects of water-level fluctuations on coastal wetland plant communities.|
|12. Profile of a typical coastal marsh from lake to upland showing changes in plant communities related to lake-level history.|
|13. Graph showing inferred late Holocene levels of Lake Michigan compared with peaks in probability of inferred dune building.|
|14. Schematic sections depicting the structural habitat provided by plant communities characteristic of regulated Lakes Ontario and
|15. Photograph showing armored shoreline on Lake Ontario that disrupts natural coastal processes and generally results in accelerated
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Whole report (10.6 MB) - 25 pages (8.5" by 11" paper)
Wilcox, D.A., Thompson, T.A., Booth, R.K., and Nicholas, J.R., 2007, Lake-Level Variability and Water Availability in the Great Lakes: U.S. Geological Survey Circular 1311, 25 p.
For more information about activities of the USGS National Water Availability and Use Program in the Great Lakes Region, see
USGS Fact Sheet 2005-3113.
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