Mobile District

Technical Note DOER-I1

July 1999 (Revised April 2000)

criteria are outlined in Engineer Manual 1110-2-1003 (Hydrographic Surveying) and control

requirements in accordance with Class I standards. An alternative differential-corrections commu-

nications link DGPS positioning system approved by the contracting officer is also required in the

event that the primary differential-corrections link is interrupted or not available. The monitoring

system generates output in a daily report in ASCII format and output to a diskette (Iomega 100

Mbyte Zip diskettes) for the previous 24-hr period of operation. These reports are delivered daily

to the Government's representative by 0730 hr local time.

All devices or systems are to be calibrated, tested, and certified by qualified personnel or agencies

prior to commencement of dredging operations. The results of these certifications are to be available

to the Government's representative during the final inspection before clearance to begin work is

given. In order to collect accurate slurry-density data, a site-by-site calibration process is used. This

calibration consists of pumping carrier water through the measurement system and establishing the

measured density as the baseline value (any densities greater than the established baseline value

represents slurry). Sufficient monitoring system backup equipment, replacement parts, supplies,

and qualified technicians are required to be available within 24 hr in order to minimize device or

system downtime.

Mobile District: The Mobile District uses rental contracts to maintain navigation on the

Tennessee-Tombigbee Waterway in Alabama and Mississippi; the Black Warrior-Tombigbee River

System and Alabama River in Alabama; the Gulf Intracoastal Waterway in Mississippi, Alabama,

and Florida; and the Apalachicola, Chattahoochee, and Flint rivers, in Alabama, Florida, and

Georgia. For the Tennessee-Tombigbee Waterway, Black Warrior-Tombigbee River System, and

Alabama River projects, the contractor's dredge is required to be equipped with recording (smoke

charts) gauges to record pipeline pressure and pump vacuum and pump rpm's during dredging

operations. Legible charts of these recordings are furnished to the contracting officer for each day's

operation on a daily basis. The contractor is also required to provide a depth-sounding device

capable of obtaining continuous depth-sounding measurements in the area of the forward hull of

the dredge. The data obtained by the depth-sounding device are displayed in the lever room of the

dredge. The accuracy of the depth soundings is verified periodically using a lead line.

The contractor furnishes, operates, and maintains a complete DGPS to provide dredge cutterhead

positioning referenced to the dredging-cut layout during the duration of the project (Figure 3). This

system uses DGPS equipment (usually with the Coast Guard's DGPS correction broadcast) to

provide real-time positioning in NAD 83 State Plane Coordinates. The contractor is also required

to have a base reference receiver-remote system in standby, but the Coast Guard broadcast has

proven to be reliable over the past 3 years. For each assignment, the Government furnishes a suitable

marked control point with proper NAD 83 coordinates and latitude/longitude designation for use

by the contractor to set up the DGPS antenna, reference receiver, and radio data link. If the

contractor elects to use other points or establish new control points, a copy of the survey data

associated with those control points must be furnished for Corps review. The contractor is provided

a diskette containing a DXF (Digital Translation File) of the dredging cut-layout for each individual

assignment. The file contains stationing, baseline information, and coordinates. The reference

DGPS receiver must at least be capable of sending correcting data every 1-3 sec in order to provide

positional accuracies in the 1- to 3-m range. Complete real-time display of the dredge cutterhead

in relation to the dredging cut, center-line ranges, and current 100-ft stationing is displayed