Emerald Ocean Engineering: What's New
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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.
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 Project Location |
Delivered products
included:
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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 harbor, outcrop, hazard, and wetland map of Butiaba,
Uganda. Not for
navigation |
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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
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The survey team
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Lake Albert color relief map. Not for navigation  |
Lake Edward contour map. Not for navigation  |
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.
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Sediment sampling sites in Lake Albert |
 Interpolated
clay/silt distribution map, Lake Edward |
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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. |
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UPDF escort vessel and crew |
 NaFIRRI survey team with DRC Marine gunboat crew |
Also, read the blog post: https://researchdata.springernature.com/posts/the-bottom-of-the-lake
