page_title: Seabed gouging by ice
section_title: Seabed survey for gouges
hierarchical_section_title: Seabed gouging by ice / Seabed survey for gouges
caption_attribution_description: English: 010406-N-0000X-002 File Photo -- An illustration depicting the underwater mapping capability of USNS Bowditch (T-AGS 62) and other ships of her class. T-AGS 60 Class Oceanographic Survey ships conduct sampling and data collection of surface, midwater and ocean floor parameters; launch and recovery of hydrographic survey launches (HSLs); the launching , recovering and towing of scientific packages (both tethered and autonomous), including the handling, monitoring and servicing of remotely operated vehicles (ROVs); shipboard oceanogaphic data processing and sample analysis; and precise navigation, trackline manoeuvering and station keeping to support deep-ocean and coastal surveys. There are 5 ships in this class. U.S. Navy Graphic Illustration (RELEASED)
context_page_description: Seabed gouging by ice is a process that occurs when floating ice features drift into shallower areas and their keel comes into contact with the seabed. As they keep drifting, they produce long, narrow furrows most often called gouges, or scours. This phenomenon is common in offshore environments where ice is known to exist. Although it also occurs in rivers and lakes, it appears to be better documented from oceans and sea expanses.
  Seabed scours produced via this mechanism should not be confused with strudel scours. These result from spring run-off water flowing onto the surface of a given sea ice expanse, which eventually drains away through cracks, seal breathing holes, etc. The resulting turbulence is strong enough to carve a depression into the seabed. Seabed scouring by ice should also be distinguished from another scouring mechanism: the erosion of the sediments around a structure due to water currents, a well known issue in ocean engineering and river hydraulics – see bridge scour.
context_section_description: Seabed gouging by ice is an eminently discreet phenomenon: little sign of it can be observed from above the water surface – the odd evidence includes sea floor sediments incorporated into the ice. Information of interest on these gouges includes: depth, width, length and orientation. Gouging frequency – the number of gouges produced at a given location per unit time – is another important parameter. This kind of information has been gathered by means of seabed mapping with ship-borne instrumentation, typically a fathometer: echo sounding devices such as a side-scan and a multi-beam sonar systems. Repetitive mapping involves repeating these surveys a number of times, at an interval ranging from a few to several years, as a means of estimating gouging frequency.
caption: Illustration of an echo sounding operation, here with a multibeam sonar used to map seabed bathymetry.
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