154
1. Atkinson
3.1 Water Quantity
Fluctuations in water levels have raised significant public concern. There is
evidence of lake-level fluctuations with periods of approximately 33 and 160
years, at least for the western lakes (Thompson and Baedke 1997; Baedke and
Thompson 2000), but these cycles are still not well understood. High water levels
were seen in the early 1990s, but currently the upper lakes (Superior and
Michigan) are near historical low levels. These fluctuations are most likely related
to natural long-term hydrologic variations in the watershed, and there have been
several attempts to correlate lake levels with climate change (Fraser et al. 1990;
Thompson and Baedke 1997). There are several places in the system where water
flow is controlled, notably at Niagara Falls (controlling Lake Erie level) and in the
st. Lawrence Seaway (controlling Lake Ontario level), where hydroelectric power
is generated. There are opposing objectives with regard to flows and water levels.
Higher flows mean that more electricity can be generated, but low water levels
pose possible hazards for shipping and are a problem for coastal marinas. Natural
fluctuations in water level are desirable for maintenance of coastal wetlands, and
proper management requires a better understanding of long-term variations in
weather (or climate).
As previously noted, a major issue currently being debated concerns whether
there should be any diversion of Great Lakes water outside the watershed
boundary, either to other parts of the country or other parts of the world. Some
diversion issues are related simply to urban sprawl, i.e., what should be done when
a community that receives its water from one of the lakes spreads over the
watershed boundary. There are already several diversions in the basin, but they
account for a negligible fraction of the water budget. Allowing and/or managing
any possible additional diversions, along with balancing other competing uses,
will be a significant challenge in the future.
3.2 Hydrodynamics and Water Quality
Hydrodynamic and water-quality modeling of the lakes has been carried out since
at least the 1960s. The first water-quality models were formulated to consider a
lake as a "mixed reactor", as in Eq. (1), which ignores spatial variations in the
system. Even until relatively recently, models tended to be of finite segment or
finite layered form and did not provide very detailed spatial resolution. The large
size of the lakes precluded detailed spatial resolution in earlier computer models.
Even now, with much greater computational power available, the kind of dataset
needed to verify a detailed spatial model is rarely available, although several
large-scale efforts have been reported. Examples of these studies include the
International Field Year for the Great Lakes (Aubert and Richards 1981), the
Green Bay Mass Balance Project (e.g., DePinto et al. 1994) and the current
EEGLE - Episodic Events Great Lakes Experiment project in Lake Michigan (see
Great
Lakes
Environmental
Research Laboratory web
site,
at
1. Atkinson
3.1 Water Quantity
Fluctuations in water levels have raised significant public concern. There is
evidence of lake-level fluctuations with periods of approximately 33 and 160
years, at least for the western lakes (Thompson and Baedke 1997; Baedke and
Thompson 2000), but these cycles are still not well understood. High water levels
were seen in the early 1990s, but currently the upper lakes (Superior and
Michigan) are near historical low levels. These fluctuations are most likely related
to natural long-term hydrologic variations in the watershed, and there have been
several attempts to correlate lake levels with climate change (Fraser et al. 1990;
Thompson and Baedke 1997). There are several places in the system where water
flow is controlled, notably at Niagara Falls (controlling Lake Erie level) and in the
st. Lawrence Seaway (controlling Lake Ontario level), where hydroelectric power
is generated. There are opposing objectives with regard to flows and water levels.
Higher flows mean that more electricity can be generated, but low water levels
pose possible hazards for shipping and are a problem for coastal marinas. Natural
fluctuations in water level are desirable for maintenance of coastal wetlands, and
proper management requires a better understanding of long-term variations in
weather (or climate).
As previously noted, a major issue currently being debated concerns whether
there should be any diversion of Great Lakes water outside the watershed
boundary, either to other parts of the country or other parts of the world. Some
diversion issues are related simply to urban sprawl, i.e., what should be done when
a community that receives its water from one of the lakes spreads over the
watershed boundary. There are already several diversions in the basin, but they
account for a negligible fraction of the water budget. Allowing and/or managing
any possible additional diversions, along with balancing other competing uses,
will be a significant challenge in the future.
3.2 Hydrodynamics and Water Quality
Hydrodynamic and water-quality modeling of the lakes has been carried out since
at least the 1960s. The first water-quality models were formulated to consider a
lake as a "mixed reactor", as in Eq. (1), which ignores spatial variations in the
system. Even until relatively recently, models tended to be of finite segment or
finite layered form and did not provide very detailed spatial resolution. The large
size of the lakes precluded detailed spatial resolution in earlier computer models.
Even now, with much greater computational power available, the kind of dataset
needed to verify a detailed spatial model is rarely available, although several
large-scale efforts have been reported. Examples of these studies include the
International Field Year for the Great Lakes (Aubert and Richards 1981), the
Green Bay Mass Balance Project (e.g., DePinto et al. 1994) and the current
EEGLE - Episodic Events Great Lakes Experiment project in Lake Michigan (see
Great
Lakes
Environmental
Research Laboratory web
site,
at