Urgent action called for: Cracks found in Hardap dam

CRACKS have been detected in the structure of the Hardap Dam and need to be repaired “as a matter of urgency”, says an expert study.

The study was conducted last year to determine the structural safety of the dam. The dam situated 17 kilometres north of the southern town of Mariental, has been at the centre of recurrent floods.Last year, Mariental experienced the worst floods in recent memory, resulting in loss of life and property.After last year’s floods, insurance companies decided not to insure property situated to the west of the town after paying out more than N$80 million in claims for damages.There have been persistent rumours in the southern town that the dam, built in 1963, has cracks in its walls.The bulk water supplier, NamWater, which is in charge of the dam, has rejected the rumours.However, an inspection done by WRC Consulting Engineers under the leadership of Professor A Rooseboom, has revealed that significant horizontal cracks appear on both dam walls.An employee of NamWater, W Du Plessis, was also part of the inspection team.”These cracks are especially significant just before the bend in the right flank embankment, as well as roughly in the middle of the left flank embankment, one-third from the left bank as well as close to the left bank,” says the inspection report.The report, a copy of which is in the possession of The Namibian, recommends that the cracks be repaired “as a matter of urgency”.According to NamWater’s latest dam bulletin, the dam is currently 53 per cent full.In addition, the report noted that some vertical cracks lower down were also visible.It further found that the capacity of the outlet works is not sufficient to lower the water level within a reasonable time under normal operating circumstances.”Improve the spillway capacity to handle the safety Evaluation Flood,” the report recommends.The report proposes maintaining the dam’s water level at 70 per cent, to which NamWater has agreed.According to the report, no formal inspection and maintenance manuals exist and it urged that these be compiled immediately.It also found damage to a rock fill toe and toe drain system caused by the flood.Erosion damage appeared on concrete stonework providing storm water erosion protection close to the crest on the left wall, the report indicated.RISK AND IMPACT In case of a dam break, a population of between 2 045 to 2 075 people is at risk, while the direct monetary loss is estimated at between N$100 000 million and N$150 000 million, the report says.Indirect monetary loss is estimated at between N$500 000 and N$750 000 million.The last rehabilitation work on the dam was completed in 1996.This was the first dam safety inspection of this nature.The dam’s water level during the inspection – done on July 26 – was 4,5 cubic metres below the full supply level.The report was presented to all relevant stakeholders, including NamWater, at the end of November last year.Mariental Municipality’s Chief Executive Officer, Paul Nghiwilepo, yesterday declined to comment on the report.He said the Municipality had sought clarity on some issues and could not divulge any information at this stage.NamWater public relations officer John Shiwedha had not responded to a request for comment by the time of going to press.Sparks are expected to fly at a community meeting scheduled for next Wednesday to inform the town’s residents of the report.The dam situated 17 kilometres north of the southern town of Mariental, has been at the centre of recurrent floods.Last year, Mariental experienced the worst floods in recent memory, resulting in loss of life and property.After last year’s floods, insurance companies decided not to insure property situated to the west of the town after paying out more than N$80 million in claims for damages.There have been persistent rumours in the southern town that the dam, built in 1963, has cracks in its walls.The bulk water supplier, NamWater, which is in charge of the dam, has rejected the rumours.However, an inspection done by WRC Consulting Engineers under the leadership of Professor A Rooseboom, has revealed that significant horizontal cracks appear on both dam walls.An employee of NamWater, W Du Plessis, was also part of the inspection team.”These cracks are especially significant just before the bend in the right flank embankment, as well as roughly in the middle of the left flank embankment, one-third from the left bank as well as close to the left bank,” says the inspection report.The report, a copy of which is in the possession of The Namibian, recommends that the cracks be repaired “as a matter of urgency”.According to NamWater’s latest dam bulletin, the dam is currently 53 per cent full.In addition, the report noted that some vertical cracks lower down were also visible.It further found that the capacity of the outlet works is not sufficient to lower the water level within a reasonable time under normal operating circumstances.”Improve the spillway capacity to handle the safety Evaluation Flood,” the report recommends. The report proposes maintaining the dam’s water level at 70 per cent, to which NamWater has agreed.According to the report, no formal inspection and maintenance manuals exist and it urged that these be compiled immediately.It also found damage to a rock fill toe and toe drain system caused by the flood.Erosion damage appeared on concrete stonework providing storm water erosion protection close to the crest on the left wall, the report indicated.RISK AND IMPACT In case of a dam break, a population of between 2 045 to 2 075 people is at risk, while the direct monetary loss is estimated at between N$100 000 million and N$150 000 million, the report says.Indirect monetary loss is estimated at between N$500 000 and N$750 000 million.The last rehabilitation work on the dam was completed in 1996.This was the first dam safety inspection of this nature.The dam’s water level during the inspection – done on July 26 – was 4,5 cubic metres below the full supply level.The report was presented to all relevant stakeholders, including NamWater, at the end of November last year.Mariental Municipality’s Chief Executive Officer, Paul Nghiwilepo, yesterday declined to comment on the report.He said the Municipality had sought clarity on some issues and could not divulge any information at this stage.NamWater public relations officer John Shiwedha had not responded to a request for comment by the time of going to press.Sparks are expected to fly at a community meeting scheduled for next Wednesday to inform the town’s residents of the report.