Upper Reach GIS Bathymetry Files ReadMe
Windward Environmental
2024-02-29

Component survey files (2019 base survey, 2020 gap-fill survey, and 2021 USACE federal navigation channel survey) used to comprise the LDW upper reach Pre-Design Investigation (PDI) bathymetry surface. The PDI bathymetry was generated using the 2019 high-resolution multibeam survey as the foundation, then survey points within the June 2020 Gap Fill-In Survey area (defined in LDW_Bathy_Gap_Fill_ln_202006_edge) and within the Jan 2020 USACE Federal Navigation Channel Survey (defined in USACE_20200121_SurveyPoint_HD_UR_edge) were removed and replaced with the survey points from the respective surveys.

Items:
2019 PDI Survey XYZ and supporting files: LDW_RM275-525_Bathy_NAD83-WA-N_MLLW_2019_Final 070119.zip
2020 PDI Gap Fill Survey XYZ: LDW_Bathy Gap Fill-In_NAD83-WA-N_MLLW_June 2020.zip
2021 USACE Federal Navigation Channel Survey XYZ and supporting files: DU_03_DUW_20200121_CS_E_12_2_1_190_A.zip (full file set available from USACE)
Polygon features used to create final UR PDI bathymetry survey points (in ESRI file geodatabase format): Upper Reach GIS Bathymetry Boundary Layers.gdb

Northwest Hydro 2019/2020 survey notes (refer to Attachment B: 2020 Bathymetric Survey Data Report of the Quality Assurance Project Plan Addendum for the Lower Duwamish Waterway Upper Reach: Pre-design Investigation Phase II (2021) for details):
1. Horizontal Datum: Nad 83-2011 Epoch 2010.00, State Plane Coordinates, Washington North Zone.
2. Units: U.S Survey Feet
3. Vertical Datum: Mean Lower Low Water (MLLW). The conversion between NAVD88 And MLLW was determined using NOAA/NOS VDatum 3.9. The VDatum calculated seperation between NAVD88 And MLLW at the NOAA/NOS Tide Station 9447130 (Seattle) is 2.34 feet. (Example: 10.00 ft NAVD88 = 12.34 ft MLLW)
4. All horizontal positioning and vessel attitude was provided in real time using an Applanix POS/MV RTK GPS aided inertial sensor. Real time RTK corrections from the WSRN GNSS network were utilized during all fieldwork for this project.
5. Soundings were collected using a R2Sonic 2022 multibeam SONAR operating at 400 khz. Data processing was completed using HYPACK HYWEEP software.
6. This bathymetric survey is representative of the general condition of the seabed at the time of the survey. The condition of the bottom may change at any time after the date of this survey.
7. All bathymetric data was collected in accordance with the U.S Army Corps Of Engineers Hydrographic Survey Manual EM-112-02-1003 (November 2013). Survey Classification: navigation and dredging support surveys, bottom classification of soft.

USACE 2020 survey notes (USACE survey name DU_03_DUW_20200121_CS_E_12_2_1_190, January 21, 2020):
1. Sounding and elevations are in feet and refer to the plane of NOS Mean Lower Low Water (MLLW ). Epoch 1983-2001. Tide correction based on Geoid2012A using Real Time Kinematic (RTK). Soundings taken above the datum plane are prefixed with a (+) sign.
2. Horizontal Datum: WGS-84. Projected coordinate system: Lambert Grid Projection, State Plane, Washington North Zone, 4601, Surveyed in NorthAmerican Datum of 1983/2011, Plotted in North American Datum of 1983/91. Horizontal units are U.S. Survey Feet.
3. The information represents the results of surveys made on the date indicated and can only be considered as indicating the generalconditions existing at that time.
4. (Project Depth, Stations, Width): (30, 0+00 to 134+00, 200); (20, 134+00 to 176+00, 150); (15, 176+00 to 270+56, 150);(15, 270+56 to 275+56, 250); Turning Basin (20, 150+00 to 160+00, 350).