OPR-K354-KR-16Approaches to Atchafalaya BayGulf of MexicoOcean Surveys, Inc.H12908430 NM SSE of Marsh IslandLouisianaUnited States400002016George G. ReynoldsNavigable Area2016-07-262016-08-192016-09-30Multibeam Echo SounderSide Scan SonarMultibeam Echo Sounder BackscattermetersUniversal Transverse Mercator (UTM)UTCAtlantic Hydrographic BranchThe purpose of this project is to provide contemporary surveys to update National Ocean Service (NOS) nautical charting products. All times are recorded in UTC. Data recorded and presented relative to UTM Zone 15 North. THE INFORMATION PRESENTED IN THIS REPORT AND THE ACCOMPANYING BASE SURFACES REPRESENTS THE RESULTS OF SURVEYS PERFORMED BY OCEAN SURVEYS, INC. DURING THE PERIOD OF 16 AUGUST 2016 TO 30 SEPTEMBER 2016 AND CAN ONLY BE CONSIDERED AS INDICATING THE CONDITIONS EXISTING AT THAT TIME. REUSE OF THIS INFORMATION BY CLIENT OR OTHERS BEYOND THE SPECIFIC SCOPE OF WORK FOR WHICH IT WAS ACQUIRED SHALL BE AT THE SOLE RISK OF THE USER AND WITHOUT LIABILITY TO OSI.ContractorThis survey provides hydrographic data for the Gulf of Mexico waters approaching Atchafalaya Bay. The general locations of the survey limits are presented in Table 1.29.143358333391.940422222228.977663888991.7560722222Survey limits were acquired in accordance with the requirements in the Project Instructions and the HSSD.Per the Hydrographic Survey Project Instructions the purpose of this project is to provide contemporary surveys to update National Ocean Service (NOS) nautical charting products. This project area is located within the vicinity of the Atchafalaya River Delta and the Port of Morgan City. The proposed project will cover both nearshore and offshore areas in the vicinity of the Atchafalaya River Basin and will update the nautical chart where depth contours have migrated. The project will cover approximately 130 square nautical miles of critical survey area in the Approaches to Atchafalaya Bay as designated in NOAA Hydrographic Survey Priorities, 2012 edition. Survey data from this project are intended to supersede all prior survey data in the common area.The entire survey is adequate to supersede previous data.All waters in survey areaComplete Coverage accomplished using either: A) Complete coverage MBES depth and backscatter data or B) 100% SSS coverage with concurrent set line spacing MBES depth and backscatter data.Survey Coverage is in accordance with the requirements in the Hydrographic Survey Project Instructions (July 26, 2016), the Statement of Work, [May 2016 (SOW)], and the Hydrographic Surveys Specifications and Deliverables, [March 2016 (HSSD)]. In all waters, Complete Coverage was accomplished by acquiring one hundred percent (100%) side scan sonar (SSS) coverage with concurrent multibeam echosounder (MBES) with backscatter. Data were acquired on a set line spacing plan. Additional SSS and MBES coverage was obtained as necessary to fill gaps in coverage, to provide a least depth for all significant SSS contacts and for charted feature disprovals. Gaps in the 100% SSS coverage were addressed with SSS fill-in lines or covered with complete MBES data. Bathymetric splits were also acquired to verify or disprove charted depths that fell between two MBES survey lines when the charted depth was shallower than the adjacent survey soundings. The final survey area covers 51.21 square nautical miles (Figure 1). Survey H12908 MBES coverage overlaid on RNC 11340.H12908_Figure_1_Coverage.jpgR/V Ocean Explorer059.2306.790854.62086.610059.2306.790854.62086.6109.48700051.212016-08-192016-08-202016-08-212016-08-222016-09-042016-09-052016-09-062016-09-072016-09-082016-09-092016-09-102016-09-112016-09-232016-09-242016-09-252016-09-272016-09-30The lineal nautical miles (LNM) for MBES only development and fill-in lines were included under the heading "Mainscheme MBES" and the LNM for SSS only fill-in lines were included under the heading "Mainscheme SSS" in Table 2. Hydrographic Survey Statistics.Refer to the OPR-K354-KR-16 Data Acquisition and Processing Report (DAPR) for a complete description of data acquisition and processing systems, survey vessel, quality control procedures and data processing methods. Additional information to supplement sounding and survey data, and any deviations from the DAPR are discussed in the following sections.R/V Ocean Explorer182Survey operations were conducted from the R/V Ocean Explorer. The R/V Ocean Explorer, O.N. 905425, is an 18-meter aluminum vessel, with a 5.1-meter beam and nominally 2-meter draft, powered by two 1,000 HP Iveco diesel engines.Reson7125MBESEdgeTech4125SSSEdgeTech4200-MPSSSODIMMVP30 w/AML SVPTSound Speed SystemAMLMicro-XSound Speed SystemApplanixPOS MV 320 V.4Positioning and Attitude SystemTrimbleProBeaconPositioning SystemTrimbleSPS 461Positioning SystemTable 5 summarizes the primary equipment used to acquire MBES and SSS data. Survey H12908 is the only survey within Project OPR-K354-KR-16 in which the towed EdgeTech 4200-MP SSS system was used. All equipment was installed, calibrated and operated in accordance with the DAPR.A total of 86.61 nm of cross line data were acquired August 19-20, 2016 (DN 232-DN233). Cross line mileage equaled 10.1% of the 854.62 nm of mainscheme MBES lines. Cross lines were run nominally perpendicular to mainscheme lines (Figure 2). Soundings from mainscheme lines and cross lines were compared periodically throughout survey operations reviewing preliminary MBES surfaces and using CARIS HIPS Subset Editor. Cross line comparisons provided confirmation that the system offsets and biases were entered correctly and verified the accuracy of sounding correctors (i.e. tide, sound speed, TrueHeave). Statistical quality control information was compiled from a difference surface, generated in CARIS HIPS, between the depth layer of a 1-meter CUBE surface composed only of cross line data and the depth layer of a 1-meter CUBE surface composed only of mainscheme data. The cross line analysis results demonstrate excellent agreement between cross line soundings and mainscheme soundings, with the depth differences less than or equal to 0.42 meters with an average difference of 0.07 meters. The allowable TVU for the range of water depths within Survey H12908 is greater than 0.50 meters. Figure 3 is a histogram showing the distribution of depth differences for all comparison grid cells considered. The total number of 1-meter comparison cells equaled 3,436,771. Of 3,436,771 possible comparison cells, 3,381,064 or 98.38% of the cells include cross line and mainscheme soundings that match within ±20 centimeters.An overview of the cross line layout on a 1-meter surface created from mainscheme MBES data and colored by depth. RNCs 11349, 11351, and 11340 are visible in the background.H12908_Figure_2_XLs.jpgThe graph shows a frequency distribution of the depth differences between the H12908 cross line data and the H12908 mainscheme MBES data. Statistics from the depth difference sample set are displayed above the graph.H12908_Figure_3_XL_Histogram.jpg0.030.09Discrete ZoningR/V Ocean Explorer11The methods used to minimize the uncertainty in the corrections to echo soundings are described in detail in Section B. Processing and Quality Control of the project DAPR. Survey H12908 did not deviate from the methods documented in the DAPR. The Total Vertical Uncertainty Quality Check (TVU QC) "Ratio Method" was used to evaluate IHO uncertainty for all finalized surfaces. The TVU QC "Ratio Method" is described in the Chapter 4 Appendices of the NOAA OCS Field Procedures Manual (FPM) dated April 2014. Per the FPM TVU QC section, "The hydrographer should use the finalized surface because this surface will identify areas where either the uncertainty or the standard deviation exceeded the maximum allowable error and the greater of these two values is used in addition to having the uncertainty scaled to a 95% CI, whereas unfinalized surface uncertainties are reported at the 68% CI." The FPM TVU QC section also states that, "[ratio] values which do not require further examination are from -1 to 0 and the values which do require further examination are from -100 to -1." Finalized surfaces were used in this analysis. Surfaces were finalized using the “greater of the two” option as the basis for calculating “Final Uncertainty” in the CARIS “Finalize Base Surface” utility. Twenty (20) MBES CUBE (Combined Uncertainty and Bathymetric Estimator) surfaces were delivered along with Survey H12908 including "H12908_MB_1m_MLLW_Final" and nineteen (19) 50-centimeter item investigation surfaces. The 1-meter surface is intended to satisfy coverage and sounding density requirements for Complete Coverage, Option B: 100% side scan sonar coverage with concurrent multibeam. The remaining 0.5-meter surfaces are intended to satisfy Object Detection Coverage and sounding density requirements over significant features. Results from the TVU QC indicate that 99.9996% of the nodes from all submitted surfaces meet IHO Order 1 uncertainty specifications, i.e. the ratio values of nearly all the nodes are less than -1. Of the 81,080,768 nodes considered, 285 had a ratio value below -1. Upon examination it was found that the nodes with ratio values below -1 were located over the various features covered by the investigation surfaces resulting in higher standard deviation values and finalized uncertainty values, which is to be expected over discrete features. Two (2) prior surveys and two (2) contemporary surveys junction with Survey H12908. Figure 4 displays the location of the prior and contemporary junction surveys for Project OPR-K354-KR-16.Survey junctions for Project OPR-K354-KR-16. RNC 11340 is displayed in the background.H12908_Figure_4_Junctions.jpgH11290200002005NOAA Time CharterENOAA Time Charter Survey H11290, a hydrographic survey conducted in 2005, overlapped the eastern side of H12908. Depth data for Survey H11290 were downloaded from the NGDC website in the form of 1-meter resolution BAGs, "H11290_1m_MLLW_2 of 4" and "H11290_1m_MLLW_4 of 4". MBES surfaces for H12908 and H11290 were acquired for 100 or 200% SSS coverage with Set Line Spacing; therefore, the overlap between the two surveys was patchy. In general, the lines from both surveys are oriented parallel to one another in the northern 1/3 of the junction area whereas the lines from both surveys are perpendicular in the southern 2/3 of the junction area. Overall there is an approximate overlap of 230 meters found along the entire eastern edge of Survey H12908. Coverage from an H11290 item investigation falls within the H12908 survey area, but is detached from the H11290 mainscheme coverage. These data were also included in the analysis described below. To conduct the junction comparison a 1-meter CUBE surface was generated from the MBES data set for Survey H12908, "H12908_MB_1m_MLLW". In CARIS HIPS, depths from the H11290 BAGs were subtracted from the depths in the H12908 1-meter CUBE surface using the CARIS HIPS Difference Surface function. A histogram of the differences is shown in Figure 5. Depths from the H12908 survey were deeper than depths from the H11290 survey, with a maximum depth discrepancy of over 2 meters and an average difference of 48 centimeters. The largest depth discrepancy, a difference of -2.25 meters, occurs at 29-05-02.99 N, 91-45-51.82 W, where it appears that footprints from a jackup barge were developed within the H11290 "investigation" area described above. The depressions from the jackup barge footprint have seen substantial infill since the 2005 survey. A second large difference of 1.69 meters occurs at 29-04-52.18 N, 91-45-42.45 W, the location of a feature that was the subject of a Survey H12908 investigation "8-063" which is included with the deliverables as a 50-cm object detection surface, "H12908_MB_50cm_MLLW_8-063". In this case, it appears that the scour hole at the base of the feature has deepened since 2005, accounting for the large depth discrepancy between the H12908 and H11290 surfaces. The overall deepening trend from 2005 to 2016 could have several causes including sediment transport that occurred over the last decade and the fact that the H11290 survey data were corrected with a different tide source than Survey H12908. The primary tide gauge for the H11290 survey was a tertiary water level station installed at Eugene Island (876-4311) and Survey H12908 soundings were corrected with water levels from the LAWMA, Amerada Pass, LA NWLON station. An unrecognized datum difference between the tide stations may contribute to consistent depth bias between surveys. Regarding sediment transport as an explanation for the junction differences the following is offered: In Survey H12906 (immediately northeast of Survey H12908) large bedforms (assumed to be mobile) are apparent. The bedforms are suggestive that this region could be prone to depth changes due to sediment transport. Furthermore, it is noted that Survey H11290 was completed on July 31, 2005. Less than a month later Hurricane Katrina made landfall in south Louisiana. Given the relatively shallow water depths in this area it is possible that this massive storm and subsequent storm events could be responsible for some depth change between surveys.Surface-to-surface difference histogram comparing Survey H12908 to H11290.H12908_Figure_5_H11290_Histogram.jpgH11415200002005NOAA Time CharterSNOAA Time Charter Survey H11415, a hydrographic survey conducted in 2005, overlapped the southern side of H12908. Depth data for Survey H11415 were downloaded from the NGDC website in the form of 2-meter resolution BAGs, "H11415_2m_MLLW_1 of 12" and "H11415_2m_MLLW_2 of 12." MBES surfaces for H12908 and H11415 were acquired for 100 or 200% SSS coverage with Set Line Spacing. Lines from both surveys meet in a perpendicular fashion across the entire junction. There is an approximate overlap of 50-200 meters along the entire southern edge of Survey H12908. To conduct the junction comparison a 2-meter CUBE surface was generated from the MBES data set for Survey H12908, "H12908_MB_2m_MLLW". In CARIS HIPS, depths from the H11415 2-meter BAGs were subtracted from the depths in the H12908 2-meter CUBE surface using the CARIS HIPS Difference Surface function. A histogram of the differences is shown in Figure 6. Depths from the H12908 survey were deeper than depths from the H11415 survey, with a maximum depth discrepancy of over 3 meters and an average difference of 39 centimeters. The largest depth discrepancies, 3.06 meters and -1.53 meters, occur around the base of a charted platform positioned approximately 150 meters SW of the H12908 survey limits at 29-00-08.10 N, 91-52-35.80 W. The large depth discrepancies are attributed to the depressions left by jack up rigs in the H11415 surface filling in with sediment (-1.53 m difference) and a change in position of a mound located at the base of the platform in the H12908 surface (3.06 m difference). Other differences appear to be a result of either tide influences or actual depth changes due to sediment transport that occurred in the last decade. These potential influences are discussed in the junction analysis for Survey H11290 (above).Surface-to-surface difference histogram comparing Survey H12908 to H11415.H12908_Figure_6_H11415_Histogram.jpgH12906400002016Ocean Surveys, Inc.NEThe overlap between the bathymetric data from contemporary Surveys H12908 and H12906 is, on average, approximately 200 meters. The overlap occurs where the northeastern corner of H12908 meets the far southwestern corner of H12906. As such, the overlap is relatively sparse. Both surveys were acquired to meet 100% SSS Coverage, not complete MBES coverage. The mainscheme line plans for H12908 and H12906 were perpendicular to one another. Depths from 1-meter BASE surfaces compiled from the MBES data from each survey, "H12908_MB_1m_MLLW" and "H12906_MB_1m_MLLW," were compared using the CARIS HIPS Difference Surface function. A histogram of the differences is shown in Figure 7. Depths from the H12908 survey show good agreement with the depths from the H12906 survey. Depth discrepancies equaled 20 centimeters or less with a mean difference of 5 centimeters. The minor biases between surveyed depths appear to be tide related, as the agreement between survey depths from H12908 and H12906 vary with survey day. Surface-to-surface difference histogram comparing Survey H12908 to H12906.H12908_Figure_7_H12906_Histogram.jpgH12907400002016Ocean Surveys, Inc.NThe overlap between the bathymetric data from contemporary Surveys H12908 and H12907 is approximately 250 meters. Overlap occurs along the entire northern boundary of Survey H12908. Survey H12908 was run on a NW-SE oriented line plan. Tracklines from Survey H12907 were run perpendicular to the Survey H12908 line plan. Depths from 1-meter BASE surfaces compiled from the MBES data from each survey, "H12908_MB_1m_MLLW" and "H12907_MB_1m_MLLW," were compared using the CARIS HIPS Difference Surface function. A histogram of the differences is shown in Figure 8. Depths from the H12908 survey show good agreement with the depths from the H12907 survey. Depth discrepancies equaled 25 centimeters or less with a mean difference of 3 centimeters. The minor biases between surveyed depths appear to be tide related, as the agreement between survey depths from H12908 and H12907 vary with survey day. Surface-to-surface difference histogram comparing Survey H12908 to H12907.H12908_Figure_8_H12907_Histogram.jpgSonar system quality control checks were conducted as detailed in the Quality Control section of the DAPR. Results from the weekly MBES bar checks are included in Appendix II of the DAPR.MBES Time Sync Errors and GapsOccasional time sync alarms were observed during acquisition on the Reson 7125 Seabat display. The field personnel noted that along with the time sync alarm a brief gap may be observed in the real time display of the Seabat waterfall window. A few small along track data gaps associated with the Reson time sync error were noted in CARIS HIPS Subset Editor during data processing of the MBES wherein there is a short break in recorded profiles (Figure 9). No gap in Survey H12908 exceeds 3x3 surface nodes in the 1-meter Complete Coverage surface. Example of a small gap in MBES data associated with the Reson time sync error as it appears in CARIS Subset Editor (top right and bottom) and the same gap as it appears in a 1-meter CUBE surface (top left).H12908_Figure_9_Time-Sync.jpgEdgeTech 4200 (towed SSS) faultsTowed SSS acquisition was periodically interrupted due to a network failure experienced by either the logging computer or the SSS topside processor. This fault was typically solved by rebooting the system. It was occasionally noted, just after a failure, that the SSS depth sensor reported a suspect value. In these cases, the SSS pressure sensor (depth) was re-zeroed above water and its relative accuracy confirmed at-depth by comparing the reported depth with the fish deployed to a known depth. This process was completed with the vessel at rest. The towed SSS pressure sensor experienced a complete failure after just a few hours of operation on August 21, 2016 (DN 234). Imagery affected by the failing/failed sensor was rejected and re-acquired after a replacement 4200 towfish was put aboard the vessel.Tide OffsetReview of surface data indicates that there were a number of minor tide-related offsets between MBES data collected on different days scattered throughout Survey H12908. There were no noteworthy tide events that affected this survey. However, for the period of the survey, a nearly consistent offset with a magnitude averaging about 17 centimeters was apparent between the predicted and verified tides at the LAWMA, Amerada Pass LA tide station. Overall, the tide correctors were modeled well for Survey H12908, showing good agreement between survey days. Tide offsets generally equaled 25 cm or less and are likely associated with local environmental effects, i.e. wind setup. Figure 10 highlights a portion of the survey area where the tidal offset varied with survey day. In Figure 10 a standard deviation surface depicts a cross line (oriented NE-SW) along with a number of mainscheme and investigation lines (NW-SE). The standard deviation surface and the subset cross section show a minor tide offset (≤ 0.2 m) between the cross line and the mainscheme/investigation lines.The left image shows a portion of the Standard Deviation layer from a H12908 1-meter CUBE surface. The green and cyan colors indicate areas of higher standard deviation in the surface due to a minor tide offset. The right image displays MBES data loaded into CARIS Subset Editor with variable tide offsets noted between a cross line from DN 233 (yellow) and survey lines from DN 234 (orange), DN 235 (purple), and DN 255 (blue). Depths and distances are in meters. H12908_Figure_10_Tide-Offset.jpgSea State Induced White Streaks in SSS Imagery and MBES "Blowouts"The Reson 7125 system experienced one documented burst of motion-induced noise or a “blowout" which affected just a few sequential profiles. It is possible that other instances of "blowouts" occurred that were not noted by the field team. Efforts were made to reduce this noise during acquisition, including adjustments to system gain and power, in addition to the multibeam pole fairing that was installed to reduce cavitation effects. Data effected by MBES blowouts did not show any gaps in coverage in the 1-meter surface. The fixed mount 4125 SSS data were impacted by sea state conditions, such that when the wave frequency and height increased more cavitation effects were observed near the transducer head with a dark return noted at the top of the water column in the raw SSS record. The cavitation noise at the transducer head resulted in intermittent "white streaks" across the SSS record (Figure 11). To ensure that 100% coverage was attained where the white streaks occurred, holiday fill-in lines were acquired over the location of the streaks with either MBES or SSS coverage.An example of the white streak as it appears in the SSS mosaic in the top left image. The top right image shows the white line in the 100% mosaic overlain by the 1-meter MBES surface, where the white line holiday was covered with Complete MBES. The middle image shows the white line as it appears in the slant range corrected SSS imagery waterfall. The bottom image shows the raw SSS imagery with the cavitation noise in the water column near the transducer head highlighted by the orange box.H12908_Figure_11_SSS_White_Line.jpgFish in SSS Imagery and MBES dataAn abundance of fish and marine sea life were seen in the SSS and MBES data, either as lone swimmers or in schools (Figures 12-13). Fish and dolphins were noted in the acquisition log by the field team, and these areas were carefully reviewed during data processing. Shadows in the SSS, usually detached from a dark return, were typically associated with fish either in the water column or at a position closer to nadir. In the cases where a visible shadow was recorded in the SSS, the contact was designated as a fish, for two reasons: 1) the possibility that the assumed fish was actually a feature and 2) to assist processors in rejecting fish-related noise from the MBES data. Dolphin pods were present within the survey area as well as large schools of shrimp or miniscule fish that amassed close to the seafloor (Figure 14), which at times created large shadows in the SSS imagery and gaps in the MBES data where soundings on fish and dolphins were rejected. To ensure that possible significant features were not located in these fish and dolphin shadows, these fish/dolphin related coverage gaps were developed with 200% SSS coverage or complete MBES coverage. An example of dolphins and/or large fish as they appear in the raw, un-slant range corrected SSS imagery from CARIS SSS Editor (top) and in the MBES data with the fish/dolphins represented by the rejected soundings colored grey from CARIS Subset Editor 3D window (bottom). Note the shadows left by the fish/dolphins in the SSS and MBES. H12908_Figure_12_Fish_in_SSS_and_MBES.jpgLarge schools of fish as they appear in the MBES data (top) with rejected soundings on fish colored grey and in the slant range corrected SSS imagery (bottom).H12908_Figure_13_Fish_in_SSS_and_MBES.jpgFish or shrimp "clouds" as they appeared in the slant range corrected SSS imagery (top) and in the MBES data (bottom). The dense fish or shrimp schools had dark returns in the SSS record and were often clustered close to the seafloor as noted in the MBES data in CARIS HIPS Subset Editor 3D, with the rejected fish soundings colored grey.H12908_Figure_14_Crustacean_Clouds.jpgSSS RefractionContrary to OSI's experience acquiring SSS on behalf of NOAA in the Gulf of Mexico, there was little to no refraction in the SSS records for Survey H12908. For the instances where refraction was encountered, it was of a short duration and occurred in the outer range of the imagery. Sound speed profile data were acquired with the ODIM MVP30 approximately every 15 minutes as documented in the DAPR. All MBES lines were sound speed corrected using CARIS HIPS' "Nearest in Distance Within Time" method with the time set to two (2) hours. Based on prior survey experience in the northern Gulf of Mexico, OSI expected to encounter high variability in the speed of sound with abrupt gradient changes linked to dynamic salinity and temperature conditions. Fortunately, with the exception of the last day of survey for Project OPR-K354-KR-16, the water column was relatively well-mixed, which reduced the incidence of refraction in the SSS and MBES data sets as compared to OSI's recent Gulf of Mexico experience. OSI submitted H12908 sound speed data in NetCDF format to the National Centers for Environmental Information (NCEI) on December 14, 2016 (DN 349) via the S2N tool. NCEI assigned the sound speed submission Accession Number 0157605. Correspondence regarding the NCEI data submission is included in Appendix II.This survey was conducted to develop 100% SSS coverage along with concurrent MBES with backscatter to a depth of 20 meters, i.e. Complete Coverage, Option B as defined in Section 5.2.2.3 of the HSSD 2016. All depths within Survey H12908 were shallower than 20 meters. Per the HSSD which states "Gaps in SSS coverage should be treated as gaps in MBES coverage and addressed accordingly," gaps in SSS coverage and holidays caused by fish, dolphins, or white line noise were developed with Complete Multibeam or a second SSS coverage. All potentially significant features located with mainscheme SSS or MBES were developed with high density multibeam sonar data to meet the HSSD requirement of Object Detection coverage. The survey methods used to meet coverage requirements did not deviate from those described in the DAPR.DensityTo confirm the HSSD Density coverage requirements, the Compute Statistics tool was utilized within CARIS HIPS and SIPS to generate statistics for the Density layer for each finalized BASE surface. The HSSD states that at least 80% of the surface nodes shall be populated with at least 5 soundings for the Complete Coverage (Option B) 1-meter surface, and that at least 95% of the nodes shall be populated with at least 5 soundings for the 50 cm Object Detection surfaces. For the purpose of obtaining the most accurate surface density statistics, the unfinalized surfaces were used for the Density QC check as it was discovered that during surface finalization a density value of one (1) was assigned to all nodes containing a designated sounding, regardless of the node's sounding density value pre-finalization. The Compute Statistics tool generates an ASCII export containing two columns: 1) sounding density value and 2) the number of nodes that returned that value. This export was used to determine the percentage of nodes with a sounding density ≥ 5 for every submitted CUBE surface. The percentage of nodes with density greater than or equal to 5 soundings for the 1-meter Complete Coverage surface was as follows: H12908_MB_1m_MLLW = 99.46%. The survey is delivered with nineteen (19) Object Detection investigation surfaces. Sixteen (16) of the 19 surfaces had 100% of the nodes populated with a density in excess of 5 soundings. Of the three (3) remaining surfaces the percentage of cells returning a density of ≥ 5 soundings per cell and an description of each case is discussed below: H12908_MB_50cm_MLLW_8-080: 99.38% ≥ 5 soundings/cell - MBES data used to generate this surface result from "boxing in" a platform to acquire SSS coverage and to investigate exposed pipeline features near its base. There is a large void in the surface where it was not possible to acquire soundings due to the presence of the platform. H12908_MB_50cm_MLLW_8-082: 99.71% ≥ 5 soundings/cell - These data were acquired over an exposed pipeline. The few cells returning a density of < 5 soundings/cell are on the outer fringes of the surface. In no case did a cell over or near the exposed pipeline return a value of < 5 soundings/cell. H12908_MB_50cm_MLLW_8-143: 99.55% ≥ 5 soundings/cell - This investigation was initiated to better describe a non-dangerous discrete feature located in over 18 meters of water. Of the few cells returning < 5 soundings /cell none were located on top of the feature.All data reduction procedures conform to those detailed in the DAPR.All sounding systems were calibrated as detailed in the DAPR.Backscatter data were acquired concurrent with bathymetry data for Survey H12908. Backscatter data were recorded with HYSWEEP SURVEY in .7K format. These data were periodically reviewed to ensure function of the backscatter acquisition process. No specific instructions were made in the Project Instructions regarding coverage, ground truthing or processing for the Backscatter data, as such, these data are delivered in raw format in the “Backscatter” directory per the HSSD, Section 8.3.4 Backscatter Deliverables.CARISHIPS/SIPS7.1.2CARISHIPS/SIPS7.1.2NOAA Profile V_5_4.Software versions described in Section A of the DAPR were used throughout acquisition and processing of data for Project OPR-K354-KR-16.H12908_MB_1m_MLLW_FinalCUBE16.5618.82NOAA_1mComplete Coverage (Option B)H12908_MB_50cm_MLLW_8-010_FinalCUBE0.59.0613.09NOAA_0.5mObject DetectionH12908_MB_50cm_MLLW_8-046_FinalCUBE0.515.3615.95NOAA_0.5mObject DetectionH12908_MB_50cm_MLLW_8-047_FinalCUBE0.515.0615.47NOAA_0.5mObject DetectionH12908_MB_50cm_MLLW_8-050_FinalCUBE0.514.3114.79NOAA_0.5mObject DetectionH12908_MB_50cm_MLLW_8-051_FinalCUBE0.510.3212.19NOAA_0.5mObject DetectionH12908_MB_50cm_MLLW_8-052_FinalCUBE0.57.9511.87NOAA_0.5mObject DetectionH12908_MB_50cm_MLLW_8-054_FinalCUBE0.513.9014.30NOAA_0.5mObject DetectionH12908_MB_50cm_MLLW_8-057_FinalCUBE0.513.1113.78NOAA_0.5mObject DetectionH12908_MB_50cm_MLLW_8-060_FinalCUBE0.513.2013.76NOAA_0.5mObject DetectionH12908_MB_50cm_MLLW_8-063_FinalCUBE0.57.029.30NOAA_0.5mObject DetectionH12908_MB_50cm_MLLW_8-065_FinalCUBE0.512.1113.37NOAA_0.5mObject DetectionH12908_MB_50cm_MLLW_8-073_FinalCUBE0.510.8511.17NOAA_0.5mObject DetectionH12908_MB_50cm_MLLW_8-078_FinalCUBE0.510.0110.23NOAA_0.5mObject DetectionH12908_MB_50cm_MLLW_8-079_FinalCUBE0.510.1510.81NOAA_0.5mObject DetectionH12908_MB_50cm_MLLW_8-080_FinalCUBE0.59.5711.01NOAA_0.5mObject DetectionH12908_MB_50cm_MLLW_8-082_FinalCUBE0.58.088.52NOAA_0.5mObject DetectionH12908_MB_50cm_MLLW_8-084_FinalCUBE0.514.6414.90NOAA_0.5mObject DetectionH12908_MB_50cm_MLLW_8-136_FinalCUBE0.514.7415.34NOAA_0.5mObject DetectionH12908_MB_50cm_MLLW_8-143_FinalCUBE0.516.8918.62NOAA_0.5mObject DetectionH12908_SSS_1m_100SSS Mosaic1N/A100% SSSH12908_SSS_1m_200SSS Mosaic1N/A200% SSSTwenty (20) MBES CUBE surfaces and two (2) SSS mosaics comprise the total surfaces delivered with Survey H12908. To demonstrate MBES coverage requirements were met for Complete Coverage (Option B), a 1-meter CUBE surface was generated for the entire survey area. Nineteen (19) small field sheets were generated over significant features and populated with 50-centimeter CUBE surfaces to demonstrate Object Detection coverage. Two 1-meter SSS mosaics were submitted as GeoTIFFs to satisfy the SSS coverage requirements of 100% coverage and 200% coverage over charted feature disprovals and SSS fill-ins. In addition, a higher resolution, 25-centimeter SSS mosaic image composed of all SSS lines was submitted in the ECW (Enhanced Compressed Wavelet) format to assist with the survey review.Additional information regarding the vertical or horizontal control for this survey can be found in the accompanying Horizontal and Vertical Control Report (HVCR) for Project OPR-K354-KR-16.Mean Lower Low WaterLAWMA, Amerada Pass, LA876-4227Eugene Island, LA876-4314Offshore Bottom Mounted Pressure Gauge N/ADiscrete Zoning8764227.tidVerified ObservedK354KR2016 Revised Zoning 20161103.zdfFinalA final verified tide file was created from verified water level data from the primary tide station LAWMA, Amerada Pass, LA (876-4227) obtained from the CO-OPS website upon completion of survey operations. The Eugene Island gauge data were used only for tide zone refinement analysis not for reducing soundings to MLLW. Discrete zoning methods were utilized to apply tide correctors in CARIS HIPS and SIPS. The survey area is located within Zones WGM282, WGM281, and WGM280 as provided in the preliminary tidal zoning scheme included with the project SOW. Pursuant to the "strong recommendation" in the Tides and Water Levels Statement of Work provided with the Project Instructions, two Bottom Mounted Pressure Gauges (BMPGs) were installed in the southwestern end of the project area in order to better understand the tidal propagation and zoning error for the discrete zones. The BMPG water level data were not used for tide correction of soundings; the gauges served as a "zoning station" acquiring data used to update the tidal range and phase correctors and to derive a tide zoning error estimate for the project area. Two BMPGs, one primary gauge and a back-up, were deployed for over 30 days from August 17 (DN 230) to September 24 (DN 268), logging data continuously for the entire deployment. OSI's subcontractor, JOA Surveys, processed the downloaded pressure data to calculate water levels and to compute the tidal datum for the BMPG zoning station. Water levels from the BMPG station were used along with data from the LAWMA and Eugene Island NWLON stations to refine the phase and range correctors provided in CO-OPS preliminary zoning scheme. The final zoning scheme, K354KR2016 Revised Zoning 20161103.zdf, includes new time and range correctors for each preliminary zone, but the preliminary zone geometry was retained along with the CO-OPS provided names. Only the LAWMA gauge data were used in reducing soundings to MLLW datum. The Eugene Island gauge data were used only for tide zone refinement analysis. Based on the results of cross line analysis, the time and range factors as provided in the final zoning scheme are adequate. Please refer to JOA's OPR-K354-KR2016 Zoning Report.pdf included with the Tide deliverables. Tide station deliverables required in Section 4.7.5 of the HSSD were submitted to CO-OPS on November 9, 2016, as documented in an email included with Correspondence in Appendix II, OPR-K354-KR-16_BMPG_Transmittal.pdf. As of this time, OSI has not received and does not anticipate receiving a station name or ID number for the BMPG Gauges.North American Datum of 1983 (NAD83)UTM Zone 15 NorthEnglish Turn, LA, 293 kHzAll data products, except the S-57 Final Feature File (FFF) are referenced to Latitude/Longitude, UTM Zone 15 North. The S-57 Final Feature File, H12907.FFF.000, is referenced to the World Geodetic System Datum of 1984 (WGS 84) as specified in HTD 2016-03, which revised the HSSD 2016 Section 2.1 Horizontal Datum such that all positions will be referenced to NAD 83 and "the only exception for the NAD 83 datum requirement is that the S-57 feature file will be in the WGS 84 datum". All MBES and SSS line and item investigation position data were acquired using an Applanix POS-MV operating in Differential GPS (DGPS) mode. The unit was configured to receive USCG Differential beacon correctors from the English Turn, LA station. A secondary GPS, used to facilitate real-time horizontal control confidence checks, was supplied with correctors from the Marinestar subscription service. Prior to and during the course of the survey, the accuracy of the primary positioning system was verified by means of a physical measurement to a horizontal control point established at the vessel’s base of operation, a dock at the Port of Morgan City. Position confidence checks were accomplished, when possible, during fuel or weather stops. Refer to the DAPR and HVCR for additional details. Horizontal offset in DGPS PositioningA horizontal offset of less than 1 meter was noted between the MBES survey lines collected over significant features developed to meet object detection coverage (Figure 15). The shift in horizontal position between lines can be attributed to the use of DGPS correctors for positioning with the survey area located over 150 kilometers from the English Turn station. The horizontal positional shift was well within the limits of horizontal accuracy as defined in Section 3.1.1 Horizontal Position Uncertainty of the HSSD 2016.Example of a feature developed with object detection MBES coverage that exhibited a horizontal positioning shift between survey lines. The image shows an unknown obstruction with soundings colored by line in CARIS Subset Editor 2D Window.H12908_Figure_15_DGPS_Offset.jpgChart comparisons were performed in CARIS HIPS/SIPS and Notebook using finalized BASE surfaces and contours and selected soundings. The latest editions of the NOAA NOS Raster Nautical Charts (RNC) and Electronic Nautical Charts (ENC) were downloaded from the NOAA Office of Coast Survey website http://www.nauticalcharts.noaa.gov/) regularly during survey operations, and after the survey was completed for final comparisons. The RNCs and ENCs used for final comparisons were downloaded on December 19, 2016 and are submitted with the survey deliverables. Local Notice to Mariners (LNM) and Notice to Mariners (NM) spanning the period beginning at the date of issuance of the preliminary Hydrographic Project Instructions (June 28, 2016) and ending on December 14, 2016 were consulted in conjunction with the chart comparison. The following sections adhere to the Descriptive Report sounding rounding system as described in Section 5.1.2 of the HSSD. Specifically, features described below having “precision” depths are presented along with the sounding's TPU. Depth and TPU are rounded to the nearest centimeter by standard arithmetic rounding ("round half up"). The chart comparisons documented below will discuss general seafloor changes, shoaling and deepening trends. All new or charted features identified, updated or disproved within Survey H12908 were addressed and attributed in the S-57 Final Feature File. For more information on the methodology that was used to build the FFF see Section B.2.5 Feature Verification in the DAPR. An overview of the areas of change between charted depths and H12908 surveyed soundings is shown in Figure 16. The figure displays a difference surface made by subtracting a 10-meter resolution depth surface generated from the H12908 MBES data from a 250-meter resolution depth surface interpolated from the charted ENC soundings within the project area. Regions of shoaling are represented by positive depth differences and regions of deepening are represented by negative depth differences. This analysis indicates a general deepening trend across the survey area (green/blue/purple shading). The magnitude of deepening appears to increase as depth increases. For example, at the relatively shallow northern end of the survey changes on the order of 2 feet (0.6 meters) are observed whereas in the relatively deep southern reaches of the survey changes on the order of 6-7 feet (1.8-2.1 meters) are apparent. A detailed description of each chart comparison follows.A depth difference surface overlaid on RNCs 11351, 11349, and 11340 provides an overview of the areas of change between charted depths and H12908 surveyed soundings.H12908_Figure_16_Chart_Comp_Overview.jpg113496480000462014-032016-11-152016-10-29The northwest corner of Survey H12908 intersects with a small portion of RNC 11349. The soundings from Survey H12908 agreed reasonably with the charted depths, with new soundings in all cases deeper than charted depths by approximately 0 to 4 feet (1.2 meters). The only RNC 11349 contour that intersects Survey H12908 is the 30-foot contour. The 30-foot contour has migrated, in nearly parallel fashion, approximately 900 meters to the northeast as seen in Figure 17. It is noted that there is a horizontal shift between charted contours and soundings where RNC 11349 meets RNC 11351. In Figure 18, the eastern terminus of the 30-foot contour as charted on RNC 11349 does not align with the western terminus of the 30-foot contour charted on RNC 11351, with a slight shift to the northeast of approximately 50 meters between the RNC 11351 contour and sounding positions and the positions on RNC 11349.This figure demonstrates the migration of the 30-foot contour as seen in the northwest corner of Survey H12908. Orange-shaded soundings represent surveyed depths from 18 to 30 feet and cyan soundings represent soundings 30 feet and greater. The black-line 30-foot contour, as presently charted, is seen approximately 900 meters southwest of the new 30-foot contour. H12908_Figure_17_RNC-11349.jpgA horizontal shift was noted in the overlap between RNC 11349 and RNC 11351, with the 30-foot contour and soundings from RNC 11351 displaying an approximate horizontal offset of 50 meters to the northeast of the RNC 11349 30-foot contour and soundings.H12908_Figure_18_30ft_Ctr_Offset.jpg113516380000432012-032016-11-292016-10-29Nearly the entire eastern half of Survey H12908 intersects with the southwestern corner of RNC 11351. The soundings from Survey H12908 agreed well with the charted depths, with new soundings in all cases deeper than charted depths by approximately 0 to 4 feet (1.2 meters). The 30-foot contour as charted on RNC 11351 has migrated, in nearly parallel fashion, approximately 700 meters to the northeast as displayed in Figure 19. The presently charted RNC and ENC contours are not in complete agreement. At the northwestern end of the 30-foot contour, the contours (RNC vs. ENC) are offset approximately 50 meters. At the southeastern end of the 30-foot contour, the contours (RNC vs. ENC) are offset up to 340 meters (Figure 19). In this figure, the H12908 30-foot contour is represented by the boundary between the orange-shaded soundings (18 to 30 feet) and the cyan soundings (30 feet and greater) while the RNC 11351 30-foot contour (black) is located approximately 700 meters southwest of the new 30-foot contour. The red contour lines represent the locations where the 30-foot contour as charted on ENCs US4LA15M and US4LA21M deviate from RNC 11351.H12908_Figure_19_RNC-11351_Ctr.jpg1134049458596792016-022016-11-292016-10-29The entirety of Survey H12908 falls within RNC 11340. The soundings from Survey H12908, in all cases, are deeper than charted depths by approximately 0.2 to 1.4 fathoms (0.4 to 2.6 meters). The only RNC 11340 contour that intersects Survey H12908 is the 5-fathom contour. The 5-fathom contour has migrated, in nearly parallel fashion, approximately 700 meters to the northeast as seen in Figure 20.In this figure, the H12908 5-fathom (30-foot) contour is represented by the boundary between the orange-shaded soundings (18 to 30 feet) and the cyan soundings (30 feet and greater) while the RNC 11340/ENC US3GC03M 5-fathom contour (black) is located approximately 700 meters southwest of the new 5-fathom (30-foot) contour.H12908_Figure_20_RNC-11340.jpgUS4LA15M80000232014-11-062016-10-24falseRNC 11349 is the source for ENC US4LA15M; therefore, the positions and values of the soundings and contours included in ENC US4LA15M are identical to those charted on RNC 11349. All chart comparison notes entered under the RNC 11349 apply to US5LA15M.US4LA21M80000272015-03-252016-12-08falseRNC 11351 is the source for ENC US4LA21M; therefore, the positions and values of the soundings and contours included in ENC US4LA21M are identical to those charted on RNC 11351. All chart comparison notes entered under the RNC 11351 apply to US4LA21M.US3GC03M459596472015-02-202016-12-12falseRNC 11340 is the source for ENC US3GC03M; therefore, the positions and values of the soundings and contours included in ENC US3GC03M are identical to those charted on RNC 11340. All chart comparison notes entered under the RNC 11340 apply to US3GC03M.No Maritime Boundary Points were assigned for this survey.The following features were assigned for investigation within the Composite Source File (CSF) provided with the OPR-K354-KR-16 Project Instructions: Eight (8) charted platforms (OFSPLF), thirty-three (33) BSSE well head obstructions (OBSTRN), and three (3) wrecks (WRECKS). Of the assigned platforms seven of the eight were found to exist. The remaining assigned platform was disproved visually, with 200% SSS coverage and partial MBES coverage within a search area centered on the CSF provided position and defined by a 50-meter radius. Platforms are discussed further in Section D.2. The BSSE well head obstructions were not charted but were submitted to be verified or disproved by OSI. Investigation requirements for the BSSE well heads were provided to OSI in an email dated April 22, 2016 which is submitted with the Correspondence in the DR Appendix II. The well head investigation requirements were as follows: - If obstruction is found and considered a danger to navigation, develop the feature (7.3.3), designate the feature (7.4), submit it as a DtoN (1.5), and include it in the FFF (7.3). - If obstruction is found and merits individual cartographic representation, develop the feature (7.3.3), designate it (7.4), and submit in FFF (7.3). - If obstruction is found and does not merit cartographic representation, do not investigate it as a feature. Include it in the FFF with “descrp = delete” and “remrks=obstruction addressed as represented in the surface” - If the obstruction is not found, in cases where 100% SSS with concurrent multibeam is being used as the primary coverage technique, a 50m disproval search radius using a technique described in Section 7.3.4 is necessary. Of the assigned BSSE well head features it is recommended that all 33 BSSE well heads remain uncharted. Multiple BSSE well heads were closely (or exactly) correlated either with another BSSE well head assignment (five cases) or with a charted platform (four cases). The majority of BSSE well heads were disproved with either 200% SSS with partial MBES or 100% SSS with 100% MBES. In a few cases, the second 200% SSS coverage required for disproval within the search area was not acquired due to the proximity of the assigned well head's position to an existing platform. For all well heads, the first 100% SSS coverage clearly showed "no feature" or a platform co-located with the well head assignment. There was one instance in which a signficant feature was developed with Object Detection MBES coverage approximately 30 meters northwest of an assigned well head positioned at 29-05-10.68 N, 91-53-46.23 W. It is assumed (but not verified with a diver investigation) that this obstruction, submitted as H12908 DtoN #3 (See DR Section D.1.6), is in fact a remnant well head or platform leg. Within the H12908 FFF, the significant feature was included as a "new" obstruction and the BSSE well head obstruction located within 50 meters was attributed as "delete" such that the obstruction would be charted at its true least depth position of 29-05-10.68N, 91-53-46.23W. See the FFF for additional information regarding the investigated BSSE well head obstructions. The source date (SORDAT) and source indication (SORIND) attribute fields were blank for the BSSE well head features submitted in the CSF; therefore, the SORDAT and SORIND fields are blank for the disproved well heads attributed with a description (descrp) of "delete" in the FFF. A charted wreck PA positioned at 29-02-00.82 N, 91-49-00.44 W was disproved with 200% SSS and partial MBES coverage within a search area defined by an 80 m radius. The AWOIS database reported the wreck as "THE GULF II A 61 FT STEEL HULLED SHRIMPER". No evidence of a 60-foot shrimper was identified in the vicinity of the search area. A charted wreck PA positioned at 29-00-41.90 N, 91-52-57.27 W was disproved with 200% SSS and partial MBES coverage within a search area defined by an 80 m radius. The AWOIS database reported the wreck as "THE JACK-UP BARGE EVELYN T...WRECK REPORTEDLY AWASH, UNKNOWN REFERENCE MAKING THE WRECK SUBMERGED". No evidence of a sunken jackup barge was identified in the vicinity of the search area. A charted wreck PA positioned at 29-06-59.91 N, 91-50-00.08 W was disproved with 200% SSS and partial MBES coverage within the search area defined by an 80 m radius. The AWOIS database reported a sunken barge. No evidence of a barge was identified in the vicinity of the search area. A number of uncharted features were identified in Survey H12908. All but two of these features were submitted as DtoNs and are therefore discussed in the DtoN section of this report. A nondescript 1.25-meter tall obstruction with a least depth of 34 feet (10.32 m, ±0.23 TPU) was developed with Object Detection coverage at 29-02-59.99 N, 91-47-12.14 W (Figure 21). The obstruction was located approximately 550 meters WSW of a 26-foot obstruction submitted as H12908 DtoN #2. A 1.2 meter tall obstruction with a least depth of 23 feet (7.02 m, ±0.23 TPU) was surveyed with Object Detection coverage at 29-04-52.14 N, 91-45-42.29 W just outside the northeastern edge of Survey H12908 (Figure 22). The feature has the appearance of a large pipe section or a long tank fitted with multiple flanges. It is recommended that a 23-foot Obstn be charted at the obstruction's least depth position, replacing the charted (RNC 11351) 23-foot sounding which is currently located 100 meters south of the obstruction.A 1.25 meter tall obstruction is represented in CARIS HIPS Subset Editor 3D and 2D views with the soundings colored by depth with depths and units in meters. A SSS image is also shown.H12908_Figure_21_Unchd_Obstn.jpgA 1.2 meter tall obstruction is represented in CARIS HIPS Subset Editor 3D and 2D views with the soundings colored by depth with depths and units in meters. A SSS image is also shown.H12908_Figure_22_Unchd_Obstn.jpg4H12908_DtoN_1_Gas_Leak.0002016-10-05H12908_DtoN_2_Obstn.0002016-10-05H12908_DtoN_3_Obstn.0002016-10-05H12908_DtoN_4_Pipelines.0002016-11-28 Four (4) Danger to Navigation (DtoN) S-57 files (.000) were submitted to the Atlantic Hydrographic Branch (AHB) for Survey H12908. H12908 DtoN #1 includes the position (29-05-51.62 N, 91-53-05.79 W) of what is presumed to be a gas leak eminating from the terminus of a charted pipe (Figure 23). AHB passed along the gas leak information to the Gulf of Mexico Navigation Manager but AHB did not forward this information to the Nautical Data Branch (NDB) or Marine Chart Division (MCD) since, according to AHB, "the leak is located on a charted pipeline and does not merit danger to navigation status." This gas leak is not included in the Final Feature File for this survey and sounding returns on the gas leak plume were rejected from the MBES data. H12908 DtoN #2 reported an 11.5-foot (3.5-meter) tall feature that appears to be the base of a ruined platform or some other industrial debris (Figure 24); however, there are no charted platforms or pipelines in the vicinity of the large obstruction. The obstruction was submitted by AHB to NDB/MCD on October 5, 2016 and has since been added to RNCs 11351 and RNC 11340 and ENCs US3GC03M and US4LA21M. The Local Notice to Mariners (LNM) Edition 44 for District 8 (44/16) included chart updates for RNC 11351 and 11340 to add the new obstruction at the following position: 29-03-06.10 N, 91-46-53.30 W. H12908 DtoN #3 reported a tall, narrow obstruction located approximately 30 meters northwest of a BSSE well head assigned for investigation positioned at 29-05-10.68N, 91-53-46.23W. As mentioned in the Charted Features section of this report, it is assumed (but not verified with a diver investigation) that this obstruction is in fact a remnant well head or platform leg associated with the BSSE well head assignment (Figure 25). The obstruction was submitted by AHB to NDB/MCD on October 5, 2016 and has since been added to RNCs 11349 and 11340 and ENCs US3GC03M and US4LA15M. The Local Notice to Mariners (LNM) Edition 44 for District 8 (44/16) included chart updates for RNC 11349 and 11340 to add the new obstruction at the following position: 29-05-11.40 N, 91-53-46.90 W. OSI submitted individual DtoNs, H12908_DtoN_2_Obstn.000 and H12908_DtoN_3.000, to AHB via e-mail on October 5, 2016. Prior to submission to NDB and MCD, AHB combined these DtoNs into “H12908 DtoN #2”. In NOS-NOAA e-mail correspondence after OSI's initial submission of H12908 DtoNs #2 and #3, the two obstruction DtoN submissions are treated as one. H12908 DtoN #4 includes positions and images for twenty (20) exposed pipeline sections within the bounds of the survey. The exposed pipeline segments were not submitted to NDB and MCD, but they were submitted to NOAA's Central Gulf Coast Navigation Manager, Tim Osbourne, on November 29, 2016 such that the information could be relayed to the proper authorities.DtoN # 1 gas leak as seen in the MBES data with soundings colored by line (left) and in the water column of the raw, un-slant range corrected SSS imagery from two survey lines (right images).H12908_Figure_23_Gas_Leak.jpgDtoN #2 depicted in CARIS HIPS Subset Editor 3D and 2D windows(left and right respectively) with soundings colored by depth. Depths and distances are in meters.H12908_Figure_24_DtoN_2.jpgDtoN #3, suspected to be a remnant well head or platform leg, is shown in a CARIS HIPS Subset Editor 3D window with soundings colored by depth (left) and as it appeared in the SSS imagery (right).H12908_Figure_25_DtoN_3.jpgA caution area (CTNARE) note on ENC US3GC03M covers much of Survey H12908. The caution area note states the following: "Gas and Oil Well Structures. Platforms, gas and oil well structures, some of which are submerged and capped, and submarine pipelines and cables are charted." Similarly, a Caution Note associated with ENC US4LA21M and RNC 11351 states: "Additional uncharted submarine pipelines and submarine cables may exist within the area of this chart. Not all submarine pipelines and sub-marine cables are required to be buried, and those that were originally buried may have become exposed. Mariners should use extreme caution when operating vessels in depths of water comparable to their draft in areas where pipelines and cables may exist, and when anchoring, dragging, or trawling. Covered wells may be marked by lighted or unlighted buoys." The caution note was included in the text files referenced in the TXTDSC (textual description) fields of the PIPSOL (pipeline) and M_NPUB (nautical publication information) features. The Caution Notes are warranted given the abundance of charted platforms, pipelines and possible well heads within the project area. As noted above numerous exposed pipelines were located within Survey H12908.No channels exist for this survey. There are no designated anchorages, precautionary areas, safety fairways, traffic separation schemes, pilot boarding areas, or channel and range lines within the survey limits.Seven (7) bottom samples were acquired to determine bottom characteristics. Bottom samples were assigned in the PRF provided with the Hydrographic Survey Project Instructions. There were no deviations from the assigned bottom sampling plan. A position and description of each sample are provided as attributed SBDARE objects in the FFF. Digital images with identification reference numbers are submitted with the survey data and referenced in the NOAA extended attributes ‘images’ field.No shoreline exists within this survey.Prior survey data exists for this survey area. However, with the exception of the assigned junction surveys, prior data were not investigated.No Aids to navigation (ATONs) exist for this survey.No overhead features exist for this survey.Multiple charted pipelines are located within Survey H12908. Pipes colored magenta represent supply pipelines for oil, gas, chemicals, or water, according to Chart No. 1: Nautical Chart Symbols, Abbreviations and Terms downloaded from the Office of Coast Survey (OCS) website. None of the charted pipelines have a buried depth value (BURDEP).That being said the majority of the charted pipelines were not visible in the SSS or MBES data. Linear contacts presumed to be exposed sections of charted pipelines were selected in the side scan records and were confirmed with MBES coverage. As mentioned in the DtoN section of this report, twenty (20) exposed pipeline sections were presented with the DtoN #4 submission for this survey. Some of the exposed pipelines had pronounced arches and some were situated in trenches. Several of the exposed pipeline segments extended from the base of a charted platform. The exposed pipeline sections' images and relevant attribution are included in the H12908 S-57 Final Feature File. Review of information contained in a shape file (.SHP) downloaded from the Bureau of Ocean Energy Management (BOEM) on April 25, 2016 suggests that there may be as many as five uncharted pipe segments within Survey H12908. The BOEM pipeline shape file that intersects with the OPR-K354-KR-16 project area was reprojected to UTM Zone 15N, NAD83 and saved as a .DXF file and converted to a .HOB file. In CARIS Notebook, the BOEM pipeline HOB file was then visually compared to the charted pipelines within the project area to identify any potentially uncharted BOEM pipelines. While the majority of the pipelines in the BOEM file corresponded with charted pipelines, up to five BOEM reported pipeline segments are not charted. Though there was no visible evidence in the MBES or SSS data of the existence of the uncharted pipelines, an overview of the uncharted BOEM-defined pipelines that intersect Survey H112908 is provided in Figure 26. The uncharted pipelines appear to terminate at charted platforms. The shape file, “ppl_arcs.shp” and re-projected .DXF file, “Pipelines_UTM_15N_NAD83_Meters.dxf” are included with the digital deliverables along with the RNC/ENC charts considered in the chart comparison. BOEM pipeline data were obtained at the following web address: http://www.data.boem.gov/homepg/data_center/mapping/geographic_mapping.asp.BOEM-defined pipelines that are not charted are highlighted in blue in reference to RNCs 11351, 11349, and 11340 with the H12908 survey shown in the background.H12908_Figure_26_Uncharted_BOEM_Pipes.jpgNo ferry routes or terminals exist for this survey.Seven (7) of the eight (8) CSF-assigned platforms were verified and given that the surveyed positions of all the verified platforms were located less than 80 meters distant from the charted positions, the platforms were attributed with a "Retain" value (80 m is equivalent to 2 mm at a scale of 1:40,000). Images were included in the FFF for all verified platforms. The verified platforms positions are as follows: 29-06-57.91 N, 91-52-16.43 W, APACHE-CORP_SMI-209-A 29-06-02.23 N, 91-52-04.94 W, Name Unknown 29-05-24.09 N, 91-45-52.09 W, MOI-EI-90-12 29-05-08.21 N, 91-52-23.61 W, Fieldstone Energy SMC-281-C 29-05-00.19 N, 91-53-29.72 W, SMI 280 H 29-04-44.78 N, 91-53-12.53 W, Name Unknown 29-04-23.92 N, 91-53-59.24 W, Apache Corp SMC-290-G The remaining assigned platform positioned at 28-59-59.06 N, 91-51-12.15 W was disproved visually, with 200% SSS coverage and partial MBES coverage within a search area centered on the CSF provided position and defined by a 50-meter radius. Two additional charted platforms not included in the CSF were investigated and are included in the S-57 final feature file. One of the unassigned platforms resides completely within the bounds of the assigned survey area at position 29-03-55.82 N, 91-52-19.03 W. The ENC-charted position of the second unassigned platform falls just outside the eastern boundary of Survey H12908 at position 29-05-06.00 N, 91-45-34.00 W. The platforms' charted positions were verified and it is recommended that they be retained as charted. A total of 10 platforms (OFSPLF) are included in the FFF. No Significant Features exist for this survey.No construction or dredging existed within the survey limits at the time of data acquisition.Marine Mammal ObservationsPer direction in Section 1.4 and 1.4.1 of the HSSD all survey and vessel operations personnel aboard the vessel used during Project OPR-K354-KR-16 were "trained" as Marine Mammal Observers prior to commencement of the survey. Training consisted of each surveyor and vessel crew member watching the US Navy video referenced in the HSSD. As noted multiple times in the survey acquisition log, large, mobile, water column sonar targets (assumed to be dolphins) were ensonified by either the MBES or the SSS. The dolphin-assumption is based on both the size and behavior of the sonar targets. Often times these observations did not coincide with a visual (above water) sighting. Visual observations, when noted, were recorded on NOAA/NMFS,AFSC/NMML Form 11US (POP) which is included as Appendix K of the HSSD. As compared to past years survey work in the Gulf of Mexico, dolphin sightings during the contemporary survey were relatively sparse. This is attributed to the area of operation for the contemporary survey. During the course of Project OPR-K354-KR-16 only 13 individual visual dolphin sightings occurred. Digital versions (.PDF format) of completed 11US (POP) forms along with the Project's marine mammal training record were compiled and transmitted to the OCS Environmental Compliance Coordinator, Jay Nunenkamp, with a CC to the Project's COR, Paul Turner. These records are also included in Descriptive Report Appendix II. Coast Pilot ReviewA "Coast Pilot Field Report" as described in Section 8.1.3 in the HSSD was not provided by HSD Operations. Per a June 2, 2016 email from the COR: "There are no specific items to investigate with regards to the Coast Pilot". OSI conducted a general review of relevant Coast Pilot excerpts. Specifically, pertinent paragraphs from the following Coast Pilot section were considered: Coast Pilot 5 - 44th Edition, 2016 updated through 13-November-2016, Mississippi River to Sabine Pass. Within the Coast Pilot Edition mentioned above there are no specific, detailed, relevant entries concerning the assigned survey area. Rather, only entries of a general nature are mentioned and are not refutable based on the observations of the OSI field team. Regarding “areas frequently transited” (as mentioned in the HSSD Section 8.1.3), there are only a few Coast Pilot paragraph descriptions that OSI's general review attempts to address. OSI's Coast Pilot Review is included in Descriptive Report Appendix II. Correspondence between OSI and the Project COR confirming OSI's understanding of the Coast Pilot reporting requirement is included in the Correspondence directory of the Descriptive Report Appendix II.No new surveys or further investigations are recommended for this area.No new insets are recommended for this area.As Chief of Party, field operations for this hydrographic survey were conducted under my direct supervision, with frequent personal checks of progress and adequacy. I have reviewed the attached survey data and reports.All field sheets, this Descriptive Report, and all accompanying records and data are approved. All records are forwarded for final review and processing to the Processing Branch.The survey data meets or exceeds requirements as set forth in the NOS Hydrographic Surveys and Specifications Deliverables Manual, Field Procedures Manual, Letter Instructions, and all HSD Technical Directives. These data are adequate to supersede charted data in their common areas. This survey is complete and no additional work is required with the exception of deficiencies noted in the Descriptive Report.George G. ReynoldsChief of Party2017-01-23Data Acquisition and Processing Report2017-01-23Horizontal and Vertical Control Report2017-01-23