OPR-R315-KR-14Bechevin Bay, AKBechevin Bay, AKTerrasond LimitedH126301Registry InstructionsApproaches to Bechevin BayAlaskaUnited States400002014Andrew OrthmannNavigable Area2014-01-082014-06-072014-08-14Multibeam EchosounderSinglebeam EchosoundermetersNAD83UTCPacific Hydrographic BranchThe purpose of this survey is to provide contemporary surveys to update National Ocean Service (NOS) nautical charts. All separates are filed with the hydrographic data. Notes in red were generated during office processing. The processing branch concurs with all information and recommendations in the DR unless otherwise noted. Page numbering may be interrupted or non-sequential. All pertinent records for this survey, including the Descriptive Report, are archived at the National Geophysical Data Center (NGDC) and can be retrieved via http://www.ngdc.noaa.gov/.ContractorA navigable area survey (H12630) was conducted in the area of the northern approaches to Bechevin Bay, Alaska, in accordance with the NOAA, National Ocean Service, Statement of Work (SOW), OPR-R315-KR-14, dated January 23rd, 2014, and Hydrographic Survey Project Instructions dated January 8th, 2014. Hydrographic survey data collection began June 7th, 2014 and ended August 14th, 2014. Supporting tide data was collected from May 16th, 2014 through September 6th, 2014. Multibeam echosounder (MBES) and single beam echosounder (SBES) operations were conducted in accordance with the project instructions, which specified a combination of set line spacing and complete coverage. Requirements called for 100 m set line spacing SBES (or MBES) from the inshore limit to 8 m water depth with reduced spacing as directed by the NOAA COR up to a maximum of 1,075 linear nautical miles (LNM) to be acquired project-wide. Complete MBES with concurrent backscatter was required for depths greater than 8 m. The inshore limit was the navigational area limit line (NALL), which is defined as the farthest offshore of; 1) the 4 m depth contour, 2) a line defined by the distance seaward from the observed MHW line equivalent to 0.8 mm at the scale of the largest scale nautical chart intersecting the area (64 m for this survey using chart 16535, with a scale of 1:80,000), or 3) the inshore limit of safe navigation as determined by the Chief of Party.55.14965163.57551455.038839163.298903Survey extents and overview.SupportFiles\1_SurveyExtents.jpgSurvey limits were generally achieved. The inshore limit (4 m depth or NALL for set line spacing, 8 m for complete coverage) was achieved except in isolated cases where it was deemed unsafe to approach closer. In rare cases, application of final tide correctors shifted data deeper, which caused some soundings that initially met the 4 m or 8 m minimum depth requirements based on preliminary tide data to no longer meet the requirement.The purpose of this project is to provide an updated survey for the approaches to Bechevin Bay. It addresses approximately 35 square nautical miles (SQNM) of area identified as “Critical” and “Priority 3” in the 2012 NOAA Hydrographic Survey Priorities (NHSP) document. The best scale chart at the time of this survey (16535) is out of date, with source soundings acquired from 1924 to 1957. The area serves as the northern, Bering Sea approach to Bechevin Bay and Isanotski Strait. The area, commonly known as False Pass, is the first pass between the Bering Sea and Pacific Ocean encountered as vessels transit down the Alaska Peninsula, and delineates the beginning of the Aleutian Island chain. Relatively shallow drafted vessels (drafts of 4 m or less) frequently transit the area while traveling to ports in Bristol Bay or beyond. Deeper drafted vessels normally take the longer but deeper route through Unimak Pass to the west. Small vessels from the nearby community of False Pass (2010 population 35) also frequent the area, usually navigating with local knowledge. Inclement, fast-changing weather is common. At the confluence between the relatively cold Bering Sea and warm Pacific Ocean, the area frequently experiences wind, sea, and atmospheric conditions (including fog) that are unfavorable for vessel navigation. Tidal current divergent to wind direction can cause significant localized stacking of seas. The area is fully exposed to the northwest, which allows for large ocean swells to build and impact the area, breaking on the shoals and sandbars along the coast. There are no anchorages in the area; vessels seeking protection must transit into Bechevin Bay to the south. Tides are complex and tidal currents extreme, making navigation especially difficult through the narrow passes between shoals. Current can frequently exceed 6 knots, resulting in whirlpools and sudden changes in vessel trackline when dissimilar current streams are intersected. The area is also subject to a high degree of bottom change and migration of shoals due to current-induced sediment transport. During operations, significant change (1 to 2 m in some cases) was observed in subsequent soundings acquired during time periods as little as 1-2 weeks apart. Change is most significant through narrow constrictions where tidal current is greatest, such as between Chunak Point and Cape Krenitzin. Due to bottom change, the USCG must resurvey the main channel through the area each spring to ensure optimal placement of navigational buoys that mark the channel edges. The buoys, which are removed each fall to avoid loss or damage from winter ice flows, frequently cannot be relocated at the same position as the previous year due to channel and shoal migration.Bering Sea, NW towards survey area, from beach near Cape ChunakSupportFiles\2_CapeChunakBeringSea.jpgThe entire survey is adequate to supersede previous data.The 100 m spacing requirement for set line spacing for 8 m depth to the inshore limit (normally 4 m depth) was met, except in isolated cases where it was deemed unsafe to proceed further inshore, or nearby shoals made safe vessel maneuvering questionable. This included the southwest side of Cape Krenitzin, where an extremely steep slope cut by current made it unsafe and unrealistic to acquire soundings to 4 m. Following acquisition of 100 m set line spacing, additional lines were collected between existing lines in selected areas per NOAA guidance to increase data density, bringing the final set line spacing interval to 25 m or 50 m in these areas. In this sheet, the main channel (in areas between 8 m and 4 m depth) received the additional lines. The work instructions called for a project-wide (all survey sheets) maximum of 1,075 LNM of set-spaced lines to be acquired in the area from the inshore limit to 8 m depth. In total, 1,293 LNM were acquired project-wide. The additional LNM was acquired to compensate for mileage unintentionally acquired in areas deeper than 8 m that were designated for complete coverage, as well as crossline mileage exceeding the 8% requirement for set line spacing. Note that single beam splits on shoals or charted soundings were not undertaken because the nature of the bottom in the area reduced the likelihood of pinnacles or shoals between lines. The requirement for complete multibeam coverage in depths greater than 8 m was met, except in cases where it was deemed unsafe to proceed further inshore or nearby shoals made safe vessel maneuvering questionable. These areas include steep banks and constrained areas on the southwest side of Cape Krenitzin. Some pockets and tongues of water deeper than 8 m identified during single beam data collection (primarily located on the east side of the survey area) did not receive multibeam coverage because the presence of nearby shoals. Survey limits were generally achieved. The inshore limit (4 m depth or NALL for set line spacing, 8 m for complete coverage) was achieved except in isolated cases where it was deemed unsafe to approach closer. In rare cases, application of final tide correctors shifted data deeper, which caused some soundings that initially met the 4 m or 8 m minimum depth requirements based on preliminary tide data to no longer meet the requirement.Survey extents and overview showing coverage.SupportFiles\3_Coverage.jpgQualifier 105095000000650Cutwater3140000004403149500000010908.7110000322014-06-072014-06-122014-06-132014-06-152014-06-162014-06-242014-06-252014-06-262014-06-272014-06-282014-06-302014-07-022014-07-052014-07-062014-07-112014-07-122014-07-132014-07-142014-07-152014-07-162014-07-172014-07-182014-07-212014-07-222014-07-232014-07-262014-07-272014-07-282014-07-312014-08-012014-08-022014-08-032014-08-042014-08-092014-08-102014-08-14Going by the HDCS line labels, there are 345 LNM of mainscheme VBES and 24 LNM of VBES crosslines collected by the vessel Cutwater, which is a 6.9% crossline to mainscheme percentage for VBES alone. When combined, the total percentage of all crosslines to all mainscheme for the survey is also 6.9%.Refer to the Data Acquisition and Processing Report (DAPR) for a complete description of data acquisition and processing systems, survey vessels, 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.Qualifier 105321.8Cutwater12.21.1The Qualifier 105 (Q105) is a 32 m aluminum hull vessel owned and operated by Support Vessels of Alaska (SVA). The Q105 acquired all multibeam data and provided housing and facilities for on-site data processing. The vessel also provided fuel and support for the smaller survey vessels, collected bottom samples, deployed Seabird tide gauges, and deployed/recovered the shoreline skiff as necessary. The Cutwater is a 12.2 m aluminum hull that is also owned and operated by SVA. The Cutwater acquired all single beam data in this sheet. The vessel also collected bottom samples in the shoaler portions of the survey area.Teledyne OdomEchotrac CV100SBESTeledyne ResonSeabat 7101MBESApplanixPOSMV 320 V5Positioning and AttitudeAML OceanographicAML SV+Sound Speed ProfilerTeledyne OdomDigibar ProSound Speed ProfilerValeportRapid SVT 200BarSound Speed ProfilerTeledyne OceanscienceUnderway SV400Sound Speed Profiler Deployment SystemTrimble5700Base StationTrimbleNETRSBase StationSea-Bird ElectronicsSBE 26+Submerged Tide GaugeXylem-WaterLOGDAA H350XL BubblerTide GaugeEquipment configurations and operations as well as data acquisition and processing are described in the DAPR.Multibeam and single beam (set line spacing) crosslines were collected to meet, respectively, the 4% and 8% of mainscheme requirements required in the HSSD. The crossline percentage for multibeam totaled 6.9% of mainscheme mileage, while the crossline percentage for single beam totaled 14.1% of mainscheme mileage. Effort was made to ensure crosslines were geographically distributed across the survey area. Crosslines were run perpendicular to mainscheme lines whenever possible to ensure higher quality nadir beams crossed lower quality outer beams. In the southern part of the survey area where vessel maneuverability was restricted, zig-zag multibeam crosslines were collected that were not optimally perpendicular to the mainscheme, but were more than adequate for QC purposes. The crossline analysis was conducted using CARIS HIPS “QC Report” routine. Each crossline was selected and run through the process, which calculated the depth difference between each accepted crossline sounding and a QC BASE (CUBE-type) surface’s depth layer created from the mainscheme data. QC BASE surfaces were created with the same CUBE parameters and resolutions as the final BASE surfaces, with the important distinction that the QC BASE surfaces did not include crosslines so as to not bias the QC report results. Differences in depth were grouped by beam number and statistics computed, which included the percentage of soundings with differences from the BASE surface falling within IHO Order 1. When at least 95% of the soundings exceed IHO Order 1, the crossline was considered to “pass,” but when less than 95% of the soundings compare within IHO Order 1, the crossline was considered to “fail.” Agreement between the BASE surfaces and crossline soundings was very good for both vessels. The vast majority of crossline comparisons pass with 95% (or more) of soundings comparing to within IHO Order 1. 4 of 60 multibeam crossline comparisons had failures, while of 13 of 53 single beam crossline comparisons had failures. Failures were investigated and found to be attributable mainly to bottom change frequently observed in this dynamic area, especially when collection periods were separated by many days or weeks. An additional source of failures were steep slopes and very rugged terrain, wherein sounding to surface comparisons often failed even though the underlying soundings and surface were within specifications. An example of a crossline failing QC is shown in the following figure. Refer to Separate II: Digital Data for the detailed Crossline QC Reports.Example from CARIS subset mode of bottom change causing QC failure – a crossline (1184-212-2A3XL-0000) collected 3 to 9 days after acquisition of the mainscheme is offset in places by up to 1 m vertically.SupportFiles\4_CrosslineFailureExample.jpg00Qualifier 10501.0400.025Cutwater2.48000All soundings were assigned a horizontal and vertical value for estimated total propagated uncertainty (TPU). Tidal error was computed based on values in the tide zone definition file (ZDF). The parameters and methods used for computation of sounding uncertainty are detailed in the project DAPR. The BASE surfaces were finalized in CARIS HIPS so that the final uncertainty value for each grid cell is the greater of either standard deviation or uncertainty. The uncertainty layer of the final surface was then examined for areas of uncertainty that exceeded IHO Order 1. Uncertainty for the SBES surface ranged from 0.12 m to 0.65 m. Uncertainty for the MBES surfaces ranged from 0.12 m to 0.62 m. Few exceeded IHO Order 1. Highest uncertainties were found in areas of varying bottom topography such as slopes and sand waves where high standard deviations are caused by the wide depth ranges of sounding contributing to each grid cell, outer edges of multibeam swathes without adjacent line overlap, and areas exhibiting sound speed error. Despite elevated TPU values for these grid cells, the data is within specifications.This survey junctions with one contemporary survey, which was collected concurrent with this sheet. Junctions were compared by way of difference surfaces. Surfaces were created at 2 m resolution for multibeam and 4 m for single beam for each area, and differenced from each other. Results were extracted and analyzed.Survey junctions with this sheet.SupportFiles\5_SurveyJunctions.jpgH12631400002014TerraSondSMultibeam agreement is good, averaging 0.036 m, with a standard deviation of 0.180 m, falling in a range of -1.423 m to 1.774 m. The larger differences were examined and found to be due to bottom change, normally in sand wave areas. A single beam comparison was not undertaken as the two single beam data sets do not have significant overlap.Echosounder confidence checks consisting of bar checks, lead lines, and acoustic comparisons between vessels were undertaken on this project. Two bar checks were completed for the multibeam system on the Q105, while three bar checks were completed for the single beam system on the Cutwater. Bar checks served as a check on both real-time as well as processed depth accuracy, and were also used to determine and refine the sonar acoustic center offsets. Results were good, with processed sonar depths comparing on average to 0.05 m (or better) of the actual bar depth. Lead line comparisons were also undertaken. Over the course of the project, four were completed successfully on the Q105 and three were completed successfully on the Cutwater. Sonar versus lead line depth differences ranged from -0.01 m to 0.12 m on the Q105, and -0.23 m to 0.16 m on the Cutwater. Results were deemed acceptable given the variables associated with lead line checks. Acoustic comparisons between Q105 multibeam and Cutwater single beam data were also undertaken. Effort was made in the field to ensure significant overlap between the two survey vessels for comparison purposes. To compare the data sets, CUBE BASE surfaces at 2 m resolution were created for each vessel and differenced from each other. Differences were extracted and analyzed. Results are good, with the Cutwater single beam 0.041 m shoaler on average then the Q105 multibeam data, with a standard deviation of 0.403 m. The relatively high standard deviation was found to primarily be caused by bottom change in this dynamic area occurring between acquisition of the two data sets, which differed by 8-10 weeks in places. Refer to the bar check and lead line logs available in Separate I: Acquisition and Processing Logs for specific results. Refer to the project DAPR for more information regarding the QC checks.7101 Beam PatternA distinct beam pattern was obvious in the data set in certain areas, with a fuzziness or “horn” like features on both sides of nadir on multibeam swaths, coinciding with the bottom detection shift from phase to amplitude detection. The pattern is common with Reson 8101/7101 multibeam echosounders in certain bottom types. Power and range settings were adjusted in acquisition to minimize the issue, with little effect. However, the “horns,” which can be as great as 0.20 m in height, appear to be largely ignored by the CUBE algorithm during surface creation, with minimal effect on the final surfaces.Sound Speed ErrorA general downward or upward across-track cupping in multibeam data, indicative of sound speed error, is present periodically in the data set. This is more evident in flatter, offshore parts of the survey area. The sound speed error adversely affected outer beams by up to 0.20 m in places. To minimize the error sound speed profiles were collected every 3 hours during multibeam operations, line spacing was reduced to 2.5 times water depth to allow generous overlap, and filters were used in processing to remove the outermost (5-10°) beams. Due to the significant overlap and filtering the effect of sound speed error on final surfaces is relatively minor, normally not exceeding 0.10 m, which is within specifications.SAR: There were sound speed errors up to 0.4 meters were noted in depths around 20 meters, which is right at the maximum allowable threshold for the sound speed error budget at that depth. However, despite the refraction errors in the data, there was no evidence of the refraction in the submitted grids.Motion ArtifactMotion artifact is occasionally visible in the final multibeam surfaces. This is the result of roll and heave error, or uncompensated effects of motion. Poor sea states (normally seas 2 m or greater) were the primary contributor. A survey-grade POSMV 320 V5 was used for motion compensation but residual error remains nonetheless. The adverse effect on outer beam soundings is as high as 0.30 m, but due to substantial overlap between adjacent lines the effect on final surfaces is minor, normally not exceeding 0.10 m, which is within specifications.Tide ErrorVertical offsets or “busts”, indicative of tide error, is present sporadically in the data set. The majority of lines show excellent matchup with adjacent lines but periodically show busts up to 0.20 m that are attributable to tide error. Four tide stations and seven zoning stations were deployed project-wide to model and correct for the movement of tides across the area, but some residual error remains since discrete tide zones cannot always compensate fully for all tide conditions. The observed amount of tide error was deemed acceptable given the complexity of the tidal regime in the area, which experiences current exceeding 6 knots at ebb and flood in constricted areas and a daily tide range of about 2 m. Despite the error, data is within specifications.Bottom ChangeBottom change due to sediment transport was a common occurrence on this survey. Bottom change is indicated by vertical busts between adjacent lines, often with an accompanying change in the shape of the bottom. The sea floor in the area is dynamic with migrating shoals and sand waves evident on the sea floor, especially in constricted areas where current commonly exceeds 6 knots during ebb and flood tides. During operations it was not always possible to survey an area to completion, necessitating a return to the area days to weeks later (to acquire crosslines, infills, or to continue working toward a contour for example), which often resulted in a different bottom. Bottom change could be minor (0.10 m or less) or major, up to 1.5 m in some cases along slopes or sand waves. Note that no additional action was taken in acquisition or processing in bottom change areas to re-run or edit soundings since the bottom return was deemed accurate and within specifications at the time of survey, and bottom change in this dynamic area was anticipated. For this sheet, the area in the narrow constriction between Cape Chunak and Cape Krenitzin was the most affected by this issue.Example of bottom change of up to 1.5 m over 5 days.SupportFiles\6_BottomChangeExample.jpg3 hours for multibeam, 12 hours for singlebeamFor multibeam operations on the Q105, sound speed profiles were taken with an Oceanscience Underway SV system, which utilized a Valeport sound speed profiler. Profiles were taken on a 3-hour interval. The profiler was deployed while underway during survey operations. The profiler was lowered as close as possible to the sea floor, and then retracted to the vessel and downloaded. For single beam operations on the Cutwater, sound speed profiles were taken with an AML Oceanographic SV+ profiler. Profiles were taken on a 6-12 hour interval. The profiler was deployed by lowering it to the sea floor manually. Up and down portions of the profiles were averaged and a combined profile at a standardized 0.10 m depth increment was output to CARIS SVP format with time and position. Sound speed profiles were applied with the “nearest in distance within time” method in CARIS HIPS, with time set to 3 hours for multibeam and 12 hours for single beam.Set Line Spacing (Single Beam) Set line spacing requirements called for 100 m spaced lines from 8 m depth to the inshore limit (generally the 4 m contour in this area), with a project-wide maximum of 1,075 LNM to be collected. Following completion of the 100 m lines, remaining line budget would be utilized by running additional lines between the existing 100 m lines per NOAA guidance in areas of navigational significance until the line budget was expended. This resulted in final single beam line spacing in some areas of 25 m to 50 m, such as in the main channel. The Cutwater acquired all single beam data for this sheet. Initial lines were collected within channels, parallel to the coast and shoals in order to provide recon and provide a starting point for survey. HYPACK acquisition software was utilized, which logged data and plotted the vessel position in real-time relative to background layers which included the chart, survey extents, coverage, and pre-plotted lines. Following completion of the channel lines, a pre-plot line plan was navigated with lines perpendicular to the coast and shoals. The Cutwater would survey each line by proceeding slowly downline towards shoaler water, backing up and breaking offline once the tide and draft corrected depth read 4 m or less. On rare occasions it was not possible to reach the 4 m contour safely because of extreme slope, such as in the narrow constriction between Cape Chunak and Cape Krenitzin. Data density requirements were met by surveying at slow rates, averaging 6 knots or less, and maximizing ping rates. Note that small along-track gaps are present on occasion where HYPACK dropped 1-2 seconds of data at Julian day rollovers as it automatically changed files. This was a common occurrence since the JD rollover occurred at 16:00 local time during prime daylight survey hours. Gaps were minor and normally not rerun unless there was an indication of shoaling. Note that although a project-wide set line spacing maximum of 1,075 LNM was in place, 1,293 LNM were actually acquired. The additional LNM were acquired after an analysis of excess mileage to compensate for mileage unintentionally acquired in areas deeper than 8 m that were designated for complete coverage, as well as crossline mileage exceeding the 8% requirement for set line spacing. Complete Coverage (Multibeam) Complete coverage was required in depths greater than 8 m. The 8 m contour was initially established during single beam operations by completion of the 100 m set line spacing scheme on the Cutwater. The Q105 acquired all multibeam data for this sheet. QPS QINSy acquisition software was utilized, which logged data and plotted the vessel position in real-time relative to background layers, which included the chart, survey extents, coverage, and pre-plotted lines. The Q105 ran lines parallel to the coast and shoals, proceeding from the survey limits to the 8 m contour previously established by the single beam data. Survey speed was minimized, averaging 8 knots or less, to maximize along-track ping density. Line spacing was normally held at 2.5 times water depth, which provided ample overlap between lines to minimize the effect of outer beam errors and ensure data density requirements were met. The Reson 7101 system was operated in a mid-density mode that provided 339 beams per swath, which provided good across-track resolution and data density meeting HSSD requirements without unnecessary data volume generated from higher beam modes. Coverage Checks Coverage was analyzed in the field by data processing. BASE surfaces were generated at the HSSD specified resolutions and analyzed to ensure requirements for data density and holidays were met. Re-runs and infills were identified and carried out by the acquisition vessels as necessary, except in areas where required coverage was not achieved for safety reasons.Corrections applied to echo soundings are detailed in the project DAPR. No deviations occurred, with the following exceptions: Inverted Heave Exception All multibeam lines from JD192 and JD193, including the JD192 patch test, have inverted real-time heave when viewed in CARIS Attitude Editor. This was the result of an incorrect sign convention applied in QPS QINSy. This was resolved from JD194 forward by changing the setting in QPS QINSy. Affected lines were fully resolved by application of TrueHeave, which was not inverted since it was logged independently of QINSy. Sound Speed Correction Exception All multibeam lines were corrected using nearest in distance within 3 hours, except the following lines which were corrected using nearest in distance within 4 hours: Area\Vessel\Day\Line SheetA3\Q105\2014-209\0901-209-2A3-0000 SheetA3\Q105\2014-209\0902-209-2A3-0000 Dynamic Draft Exceptions Q105 - As described in the DAPR, Q105 engine RPM data was logged to file continuously by a custom TerraTach system for later use during dynamic draft corrections. The following lines were missing logged RPM data, and instead received interpolated average dynamic draft values from multibeam lines closest in time: Area\Vessel\Day\Line SheetA1\Q105\2014-192\0042-193-2A1-1780_-_0001 SheetA1\Q105\2014-192\0043-193-2A1-1840_-_0001 SheetA1\Q105\2014-192\0044-193-2A1-1900_-_0001 SheetA1\Q105\2014-193\0060-193-2A1-2645_-_0001 Cutwater – As described in the DAPR, Cutwater engine RPM data was manually noted in TerraLog software for later use during dynamic draft corrections. The following lines were missing logged RPM data, and instead received dynamic draft values from closest in time RPM entries: SheetA\Cutwater\2014-166\1A-2014CU1661807 SheetA\Cutwater\2014-186\1A-2014CU1861733 SheetA\Cutwater\2014-215\1A-2014CU1861733 SheetA\Cutwater\2014-215\1A-2014CU2152116 SheetA\Cutwater\2014-215\1A-2014CU2152126 SheetA\Cutwater\2014-215\1A-2014CU2152231 SheetA\Cutwater\2014-215\1A-2014CU2152300 SheetA\Cutwater\2014-215\1A-2014CU2152358 SheetA\Cutwater\2014-221\1A-2014CU2211908 SheetA\Cutwater\2014-221\1A-2014CU2212132 SheetA\Cutwater\2014-221\1A-2014CU2212141 SheetA\Cutwater\2014-221\1A-2014CU2212201 SheetA\Cutwater\2014-222\1A-2014CU2220042Calibrations were undertaken as described in the DAPR, no deviations occurred.Multibeam backscatter was logged during this survey, but not processed. The vessel Q105 multibeam DB and XTF files contain the backscatter records.SAR: Backscatter was collected with Reson 7101 and submitted in DB and XTF formats, none of which work in the processing branch backscatter pipeline. Therefore, no backscatter products were generated for this survey.V5.3.2There were no software configuration changes after the DAPR was submitted.H12630_MB_1m_MLLWMBES1020NOAA_1mMBES Complete CoverageH12630_MB_2m_MLLWMBES21840NOAA_2mMBES Complete CoverageH12630_SB_4m_MLLWSBES4040NOAA_4mSBES Set Line SpacingThe final depth information for this survey was submitted as three CARIS BASE surfaces which best represented the sea floor at the time of the 2014 survey. The surfaces were created from fully processed soundings with all final corrections applied. The surfaces were created using CUBE parameters that ensured a maximum sounding propagation distance of the grid resolution divided by √2. Resolutions of 1 m, 2 m, or 4 m were selected based on the requirement by depth for complete multibeam coverage described in the HSSD. Surfaces were finalized according to the same depth thresholds, and designated soundings were applied. Horizontal projection was selected as UTM Zone 3 North, NAD 1983. A CARIS HOB file was submitted (H12630_FFF.HOB) with the survey deliverables as well. The final feature file (FFF) contains meta-data and other data not readily represented by the final surfaces, such as bottom samples and shoreline features (where applicable). Each object is encoded with mandatory S-57 attributes, additional attributes, and NOAA Extended Attributes (V#5.3.2). Refer to the DAPR for more detailed discussion of the steps followed when acquiring and processing the 2014 survey data.Additional information discussing the vertical or horizontal control for this survey can be found in the accompanying HVCR.Mean Lower Low WaterDiscrete ZoningUnalaska9462620Port Moller9463502King Cove9459881Cape Chunak9462941Neumans Cove9462948False Pass9462955Isanotski Strait94629619462620.tidFinal Approved9462941.tidFinal Approved9462948.tidFinal Approved9462955.tidFinal Approved9462961.tidFinal ApprovedOPR-R315-KR-14_20141121.zdfFinal2014-11-212014-11-21In addition to four subordinate tide stations installed to support the project, submerged BMPG (bottom mounted pressure gauges) were also deployed throughout the survey area to capture zoning characteristics. Data from all stations were used to derive the tide zones. Preliminary tide zones were not provided for this project.NAD83UTM Zone 3NSingle BaseFALSFalse PassOUTECape Chunak NETRS5240Cape Chunak T5700Base stations at False Pass (FALS) and Cape Chunak (OUTE) also broadcast RTK corrections for real-time and preliminary positioning. Project base stations continuously logged data at 1 Hz, enabling PPK processing. All real-time positions were replaced in processing with PPK positions.The chart comparison was performed by examining all Raster Navigational Charts (RNCs) and Electronic Navigational Charts (ENCs) that intersect the survey area. The chart comparison was accomplished by overlaying the finalized BASE surfaces with shoal-biased soundings, and final feature file on the charts in CARIS HIPS. The general agreement between charted soundings and survey soundings was then examined and a more detailed comparison was undertaken for any shoals or other dangerous features. Results are shown in the following sections. It is recommended that this survey supersede charted data where they overlap. USCG Notice to Mariners (NM) and USCG Local Notice to Mariners were checked for updates affecting the area. None were found that were issued subsequent to issuance date of the project instructions.16535252780660122000-112014-11-042014-11-15Sounding agreement is excellent offshore, where soundings from this survey agree to the chart within 1 fathom or better. Agreement becomes more sporadic as shallower water is approached. The largest changes are observed northwest of the entrance to Bechevin Bay in the vicinity of Cape Chunak and Cape Krenitzin, where bottom change is evident and water has shoaled or deepened by 2-3 fathoms in many locations.Example area of significant change at the entrance to Bechevin Bay. Depths of 3-4 fathoms were found in area of charted ¾ fathom soundings.SupportFiles\7_SoundingChangeExample.jpgUS4AK5CM8066022011-08-092014-08-06falseThe same differences observed for the RNC apply to this ENC.No AWOIS items intersected the survey area.No maritime boundary points were assigned for this survey. Maritime boundary points were provided for information purposes only and were not investigated.There are no charted features labeled PA, ED, PD, or Rep. within the survey extents.No uncharted features were found during this survey.No specific DTONs were found during this survey, though change is evident, especially at the approach to Bechevin Bay. ‘Note C’ is still valid and should be retained (“Mariners are urged to use extreme caution while navigating in Bechevin Bay. The channel through the north entrance and Bechevin Bay is subject to frequent shoaling. Local knowledge of the area is essential for safe navigation.”)As noted in ‘Note C’, shoaling is evident at the north entrance to the bay. This survey was not tasked with obtaining least depths on or determining the limits of shoals in less than 4 m depth, but their position can be determined by the absence of single beam data where the survey vessel reached the 4 m contour and stopped. The “Breakers” area on the north side of Cape Krenitzin is a dangerous shoal with breaking waves and steep edges.Arrows indicate shoals of unknown depth in unsurveyed areas of less than 4 m water depth indicated by lack of single beam soundings. Soundings are colored by depth - red soundings are 4 m or less.SupportFiles\8_Shoals.jpgA “channel” is chosen by the USCG each spring and marked with buoys. Buoys are removed prior to winter to avoid loss or damage from ice flows. The channel is not dredged or otherwise maintained and shifts position annually.Bottom samples were collected for this survey. All returned black sand, from fine to course. Bottom characteristics are encoded as SBDARE objects in the FFF included with the survey deliverables.Silt/ooze, gravel and shells were also found in the bottom samples collected for this survey.Limited shoreline verification was accomplished for this project. However, no limited shoreline verification was undertaken in this sheet because no assigned features intersected the survey extents.Comparison with prior surveys was not required. See Section D.1 for comparison to the existing nautical charts.ATONs were not specifically assigned for investigation. Charted buoys marking the channel were observed during operations, but are seasonal and were not investigated. The “Chunak Point Daybeacon 2” and “Cape Krenitzin Light 7” were observed from the survey area to exist at the charted location and were serving their intended purpose. It is recommended that updated positions of buoys be obtained from the USCG for charting purposes.No overhead features existed within the survey area.None to note.Ferry routes and terminals do not exist within the survey area.Platforms do not exist within the survey area.All significant features and conditions encountered have been described previously.No construction or dredging was occurring within the survey extents, nor are there any known future plans for construction or dredging in the survey area.No new surveys are recommended in this area.No new chart insets are recommended in this area.Field operations contributing to the completion of survey H12630 were conducted under my direct supervision with frequent personal checks of progress, integrity, and adequacy.This report, digital data, and all other accompanying records are approved. All records are respectfully submitted and forwarded for final review.The survey data was collected in accordance with the Statement of Work and meets or exceeds the requirements set in the 2013 NOS Hydrographic Surveys and Specifications Deliverables document. This data is adequate to supersede charted data in common areas. This survey is complete and no additional work is required with the exception of any deficiencies noted in the Descriptive Report.Andrew Orthmann, C.H.TerraSond Charting Program Manager2014-12-22OPR-R315-KR-14 Zoning Report2014-12-12Coast Pilot Review (CPB9_E32_C06_20141031)2014-11-06Removal report for 9462941 Cape Chunak2014-10-30Removal report for 9462955 False Pass, Isanotski Strait2014-10-21Removal report for 9462961 Isanotski Strait Entrance2014-10-20Removal report for 9462948 Neumans Cove2014-10-17