Coast Survey Taps 13th Century Technology Following Gustav

Lori Knell
Office of Coast Survey
NOAA National Ocean Service

November 4, 2008 — Sometimes old technology is the best technology.

After Hurricane Gustav rolled through the Gulf region, NOAA’s Office of Coast Survey (OCS) turned to a technique developed hundreds of years ago to measure channel depths leading into Lake Charles, Louisiana.

With high-tech sonar systems rendered useless by ten feet of sludge (often referred to as “fluff” by local mariners), NOAA contractor C&C Technologies opted to use a less sophisticated but readily available method for depth determination.  They used ‘lead lines,’ a centuries-old method of gauging water depths.

 

This adaptability is par for the course for OCS, the National Ocean Service office charged with gathering data by any means necessary to update nautical charts following major storms.

"While this is not a methodology commonly used for determining water depth, the surveyors needed to make a rapid assessment of the channel so vessels could begin transiting. The Lake Charles Channel is the 11th largest seaport in the U.S. and accommodates 5 million tons of cargo annually," said Crescent Moegling, Chief, Data Acquisition and Control Branch, Hydrographic Surveys Division, NOAA's Office of Coast Survey.

Lead-lining is a method to measure water depth from a slow moving vessel.  While the lines used today are more sophisticated than the hand-held ropes used by early hydrographic surveyors, the basic technology is the same: the lead line is lowered until it touches bottom. Then the depth is recorded from markings on the line.  In olden days, surveyors would use sextants fixed to mapped reference points on shore to determine the position of each reading.  Today, surveyors rely on GPS.

OCS is responsible for providing emergency hydrographic services to port areas to keep the Marine Transportation System flowing—a system that contributes more than $1 trillion annually to the nation’s economy.

When hurricanes make landfall, the intense weather systems often create stronger than normal ocean currents that can shift navigational channels. This threatens the ability of vessels to navigate safely.

While hydrographic surveys are also used for port and harbor maintenance, coastal engineering, coastal zone management, and offshore resource development, their primary use is for nautical charting.

Surveys determine if a given waterway is safe to travel by locating and plotting wrecks and obstructions.  In addition, surveys mark exact locations of aids to navigation and least depths on dangers to navigation.