Dam levels exceed capacity, flooding possible in downstream areas

The department of water & sanitation has warned residents living downstream from major dams like the Vaal or Gariep of possible flooding of settlements in lower-lying areas within the 100-year floodline.

The department’s spokesperson, Wisane Mavasa, said water levels in the areas had prompted the government to warn residents..

“Water levels have risen rapidly overnight in the Vaal Dam due to heavy inflows on the upper catchments as a result of the continuous above-normal rainfall on already saturated catchments,” Mavasa said.

“As such, the department of water & sanitation (DWS) will be opening an additional four sluice gates gradually today from 9am, 10am, 12 noon and the last one at 1pm this afternoon.”

This will bring the total number of gates open at the dam to 10.

“The dam is sitting at 118.48% with an inflow of 2,448 cubic metres per second (m3/s) into the dam. At Bloemhof Dam, water outflows are also being increased incrementally at different times from 2,000m3/s to 2,200m3/s at 9am; 2,400m3/s at 11am; 2,600m3/s at 1pm; and 2,800m3/s by 3pm.”

The dam level was at 110.27% on Saturday morning.

“These adjustments are necessary to manage the continuous rising inflows and safe operation of the Vaal and Bloemhof dams. With more inflows anticipated into the dams, especially the downstream Bloemhof Dam, outflows may potentially be increased later in the afternoon or tomorrow, “Mavasa said.

“At Grootdraai Dam, the already opened gate has been increased to 2.5m due to the higher inflows of 967.47m³/s. The storage level is at 110.08%. The gate will be increased to 3m at 9am, and a second gate will be opened at 11am to 1m.

“In the Orange River, the Gariep and the Vandekloof Dams are sitting at 108.25% and 106.09% respectively and overspilling. The controlled and uncontrolled water releases at all these dams will lead to overtopping of riverbanks downstream of the Orange and the Vaal rivers, resulting in flooding of settlements that are in the lower-lying areas within the 100-year floodline.

“People living within the floodline downstream of the Vaal and Bloemhof dams, and have had to evacuate, should continue to avoid the flooded areas as the river catchment remains oversaturated,” Wisane said.

Vaal-Orange River System dam levels on Saturday:

• Vaal Dam — 120.69%. Inflow: 2214.48m³/s; 10 sluice gates remain open
• Bloemhof Dam- 112.88%. Water releases increased to: 3,200m³/s at 10am on Saturday
• Grootdraai Dam -110.58%. Two sluice gates remain open, first at 3m and second at 1m.
• Vanderkloof Dam- 106.54% and Gariep Dam — 109.29%. These two have uncontrolled overflows and are overflowing.

TimesLIVE