Emerald Ocean Engineering: What's New

AFRICAN GREAT LAKES SURVEY

 

In 2019 the Nile Basin Initiative / Nile Equatorial Lakes Subsidiary Action Program (NBI/NELSAP)  contracted Emerald Ocean Engineering LLC (EOE), with subcontractors Gulf Coast GIS and the Ugandan National Fisheries Resources Research Institute (NaFIRRI), to conduct shoreline and  bathymetric surveys of Lakes Albert and Edward, both shared between the Democratic Republic of Congo (DRC) and Uganda, and Lake George in Uganda. The resultant maps and associated survey outputs will guide and strengthen fisheries research and its related sectoral activities; water resources planning and management; navigation and maritime safety; and other lake-based activities. Existing maps used data collected over 90 years ago. Now these three lakes have the most accurate and highest resolution maps of any in Africa. The project was completed in 2020.

 

Project Location
Project Location
Delivered products included:


High-resolution lake shoreline and island maps

Very high-resolution harbor, outcrop, hazard and wetland maps

Lake Project Sounding Datums and lake level benchmarks referenced to EGM2008

Lake bathymetry data and maps to International Hydrographic Organization (IHO) standards

Lake bottom sediment sampling & analysis and lake bottom classification maps


All data received error and uncertainty analysis and are maintained in an accessible ½ terabyte database

 

LAKESHORE MAPS

We constructed high-resolution shorelines for each lake from spaceborne (Sentinel-2 and Landsat 8) imagery at a combination of 15 m resolution, 10 m resolution, 5 m resolution, 3 m resolution, 50 cm resolution, and 30 cm resolution.
In highly dynamic vegetative areas where Sentinel-2 or Landsat-8 cannot delineate a clear shoreline, very high resolution (VHR) imagery was obtained and substituted. For example, the southern wetland of Lake Albert across both the DRC and Uganda uses 50 cm Worldview 2 and 30 cm Worldview 3 imagery, as this region has ephemeral floating grasses and sub-aquatic vegetation. Finally, sub-meter resolution imagery was obtained with a drone (Sensefly w/ SODA camera system) flown over Lake Albert marshes and selected harbors to ascertain the shorelines' positional accuracies. Once the accuracy statistics were calculated, the drone imagery was incorporated back into the shorelines for VHR mapping of these areas.

VHR Harboretc

VHR harbor, outcrop, hazard, and wetland map of Butiaba, Uganda. Not for navigation




BATHYMETRIC SURVEYS

Depth data was measured using a single beam acoustic echosounder (CEESCOPE 100) mounted on the NaFIRRI research vessel Nkejje. The vessel navigated a fixed grid of approximately E-W transects while taking near-continuous echo soundings. The spacing of the transects on Lake Albert was 5 km and on lake Edward and George was 2.5 km.  The transects extended to within 1 km of the lakeshore when accompanying security forces deemed it safe to do so (see SECURITY).

Survey vessel Nkejje      
Survey vessel
The survey team      
survey team

 

 

Lake Albert color relief map. Not for navigationLake Albert map



Lake Edward contour map. Not for navigation
lake edward


LAKE BOTTOM CLASSIFICATION

Lakebed sediments were collected with a Ponar sampler in conjunction with the bathymetric surveys. One shallow water and one deep water sample was retrieved along each transect. In addition pH, conductivity, and temperature data were measured for each sample. Standard sieve analyses were performed by NaFIRRI at their lab in Jinja, Uganda.

 

Sediment sampling sites in Lake Albert

clay-silt Lake Edward

 Interpolated clay/silt distribution map, Lake Edward

SECURITY CHALLENGES

 Because of ongoing threats from insurgents  on both lakes and some recent criminal assaults on tourists in the vicinity , security for the survey crew was a major consideration. Armed escort support vessels were provided throughout the survey by the Ugandan Peoples Defense Force in Ugandan waters and the République Démocratique Du Congo Marine Nationale in the DRC waters. Almost all of the project proceeded without incident, but on one occasion the survey vessel came under fire from unknown hostiles on the south shore of Lake Edward when it ventured close to shore. The DRC gun boat quickly returned fire and the survey was resumed. This incident amply demonstrated the value of these professional security team members.

UPDF escort vessel and crew

 


NaFIRRI survey team with DRC Marine gunboat crew
 



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