Mohale Dam Technical Description
The Mohale Dam consists of the following principal components:
The Mohale Dam contractor is also responsible for the maintenance and operation of the advanced infrastructure in t he Mohale area and maintenance of the Mountain Road from St Michaels to the site.
Construction materials are extracted from quarry 1 and quarry 2, consisting of basalt and doleritic basalt, which serves as the source for rockfill and aggregates respectively.
Main Characteristics
|
Full supply level (FSL) |
2075masl |
|
Minimum operating level (MOL) |
2005masl |
|
Probable maximum flood level |
2084masl |
|
Reservoir area at FSL |
21.2 x 106m2 |
|
Capacity at FSL |
946.9 x 106m3 |
|
Live storage capacity |
857.1 x 106m3 |
|
Storage at MOL |
89.8 x 106m3 |
|
Mean annual runoff(March) (1930 - 1996) |
317.5x 106m3 |
|
Treaty compensation flow |
0.3m3/s |
|
Maximum compensation flow at FSL |
4.25m3/s |
| Low Level outlet capacity at FSL |
57m3/s |
|
Estimated average annual sedimentation Load |
306 000m3 |
|
Total Rockfill volume |
7.80 x 106m3 |
|
Total concrete volume |
100 450m3 |
River Diversion
|
Number of Tunnels |
2 |
|
Diversion Tunnel 1: Excavated/lined diameter |
5.6m/5.0 m |
|
Diversion Tunnel 2:Excavated diameter Unlined |
6.7 m |
|
Diversion Tunnel 1: Length |
591 m |
|
Diversion Tunnel 2: Length |
674 m |
|
Pre-cofferdam crest elevation |
1951 masl |
|
Upstream Cofferdam crest elevation |
1967.5 masl |
|
1:5 year water elevation |
1967 masl |
|
1:500 year water elevation |
1996.76 masl |
|
Fill volume of upstream cofferdam core |
54 500 m3 |
|
Fill volume of upstream cofferdam rockfill |
88 350 m3 |
|
Crest level of upstream section of main dam |
1997 masl |
|
Tunnel 1 Plug Temporary valve Type Number Diameter |
|
|
Gate Valve |
|
|
1 |
|
|
250 units |
|
|
Tunnel 1 Plug Temporary valve Type Number Diameter |
|
|
Gate valve |
|
|
2 |
|
|
400 units |
Senqunyane River Hydrology
|
Catchment Area |
938 km2 |
|
1:20 Year Peak Inflow |
1 300 m3/s |
|
1:100 Year Peak Inflow |
1 979 m3/s |
|
PMF: Peak Inflow (8 hour rainfall duration) |
10 519 m3/s |
|
PMF: Peak Discharge (24 hour rainfall duration) |
2 477 m3/s |
Spillway Characteristics
|
Approach canal width |
60 - 100 m |
|
Spillway type |
Ungated ogee |
|
Ogee weir crest length |
50 m |
|
Ogee weir crest level |
2075 masl |
|
Length from Ogee Weir to Flip Bucket toe |
318.1 m |
|
Chute width (Upstream/Downstream) |
50/26 |
|
Flip Bucket Width |
26 m |
|
Ogee design discharge |
1 857.8 m3/s |
|
Spillway PMF outflow |
2 477 m3/s |
Dam Description
|
Maximum height |
154 m |
|
Crest Length between abutment walls |
540 m |
|
Crest width |
10 m |
|
Top of rockfill(max. section incl. Camber) |
2084 masl |
|
Top of rockfill at extreme abutments |
2083.5 masl |
|
Top of parapet wall (max. section incl. Camber) |
2085.5 masl |
|
Upstream slope |
1V:1.4H m/m |
|
Downstream slope |
1V:1.25H+berms m/m |
|
Downstream average slope |
1V:± 1.45H m/m |
|
Assumed excavation volume |
243 000 m3 |
|
Rockfill volume: Zone 3B, 3C, 3D and 3E Zone 2A, 2B and 3A |
7.35 x 106 m3 |
|
0.35 x 106 m3 |
|
|
Total rockfill volume |
7.7 x 106 m3 |
|
Face slab surface area |
81 000 m2 |
|
Plinth length |
727 m |
Compensation Outlet Data
|
Compensation pipe diameter |
1000 mm slopping |
|
Intake valves: Type Number Diameter |
Gate |
|
8 |
|
|
600 mm |
|
|
Maintenance valve for control valve: Type Number Diameter |
Butterfly |
|
1 |
|
|
400 mm |
|
|
Provisory closure valve for turbine: Type Number Diameter |
Gate valve |
|
1 |
|
|
400 mm |
|
|
Control valve: Type Number Diameter |
Howell - Bunger |
|
1 |
|
|
400 mm |
Low Level Outlet Data
|
Maintenance Valves: Type Number Diameter |
Butterfly |
|
1 |
|
|
1 400 mm |
|
|
Control Valve: Type Number Diameter |
Howell - Bunger |
|
1 |
|
|
1 400 mm |