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Hardap no fuller than 70 percent

Avatar of inke inke 24. February 2017 - Weather

Along the main street, at the crossroads to the eastern part of the town, stood a motorboat with which locals had to visit their houses that were located in the western parts of town. No vehicles could use the main road, the B1 highway or the minor roads in the western areas of Mariental during the 2006 floods. Photo: Dirk Heinrich

On 23 February 2017, the Hardap Dam, near Mariental’s sluices were opened for a second time in this rainy season, 2016/17. At first, only two sluices were opened at 8 o’clock for an hour, 1.2 metres and 224 cubic metres of water was drained per second. At 9 o’clock a third sluice was opened, 1.2 metres and 336m3/sec flowed into the Fish River below the dam wall. 11.5 million cubic metres of water was drained within nine hours, to reduce the dam’s level from 75 percent (218 million cubic metres) to 72 percent of its capacity. On 20 February 2017, two sluices were already opened for the first time, when the dam passed the 70 percent mark and further inflow reached the reservoirs. For eleven hours, 200m3/ sec flowed from the dam, into the  - at times – kilometre wide, dry river bed filled with rime (reeds).

It took a few hours before the water reached Mariental 29 kilometres downstream, because the water’s flow was hindered by the dense vegetation in the river. Hours after closing the sluices, water flowed past Mariental. 

Since the flood in 2006, when half of Mariental was almost a metre under water, the Namibian Cabinet decided in 2007 that the Hardap Dam cannot be allowed to pass the 70 percent capacity mark. This is done to avoid that more water is drained than the Fish River can hold.

On 25 February, eleven years ago, a total of 122 houses and 78 shops in Mariental were flooded. No vehicle could pass the town or go down the main road. Instead, residents navigated the main road and a few side streets with a motorboat. On the Saturday afternoon of 2006, the water from the Hardap Dam that moved into the Fish River had already surpassed the flood marks from the year 2000, when the town was flooded for the second time since 1972. The situation got worse when the state-owned water company, NamWater, opened the sluices at 11:00 pm on 25 February 2006. This released 3500m3/sec, as 4000m3/sec flowed into the other end of the dam. In the days before, water had already been released from the dam, after the water level stood at 96 percent (7 February 2006). On 2 February 2006, the Hardap Dam stood at 84.4 percent.

For the first time in the 2006 rainy season, the sluices of the largest artificial lake in Namibia were opened on 26 February, after the dam was filled well over 80 percent. Unexpectedly high precipitation of over 100 millimetres in two days in the Hardap Dam catchment area, led to more water than the Fish River could hold, to be drained from the dam. This resulted in the flood of the small settlements, fields and western part of Mariental on 25 February 2006.

Plans for the construction of the dam were developed in 1908, during the German Colonial period. The Hardap dam was planned between 1949 and 1960. Construction finally began in 1960, and on 16 March 1963, the then Administrator of South Africa, D.T. du P. Viljoen declared the Hardap Dam officially open. The first major flood in Mariental took place on 16 March 1972, when the sluices had to be opened because 6393 cubic metres of water per second flowed into the Hardap Dam. The second flood was triggered by an inflow of 3387m3/sec into an almost filled dam on 19 February 2000, and the sluices had to be opened.

After the floods in Mariental and the small settlements lying between the town and the dam, damage to urban and private infrastructure reached into the millions. There were problems with the water and electricity supply and fuel tanks at petrol stations were flooded and partly drained of fuel. Insurance companies had to pay out millions. As a consequence, the insurance companies refused to continue insuring Mariental’s inhabitants and the surrounding farmers against flood damages.

In order to avoid future flooding and the resulting damages, the Namibian Cabinet decided in 2007 that the Hardap Dam is not allowed to reach more than 70 percent of its capacity, in order to absorb high inflow and allow for low outflow through the sluices.

Dirk Heinrich

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