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(when runoff: rainfall relationships were plotted). that hydrological zones Zl - Z3; Z6 - Z8
and Z13 had to be subdivided, sometimes into a number of sub-zones, for example. 8a,
Bb and 8c. Accordingly. zones of similar hydrological response in NatallKwaZulu were re­
organized into 21 ACRU {Agricultural Catchments Research Unit} runoff regions. It should
be noted that region 01 designates the area in north eastern Natal/KwaZulu stretching
from St Lucia to Kosi Bay and inland. where no runoff records for simulation are available,
effectively resulting in 20 runoff regions rather than 21. For each of the ACRU regions.
mean annual runoff {MAR} versus mean annual precipitation (MAP) was plotted for all
quaternary sub-eatchments in a specific runoff region. The resultant runoff equations in
terms of rainfall and other relevant data for the 20 ACRU runoff regions are presented in
Table J11. Where apparent errors were found in the HRU quaternary catchments data
(38% of cases), subsequently corrected by Midgley, Pitman and Middleton (1983)*.
runoff: rainfall plots had to be constructed by Schulze, from the simulated runoff and
rainfall data provided by the Hydrological Research Unit. Several runoff maps. brieflY
discussed later in the chapter. can be found in Schulze (1984).
Table J6: Mean annual runoff and other data for secondary drainage regions in
NatallKwaZulu.
Secondary Area of region Mean annual Mean annual Percentage of
drainage (km 2 ) precipitation runoff total annual
region (mm) (10 6 m 3 ) South African
runoff
W
Wl0 5639 1030 969 1,81
W20 10061 849 885 1,65
W30 9574 792 395 0,74
W40 11 785 828 1 253 2,34
W70 2638 648 100 0,19
Summation 39697 - 3602 6,73
V
Vl0 7600 984 1 795 3,35
V20 2880 892 522 0,97
V30 9792 848 1290 2,41
* See Midgley, D.C., Pitman, W.V. and Middleton, B.J., 1983. An addendum to "Surface Water
Resources of South Africa" (l98t), Water Research Commission, Pretoria, various pages.