4.1 What is the purpose of the hydropower projects?
The main objective of the hydropower projects is dependable water flows for hydropower generation. This is reflected in a series of criteria and requirements in the International Joint Commission's (IJC) Orders of Approval allowing for the construction and operation of the project.
4.2 What caused changes in lake levels before regulation, and what is causing changes after regulation?
The same natural factors that changed lake levels before regulation continue to influence the levels after regulation. These factors include natural inflows (precipitation, runoff), outflows (evaporation) and other variable influences of weather (winds, temperatures), which collectively drive the hydrological system. Short-term adjustments to the outflows of Lake Superior have little impact on the lake level in comparison to these natural factors. Refer to Section 3 for more information about the major influences on water levels and flows.
4.3 What was the "natural" annual cycle of lake levels before regulation in comparison with after regulation?
The Board’s degree of control over lake levels is, in fact, very small. Over the years, the pattern of a summer peak and a late-winter to early-spring low has continued, on average, before and after regulation. Annual variations in the hydrologic cycle can shift the timing of these highs and lows.
4.4 Why were lake levels different prior to regulation than they have been since regulation?
In general, this is primarily the result of differences in natural hydrologic factors before and after regulation, and not the effects of regulation itself. However, regulation has successfully reduced the severity of extremes in lake levels in general. Flooding of Lake Superior was reduced (primarily in the 1950s and 1980s), and low levels were raised during periods of extremely low water supplies in the 1920s. Likewise, flooding of Lake Michigan-Huron was reduced (primarily in the 1980s) and low levels were raised, such as in the 1960s and early 2010s.
4.5 What has caused changes in levels of the St. Marys River since regulation?
The St. Marys River starts at the mouth of Lake Superior and flows to Lake Huron. The effects of the regulation of Lake Superior outflows reach as far downstream as the Sugar Island area.
Natural factors such as precipitation, runoff, and surge effects from strong winds continue to influence water levels in the St. Marys River after regulation, as they did before. The series of control structures used to regulate the outflow from Lake Superior also affects levels.
Given the immensity of Lake Superior upstream and the steep drop provided by the St. Marys Rapids, levels in river upstream of the control structures are not heavily affected by the flow rates through the structures, but can be influenced when strong winds blow the water in a surge effect on Lake Superior.
Downstream of the structures, water levels in the St. Marys Rapids, Soo Harbor, and around Sugar Island can be impacted by regulatory operations, such as the spillage of water through the Compensating Works, fluctuating flows, and peaking and ponding operations performed by the hydropower entities (see 5.4.3). Certain low-lying areas of Whitefish Island are prone to flooding during periods when multiple gates are open at the Compensating Works.
Gate #1 of the Compensating Works remains partially open at all times with an equivalent of approximately 15 m3/s of water passing through to continuously feed the Fishery Remedial Works (see 5.5.3) located downstream of its location. This is an area of enhanced fisheries habitat located along the south shore of Whitefish Island and to the north of the Fishery Remedial Works dike, completed in 1985.
4.6 What were the "natural" levels in the St. Marys River downstream of Sault Ste. Marie before regulation?
Prior to regulation, the St. Marys River downstream of Sault Ste. Marie experienced extreme level and flow fluctuations correlating with the fluctuating water level on Lake Superior. These fluctuations were moderated to some extent by the St. Marys Rapids. For areas further downstream, river flows and levels were also influenced by fluctuations in Lake Huron’s water level, especially during wind-driven storm events. The most extreme fluctuations, however, were due to the frequent occurrence of ice runs and ice jams in the St. Marys River. The regulatory ability of the control structures at Sault Ste. Marie and the hydropower operations there have virtually eliminated the risk of flooding from ice jams. Ponding restrictions imposed by the Board on the power entities during times of low water levels also limit the impact of such operations with respect to their ability to further reduce extremely low water levels in the lower St. Marys River nowadays (see 5.4.3 for more information).
4.7 How are the long-term, lake-wide average water levels computed?
A network of automatic, continuously monitored and maintained water level gauges has been operated by the National Oceanic and Atmospheric Administration in the U.S. and the Canadian Hydrographic Service since 1918. Daily mean data are obtained from the following gauges on Lake Superior: Point Iroquois, MI; Marquette, MI; Duluth, MN; Thunder Bay, ON; and Michipicoten, ON; and on Lake Michigan-Huron, daily mean data are obtained from: Harbor Beach, MI; Mackinaw City, MI; Milwaukee, WI; Ludington, MI; Tobermory, ON; and Thessalon, ON. These data are then averaged and the resultant mean values are the lake-wide average lake levels for the date in question. These lake-wide average values are used in regulatory computations as opposed to individual gauge readings since individual readings can be impacted by secondary factors such as wind-induced storms, glacial isostatic adjustment, and barometric pressure changes. Long-term statistics (e.g., average, maximum, and minimum values) are computed from 1918 through the most recent full year of data available.
4.8 How do the actual levels on Lake Superior and Lake Michigan-Huron differ from the Plan-specified levels?
The actual levels on Lake Superior and on Lake Michigan-Huron are the observed lake-wide average water levels measured using a network of gauges around each lake. Since the Board usually specifies outflows from Lake Superior according to the regulation plan, normally the actual observed water levels are the same as the Plan-specified levels. However, at times, the Board may deviate from the regulation plan and prescribe outflows other than those specified by the Plan, in which case the actual levels may differ from the levels that would have occurred had the regulation plan been strictly followed. Up until 2015, the Board was not authorized to deviate from the Plan-specified outflow without IJC approval, and was required to "pay back" such deviations in some manner (i.e., either with equal, off-setting deviations in subsequent months, or by permitting the Plan to automatically self-adjust over the course of several months). As of 2015, with the advent of the IJC’s Directive on Deviations, the Board is authorized to undertake minor deviations, such that they do not have a cumulative, measurable impact on lake levels (defined as exceeding +/- 0.5 cm added or removed from either Lake Superior or Lake Michigan-Huron). The Board will often allow the regulation plan to automatically adjust for these very small deviations over the course of several months (as has been the case during previous practice as well). However, at other times, particularly if the Board requests permission from the IJC to allow major deviations resulting in effects in excess of the +/- 0.5 cm limits, the Board may choose to further intervene and prescribe additional deviations to offset the effects on water levels. Any deviations from the Plan that are undertaken are summarized in the Board’s semi-annual reports to the IJC.
4.9 What actions does the Board take to manage ice conditions in the St. Marys River during the winter?
Following severe ice jams and subsequent flooding in the winter of 1916-17, the Board limited the maximum wintertime outflow from Lake Superior to 2,410 m3/s (i.e., an approximate flow of 90 m3/s via a 1/2-gate equivalent opening through the Compensating Works, plus another approximately 2,320 m3/s passed through the hydropower plants, locks, and other structures). This limit was reviewed during the International Upper Great Lakes Study, and under Plan 2012, it was determined that if the beginning-of-month Lake Superior level is extremely high and exceeds 183.90 m, the maximum wintertime outflow from Lake Superior can be increased to 2,690 m3/s without increasing the risk of ice jams. This will typically equate to a 2-gate equivalent opening through the Compensating Works, plus an additional 2,320 m3/s or so passed through the other structures. Additionally, the maximum allowable water level at the tailwater of the Cloverland Electric Cooperative hydropower plant is limited to 177.77 m (IGLD 1985).
4.10 Why can’t the Lake Superior level be kept at the average level all year round?
In order to keep Lake Superior at a constant value, the outflows would have to continuously match the net inflows to the lake. There are three major components to these inflows: the precipitation that falls directly onto the lake, plus the runoff that enters the lake from creeks and streams that are tributary to it, minus the evaporation that exits directly from the lake surface. Note that none of these factors can be accurately forecasted or directly measured precisely and in a comprehensive manner, and so it is impossible to predict or know how much water is entering or exiting the lake at any given time. Moreover, the degree of variability in the inflows far surpasses the Board’s ability to control the outflows. The Board simply could not keep up with the massive swings (both plus and minus) in inflows over the course of a year. Furthermore, trying to do so would adversely impact the various stakeholders that make use of the system both upstream and downstream of the control structures, and throughout the Great Lakes.
4.11 The water levels have changed a lot recently. What has the Board done?
Most likely, the Board has done very little or nothing to the Lake Superior outflows. First of all, regulation operations are typically performed monthly, and Lake Superior flow changes are typically performed only once per month, usually around the start of the month. If extenuating circumstances require unforeseen flow changes within the month, special media releases and online postings keep people informed as much as possible. Moreover, the Board’s degree of control over lake levels is very small compared to the other natural factors involved (see section 3). For those on Lake Superior, consider that the historical range in Lake Superior outflows would equate to a reduction in lake level of between 4 to 12 cm (1.6 to 4.7 in) in one month, while natural factors have caused Lake Superior to fall by up to 9 cm (3.5 in) or rise by up to 34 cm (13.4 in) in just one month. For those on Lake Michigan-Huron, the numbers are similar. The historical range in Lake Superior outflows possible would equate to a rise in the level of Lake Michigan-Huron of between 3 to 8 cm (1.2 to 3.1 in) in one month, whereas natural factors have caused Lake Michigan-Huron to drop by up to 12 cm (4.7 in) or rise by up to 32 cm (12.6 in) over the course of a month. And what about the impact of the St. Clair River outflows? It, too, is relatively small, and would equate to a range of reduction in Lake Michigan-Huron levels of 7 to 15 cm (2.8 to 6.0 in) per month. In short, modest fluctuations in water supply conditions can far outweigh the impact of even significant outflow changes.
4.12 Why is the flow in the St. Marys Rapids high when Lake Superior flows are high? What are the benefits and/or disadvantages of such a situation?
Under low water level and flow conditions, a minimum flow is passed through the gates at the Compensating Works in order to maintain fish habitat in the St. Marys Rapids. The vast majority of the remaining total flow out of Lake Superior can be passed through the hydropower plants to generate electricity (a much smaller amount of water is first passed through the navigation locks and used for domestic purposes). However, while the capacities of the three hydropower facilities is quite impressive, it is finite, and there are also times when it is necessary to undertake hydropower turbine shutdowns for power outages or maintenance, which may lead to reductions in available hydropower capacity. Extra water that cannot be passed through the turbines is spilled and passed through the gates at the Compensating Works, ultimately passing down through the Rapids. So during times of high flows, when more water must be released from Lake Superior, more gates are opened and more water must be passed down through the Rapids. This additional water may provide additional habitat for the various fish and other aquatic species that use the Rapids for shelter and spawning. However, increased flows in the area can also create dangerous conditions for anglers wading in the Rapids or standing on the Fishery Remedial Works Dike. Furthermore, when more than about a 4-gate open equivalent is required, the crest of the dike is typically overtopped with water. When more than about a 6-gate open equivalent is required, certain low-lying areas of Whitefish Island are inundated, and some recreational trails and structures may become impassable and dangerous to use.
4.13 How does regulation of Lake Superior mitigate flooding conditions in Soo Harbor area?
The Lake Superior regulation plan contains provisions that protect Soo Harbor area from extreme high and low levels. Notably, Criterion (b) of the 2014 Supplementary Orders of Approval restricts the outflow of Lake Superior to no more than the preproject outflow when the water level in Soo Harbor is expected to exceed 177.94 m or 583.8 ft. (IGLD 1985).