TopoBathyContours2022
TBS survey crews began their survey of the project by conducting GNSS Static Network Sessions to establish updated horizontal and vertical control for the control monuments “CRMSBA-SM-20” and “TBM_1000”. The location of Secondary Monument “CRMSBA-SM-20” was found to be located near middle of existing island and accessible by airboat. The “CRMSBA-SM-20” monument is part of the Louisiana Coastal Zone (LCZ) Secondary GPS Network, and “TBM_1000” is a temporary benchmark set on this project established for additional bathymetric data collection. All survey data was recorded utilizing Trimble R10 and R12 Model base stations equipped with R12 antennas. The horizontal and vertical positions for these secondary monuments used at the start of data collection were obtained from the published position provided on the datasheet for “CRMSBA-SM-20” supplied by CPRA. For static data collection, the GPS base receivers were set to record L1 and L2 data from GPS and GLONASS satellites only, at a 5 second epoch rate with a 10-degree elevation mask. Base stations simultaneously collected static GPS data observations on three (3) separate days for a minimum of 4 hours each on the Secondary Monument “CRMSBA-SM-20” and “TBM_1000”. The GNSS Static Network Sessions completed for these control points are shown in Appendix “B”.  The program used to process the GPS network adjustment and all project data was Trimble Business Center (TBC), version 5.60, GNSS 2.20.2.3289. The static data for the selected Continuously Operating Reference Station(s) (CORS) were downloaded for the occupation times of the data collection to be included in processing of the final GPS network adjustment. The CORS used in the processing of the GPS network were stations “BVHS” (Boothville, LA), “DSTR” (Destrehan, LA), “GRIS” (Grand Isle, LA), “MARY” (New Orleans, LA), and “SBCH” (Shell Beach, LA). Static data from each CORS were downloaded into TBC, where baselines were created from CORS to the control points occupied in the GPS network for redundancy checks used in the network adjustments. After all static data and precise ephemeris were downloaded and imported into the overall network session in TBC, a 2D minimally constrained least squares adjustment was performed on all points using one CORS fixed in latitude, longitude, and ellipsoid height. After all baseline errors were fixed or removed, the GPS network was found to fit existing control values within acceptable limits. Processing continued to a fully constrained least squares network adjustment, holding all the CORS fixed in latitude, longitude, and ellipsoid heights to produce updated positions for project control points. The data collected was processed into the State Plane Coordinate System, Louisiana South Zone (1702) NAD83, US Survey Feet with vertical datum of NAVD88 (Geoid12B). Geographic coordinates are provided as NAD83(2011) (2010.00) latitudes and longitudes. The adjusted data was also converted to UTM, NAD83 (Zone 15) meters. ll static data collection and processing was performed following applicable guidelines set forth in Sections D and F of “A Contractor’s Guide to the Standards of Practice for CPRA Contractors Performing GPS Surveys and Determining GPS Derived Orthometric Heights within the Louisiana Coastal Zone”, July 2019 version. All positions listed in this report and Final Deliverables dataset are based on the final values established through Trimble Business Center (TBC) network adjustments and Real Time Kinematic (RTK) survey methods.As part of this task, an updated control monument data sheet for “CRMSBA-SM-20” was prepared and is shown in Appendix “C”. TBS performed a topographic survey along transects as provided by CPRA and as shown in the project site map in Appendix “A”. These topographic surveys were performed on June 6th, 2022, through December 16th, 2022 utilizing Global Navigation Satellite System (GNSS) with Real Time Kinematic (RTK) surveys. The project site was accessed via an airboat and a dual outboard survey vessel. Survey points were acquired where the marsh platform meets the toe of the dune, at the crest of the dune, and/or at the toe of the dune as it meets the beach. Position, elevation, water depths were recorded every twenty-five (25) feet along each transect and profile or where elevation changes of greater than one half foot (0.5) occurs. A half foot (0.5) diameter metal plate was attached to the bottom of the survey rod to prevent the rod from sinking. In shallow water areas (water less than approximately 3-4’ depths), both topographic and bathymetric survey methods were used as applicable to obtain all profiles and transects. RTK topographic survey data collection was performed in conjunction to bathymetric survey collection efforts. The bathymetric data collection was analyzed to help identify the limits of bathymetric data collection, and to calculate beginning points along transects for the topographic portions of all transects. This process was to assure that the data collected on topographic portions of transects were merged with the bathymetric portions of transects at the land/water interface to create overlaps in data collection of no less than one-hundred and twenty-five (125) feet. These overlapped areas helped with QA/QC of project data collected along transects. For the subaqueous portions of transects, water bottom data was collected using a standard 2.0-meter range pole fixed with a 6” diameter bottom plate, and by taking manual soundings using a stadia rod with a 6” diameter bottom plate. All soundings were gathered utilizing an RTK GPS for horizontal positioning and observed top of water elevation for soundings at the time of survey. The topographic survey data was downloaded from the Trimble TSC-7 Data Collector into the Trimble Business Center software for processing. This software allows for additional QA/QC of GPS data, and was used to check for instrument setup errors, antenna height errors, and other blunders. Manual sounding data was processed and reduced to NAVD 88 (Geoid 12B) elevations exported to digital (.csv) files and then imported into AutoCAD for further processing. RTK Topographic data can be found in the Transect Profiles on pages 4-39 of the drawing deliverables in Appendix “D”.Digital photos were acquired during the survey at four (4) separate locations along each transect. At each of the photo locations along the transect, four (4) additional photos at each location were taken with one facing northward along the transect, one facing southward along the transect, and the other two perpendicular to the transect facing eastward and westward. The two end photographs were taken near the gulf or bay edges along transects. Photos were acquired with a GPS enabled camera showing approximate coordinates of the location and the azimuth direction where they were acquired. All transect photographs and metadata associated with each individual picture can be found in the final digital deliverables.Water level elevations (NAVD88, Geoid12B) were collected each day at the project site for the duration of all field work. Water Levels as shown in the deliverables indicated as mean high water (MHW) and mean low water (MLW) were derived from water level data taken from the Continuous Recorder (H01) located at the CRMS0171 site located near the project area. The available hourly water level elevation data was downloaded from the CRMS Site, ranging from May 22, 2007 through June 2, 2022. All water level data downloaded was reduced to the project elevation datum of NAVD88, Geoid 12B. The daily high and low top of water elevations were taken from the data, and then used to calculate the MHW and MLW averages for this project site as shown in the project drawing deliverables in Appendix “D”.TBS surveyed positions provided by CPRA of the existing ten (10) settlement plates using RTK methods. At each location, TBS located the existing settlement plate and obtained ground elevations at a minimum of 4 locations (cardinal directions), top of collar elevation, and top of pipe elevation of the settlement plates. Two of the settlement plates (“SP-01” and “SP-03”) were not found during the survey, therefore no data was collected at these locations. Settlement plates (“SP-05” and “SP-08”) did not appear to have collars present during time of survey, therefore no top of collar elevation data was collected at these locations. Field notes and digital photographs were taken to document all the settlement plate site conditions. The updated location for settlement plates as surveyed are as shown in the table below and additional settlement plate data is shown on drawing deliverables in Appendix “D”.In conjunction with topographic surveys, TBS also performed bathymetric surveys along the transects as provided by CPRA and as shown in the project site map in Appendix “A”.  The hydrographic survey was performed by a two-man survey crew aboard the M/V Surveyor 7 on June 3rd, 2022, and June 6th, 2022. Upon arriving at the job location each day, the crew set an RTK base station on the control point “TBM_1000” and broadcast horizontal and vertical corrections from this control via radio to the survey vessel. The horizontal datum for this project was Louisiana South State Plane NAD83 and vertical datum was NAVD88 Geoid12B. Vertical corrections were applied during post processing, to adjust the data for tidal fluctuations, to 0.0’ NAVD88 Geoid12B. Elevations on top of water were taken periodically throughout the day to QA/QC the real-time tide corrections. Prior to and upon completion of the hydrographic survey (daily), a bar check was performed. The bar was lowered to a depth of 5’ directly beneath the transducer. The technician then checked the draft, index, and sound velocity values for correct values and adjusted as necessary. A sound velocity cast was performed twice daily to obtain an accurate average sound velocity to be input into the echo-sounder. Average sound velocity during bathymetric data collection was 5,003 m/s. Post processing of the bathymetry data was done in Hypack software suite’s single beam editor (64-Bit). Upon loading the raw data files, offsets were checked against values measured in the field, and documented in the field notes, for QA/QC. Real-time tide values were checked against the top of water elevations taken throughout the day for QA/QC. Post processing of the data consisted of cropping any outlying soundings in the data (cleaning of the data). Upon completion of data processing, an xyz file was exported for use in preparing survey transects as shown in the drawing deliverables attached in Appendix “D”.
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