Table 5 Current physical safety problems associated with the ten dams surveyed
Dam components |
Actual problems |
Details of problems |
Percentage of dams* |
Reservoir |
Inability to store design water capacity |
Sediment accumulation; Irrigation gate leakage; Spillway leakage |
100% |
Crest |
Overtopping |
Inaccurate estimation of hydrographical parameters; Spillway is blocked; Flooding is over the design flood capacity; The top is constructed lower than designed |
60% |
|
Settlement on the crest |
Traffic damage; Animal burrowing activities; Instability of the embankment |
80% |
|
Transverse cracking |
The dam foundation is depressed; Instability of the embankment; Shrinkage of surface materials; Materials are low quality |
20% |
|
Longitudinal cracking |
Water in the reservoir increases or decreases suddenly. This sudden change of water level creates depression on the top; The dam foundation is depressed; Slide occurs on the embankment |
40% |
|
Ruts along the crest |
Traffic damage; The movement of foundation |
30% |
Upstream slope |
Seepage under the foundation |
The quality of material is low. Hence, water is eroding the material; Rodent activity; Geological assessment is inaccurate |
20% |
|
Slide and slump |
The lack or loss of embankment material; Rodent activity; Erosion; Traffic damage; Downstream slope is too steep |
80% |
|
Sinkholes |
The movement of foundation create holes; Material is seeped; Animal burrows |
20% |
Downstream slope |
Seepage through the embankment |
Rodent activity creates open pathway through embankment; The abutment is not properly designed and constructed |
70% |
|
Seepage at the abutment |
The abutment is not properly designed and constructed; Plants/trees are not removed completely in construction |
30% |
|
Slide and slump |
The lack of or loss of embankment material; Rodent activity; The downstream slope is too steep |
80% |
Spillway |
Eroded spillway |
Erosion; The gradient of the channel is too steep |
20% |
|
Blocked spillway |
Soil and stone erosion; Trees and plants; Inaccurate design |
50% |
Outlet |
Eroded outlet |
Outlet is too small; Conduit is eroded; Foundation movement |
20% |
|
Leaking and breaking |
Valve is broken; Vandalism; Outlet is too old |
40% |
Note: * On the basis of ten dams