Ziooo
1 Dewatering
1 Implications of dewatering on the dolomite compartments
The term dewatering tends to create a concept of completely dry mines or aquifers. This is not the case as dewatering is a state where the inflow to the mine is reduced by removing water that is in storage in the dolomites. When the compartment is dewatered the mine still experiences a continuous inflow, often very significant, with inflow rate equal to the recharge rate.
Dewatering is achieved when Pumping rate = Recharge rate
Thus even when a compartment is dewatered, substantial volumes of water must be pumped from the mines.
For example: In the Oberholzer compartment, dewatering began in September 1955 and was accomplished in April 1973. During this period maximum pumping rates reached 170 ML/day while the steady state pumping, after dewatering, is 50 ML/day. The advantage of dewatering is that under steady state conditions the water inflow to the mines is controlled and predictable. Sudden catastrophic inflows are not likely to happen.
Bredenkamp (1993), shows that the Gemsbokfontein compartment has been dewatered by WAGM since 1986, while in the Bekkersdal compartment north of the Gemsbokfontein compartment and separated by the Panvlakte dyke, water levels are apparently unaffected. The eastern Gemsbokfontein compartment leaks through the Magazine dyke, to prevent drawdown from occurring to a level where sinkholes may develop. This compartment is artificially recharged with dewatered water. The Zuurbekom compartment is affected by dewatering.
Bredenkamp’s (1993) study confirms leakage from Gemsbokfontein east Compartment and suggests that a substantial amount of recirculation is taking place. The recharge is estimated to be 24% of the average rainfall of the preceding 12 months. Water levels in the Gemsbokfontein West Compartment are declining at 0.375 m/month.
2 Pumping rates and water levels
The available data on
1 Implications of dewatering on the dolomite compartments
The term dewatering tends to create a concept of completely dry mines or aquifers. This is not the case as dewatering is a state where the inflow to the mine is reduced by removing water that is in storage in the dolomites. When the compartment is dewatered the mine still experiences a continuous inflow, often very significant, with inflow rate equal to the recharge rate.
Dewatering is achieved when Pumping rate = Recharge rate
Thus even when a compartment is dewatered, substantial volumes of water must be pumped from the mines.
For example: In the Oberholzer compartment, dewatering began in September 1955 and was accomplished in April 1973. During this period maximum pumping rates reached 170 ML/day while the steady state pumping, after dewatering, is 50 ML/day. The advantage of dewatering is that under steady state conditions the water inflow to the mines is controlled and predictable. Sudden catastrophic inflows are not likely to happen.
Bredenkamp (1993), shows that the Gemsbokfontein compartment has been dewatered by WAGM since 1986, while in the Bekkersdal compartment north of the Gemsbokfontein compartment and separated by the Panvlakte dyke, water levels are apparently unaffected. The eastern Gemsbokfontein compartment leaks through the Magazine dyke, to prevent drawdown from occurring to a level where sinkholes may develop. This compartment is artificially recharged with dewatered water. The Zuurbekom compartment is affected by dewatering.
Bredenkamp’s (1993) study confirms leakage from Gemsbokfontein east Compartment and suggests that a substantial amount of recirculation is taking place. The recharge is estimated to be 24% of the average rainfall of the preceding 12 months. Water levels in the Gemsbokfontein West Compartment are declining at 0.375 m/month.
2 Pumping rates and water levels
The available data on