Metsi Consultants - DWA Home Page

Report No 678-F-001
METSI CONSULTANTS: SUMMARY OF MAIN FINDINGS FOR PHASE 1 DEVELOPMENT
reverse this trend. Geomorphological impact would be at most a slight reduction of inundation of wider, macrochannel
elements (bars, benches and mini-floodplains) that would reduce the exchange of sand, nutrient-rich fine
sediments and organic matter between rivers and banks.
Table 5.1 Hydrological summary for the Minimum Degradation Scenario. Shaded sites
represent reaches immediately downstream of Phase 1 dams. MCM a -1 = millions
of cubic meters of water per annum.
IFR Site Historical MAR Minimum Degradation Scenario
MCM a -1 MCM a -1 As % of MAR
1 87 51 59
2 554 366 66
3 774 436 56
4 1572 866 55
5 1924 1194 62
6 3330 2171 65
7 355 231 65
8 592 397 67
Water quality changes are difficult to predict without details of the chemical and physical characteristics of the
outflows, but in general it is considered that there would be mild increases in dissolved nutrients and suspended
solids in the river water. Thus, in quiet waters where the suspended solids could settle out, an increase in the
occurrence of algae is expected, and in faster-flowing areas, the water is expected to be slightly more turbid than
under present-day conditions.
The channel and inundation changes described above would affect the riparian vegetation, whilst both these and
the water quality changes would impact aquatic plants and animals. There would be a negligible to low decrease
in the abundance of annual plants, shrubs and trees growing at all levels up the banks. The most important social
use of these is for medicines, while other uses listed are firewood, traditional attire, handicrafts, food, building
construction, grazing, ropes, yokes, bank stabilisation, fodder and grazing. Their loss may be partly countered by
a very mild increase in grasses and sedges in the same areas, and of large water plants (macrophytes) in the
river itself. These kinds of shifts in plant communities, including the proliferation of algae, would be most obvious
closest to the dams, diminishing downstream, with a change in abundance of only 0-5% predicted for IFR
Reaches 5 (Whitehills) and 8 (lower Senqunyane). IFR Reach 6 (Seaka Bridge) differs from this trend, with a
higher (10-20%) shift from shrubs and trees to sedge and grasses, which is mainly a reflection of the different
shape of the river channel in this reach.
The changes in river-bed substrata, temperature and water quality would encourage a mild shift in aquatic
invertebrate communities from fast-water to slow-water species. Conditions would be slightly more conducive for
aquatic worms, the intermediate snail hosts of liver fluke parasites in domestic livestock, and the blackfly pest that
targets poultry.
The major impact on fish would be confined to the Matsoku River, where the simple presence of the weir would
disrupt movement of fish along the channel and might affect spawning and migration cues. It is predicted that
there would be a moderate to severe (11-50%) decrease in abundance of the Maluti Minnow and a severe (40-
80%) decrease in trout numbers. Other fish species do not occur in the Matsoku River upstream of the waterfall
26