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Report No 678-F-001
METSI CONSULTANTS: SUMMARY OF MAIN FINDINGS FOR PHASE 1 DEVELOPMENT
11.2. OPPORTUNITIES FOR MITIGATION THROUGH FLOW RELEASES
Mitigation of downstream impacts through adjustment of flow releases through the LHWP structures is inherent in
the scenarios described above, e.g., the Minimal Degradation Scenario represents a very high level of mitigation
(with a considerable cost in potentially divertible water) while the Treaty Scenario represents a very low level of
mitigation with near-maximum diversion of the water resource. However, mitigation to meet required objectives
can be fine-tuned and guided by information from the monitoring programme. The physical constraints on water
releases created by the design of the various outlet facilities will affect the ways and timing of these releases.
Annex E describes the LHWP outlet structures, and the salient features of the releases are as follows.
Katse Dam can release a maximum of 1.2 - 1.9 m 3 s -1 through the mini-hydro bypass, a maximum of ~0.5
m 3 s -1 through the mini-hydro station itself, and between 150 to 400 m3/s through the low-level outlet.
The amounts of all maximum discharges depend on reservoir surface elevation. If water transfers from
Katse are made according to current plans, then floods overtopping the spillway are expected to occur
very infrequently in the future. The opportunities for mitigatory flow releases at Katse are thus very
limited.
Mohale Dam can release between 2.5 and 4.25 m 3 s -1 from its multiple-level off takes and ~45 m 3 s -1
through the low-level outlet. The amounts of maximum discharges depend on reservoir elevation. Floods
over the spillway are expected to be rare events. There is therefore a better opportunity for mitigating
impacts in the Senqunyane through planned flow releases.
Matsoku can discharge a maximum 0.65 m 3 s -1 through its weir outlet, while flows exceeding 47 m 3 s -1 will
pass through the scour gate to downstream, and flows exceeding 96 m 3 s -1 will overtop the spillway.
Discharges through the scour gate and/or over the spillway are expected to occur each year in most
years.
It will be necessary to carefully balance the advantages, disadvantages, costs and benefits of mitigation (i.e.
reducing impacts) versus compensation (i.e. replacing losses), and the eventual programme to address flowrelated
losses would be most effective as a blend between the two. Some important resources, e.g. wetbank
vegetation which provides a basis for medicinal plants and wild vegetables, would be responsive to mitigation via
flow releases while being difficult if not impossible to replace via compensation programmes. Other impacts, on
the other hand, would be more effectively addressed through non-flow-related mitigation, e.g. reducing public
health risks through sanitation and educational programmes.
A significant problem in applying mitigation to the LHWP as it currently exists is that the entire scheme and its
yields are designed on the basis of one set of engineering, economic and environmental assumptions (nearmaximum
diversion of water, maximisation of economic values of the yield) while the basis for application of an
IFR is quite different (maximum concern for downstream environments and communities, optimisation of overall
economic opportunities).
11.3. OPPORTUNITIES FOR COMPENSATION
Under the Treaty Scenario, compensation will likely have to be provided to the 8250 households living along the
lower Matsoku, Malibamats’o and Senqunyane rivers (IFR reaches 1,2,3, 7 and 8) where biophysical impacts are
predicted to be severe to critically severe. Further down the system the impacts are predicted to be low to
moderate and the actual extent of resource reduction and need for compensation will have to be verified by
monitoring. Compensation is unlikely to be required along the mid-to lower Senqu River where biophysical
changes will be low or even negligible; here too monitoring should be implemented to confirm this (see Section
12).
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