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10.7 Mean annual runoff in NatallKwaZulu*
The mean annual runoff (MAR) in NatallKwaZulu varies from less than 50 mm in the north
east, to over 800 mm in the Drakensberg. If the 100 mm MAR is used as a threshold,
then East Griqualand and almost the entire northern half of the province has relatively
limited surface water resources. Some difficulties accordingly, may arise with longer term
economic development in the northern half of the Tugela Basin, unless water is imported
from further afield. The most severe shortage of surface water is found in the area
bounded by Louwsburg, Ulundi, Mtubatuba, Ndumu and Ingwavuma. A large portion of
the latter region produces an MAR of less than 50 mm, with a significant area yielding less
than 15 mm MAR. For the north eastern part of NatallKwaZulu where data are non­
existent, Schulze (1984) estimated that the MAR would be less than 15 mm and certainly
less than 50 mm.
10.8 Median monthlv runoff in NatallKwaZulu
Schulze (1984) found that there are considerable variations in runoff produced in different
parts of Natal/KwaZulu in all months of the year. With the beginning of the rainy season,
marked increases in runoff are evident during November and December. Over much ofthe
province the highest flows occur during January to March, with the Drakensberg area
'yielding in excess of 60 mm of runoff in each of the months, January to March. The
summer runoff in most other parts of NatallKwaZulu is a steady 5 - 10 mm per month,
with the north eastern part of Natal/KwaZulu producing less than 2,5 mm of runoff. It
should be noted however, that during seven months of the year, the north eastern region
produces less than 1 mm of runoff. Minimum flows in NatallKwaZulu occur during August
and September when most parts of the province yield less than 1 mm, with only a few
isolated areas producing more than 5 mm of runoff.
*
Discussion based on Schulze, R.E., 1984. An assessment of the surface water resources of Natal,
Natal Town and Regional Planning Commission Report, VOl 63, Pietermaritzburg, 44 p. and map.
(Mean annual runoff was converted into a depth equivalent in mm for the purposes of the original
discussion, by Schulze (19841). Runoff data for individual rivers in Natal/Kwazulu are presented in
the chapter on -estuaries·, elsewhere in this publication.