Bathymetric Surveys. The USACE will provide BOEM with pre- and post-dredging bathymetric surveys of the borrow area. BOEM recommends that the pre-dredging survey of the Borrow Area be conducted within 90 days prior to dredging for each Borrow Area. However, the surveys will not be conducted before a notice to proceed is issued by USACE to the dredge contract for work in each Borrow Area. The post-dredging survey of each borrow area will be conducted within 30 days after the completion of dredging. BOEM recommends that USACE conduct additional bathymetric surveys of the Borrow Area as part of the MsCIP Monitoring and Adaptive Management Program five (5) and ten (10) years after the completion of dredging to document borrow area evolution and provide information to inform future decisions and consultations regarding the use of OCS sand resources. Surveys, error analysis, and reporting will be performed in accordance with the most recent edition of USACE’s Hydrographic Surveying Manual EM 0000-0-0000 unless specified otherwise. For bathymetric surveys, 100 percent coverage using interferometric swath or multibeam bathymetric survey methods is required. All bathymetric data will be roll, pitch, heave, and tide corrected using best practices. Sound velocity corrections will be applied based on measurements made during and throughout the duration of the survey using a profiling sound velocity meter to obtain water column sound velocities with casts that log the entire water column to the seafloor. Survey lines of the specific dredge area will be established at intervals necessary to provide 100 percent coverage. All survey lines will extend at least 100 meters (328 feet) beyond the edge of the Borrow Area’s limits (including Allowable Anchorage Area; Attachment 1) as defined in this MOA. All data will be collected in such a manner that post-dredging bathymetric surveys are compatible with the pre-dredging bathymetric survey data to enable the latter to be subtracted from the former to calculate the volume of material removed, shape of the excavation, and nature of post-dredging bathymetric change. Pre-dredge bathymetric survey transects will be reoccupied during the post-dredging surveys. Surveys will be conducted using kinematic GPS referenced to a GPS base station occupying an established (NAVD 88 vertical control) monument within 15 kilometers (9 miles) of the survey area, a National Geodetic Survey real-time network, or a water-level gauge deployed within the vicinity of the Bor...
Bathymetric Surveys. The USACE will provide the BOEM with pre- and post-dredging bathymetric surveys of XX XX. The pre-dredging survey will be conducted within the 60 days prior to dredging. The post- dredging survey will be conducted within 60 days after the completion of dredging. Additional bathymetric surveys are recommended within one (1) year and three (3) years following the completion of dredging. Hydrographic surveys will be performed in accordance with the USACE Hydrographic Surveying Manual EM 0000-0-0000, providing 100 percent seamless coverage using interferometric swath or multibeam bathymetry. All bathymetric data will be roll, pitch, heave, and tide corrected using accepted practices. Survey lines of the specific dredge area, within Borrow Area XX XX, will be established at intervals necessary to provide 100 percent coverage. Three equidistant cross-tie lines will be established parallel to the principal survey baseline. All survey lines will extend at least 100 meters beyond the edge of the dredge areas. All data will be collected in such a manner that post-dredging bathymetry surveys are compatible with the pre-dredging bathymetric survey data to enable the latter to be subtracted from the former to calculate the volume of sand removed, the shape of the excavation, and nature of post- dredging bathymetric change. Copies of pre-dredging and post-dredging hydrographic data will be submitted to the BOEM electronically within ninety (90) days after each survey is completed. The delivery format for data submission is an ASCII file containing corrected x, y, z data. The horizontal data will be provided in the North American Datum of 1983 (NAD ’83) Florida State Plane, U.S. survey feet unless otherwise specified. Vertical data will be provided in the North American Vertical Datum of 1988 (NAVD ’88), U.S. survey feet, unless otherwise specified. An 8.5-x-11-inch plan view plot of the pre- and post-construction data will be provided showing the individual survey points, and/or vessel track lines, as well as contour lines at appropriate elevation intervals. These plots will be provided in PDF format. Survey metadata will also be provided.
Bathymetric Surveys. Soundings using a multibeam echosounder system shall be used for all required surveys (i.e., pre-dredge, post-dredge, and progress surveys).
Bathymetric Surveys. Geosyntec will subcontract Xxxxxxx Marine to perform bathymetric surveys for the areas downstream of the spillways and powerhouses of Xxxxxx and Superior Dams. Xxxxxxx Marine will use a multi-beam echosounder to perform the bathymetric surveys in areas that can be accessed by the echosounder, but also plans to bring equipment to perform land surveys in regions where a surface vessel cannot be used due to shallow water (e.g., spillway apron of Xxxxxx Dam). Geosyntec proposes performing the bathymetric surveys prior to the field inspections. The surveys will be reviewed by Geosyntec prior to the field inspections to identify any areas of potential concern (i.e., areas exhibiting settlement or scour) to be evaluated further during the field inspections and future dive inspections.
