The initial idea for the creation of the Watershed Database for sub-equatorial Africa was based on ALCOM's need for digital fish species distribution maps. Digital fish species distribution maps allow assessment of what fish are potentially present in a certain catchment and therefore what species can be recommended for stocking of dams. The Watershed Database and the complete Water Resource Database (WRD) have however developed into a much more versatile tool for general water resource management.
The first practical work on the Watershed Database started beginning 1997 when a consultant (J. Dooley) was approached for the delineation of watersheds in the mainland SADC region. When WWF offered to co-fund the delineation and species distribution work, the first watershed model was created in April 1997. The delineation, naming and ordering of the watersheds was examined and commented thoroughly by several experts from different countries and formed the basis for a major revision which came out in September. The delineation procedure is explained in a separate report by the consultant and is included in this document as appendix II.
The current watershed model holds 1157 watershed polygons, starting 40 minutes South of the Equator and including all current mainland SADC countries. All subwatersheds were ordered and named. Surface areas were calculated and are included in the database. Summary statistics for all megabasins in the database are provided in appendix III and show that the largest watersheds in the region are the Zaire, Zambezi, Orange, Okavango and Limpopo basins.
ALCOM developed an interface for the watershed model which does not require the use of a major GIS software package. The interface combines regular database software with a simple mapping program and allows visualisation of upstream and downstream watersheds, calculation of surface areas of catchments and calculation of other catchment statistics based on raster images. It also enables the user to “cut out” selected watersheds or groups of watersheds from the main watershed polygon file to work with selected areas only. Visualisation of changes in elevation throughout the course of a watershed are simple and straightforward.
The currently developed interface needs Lotus Approach (Lotus Development Corporation©) and Mapviewer (Golden Software©) or alternatively Windisp3 (Map and image display system by E. Pfirman and J. Hogue with support from many organisations such as FAO, USAID, USFS, USGS and SADC/RRSP). It is planned to develop alternative interfaces for MS Access and Dbase (Contact ALCOM for the latest updates).
The presented database and interface are only a part of the much broader SADC Water Resource Database which was developed by ALCOM (Verheust, 1997; Verheust, in press; Verheust and Johnson, in prep). The SADC WRD holds various data on surface water bodies, rivers, fish species, bibliographic records, a mailing list and much more water resource related information.
This working paper explains the development and structure of the current watershed database as well as the developed interface. Best use can be made of this document in combination with the digital watershed model which can be obtained in digital format from ALCOM.
