After merging of the databases, entries were checked again for obvious mistakes and corrected accordingly. Most obvious mistakes were found in relation with co-ordinates and construction date. Related to the coordinate problem is the occurrence of duplicate locations for apparently different water bodies.
A co-ordinate file of the SWBs was created and overlayed with the South African country border and hydrological zones. A number of SWBs were located outside of the country border. Many of these were located on the map in Mozambique while they should have been in Cape Province. It appeared that latitude and longitude of these co-ordinates had been inverted. These coordinates were subsequently interchanged by ALCOM, providing this located the water body in the correct drainage region. The above leads to the possibility of further undetected instances of inverted co-ordinates especially in the 30 degrees latitude and 30 degrees longitude zone. A list of SWBs with inverted co-ordinates is provided in annex I.
A number of SWBs that were plotted outside of South Africa's borders did not appear to have inverted co-ordinates, indicating wrong latitude or longitude figures. This also leads to the possibility of other SWBs having wrong co-ordinates which are less conspicuous due to the nature of their plotted location. It was noted that several SWB points were plotted in Lesotho which should have been plotted in Harrismith. SWBs were plotted region by region and where it was noticed that SWBs were wrongly located, the co-ordinates were removed from the co-ordinate field and placed in the comments field where they would be easily accessible for further examination. There still remains some work to be done in identifying SWBs with wrong co-ordinates, especially within the drainage regions at the secondary and tertiary levels. A list of SWBs with possible wrong co-ordinates is provided in annex II.
A special search was done to find duplicate records in the database, based on SADC_ID, NAT_ID (national identifier) and NAT_INDEX (national index number). In the event of two very similar records with minor differences in several fields, but one major difference, the records were entered uniquely. An additional entry was made in the DUPE_ID (duplicate identifier) field should a query arise at a further stage as to their similarity.
Records with the same latitude and longitude could not be considered necessarily as duplicate record due to the precision of coordinates. It happens quite often that two water bodies (e.g. in the case of a silt-trap dam) are situated so close to each other that there is no difference in coordinates to the nearest minute. A list of SWBs with the same co-ordinates as at least one other SWB is provided in a separate file (za_check.dbf).
Impossible construction dates such as 1147 were changed to 1947 when indications existed about the right date.
