7. PO75 100408 Survey Report.pdf

Survey Report Page i Labranche East Marsh Creation September 2, 2010

LABRANCHE EAST MARSH CREATION

PROJECT NO. PO-75

SURVEY REPORT

PREPARED FOR:

SEPTEMBER 2, 2010

SUBMITTED BY:

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Prepared for: U.S.D.A.

Natural Resources Conservation Service 3737 Government St.

Alexandria, LA 71302

Submitted By: T. Baker Smith, Inc 412 S. Van Ave.

Houma, LA 70363

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LABRANCHE EAST MARSH CREATION

TABLE OF CONTENTS

1.0 INTRODUCTION

2.0 PROJECT OVERVIEW

3.0 DATA COLLECTION SUMMARY

3.1 GEOTECHNICAL SURVEYS

3.2 MARSH CREATION FILL AREA SURVEYS

3.3 LAKE PONTCHARTRAIN BATHYMETRIC SURVEYS

3.4 MARSH ELEVATION SURVEYS

3.5 MAGNETOMETER / SIDE SCAN SONAR SURVEYS

4.0 METHODOLOGY

4.1 SURVEY CONTROL AND DATUM INFORMATION

4.2 TOPOGRAPHIC SURVEYS

4.3 BATHYMETRIC SURVEYS

4.4 GEOPHYSICAL SURVEYS

LIST OF APPENDICES

APPENDIX 1---- Survey Control Monument Datasheets APPENDIX 2---- Marsh Creation Area – Elevation Contours APPENDIX 3---- Marsh Creation Area – Average Marsh Elevations APPENDIX 4---- Borrow Area – Elevation Contours and Survey Transects APPENDIX 5---- Borrow Area – Magnetometer and Side Scan Sonar Survey

Digital Appendix (presented on accompanying CD)

Data Collection Report file (PDF format) Project digital drawing files (AutoCAD, PDF, and Microstation formats) Topographic and Bathymetric digital survey point data (ASCI II format) Survey Field Notes (PDF Format)

Survey Report Page 1

1.0 INTRODUCTION

The purpose of the data collection tasks summarized in this report is to provide critical support information for planning and design of the Labranche East Marsh

Creation Project (PO-75). The Services provided under this task order involved topographic and bathymetric field data collection, related data processing, and the organization of all data into a workable format for design purposes.

2.0 PROJECT OVERVIEW

The Labranche East Marsh Creation Project is an authorized PPL 19 Coastal

Wetlands Planning, Protection, and Restoration Act (CWPPRA) Project. The project is co-sponsored by the Natural Resources Conservation Service (NRCS) and the Louisiana

Office of Coastal Protection and Restoration (OCPR). The primary objective of this project is to convert an existing 729 acre shallow pond area to a healthy marsh platform by dredging sediment from Lake Ponchartrain. In addition, the project will nourish approximately 202 acres of existing marsh. The marsh creation site is located approximately 2 miles west of the eastern guide levee of the Bonnet Carre Floodway, between Interstate 10 and Lake Pontchartrain. The proposed borrow site is located in

Lake Pontchartrain, approximately 2000’ north of the end of the Eastern Guide levee of the Bonnet Carre Floodway.

3.0 DATA COLLECTION SUMMARY

During the period of June 2010 through August 2010, T. Baker Smith, Inc. (TBS) collected field data throughout the project area. This data collection task consisted of numerous topographic, bathymetric, and geophysical surveys throughout the marsh creation and borrow areas. Topographic and Bathymetric data was collected by a three-

Survey Report Page 2 man survey crew aboard an Airboat or Survey vessel w/ outboard motors. Geophysical data was collected by a two-man crew aboard a 26’ hydrographic survey vessel.

3.1 GEOTECHNICAL SURVEYS

A total of sixteen (16) Geotechnical Bores were staked for position and surveyed for potential underground obstructions. The Bore positions were staked with cane poles and a magnetometer survey was performed within a 100’ radius around each location.

No significant magnetic anomalies were found within the specified radius at any of the bore locations.

3.2 MARSH CREATION FILL AREA SURVEYS

Topographic and Bathymetric surveys were performed along 46 transects located throughout the 729 acre marsh creation area. Surveys were also performed along an additional 31 cross-sections located at various bayous, cuts, and tidal openings connected to the marsh creation area. The spacing for elevations obtained in these surveys was every 25 feet or major changes in grade. Also, the perimeter marsh edge of the marsh creation area and interior islands was surveyed at 50’ intervals or greater to accurately depict the feature. The results of the Marsh Creation Fill Area Surveys can be seen in

Appendix 2.

3.3 LAKE PONTCHARTRAIN BATHYMETRIC SURVEYS

Bathymetric data was collected along thirteen (13) tracklines within the Lake

Pontchartrain Borrow Area. Survey tracklines were spaced in an east to west configuration at 250’ intervals. These tracklines were surveyed in a continuous manner using a 24’ Hydrographic Survey vessel utilizing a 200 kHz fathometer and RTK positioning. Acoustic soundings were collected along each trackline at a 10 Hz rate. The results of the Lake Pontchartrain Bathymetric Survey can be seen in Appendix 4.

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3.4 MARSH ELEVATION SURVEYS

In order to determine the average healthy marsh elevation for marsh creation construction, elevation surveys were performed at nineteen (19) different sites selected by

NRCS field personnel. At each location, three marsh elevations were observed at the base of the plant root mass using RTK GPS. The results of the Marsh Elevation Surveys can be seen in Appendix 3.

3.5 MAGNETOMETER / SIDE SCAN SONAR SURVEYS

Magnetometer surveys were performed in both the borrow area and marsh creation area to determine the location of any possible oil and gas pipelines and other mettalic obstructions. The marsh creation area magnetometer survey was performed using a magnetic gradiometer from an Airboat. The survey was run on tracklines spaced at 500’ intervals oriented in a manner to provide complete coverage of the area. This survey did not show any significant magnetic anomalies within the marsh creation area.

Many PVC markers were found within the marsh creation area, but surveys did not register any magnetic signatures around the markers. Based on field investigations, these markers appear to have been placed to mark boat travel lanes and not underground utilities.

The Magnetometer survey performed in the Lake Pontchartrain Borrow area was performed using a 24’ Survey Vessel and a Proton Magnetometer. The magnetometer survey was run on tracklines spaced at 100’ intervals, oriented from East to West. The survey showed the existence of 2 possible pipelines crossing the proposed borrow area.

The surveyed location of one of the pipelines (Air Products and Chemicals, Inc.) was confirmed by the LDNR pipeline database. However, the second pipeline was not documented in any of the known pipeline databases. One additional pipeline was detected outside of the borrow area boundary (Shell Pipeline), near the southeast corner of the area. A total of 284 magnetic anomalies were detected and identified during this survey. The large majority of these anomalies were determined to be crab traps placed by local fishermen. The results of the Borrow Area Magnetometer Survey can be seen in

Appendix 5.

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The Borrow Area was also surveyed using a Side Scan Sonar System. This survey was performed to determine the presence of any potential non-metallic obstructions located on or above the lake bottom within the borrow area. The Side-Scan

Survey was performed concurrently with the Magnetometer survey, on identical tracklines. This survey did not reveal the presence of any significantly visible bottom obstructions. The survey does show a large area of anchor scars near the Air Products and Chemicals pipeline in the north–central portion of the borrow area. Also, several areas of unidentified bottom formations are visible at the north east corner of the borrow area. These areas are most likely clam shell (Rangia cuneata) reefs, which are known to exist in this area of the lake. The side scan sonar mosaic image can be seen in Appendix

5.

4.0 METHODOLOGY

4.1 SURVEY CONTROL AND DATUM INFORMATION

The horizontal and vertical survey control used for all data collection on this project was Benchmark “876 2372 F TIDAL”. This benchmark is part of NOAA’s tidal benchmark network. Before this Benchmark was used for control purposes the published elevation and horizontal coordinates were verified from LSU’s GULFNET Real-time

RTK Network. The horizontal datum for all survey data collected is Louisiana State

Plane, South Zone (1702), NAD 83, in U.S. Survey feet. The vertical datum for all data is NAVD 88, in U.S. Survey feet. Published data for the benchmark can be seen in

Appendix 1.

4.2 TOPOGRAPHIC SURVEYS

Topographic Surveys were performed using a standard three-man survey crew, accessing the survey area by airboat. In areas with a clear, unobstructed view of the sky, a Trimble model R7/R8 GPS RTK unit was used to collect the topographic field data.

The manufacturer’s stated accuracy of this unit is 2-3 cm horizontal, and 3-4 cm vertical.

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All RTK GPS Survey information was stored digitally using a Trimble TSC-2 Data

Collector.

In areas where tree canopy or other obstructions made RTK GPS impractical, the survey crew used conventional survey methods to collect the topographic data.

Typically, two control points were set with RTK GPS in an unobstructed area. A 200’ surveyors tape and level were then used to reference the surveyed point to the control points. Handwritten field notes were used to document all conventional survey data. For the subaqueous portions of cross-sections, data was collected by taking hand soundings using a Standard 25’ Stadia Rod with a 6” diameter bottom plate. RTK GPS was used for horizontal positioning of each sounding. The soundings were also referenced to an RTK

GPS observed tide reading for elevation reduction.

Topographic survey data was downloaded from the Trimble TSC-2 Data

Collector into the Trimble Geomatics Office software for processing. This software allows for QA/QC of GPS data, and was used to check for instrument setup errors, antenna height errors, and other blunders. Sounding data was processed by manually entering the soundings and observed tide readings into a formatted spreadsheet. The spreadsheet was configured to automatically reduce each sounding from depths to

NAVD88 elevations. These points were then exported and entered into AutoCAD Civil

3D for further processing. Using this point data, 3D surface models were produced for all areas. These surface models were used to generate elevation contours and profiles for the final deliverable drawings. The processed survey data was also exported to one complete digital text file containing point numbers, X, Y, Z coordinates, and point descriptions.

4.3 BATHYMETRIC SURVEYS

Bathymetric Surveys were performed using a standard three-man survey crew aboard the 24’ Survey Vessel “Surveyor X.” The bathymetric data was collected using a

Hydrotrac digital echosounder interfaced with the HYPACK MAX survey navigation software in conjunction with the Trimble RTK GPS unit previously mentioned. Real -time position data was output from the GPS receiver to the HYPACK software 10 times

Survey Report Page 6 each second. Digital water depth data was also output from the depth sounder 20 times each second. The HYPACK software is able to use the above information to display course corrections to help the surveyor navigate the predefined track line. The software is also able to compute a precise, centimeter level, position of each sounding.

In order to ensure accurate measurements were being recorded, equipment checks and calibrations were performed several times each day. The digital depthsounder was calibrated several times a day for sound velocity corrections. This is performed by lowering an acoustic target, with precisely measured marks, below the transducer to the desired survey depth. The depthsounder’s sound velocity correction factor is then adjusted so that the depthsounder reads the precise depth of the acoustic target. The measurements of the onboard GPS system were also checked by observing navigation checkpoints, or “Nav-checks”, set throughout the project area.

Bathymetric survey data was transferred from the onboard laptop computer to the office for processing. The processing was accomplished by using Hypack’s Single Beam

Editor. The Hypack software allowed a profile-type review of the data, where any position or sounding outliers were manually removed. Once the data had been processed and gone through an internal QA/QC review, it was presorted and points spaced at 10’ intervals along the line were exported in X,Y,Z format. These X,Y,Z point files were then imported into AutoCAD Civil 3D for grouping, management, and further QA/QC.

4.4 GEOPHYSICAL SURVEYS

Geophysical instruments used during this survey consisted of a Klein Model 3000 side scan sonar and a Marine Magnetics SeaSPY marine magnetometer. Horizontal positioning of the survey vessel was accomplished using HyPack® navigation software with a Trimble Model DSM 232 global positioning receiver. Horizontal accuracy of this positioning as stated by the manufacturer is 3 meters. The magnetometer sensor was deployed 50 feet behind the positioning antenna and set at .1sec/gamma. The side scan sonar fish was towed alongside the vessel and was set at the 40-meter range, with frequency settings of 100 and 500 kHz simultaneously. Horizontal positioning of the

Survey Report Page 7 survey vessel was accomplished with a Differential Global Positioning System, which has a field accuracy of 3 meters.

All Magnetometer data was digitally recorded by an onboard laptop computer using the SeaSPY interface linked with the HYPACK MAX survey navigation software mentioned above. The magnetometer was set to a collection frequency of 10 Hz. The magnetic data was processed in Hypack to obtain the exact position, signature type, and strength of each anomaly. The Hypack processing software allows the user to view the magnetic data as actual magnetic field values along a continuous line. The user is able to easily pinpoint anomalies as deflections from the normal magnetic field and note the position based on the center of the signature. The magnetic contours are then exported in

20 gamma intervals to show the magnetic variation across the site. Each magnetic anomaly is interpreted based on its size, signature type, and actual field observations.

The Side scan sonar images were collected using a system consisting of a topside computer, VGA monitor, keyboard, mouse, graphic recorder, tow cable, and sonar towfish. The system contains an integrated navigational plotter which accepts standard

NMEA 0183 input from the previously mentioned DGPS system. This allows vessel position to be displayed on the monitor and speed information to be used for controlling sonar ping rate. Sonar sweep can also be plotted in the navigation window for monitoring bottom coverage in the survey area. The hardware listed above is interfaced to the Klein

SonarPro data acquisition and playback software package which runs on the topside computer. All sonar images are stored digitally and can be enhanced real-time or post-survey by numerous mathematical filters available in the program software. Digital side scan sonar imagery were processed and mosaiced using Triton Isis Software to produce geo-referenced TIF image files and plotted in plan view. The resulting mosaic was then used to identify individual acoustic targets representative of natural or man made objects resting on the bottom.

Survey Report

APPENDIX 1

Survey Benchmark Data Sheet

APPENDIX 2

Marsh Creation Area Elevation Contours

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APPENDIX 3

Marsh Creation Area - Average Marsh Elevations

APPENDIX 4

Borrow Area - Elevation Contours and Survey Transects

APPENDIX 5

Borrow Area – Side Scan and Magnetometer Survey Results