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time (mean exceedance flow), during the four driest months of the year*. The area
which can be irrigated by this flow, divided by the potentially irrigable area, is known as
the Theoretical Abstraction Right (T.A.R.) which is expressed as a percentage, for
example, 65% on the Tugela River.
"Surplus water" in a public stream by contrast, refers to public water flowing or found in
the stream (other than normal flow), if any. Surplus water implies some form of storage.
Where surplus water is stored in a public stream, the normal flow of downstream users
must be allowed to pass without interruption.
In most instances, it is assumed that irrigators are aware of the limitations imposed by the
WaterAct. However, in irrigation districts (discussed later), irrigation boards assume some
of the responsibilities of the Water Act. In Government water control areas (discussed
below), the Minister of Water Affairs and Forestry determines, and then publishes the
water rights of individual properties in the Republic of South Africa Government Gazette,
with due regard to the fair share principle.
In areas outside formal Government water control areas the same fair share principle
operates with respect to normal flow (as within control areas), except that water rights
are not determined and published, unless the land owners voluntarily apply to the Water
Court, or objections are lodged by aggrieved ownerl! who believe that other land owners
are exceeding their rightful share of water. The only control that the Department of Water
Affairs and Forestry has over such abstractions, is in terms of Section 98(1) of the Water
*
Frequency distribution curves of monthly flows can be found in Pitman, W.V., Middleton, B.J. and
Midgley, D.e., 1981. Surface water resources of South Africa, VOL VI: drainage regions UVWX.
The eastern escarpment Part 1 (Text), various pages, and Part 2 (Appendices), various pages, HRU
Report No. 9/B1, Hydrological Research Unit, University of the Witwatersrand, Johannesburg. The
curves express monthly flows for various hydrological zones, as a percentage of mean annual runoff,
thereby enabling an estimation of normal flow to be made. Proceed by measuring all the irrigable land
of riparian owners up to the point where the normal flow is calculated. In the case of a stream
contributing less than 1 5% to the normal flow of the main stream, normal flow is usually calculated
at the confluence with the main stream, and the division of water for the smaller stream is done
separately. The same is done for the main stream, subtracting the normal flow required for irrigation
in streams contributing less than 15% of the normal flow of the main stream. The normal flow is
then divided proportionally between all the riparian owners, bearing in mind the restrictions of the
Pietersburg principle (described in Pitman, Middleton and Midgfey (1981)), which states that none of
the competing properties may compete with more than a share equal to the total normal flow at that
point. A useful background publication on the distribution ofagricultural water is the following: 8arry,
A.H. and Le Row