Great Lakes Water Levels
STATEMENT FOR THE RECORD
LEON M. CARL
U.S. GEOLOGICAL SURVEY
U.S. DEPARTMENT OF THE INTERIOR
BEFORE THE COMMITTEE ON TRANSPORTATION AND INFRASTRUCTURE
SUBCOMMITTEE ON WATER RESOURCES AND ENVIROMENT
U.S. HOUSE OF REPRESENTATIVES
APRIL 18, 2008
Madam Chairman and Members of the Subcommittee, thank you for the opportunity to provide this statement for the record on water levels in the Great Lakes. I am the Center Director of the U.S. Geological Survey (USGS) Great Lakes Science Center (GLSC) in Ann Arbor, Michigan.
Scientists at the USGS have conducted research on water levels in the Great Lakes for over 20 years. Our scientists have played a major role in the environment portion of the International Joint Commission studies of potential lake-level regulation following the high water levels in 1986, as well as the recently completed studies of Lake Ontario regulation plans. USGS scientists have also conducted research on the effects of climate change on Great Lakes wetlands by studying the effects of past climate variability. Scientific understanding of pre-historical lake-level history and behavior in the Great Lakes is based largely on these studies.
Water levels in the Great Lakes vary naturally on time scales that range from hours to thousands of years. Seasonal changes are driven by differences in basin water supply during the year associated with snow melt, precipitation, and evaporation. Annual-to-millennial changes are driven by subtle-to-major climatic changes affecting both precipitation, and resulting streamflow, and evaporation. Observed water levels in the Great Lakes are also affected by very short-term changes resulting from storm surges and other fluctuations caused by wind, changes in barometric pressure or seismic disturbances (or seiches) and by very long-term changes caused by the rebound of the earth’s crust which had been depressed under the massive weight of ice sheets during the last glacial period.
USGS research quantifies the amount and timing of the natural variability in Great Lakes water levels going back nearly 5,000 years. For example, the reconstructed water-level history of Lake Michigan-Huron over the past 4,700 years shows three major high phases. The first phase occurring from 2,300 to 3,300 years ago, the second from 1,100 to 2,000 years ago, and the most recent from present to 800 years ago (Figure 1). Within this 4,700 year record is an apparent periodic rise and fall fluctuation lasting about 160 (±40) years in duration and a shorter fluctuation of 32 (±6) years that is superimposed on the 160-year fluctuation. Independent investigations of climate variability in the Great Lakes Basin over the long-term period of record confirm that these changes in lake level are a response to climate change, with higher lake levels during cool periods and lower lake levels during warm periods. Recorded lake-level history from 1860 to the present (Figure 2) is consistent with the longer-term pattern and appears to represent one 160-year quasi-periodic fluctuation. The current low water levels in the upper lakes that began in 1999 fall within the 30- to 32-year fluctuation which has been observed during the mid-1960s, mid-1930s, late 1890s, and late 1860s. Please note that the water level of Lake Superior and Lake Ontario has been regulated since about 1914 for Lake Superior and since about 1960 for Lake Ontario (Figure 2). The range of Lake Superior water-level fluctuations has not been altered greatly by regulation. However, fluctuations in Lake Ontario have been reduced from 6.6 feet before regulation to 4.3 feet over the past three decades since regulation has been implemented.
Natural variability of lake levels has been linked to the diversity and viability of nearshore wetlands in Lake Ontario. Periodic high lake levels kill trees, shrubs, and canopy-dominating emergent plants in nearshore wetlands, and low water levels following the high levels result in seed germination and growth of a multitude of species (Figures 3 and 4). Occasional low water levels are also needed to restrict the growth of plants that require very wet conditions, such as cattails, in wetlands higher up the shoreline that are typically colonized by wetland plants 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. In Lake Ontario the effects of regulation have eliminated or significantly reduced the natural pattern of high and low lake levels. As a result, extensive cattail stands have become established in nearly all wetlands in Lake Ontario, mostly at the expense of wetland rushes and grasses, substantially reducing the diversity of shoreline habitat (Figure 5).
In addition to USGS research on Great Lakes water levels, the USGS has also examined trends in tributary runoff into the Great Lakes. These trends are based on measurements of streamflow at USGS streamgages throughout the Great Lakes region. Runoff is a significant component of the Great Lakes water balance, especially in Lake Superior which has no inflow from an upstream Great Lake. Clearly, decreases in runoff result in decreases in lake level. Recent trends show decreased runoff in the Lake Superior watershed. This has contributed to lower lake levels in Lake Superior as well as the downstream Lakes Huron and Michigan.
Examination of very long-term trends in lake levels and recent trends in streamflow indicate that current low water levels in Lakes Michigan, Huron, and Superior are greatly influenced by natural variability in climate. Furthermore, this natural variability is critical to the health and viability of natural ecosystems, such as nearshore wetlands.
The USGS report on historical lake-level change, as well as analysis of trends in tributary runoff to the Great Lakes, was funded by Congress as part of a national pilot study of water availability in the Great Lakes. The Great Lakes pilot study includes analysis of historic trends in streamflow and preciptation, estimates of consumptive water use, rates of ground water recharge, and estimates of the amount of potable water available in the Great Lakes Basin. Reports produced through this pilot effort can be viewed on the pilot study website at: http://water.usgs.gov/wateravailability/greatlakes/index.html. The USGS is requesting a net increase of $8.2 million along with an internal redirection to provide $9.5 million to conduct a water census and upgrade the Nation’s stream gage network as part of the Department’s Water for America initiative in 2009. Future studies of this kind are being planned by the USGS as part of this larger initiative.
Thank you for the opportunity to submit this statement for the record.