The 1981 Laingsburg Flood was a catastrophic event that occurred on 25 January 1981 in the town of Laingsburg, Western Cape, South Africa.[1] The flood killed at least 104 residents, and the bodies of 72 people were never found. A total of 184 houses were destroyed.

Flood Waters

The Buffels River catchment, which includes the Buffels, Wilgehout, and Baviaans rivers, lies in the rain shadow of the Langeberg, Swartberg and Witteberg Mountains.[2] Occasionally, a high-pressure system offshore of the Western Cape can push moist air from the coast over the mountains, resulting in increased rainfall in the Buffels River catchment. This weather phenomenon led to increased water flow in the three rivers within the catchment, which converged at the outskirts of Laingsburg.

The heavy rainfall over the area was caused by a typical black south-eastern synoptic situation that developed over the south-western parts of the country during the weekend of 24 and 25 January 1981. In this situation, a strong high south of the continent feeds moist, warm air into a low-pressure area over the country's southern parts. Such a low-pressure region is also reflected in the upper air as a cold cut-off low that extends well into the upper troposphere.[3]

On January 25, 1981, such an event occurred when unprecedented rainfall in the catchment area caused the combined Buffels River overflowing its banks.[2] The rain started on the weekend of 24 and 25 January 1981. The Buffels River overflowed its banks around 08:00 on Sunday, January 25, 1981.

At the same time, two rivers named Baviaans and Wilgehout integrate with the Buffels, meaning there was a much higher volume of water accumulated at one time. The water level started to rise in town at about 12:00; by 14:00, the town (CBD) was almost fully covered.[4] This caused flood waters and mud to sweep through Laingsburg, with some areas experiencing water levels reaching 10 metres above the usual flow level.

The river current was estimated at its peak at 8000 cubic metres per second.[5]

Damage

The flood destroyed two-thirds of Laingsburg's infrastructure, destroying 184 houses and 23 commercial buildings, including the town's old-age home. The flood claimed 104 lives, with 72 bodies never recovered.[6]

In a report published in January 1982, the flood damage identified the position of Laingsburg relative to the confluence of the Buffels, Wilgehout, and Bobbejaans Rivers, and the narrow poort downstream of the confluence makes it particularly vulnerable to damage from large floods. Laingsburg is situated on a natural flood plain on the inside bend of the Buffels River.[7]

A geographical factor that contributed to the damage caused by the flood was the effect of the east-west orientation of the topography to the south of the town. The confluence of the two large tributaries and the Buffels River was immediately upstream of the poort through the ridge, and the ridge directed the flow in the tributaries towards the southern part of the town on the opposite bank. The combined effects of all three rivers and the poll's constriction of the poort which accounted for much of the damage in the southern part of Laingsburg between Swartberg St and the river.[7]

The deposition of sediment is considered the widespread form of flood damage in the drier regions of South Africa. Rivers in the Cape Midlands and the Karoo carry high sediment loads in high floods. The sediment-carrying capacity of flowing water is susceptible to the velocity of the water. When the river overflows its banks, the velocity decreases rapidly, particularly where it flows through a built-up area. Heavy sediment deposits can be expected in the vicinity of houses nearest to the enlarged river channel, where the flowing water's velocity is rapidly decreasing. The slower-moving water can no longer carry the sediment loads associated with the mid-stream velocities and deposition takes place. Sediment deposits in Laingsburg were up to 3 m deep in many places and the total sediment volume deposited was about 200 000 m³.[7]

Another factor that caused much damage in Laingsburg was the large amount of floating debris. This consisted mainly of trees washed down the river from upstream, but it also included debris from buildings in the town itself. The debris caused physical damage to the buildings and aggravated sediment deposition.[7]

Laingsburg Flood Museum off the main street

Many buildings in Laingsburg collapsed due to high water levels alone. These were mainly the older buildings. Newer, more soundly constructed buildings were not seriously damaged except those subjected to high scouring velocities.[7]

First Reports

The first flood reports emerged after SADF Super Frelon helicopters flew over the town at 09:00 on Monday morning the 26th of January 1981.[8]

References

  1. ↑ "At least 100 people drown in a flood at Laingsburg | South African History Online". www.sahistory.org.za. Retrieved 20 July 2023.
  2. 1 2 "Dark tourism disaster and the terrible Laingsburg flood of 1981 | The Heritage Portal". www.theheritageportal.co.za. Retrieved 21 July 2023.
  3. ↑ Kovacs, Z. P. (1983). Documentation of the January 1981 floods in the South Western Cape. Republic of South Africa.
  4. ↑ Hoorn, Angelo Ricardo (29 January 2021). "Remembering the Laingsburg Floods (40 Years)". Weatherblog.co.za.
  5. ↑ "Black Sunday: Remembering Laingsburg Flood, 25 January 1981". SAPeople - Worldwide South African News. 25 January 2022. Retrieved 21 July 2023.
  6. ↑ "History of Laingsburg". The Karoo, South Africa. Retrieved 21 July 2023.
  7. 1 2 3 4 5 Roberts, C P R; ALEXANDER, W J R (1982). "Lessons learnt from the 1981 Laingsburg Flood". Die Siviele Ingenieur in Suid-Afrika. 24 (1): 17–27.
  8. ↑ "190 Feared dead". The Argus. 26 January 1981. p. 1.
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