Digital maps will water down flood risks
$1.8M plan will ensure Grand River towns won’t be caught off guard
CAMBRIDGE — A $1.8-million project to create digital maps of the floodplain using cutting-edge laser technology will allow the Grand River Conservation Authority to forecast, in almost real time, how a flooding river will act downstream and which areas are at imminent risk.
The authority plans to map most of the floodplains for the Speed and Conestogo rivers, as well as the entire floodplain of the Grand River over the next five years using sophisticated LiDAR technology, which bounces laser beams from a plane and measures the distance the light travels to create a highly detailed 3D map.
The technology, which stands for light detection and ranging, is used for everything from mapping archeological sites in dense jungle to mapping the sea floor and helping driverless cars navigate their surroundings.
Most of the authority’s existing floodplain mapping is on hard copies on plastic sheets, and many of those maps are more than 40 years old.
“It’s fantastic. It’s exciting,” said authority spokes-
person Cam Linwood. Having digital maps will allow the authority to tie in the maps with new flood forecasting software from the U.S. Army Corps of Engineers and provide real-time flood forecasts.
That kind of accurate, up-to-the-minute information can be crucial, Linwood said, especially when a flood hits without much warning. That’s what happened in June, when 100 mm of rain thundered down in the space of just two hours, dumping water into nearly full reservoirs and washing out local golf courses, parks and trails.
“It gives us the ability to communicate to our flood emergency response co-ordinators, and to understand which properties may or may not be affected, and who they should be notifying” when a flood is about to hit, Linwood said.
The LiDAR technology allows the authority to create three-dimensional pictures of not only the land around the river, but also models of the actual riverbed — where there are deep gullies, or where banks are shallow and water can easily spill over land. In 1975, there simply wasn’t the technology to do that.
Updating the maps is important because “the river is dynamic,” Linwood said. “The river does change over the years. It’s certainly a different river than it was in the mid-’70s. There could be sandbars that didn’t exist or debris that’s moved downstream.”
The mapping project has been in the works for some time, and wasn’t prompted by calls for better flood warnings after the unexpected flood in June, Linwood said.
The project is expected to cost a total of $1.8 million; funding from the province is expected to cover about a third of the cost, and federal disaster mitigation funding will cover another third, leaving the authority to cover about $575,000.
The hefty price tag is one reason the authority isn’t mapping the whole floodplain. This project will cover the main towns and cities in the watershed, about two-thirds of the communities with buildings in the floodplain, and all of the 19 trailer parks within the watershed, according to Scott Robertson, a senior water engineer with the authority.