Exploring the Seabed in Quebec

Newly collected Hydrographic data and technological advances have made it possible to study morphological features of the seabed, including canyons, hills, ravines and craters, which until recently remained hidden beneath the sea. Seabed mapping provides essential information for navigation and for marine science research.

The mission of the Canadian Hydrographic Service (CHS) is to produce and publish data and information to ensure the safety of navigation, scientific research and other marine activities. CHS publications, including nautical charts, tide and current tables, and sailing directions, are useful for boaters, fishing vessels, and the Canadian and international marine transportation industry.

One of the teams responsible for compiling this important information is headed by Richard Sanfaçon, a manager in the Hydrographic Data Acquisition Division, Quebec Region. The division's work consists of making depth measurements in navigable bodies of water, including oceans, lakes and rivers, and detecting and mapping shoals that present hazards to navigation.

A variety of state-of-the-art technologies and equipment are used to carry out these operations. Hydrographer Richard Sanfaçon, described the major advances that have been made in hydrographic methods and instrumentation over the years. In the past, depth measurements were made using a lead-weighted line with marks on it: a hydrographer dropped the line off the side of a vessel and when it touched bottom took up the slack. The vessel's position was determined with a sextant. With this method, however, the dataset was limited to the points actually measured. Rapid technological advances during World War II led to the development of the echosounder, an instrument that sends out an acoustic pulse that travels to the sea bottom and back. Water depth is calculated from the time it takes the pulse to return and the speed of sound in water. This technique can be used to obtain seabed profiles as the ship moves from one position to another. Thanks to this technology, hydrographers are now able to obtain a continuous set of data along the ship's track, instead of just point measurements. However, data were still acquired only along the track lines.

Technology has continued to advance. In the late 1980s, the Quebec region was the first region in Canada to purchase a multibeam echosounder. This equipment transmits multiple beams of sound, as opposed to a single beam perpendicular to the bottom, thereby covering a fan-shaped area of the seabed. Multibeam sonar provides full seabed coverage and has permitted the discovery of a variety of underwater topographic features. The images that are obtained are very detailed and can be likened to aerial photographs.

To date, complete coverage has been obtained for 15 to 20% of the seabed of coastal Quebec and its watershed. The remaining areas have been mapped using point data from lead-line surveys or linear profiles obtained with conventional echosounders. Multibeam sonar technology has been used for seabed mapping in many areas of Quebec, particularly a large zone of the St. Lawrence River between Quebec City and Sainte-Anne-des-Monts, extending to the south shore of Méchins. In some locations, shallow water depths present challenges because the beam does not travel far enough to cover a broad swath and hence narrow bands are generated. To obtain complete bottom coverage in shallow waters, it is necessary to reduce the spacing between track lines and cover a distance of several kilometres. Full coverage has been obtained for other large expanses of seabed, including Honguedo Strait and Jacques Cartier Passage, on either side of Anticosti Island. Several extensive areas along the Lower North Shore, around the Magdalen Islands and off Sept-Îles have also been completely mapped.

This seabed mapping has enabled CHS specialists to make discoveries that have enhanced knowledge of the marine topography and geology of Quebec. For example, a crater 4.5 kilometres in diameter was discovered off Sept-Îles, and a team of geologists is currently studying the data collected to determine whether this feature was caused by meteorite impact or whether it is of magmatic origin. Other interesting seabed features have been identified around the Charlevoix, particularly submarine landslides. According to the geologists, the landslide events appear to be linked to the 1663 Charlevoix earthquake, which caused severe damage in the Éboulements region.

In addition to identifying morphological features, CHS specialists have located a number of interesting and significant shipwrecks. In 2004, a research team using multibeam sonar technology near Rimouski located the Vulcano, a large vessel that sank in 1927, at a depth of 115 metres. The same technology permitted the 2005 discovery of the wreck of the SS Nicoya. It is believed to be the first Canadian merchant ship sunk by German U-boats during the Battle of the St. Lawrence, in 1942. The shipwreck, 115 metres long, was discovered in 290 metres of water, off Saint-Yvon in the Gaspé. The team also found a major shipwreck, the SS Carolus, at a depth of 245 metres offshore from the site of the Maurice Lamontagne Institute. The SS Carolus was torpedoed by a German U-boat in 1942 and sank off Métis-sur-Mer. This shows just how far enemy submarines were able to penetrate into Canadian territory.

Two other significant shipwrecks were found in the Gaspé. The Bernier et Frères, which sank in 1952 with the loss of 10 people, was located in 2006. This ship was transporting timber from the Gaspé to Trois-Rivières but never reached its destination. In 2002, the wreck of the Brier Mist, a scallop dragger, was found on the bottom about 10 nautical miles from Rimouski. This vessel sank in November 1998 while crossing from Les Escoumins to Rimouski. Two crew members drowned. The bodies of three other crew members were found in the wreck.

Discoveries like these raise awareness of the technological advances that have been made in this field and the important benefits of seafloor mapping.

Hydrographer Richard Sanfaçon and his team are continuing the seabed mapping effort and updating cartographic products. Their mission is to someday obtain a complete picture of the morphology of the seabed in Quebec and Canada.