Metsi Consultants - DWA Home Page

METSI CONSULTANTS: SUMMARY OF MAIN FINDINGS FOR PHASE 1 DEVELOPMENT
b. Scour outlet:
The 18 m weir will be provided with a gated structure located at the downstream end of the forebay, which will
release water from bed level. Will be equipped with a buoyancy tank, which will cause the gate to open
automatically when the tunnel intake is submerged and the reservoir level is approaching FSL. Under normal
operation all flows up to ~47 m 3 s -1 (less the environmental releases) will divert through the tunnel to Katse
reservoir, flows higher than 47 m 3 s -1 will pass through the scour gate to downstream. Flows exceeding 96 m 3 s -1
will overtop the spillway. Any proportion of the inflow can be released through the weir if the outlet tunnel gates
are closed. Discharges through the scour gate and/or over the spillway will occur each year in most years, the
frequency and magnitude will depend on the sequence of inflows, the capacity of the reservoir, and the way in
which the isolating gate in the tunnel inlet is operated. Analysis of frequency, magnitude and duration of outlet
releases has not been done. The reservoir will have a small volume and released water quality is expected to be
similar to that of the upper Matsoku River. Water released may have a high suspended-sediment concentration,
depending on the flow released and the length of time preceding the releases.
Report No. 678-F-001 E-2