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| Earth Resources Observation and Science (EROS) |
The map below displays the major drainage basins extracted from the 1 KM African DEM. A drainage basin or catchment is a land area surrounded at its perimeter by higher elevation that cause precipitation falling within its bounds to flow to the basin's outlet points. By using techniques developed by Jenson and Domingue (1988), Arc/Info GRID functions were used to process the DEM by removing spurious sinks in the DEM by filling the depressions and calculating flow directions. Then upon completion of the flow direction processing, basins are extracted.
To ensure that proper basins in terms of area and spatial extent are obtained, a verification process needs to be implemented. Such a process has been developed at the EROS Data Center by Verdin and Jenson (1996) that was used for verifying the African basins. For example Lake Chad is one the 12 largest African basins. If one were to fill all the sinks, this major basin would become part of the North-Interior basin. Therefore, the subsequent verification stage is important to process closed basins, Lake Chad differently from spurious depressions. Verification is the process whereby it is decided whether the depressions (sinks) drain to the ocean, or are closed basins. If a sink is found to be an artifact of the DEM processing techniques, (as is usually the case), it is filled to allow continuous flow across the DEM surface. If a sink is found not to drain by verification with relevant source maps and related information, then the depression is marked and left unfilled. These procedures are executed recursively until all depressions in the DEM are verified.
Return to Delineation of Drainage Basins Title Page
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For further assistance, please contact: Customer Services U.S. Geological Survey Center for Earth Resources Observation and Science (EROS) 47914 252nd Street Sioux Falls, SD 57198-0001 Tel: 800-252-4547 Tel: 605-594-6151 Fax: 605-594-6589 Email: custserv@usgs.gov Business Hours: Monday thru Friday, 8:00 a.m. to 4:00 p.m., central time |
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