By Dr. Michael Izard-CarrollJuly 26, 2017
The 2017 spring and summer flooding event along Lake Ontario garnered considerable media and community interest about how water levels in the Great Lakes are monitored, who does the monitoring, and how often the monitoring is done. Just as the historic three feet higher than average lake levels witnessed in the past few months has drawn nationwide attention, interest in flood prevention strategies has also risen.
Monitoring lake levels provides leaders critical information in order to make educated decisions about what their communities may need to protect its public and private assets from high waters and destructive wave action.
The Corps of Engineers recently celebrated its 242nd birthday, and the civilian, Corps side of the U.S. Army is older than our nation. The organization has records of Great Lakes lake mean water levels back to the 1860s, while the binational, coordinated dataset begins in 1918. This year, 2017, makes a century of binational coordinated data sets that are being used in managing the international forecast for the Great Lakes, past, present and forecast.
The Great Lakes lake wide mean water levels are published daily by the Detroit District office. However, the U.S. Army Corps of Engineers is not the government entity who owns and maintains the Great Lakes water gauges but rather the National Oceanic and Atmospheric Administration (NOAA) -- National Ocean Service (NOS) -- Center for Operational Oceanographic Products and Services (CO-OPS) office in Silver Spring, MD.
The Corps of Engineers and Environment Canada use the data NOAA and the Canadian Hydrographic Service (CHS) collects and then provides jointly the levels to be internationally forecasted. The data is communicated to the Lake Ontario -- St. Lawrence River Board, which is a binational Board created by the International Joint Commission, and who manages the water levels for Lake Ontario.
"The Corps of Engineers, Buffalo District, has a technical advisory role with the Lake Ontario -- St. Lawrence River Board," said Keith Koralewski, Chief of Hydrology and Hydraulics and Water Management, U.S. Army Corps of Engineers, Buffalo District. "Based on the mean data we've analyzed, we make recommendations to the Board and provide projections. In the past few months, we've seen some sudden and dramatic increases in water levels due to heavy snow-packs in the late winter months, followed by heavy spring rains. We are now beginning to see Lake Ontario's levels start to decrease."
The United States currently operates 53 water level gauge stations through NOAA, along the Great Lakes extending from Lake Superior to the St. Lawrence River, and there are over 34 gauges on the Canadian side, operated by the Canadian Hydrographic Service. The gauge station sumps are typically six feet in diameter with an 8-foot by 8-foot brick and block structure, which houses the electronic water level measuring equipment. The sumps, stilling wells have a six-inch intake pipe, with varying lengths, from 10 feet to 1,900 feet in length, in order to always be able to measure the water levels in both extreme high and extreme low levels. The intakes are valve-controlled, removing wave action, providing the ability to truly measure the accurate water level elevations. Each station operates dual shaft angle encoders, with a primary and a redundant sensor. These encoders with optical sensors are absolute, ensuring that even when the power goes out they remain on datum, storing the water level elevations in the data collection platforms (DCPs), retrievable by GOES or phone line.
The primary water level gauge used by NOAA is the MT40 series encoder manufactured by Baldwin Electronics Incorporated. The BEI� MT40 series absolute encoders have been in operation in the Great Lakes since 1994, according to Jeff Oyler of NOAA, a 44-year veteran in the field of hydraulics and hydrology. The gauge model is installed as the primary sensor in all 53 gauging stations, he said. The encoders are precisely calibrated, readings maintained to within +0.003 meters (+0.01 ft.) to the reference elevation, which is the International Great Lakes Datum of 1985 (IGLD 1985).
Perhaps surprising is the fact that the majority of the Great Lakes brick-block gauge stations are on land, with the longest intake shaft reaching nearly 2,000 feet out into Lake Erie.
"It's an important thing that it's [the encoder] in a stilled water environment, and that's why they use these well set ups, said Keith Kompoltowicz, Chief of Watershed Hydrology with the U.S. Army Corps of Engineers, Detroit District. "If you try to go measure water levels out in an open lake, you'd see the impacts of waves, and these wells still the water to get a true surface elevation at that location."
"The ice that forms on the Great Lakes poses significant challenges for properly measuring water levels," said Oyler. "Wave action on the lakes would prevent accurate readings so the on-land stations allow us to take still water measurements."
Each water gauge station is equipped with an electrical power source, which provides sump lighting, and heat lamps to ensure the water in the wells do not freeze. The heated units allow gauges to be fully functional even in the harshest Northern winter conditions. NOAA performs scheduled maintenance on the gauges annually starting in mid-April through November of each year, and typically performs the work with in-house staff. However, the organization does have a cache of contractors on standby in the event of an emergency such as a sudden Data Collection Platform or gauge malfunction.
"NOAA doesn't have an operations center physically located within the Great Lakes proper and that is something I'd like to see reinstated someday," said Oyler, who works out of NOAA's - Center for Operational Oceanographic Products and Services (CO-OPS) engineering office in the Chesapeake, VA office.
The majority of the gauge stations are over 50 years old, Oyler says, and new stations cost approximately $500 thousand dollars each. Eight new stations have been constructed since 1970. The stations are outfitted with meteorological sensors that provide data to a number of reporting agencies, and all data is transmitted wirelessly via satellite.
Like many operations that are technology-dependent, redundancy of sensory equipment provides a backup for data collection. There are even redundant satellites used to transmit data should one satellite be inoperable for a time. Transmission of data is near real-time, transmitted at six-minute intervals. There is also a secondary, backup sensor, at all of the Great Lakes stations, says Oyler. It is also a shaft angle encoder but a little different structure than the BEI, and is made by Xylem�.
There are currently five stations on Lake Superior, six on Lake Michigan and Lake Huron, four on Lake Erie and six on Lake Ontario that are used for computing lake wide average reporting.
The water gauges used in the Great Lakes are not the only gauges available on the market, but some of the new radar-based units are not useful in the colder climates, since radar cannot see through ice--a major problem on the Great Lakes in wintertime. Solar-powered gauge equipment is mostly absent from the Great Lakes because of the long periods of limited sun that the region sees during the winter months. Solar is used for operating such sensors during the summer months (seasonal gauge data sets, June through September) to establish datums in ports, harbors of refuge, recreational harbors, and for maintaining the datum for dredging operations.
The Detroit District office obtains the raw daily mean water level for all of the gauges on the Great Lakes, and they are primarily interested in the data from the coordinated gauge network for each lake. The Coordinating Committee on Great Lakes Basic Hydraulics and Hydrology Data decides which gauges will be used for determining the mean average for a particular lake, said Kompoltowicz.
"On a daily basis, our servers go out and grab the daily means from the prior day from both the Canadian gauges and the U.S. gauges and then our systems average those daily gauge means into a lake wide mean", said Kompoltowicz.
On Lake Erie, for example, there are four gauges that are used in the coordinated gauge network--two in the United States, and two in Canada. They are at Toledo, Ohio, Cleveland, Ohio, and Port Stanley and Port Colborne in Ontario, and those gauges averaged together make up the lake wide mean water level.
The Detroit District office publishes average daily mean water levels but for those interested in the raw data for lake levels, they can be found on NOAA's "Tides & Currents" website, as well as the Canadian Hydrographic Service website.