GLDT Annual Meeting Addresses Important Datum Changes and Water Level Predictions
On June 3, the Great Lakes Dredging Team (GLDT) held its annual meeting, and rather than gathering in person, the group held a virtual conference. The morning sessions addressed the water level forecast on the Great Lakes for 2020; the important updates to the International Great Lakes Datum and Low Water Datum and its impacts on the navigation industry; and the collaboration involved in the Great Lakes dredging program.
GLDT co-chairs Karen Keil of the U.S. Army Corps of Engineers Buffalo District, and Tom Rayburn of the Lake Carrier’s Association, welcomed the group to the webinar. Keil said the group was pleased with the turnout for last year’s in-person conference in Buffalo, and that this year’s virtual conference had almost twice as many attendees.
“Many of the challenges we face are too large to be handled by one entity; one challenge is the maintenance of the Great Lakes navigation system. It can only be accomplished in a collaborative manner,” Keil said.
Rayburn said that though cargo was a little bit light across the Great Lakes due to Covid-19 restrictions, construction projects are still moving throughout the region. “And even though we’re not loading as much cargo, we’re still moving boats,” Rayburn said. “Dredging is still a big deal, especially with the types of rains we’ve been getting that push lots of sediment.”
International Great Lakes Datum
John Allis of the Corps Detroit District and the Great Lakes hydrology office, gave an overview of the changes to the International Great Lakes Datum (IGLD) and the Low Water Datum (LWD). In the past, the U.S. and Canada have maintained their own datum references, despite having shared boundaries. The slight differences in vertical and horizontal datum references can cause challenges when both countries are trying to manage one body of water together. The new IGLD will be adopted by both countries.
The IGLD was first established in the 50s and updated in 1985. IGLD 85 is the current standard. “These should be updated every 30 years or so,” Allis said. The elevations of the Great Lakes are constantly changing, experiencing glacial rebound from the last ice age. “Where the earth’s crust was squished under the weight of ice and glaciers, the earth is still rebounding,” Allis said. Other areas that were pushed up from glacial movement are subsiding.
“You have this non-uniform shifting of the earth’s crust all throughout the Great Lakes region, so it’s important to update the datum and the elevations we’re assigning throughout the basin to make sure they’re representative as the lakes have shifted over time,” Allis said.
In the northern parts of the watershed, the land is rebounding upwards a few inches every 10 years, and on the south end, the land is subsiding at a similar rate. While not huge amounts, it’s enough that it matters, Allis said. The new datums will also affect authorized depths and dredging on Great Lakes harbors.
In the nearly 35 years since the last datum updates, methods for collecting the information have advanced. Traditionally, elevations were taken with physical measurements
throughout the country, but GPS receivers will report the new elevations much more accurately.
Low Water Datum
Even more significant to dredging than the updates to IGLD are the updates to the LWD, which defines channels depths. “Authorized project depth is in relation to that datum plan,” Allis said.
Further changes will be seen in the 2020 updates because in the last IGLD update, the LWD was not technically recalculated, but rather shifted uniformly to match the new elevations throughout the basin. Those numbers were originally based on numbers from the 1930s, calculated to be set so low that the water levels seldom fall below that level. “Over time we’ve obviously experienced significant low water periods,” Allis said. “We’ve also experienced high water. Data sets from the 1930s might not be representative anymore, as the Great Lakes system has changed over time.”
The Corps has also made physical changes to the system, deepening the connections between the lakes for larger vessels, which has caused the relationship of water levels between the lakes to also change over time. “It’s time for the actual LWD to be calculated to better reflect the actual water levels on the Great Lakes right now,” Allis said.
The team has started to put together some rough numbers, based on the recorded water levels from 1918 to present, noting there will be a general lowering on the upper lakes and a raising of elevations on the lower lakes. The work is being done by a group coordinating committee, made up of all the U.S. and Canadian federal entities responsible for water management. The committee is currently establishing draft methods, and Allis said they hope to have more solid numbers next year. At that point, they will solicit formal feedback from the navigation industry and federal agencies. The new datums are scheduled to go into effect in 2025.
Budgeting for Water Level Changes
Cynthia Jarema, chief of operations for the Detroit District, discussed what the new numbers would mean for dredging and operation and maintenance of the Great Lakes harbors. She presented some harbor examples showing a range of elevation changes, with the middle range showing an 11-inch change.
She said the impacts of elevation changes on the Great Lakes would mean areas will need a one-time lowering of the channel bottom to maintain new authorized depths. The areas may also see potential increases to the top elevations of navigation structures and the potential need to increase the top elevation of confined disposal facility (CDF) dikes that are built in the water or adjacent to the lake.
“What we need to do is be prepared for that 2025 mark,” Jarema said, in terms of funding. She presented some slides that calculated some dredging scenarios, based on the cost in typical dollars per cubic yards. One example, in the middle range of the predicted elevation changes, required $8 million in funding to meet new level changes. “Multiply that by all the harbors on Michigan/Huron,” Jarema said. “We have to have it in hand, so we can remove the material ideally before 2025.” In some cases, the sediment volumes for removal might not be high but involve the removal of hard-bottom channels. “The pressure is really on, and the
numbers that they select will be very important to us,” Jarema said. She said they expect to have a good indication of those final numbers by 2022/2023, so they can pursue the correct funding amounts. “We’ll have to do a lot of preparation and survey data through every harbor and see how much material is out there,” Jarema said.
2020 Water Level Forecast
Keith Kompoltowicz of the Corps Detroit District, chief of watershed hydrology, manages all the water level forecasts. To make sure the forecasts are consistent across the border, his office works closely with its Canadian counterparts at Environment and Climate Change Canada.
“The primary drivers of water level fluctuations are changing weather patterns and the resulting fluctuations in water supply,” Kompoltowicz said. “We’re really focused on the Great Lakes basin as a whole.” He said they study the weather patterns, such as the snow pack, the ice cover, the stream flow, and all the meteorological and hydrological information available to guide the forecast.
The net basin supply of the lakes is ultimately what impacts water levels, calculated as the precipitation that falls on the lake, plus the runoff, minus the evaporation. “We spend a lot of time studying and analyzing the changes in that supply over time,” Kompoltowicz said. The net basin supply is generally lowest in the winter, as precipitation falls as snow and accumulates on land. In spring, the snow melt combined with liquid precipitation drives a seasonal rise in water levels. Depending on the lake, the difference between the seasonal peak water levels and the low is 12 to 15 inches, Kompoltowicz said.
For more than a decade, previous to 2012, the system experienced its longest stretch of continuous low water periods. Then, the Great Lakes began experiencing a record rise in water levels. “That started with a couple very cold snowy winters, followed by record rain fall in the spring,” Kompoltowicz said. The lakes experienced record highs in 2019, and more record highs are predicted for this year.
The predictions for most of the lakes call for high levels but slightly below the record highs of last year, except for Lake Michigan/Huron, which might see record highs again this year. Many areas might still see negative impacts from coastal flooding. “Impacts of high water will certainly be felt through the rest of 2020. It would take a significant dry spell to get the lakes declining,” Kompoltowicz said.
Great Lakes Dredging Program
Marie Strum of the Corps Detroit District and lead for the Great Lakes Navigation Team, talked about the general mission of the Great Lakes dredging program and the importance of state and district collaboration. The Great Lakes navigation system is a system of interdependent ports and harbors. “It’s very different from coastal ports and harbors,” Strum said. “Because of the interdependence of the Great Lakes harbors, we can’t just take care of one harbor. Commercial ports are dependent on each other.” She said 95 percent of traffic on the Great Lakes is internal.
Strum noted that actions from the Water Resources Reform and Development Act of 2014 have helped to fund much-needed Great Lakes dredging projects. Ten percent of the taxes collected from the Harbor Maintenance Trust Fund were dedicated to small harbors, and another $10 million was set aside for emerging harbors. “There was a time around 2012 when we were not getting any funding, and things were looking bleak, but that has turned around,” Strum said.